Contents

3 DMRSION WORK5 ....

3.1 Overview...

3.2 Generol princi

3.3 Intoke locotio

3.3.1 Charocteristics

3.3.2 Exomple

77

77

77

18

18

20

3.4 Intoke types

vll

1

tf't,'

66

vll l

5.6 Checklist for grovel trop, settling bosin

6.5.4 Quick method for smoll schemes with crossflow turbines ................ ............. 95

ix

7.

1 0

11

APPENDICES

Appendix A

Appendix B

Appendix C

LIST OF PHOTOCMPHS

Ph0t0 2.2 0bstructions coused by debris folling from on unstoble slope ......... ..................... 9

Photo 3.2 Side intoke of the Golkot micro-hydro scheme, Boglung, Nepol .........22

Photo 3.3 Where on intoke is lioble to ottroct flooting debris, o troshrock moy be necessory (Sri Lonko) .............22

Ph0t0 3.5 Timber plonks ploced horizontolly in grooves provide o low-cost gote in q chonnel (Mhopung) ...........25

Ph0t0 3.11 Gobion wolls ot the heodworks of the 30 kWJhorkot micro-hydro scheme, Mustong, Nepol ................. 35

Ph0t0 4.3 Stone mosonry in cement mortqr heodrqce ccnql of the 50 kW Golkot MHB Gqlkot, Boglung, Nepol ..................... 38

Photo 4.4 Reinforced concrete cover slobs provide protection from folling debris (Bolivio) ................... 38

Photo 4.6 Timber conol with brocing supporting the sides, Thuptenchuling ........ .............. 39

Photo 4.11 Overflow from the foreboy dischorged over o rock cliff, Dhoding micro-hydro, Nepol .......... 50

Photo 4.12 Spillwoy on o crossing where the excess flow is dischorged into q gully,

Photo 4.13 HDPE pipes provide qn overflow from o timber chonnel (Mhopung) .................... 53

Ph0t0 4.15 Ghqndruk micro-hydro heqdroce crossing, Ghondruk, Nepcl ............ 54

Photo 4.u Flush-outs should be provided qt low points in pipelines so the heovy debris cqn be

Photo 4.18 HDPE heodroce pipe olong unstqble olignment, Ghondruk micro-hydro scheme, Nepol ...... 56

Photo 4.19 Bend prepored by cutting ond welding the HDPE heodroce pipe ot Ghqndruk ...................... 56

xl

Photo 4.21

Photo 4.22

Photo 5.1

Photo 5.2

Photo 5.3

Phoro 5.4

Phoro 5.5

Photo 5.6

Photo 5.7

Photo 5.8

Phoro 5.9

Phoro 5.10

Phoro 5.11

Phoro 5.12

Photo 5.11

Phoro 5.14

Photo 5.15

Photo 6.1

Photo 6.2

Phoro 6.3

Photo 6.4

Phoro 6.5

i'iroto 6.6

Phot0 6.7

Phoro 6.8

Photo 6.9

Photo 6 .10

Photo 6.11

Photo 6.12

Photo 6 .11

Photo 6.14

Phor0 6 .15

Photo 7.1

Ph0t0 7.2

Phoro 7.3

Photo 7.4

Photo 7.5

Photo 7.6

Joining HDPE pipes by pushing

Collors used to join HDPE pipes

th€m while hot

57

colkot grovel trop .... ' . . . ' ' , , . . . . . . . . . . . . . ' ' ' ' ' . . . . . . . . 71

Sliding got€ ot settling bosin entronce, Peru ....___........... ?5

Jhorkot setti ing bosin ....... . . . . . . . . . . . .76

se( l ing Dosrn o t Jhorkor . . . . . . . . . . . . 1'7

sqll€ri Chioiso setl l ing bosin

chondruksef i l rng bq) in . . . . . . . . . . . . . . . . . . . . . 78

81

8l

84

crovel trop. settling bosin ond foreboy ofJhonhe mini'hydro ................

A dry stone mosonry foreboy showing the connection with the penstock .........,..............

A cem€nt mosonry chonn€l qnd foreboy ot the top ofo ste€p slope (DhqdingJ .............

82

. . . . . . . . . . . . .8 l

Cleoning con be difiicult with horizontol bors

submerged troshrock, Solleri Chiolso mini-hydro scheme............

overflow weir for the settl lng bosin qt Jhorkot .................................

An expqnsi0nj0int should b€ locotedjust below qn onchor block to protect the block

from forces which mqy Ilot be designed to resist (Siklis) ..................

chondruk peoking reservoir during construction ............. ................. . . . . . . . . . . . . . . . . . . . . . . 85

Ghondruk DeokiD0 reservoir ofter construction .............................

P€nstock qlignment of the 36 kW Jhorkot micro-hydm sch€me, Mustong, Nepol ........................................................ 87

Pen( toLk . Purong. . .

84

85

Penstock olignmert ofthe 50 kW Borpok micro-hydro scheme, Corkho. Nepol

Excovotion to reduc€ the cost oflh€ penstock ond reduce the need foronchors {Siklis) ..... .............. ......... ....... ... 88

Penstock instollotion is often chollenging ond requires sofe ond cor€ful work .... ................ 89

Penstock oiignment high obove the ground to ollow occess for people 0nd cottleJhonlre mini-hydro ................... 89

HDPE-mild ste€l c0upling. Jhong micro-hydro sch€me, Mustong, N€pol .................. .................................................. 9i

Penstock ot Ghondruk with vil log€ in the bqckground ............

Temporory suppon for site welding work,Jhonl(Ie minihydro, Nepoll08

A strolqht p€nsrock with four suppons cnd on onchor block before th€ power house.....

Jhonkre minihydro onchor block for on upword verticol bend

slrdlng expqn5ion jornt, Jhonkre mrni.hydro

crocking 0f the upper surfoce of on unreinforced oDchor block......

U5e o l d ry s tone wo l l fo r fo rm work , JhunLre mrn1.hydr0 . . . . . . . . . . . . . . . . . . . . . . . . . . .

droinqge ond prevelting corrision betwe€n the block ond the pipe (Kiomche) ............................

104

105

106

108

l l l

u 1

l l 2

1 1 3

I l lstone mosonry suppoft piers,lhonkre mini'hydro scheme ...........

The use ofon exlension t0 the concrcte supp0n lifts the pipe cleor 0l on block, ollowirlg

Photo7.7 Wooden support piers ot Komche micro-hydro scheme, Nepol ....................... ........................... I16

Photo 8.2 Powefhouse ond loilroce oi the solleri Chiolso mi[i 'hydro scheme . . ... . . ..... .... ..... 130

Phot0 9.1 Unsroble slopes (re o thr€ot l0 schemc. This polvefhouse wos destroyed by o londslide ........................................... 119

Photo 9.2 Mosonry steps for entrgy dissipotion ond contr0l 0f spil lwov woter ............ ........................... 140

x I

;))l

I

t

6

J

0

Ph0t0 9.4 Stone mosonry con provide slope stobilisotion olong the route of the penstock (Barpok) ......... ........ 141

LIST OF FIGURES

Figure 1.2 Heod is the verticol height through which the woter drops ................ 3

Figun 2.1 Viewing the site from o vontoge point gives the opportunity to ossess the options for

Figure 3.7 A temporory weir proposed for the 18 kW Thorong Phedi micro-hydro scheme, Monong, Nepol .............................26

Figure 3.8 Heodworks orrongement of the 500 kWJhonkre mini-hydro scheme, Nepol .............. ........................27

Figure 3.10 A stone mosonry permonent weir proposed for Ghomi micro-hydro scheme, Mustong, Nepol ................................ 29

Figure 3.11 A plum concrete permonent weir proposed for Ghqmi micro-hydro scheme. ............ 30

Figure 3.15 Heodworks orrqngement of the 80 kW Bhujung MHP, under construction in Lomjung, Nepol ................................. 36

Figure 4.3 Buried membrone lining proposed in Design Mqnuols for Irrigction Projects in Nepol ..................... 4l

Figure 4.11 Heqdworks of the 100 kW Siklis micro-hydro scheme (Siklis, Nepol) ........................... 62

Cqnol lining with stone mosonry in cement mortor 66

72

57

81

83

An ideol settl ing bq\rn

Foll velocity ofquonz spheres in woter

A typicol settl ing b0sin ond its components ..............

Exponsion 0nd controction rolio in s€t0ing bosit

Flushing o settling bosin using th€ verlicol flush pipe method

V€rticol flush pip€ section in o settiing bosin

Flushing system of jhqnkr€ minihydm

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ?4

Foreboy

Figure 4.13

Flgure 5.1

Figurc 5.2

Figure 5.3

Figure 5.4

Figure 5.5

Figurc 5.6

Figure 5.7

Figurc 5.8

Figure 5.9

Figure 6.1

Figurc 6.2

Ilgure 6.3

FrguIe 6.4

Figure 6.5

Figur€ 6.6

Figur€ 6.7

Figur€ 6.8

FiguI€ 7.1

Figure 7.2

Frgure 7.3

Figure 7.4

Figur€ 7.5

Flgure 7.6

Figure 7.7

Figure 7.8

Fjgure 7.9

Figurc 8.1

Figur€ 8.2

Flgur€ 8.3

Figur€ 8.4

Flgure 8.5

Figun 8.6

Figure 9.1

Figure 9.2

Figure 9.3

Fiqure 9.4

Fiqure 10.1

tiqure 10.2

Figur€ 10.3

Figure 10.4

Table 3.1

Tqble 3.2

Wolls ood floon ofwot€r retqining structur€s

Typicol penstock profile

..... 142

90

9l

93

to2

105

106

107

108

112

112

4

1 1 5

1 1 9

122

125

127

127

131

133

133

133

135

136

142

142

144

149

lypicol HPDE mild steel pipe coupling

Surge pressures

Jhonkre mini-hydro p€nstock olignment ot downstrcom end

Tronsition from buried to exposed penstock, jhonkre mini-hydro

Sliding rype exponsion joint

Thermol exporsion ofo p€nstock pipe

Setting out rh€ c€$tr€lin€ ofth€ pensto(k 6lignm€nt

Anchor block s€ction.

Composit€ onchor block section

Arrangement ofweor plote ot a suppon pier

Typicol s€ction through o support pier

Diston(es ond ongl€s used in onchor block ond support pier equotions

Proposed onchor block shope

Force diogrom on th€ qnchor block

Suppon pier for smoll schemes with ground height ofless thon 1 m

Suppon pier for smoli schemes with ground height of 1 m to 2 m

Powerhouse floor plon ofth€Jhonk€ mini'hydro scheme

Mochine foundotion section

Mochine foundotion plon......

Resolution offor€s on the mqchine foundotion ...........

Proposed mochin€ foundotion section for Exomple 8.1

R€inforced concrcte toilroce chonnel

Gobion retoinirg w011..............

Stone mosonry r€toining woll................

T€rrocing ond dry stone wolls to retoin slop€s ....

A gobion check dom 0t the intok€ ofjhorkot micro-hydro scheme

A Coondo intoke scr€en ..........

Propos€d orrongemenr for bursting disc instollotion in micro-hydro s(h€mes

Flexible steel suppon pier forJhorkot micro-hydro scheme

Foundotion for theJhorkot f lexible support pier...........................

145

'150

LIST OF TABLES

Toble 1.t

Toble 2.1

Tobie 2.2

Dillerenc€s between micro'hydro ond lqrge hydro schemes

Indicotors of slope instobility

Possibl€ use 0fsoil & rock in micro-hydropower .......... 10t2Tqble 2.3 Cqnol se€pdge loss€s......

cot€gories of Nepolese rivers

Selection criterio tor side qnd bottom inrcke

19

Toble 4.1 Roughness

Toble 6.1 Advontoges ond disqdvontoges of different penstock moteriol .......... 90

Toble 7.3 Unit weight (y), ongle of friction (Al ond ollowoble beoring pressure for diflerent soil types .......... 121

UST OF WORKED OUT EXAMPLES

UST OF BOXES

Box 3.1 Composite gobion concrte PVC sheet

Box9.1 Use of mosonry grid to stobilise theJhonke mini-hydro powerhouse orec slope ........743

1. Introduction

1.1 Hydropower ond micro-hydropower

Hydropower is the generotion ofpower (mechonicol ond/or

electricol)using the foll ofwoter In the cottext ofN€poi, o

hydropower scheme with on instolled copocity ofless thon 100

kW is clossified os micro hydro. Schemes in the rong€ 100-1000

kW ore clossi{led os mini hydro, ond shore some ofthe choroc-

teristics 0f micro-hydropower schenes. Apqft frorn the power

output ofschemes, some 0fthe mojor differences between lorge

ond micro hydro cre shown below in Tobie Ll.

SOMI DENNITIONS

. Civil engineering is the opplicotion ofscience to the

pr0ctic0lbuildirg ofsofe ond cost effective structufts.

. A structure is on ossembly of motencls which serves the

pueose for lvhich it is designed (occommodote people,

conv€y Ilou trofi ic, etc.) ond c0rries the ossocioted

loods . A c rv r l e r ,g rnecr ing s r ru , ru re r ' spr r . f i co l l y

designed to fulfil o purp0se ond/0r pe orm o function qt

0n opprop ore quolity ond to qn occeptoble time scole

ond cost.

r Civil rvorks are cll octivities necessory for the building of

structures.

. Sforoge schemes moke us€ ofo dom to stop river flow

building up q reservoir 0fwoter behind th€ dom. The

wotrr is then reLeosed through turbines when power is

n€eded.

r Run-oiriyer sche mes do not stop the river flow, but

insteod divert p0n ofthe flow vio o heodroce ond

Toblt l.l Differenc€s b€tween micro-hydro ond lorge hydro schemes

The design ond construction 0fcivil €ngineering works hove

some important chorocteristics:

They ore depeodent 0n conditi0ns ot the site. No two

sltes orc the some.

They olwoys involve structures thot ore in contoct with

the ground. Design engineers moy hcve controloverthe

mot€riols used in corstruction, but hove li lnited conrr0l

over the ground on wh i , h lhe \ t ru ( lu re s l0nds . They

must therefor€ toke occount ofthe ground conditions,

ond moy hove to consider olternotive sites to ovoid

stobil ity probleIns

They oiten involve o number 0fpeople working on

design, supervision ond constructi0n ot the site. Vorious

skills ond moteriols ore involved, usuolly over o period

of severoi months. Therefore plonning, communicotion

ond occount0bility ore very importont.

Foilure ofcivil works con be very dongerous ond very

expensive. Similorly, poor performonce or over-design

ore uneconomicol.

On€ importont point should b€ recognisedi complete

stondordisotion 0fcivil works is not possibl€ due to the

vori0tion in site conditi0ns. Insteod, stondord 0pprooches to

penstock to q turbine. Micro-hydro schemes qre olmost

olwoys run'of-th€-river.

1.2 Aspects of civil engineering worlc

DESCzuPNON MICRO HYDRO SCHEMES LARCE HYDRO SCHEMES'IYpe

Pow$ generotion

Noture oi intoke

funnels & underground structuri,s

Penstock oliqnment

surge shoft

Distribution system

Unlined conol

N'lostly run-ol:river

Electricol ond/or rnechonicol

Usuolly t€mporory 0r semi-permonent

Rore

Verticol & Irorizontol bends

Rore, fbreboy octs os surge tqnk

Isolot€d (i.e. not coonected to then n r i ^ f n 1 o l , . f r , . , r v n r i . l r

Cor0rnon

Both run'of'r iv€r ond storoge

Electricolonly

Pefmonent

CoII]mon

Fewer verticol bends ond usuolly no h0nzontol

bends

Comrnon

Ilostly grid connected

Rqre

I

II

design ore used. providing methods ond crireriq thot enoble o

design to b€ odopt€d to conditions ot o site

Of course, scfe. occurote ond economic design is essenti0l

in civil engineering but, becouse ofsite voriotions, o procticol

understonding ofdesign is olso cruciol. Fqilures in civil engi-

neering do not usuclly 0ccur through on error in colculotions

but becouse of o seemingly nrinor €vent or cjrcumstonce lvhich

drd not s€€n1 imponont. A thoiough understqnding is needed of

which elemenls ore crit icql.

1.3 Components of micro-hydro schemes

Alth0ugh no two micro hydro sites 0re sirl l iLqr, oll ofthem

require specific common components ofdifferent dimensions to

convey the streom w0ter to the power generoti0n units ond

bcLk r i lo t :? s l reom :he 'c io r : :ponent ' oD 'sho l ln rn Frgure

1.1. Thc civil conponents or€ briefly discussed below:

HEADWORI(s

Structures ot the ston oithe scheme or€ collectiv€ly cqlled the

heodworks. In micro-hydro schemes, the heodriorks ohvoys

include the diversion weir, intoke ond grovel trop. A spillwoy

ond o settling bosin ore qlso usuolly ot the h€odworks.

DIVERSION WEIR

A diversion weir is o low structure (smqll dqm) ploced ocllss

the river which diverts some ofthe dv€r flow into the

hydropower scheme. The weir con be of o permonent, semi-

permon€nt 0r temporory n0ture.

INTAJC

This is ot the riverborlk upstreom from the diversion weir

where w0ter is init iolly drown into o c0nduit (conol or o pipe).

Usuolly 0 flow contrcl structuI! ond o coorse troshr0ck 0rc

incorporqted ot th€ inroke.

GMVEL TRA"P

This is 0 bosin (pond) clos€ to the intoke wherc grovel 0nd oth€r

coorse mot€riols ore tropped ond then remov€d. In the obs€nce

ofthis structur€ grovel con s€ttle olong the gentler s€ction of

the heodroce or in the settling bosin.

SETTUNG BASIN

Thl5 LS qLso o bosin where sqnd 0nd 0lher Iine 'uspended

porticl.s present in the river woter ore sertied ond then

renoved. lf ollowed t0 enter the p€nstock. such porticles wordd

obrode lhe penstock pipe ond the turbine 0nd hence shonen

thcir opLrqtl()n0l l i \ ' fs.

HEADRACE

This is o conql or o pip€ thot conveys the woter ftom the

heodworks to the foreboy structure. The heodroce olignmenl is

usuolly on even to gently sloping ground; o heqdroce pip€ is

generolly not subject to srqnificont hydrculic pressure.

FOREBAY

This is o tonk ot th€ entronce to the penstock pip€. ihe foreboy

tonk ollows for fl0w tronsiriorI from open chonnel to pressure

flow ond provides storoge wh€n there ore flow fluctuotions in

the turbine. It con olso serve os o finol settling bosifl. ln fqct,

sometimes the settl ing bosin ond the foreboy structur€s om

combined.

SPILLWAYS AND ESCAPES

Spillwoys orc openings in h€odroce conols thot divert €xcess

flows ond 0nly ollow the design flow d0lvnstr€qm. Note thot

some literoture moy us€ th{ terms spillweir 0r overflow t0 r€f€r

to the spillwoy. Escopes ore similor structures but their function

is t0 diven flows from the heqdrqce conols in cose the upstrcom

sectjons get blocked such os if there ore l0ndslides.

CROSSINGS

Thes€ ore structur€s thot convey the flow over streoms, gullies

or ocross unstoble telloin subject to londslid€s ond €rosion.

Aqueducts. culverls dnd susp€xded crossings ore examples of

such structures.

PENSTOCK

This is o pipe thot conveys wot€r und€r pressur€ from the

foreboy to the turbine. Th€ penstock pipe usuqlly storts wher€

the grcund profile is steep.

ANCHOR BLOCI(

An onchor block {thrust block)is on encosement of o penstock

design€d to constroirl the pipe m0vem€nt in qlldiltctiors.

Anchor blocks ore ploced ot oll shorp horizonrol orld verticol

bends, since there ore forces ot such bends thqt will t€nd to

move the pip€ 0ut ofolignment. Anchor blocks 0re olso

required to resist oxiolforces in long strcight sections of

penstock.

SUPPORT PIER

suppon piers (olso colled slide blocks or soddles) orc structures

thot ore used olong stroight runs ofexpos€d perutockpip€

(betwe€n onchor blocks), to prevent the pipe from sogging ond

becoming overstressed. They need to resist oll verticol forces

such os the weight ofthe penstock pipe ond the wot€r. However,

they should ollow m0vement poroliei to the penstock olign-

ment, which occurs during thennol exponsion und controction

Pr0cesses.

POWERHOUSE

This is o building thot oc(omrnodotes ond proteds the el€ctr0-

mechonic0l equlpment such os the turbine, generotor ond moy

include oqro'plocessing units. Thc electro nechonicol equip-

ment in the powerhouse convens the potentiol 0nd kinelrc

energy 0Iwoter int0 €lectficol power

TAILMCE

Thrs is 0 chonnel 0r o pipe thot conveys rvoter lr0m the turbine

(0fter p0wer g€neroti0n) bock int0 the streqm; g€nerolly the

s0m€ str?0m lronl wirich water wos init iolly withdrown.

Det0iled d€s.riptions of th€se comp0nents includinq

selection, design qnd c0nstruction lneihod0logy 0rc discussed in

subsequent chopt€.s.

A

Toilr oce

l)oul? l.l Components ofo micrc hydro saheme

1.4 The power equotion

'Ilte powerovoiloble from c hydropower scheme is dep€ndent

on the volume llowing in the system ond ils drop jn heighr. The

Rloti0nship ls exprcssed by lhe po!ver equotr0nl

P = 0 x o x h x €

rvhere:

t ' is the power produced in kw

Q is the flow in the penstock pDe in mr/s

g js the occeleration due t0 grovity = 9.8 m/s':

hq,,,, is the gross heod ovoiloble in m

e is the overoll s!'st€rn eiliciency

Gross heod, h,, ,., is the dilference bet!\r€en the lvoter level

ot the f0reb0y ond the turbjne centreljne level (or toilroce woter

surioce ifo drqft tube is uscd). This is shown schemoticolly in

F igure 1 .2 .

Nel h€od, h , is the pressur€ heod ot the entronce to the

lurbjne. Thot is lhe gr0ss head mirus conveyonce losses in lhe

penstock. For micr0-hydropower schemes the penstock 1s

generolly designed such thoI the net heod is 90'95q,r ofthe gross

heod meosured from the Ibrcboy (reier to Secti0n 6.4 for

penstock sjzing).

The 0veroll systeln ell iciency, e", is the rotio ofuselul

po$,er output t0 hydr0ulic power input. It is the prOduct of

s€pqrate effl. iencies for severol components ofthe system. i.e.

e : € i r e L e q e , ,

wherc:

er is the pensto.k efficrerrcy. rypicoliy 0.90 0.95

i h = h e )

e, is the turbine efl)ciency. typic0lly 0.65 - 0.80 depending on

rurDlne ryp€

er ls the generot0r efl iclency, typicolly 0.65 0.90 depending

on s izepL is thr lronsmissi0n emciency rncluding trcrnsforners i l

used, typicolly 0.85 0.90

F0r preliminory plonning of rnicro-hydropower schemes

in Nepol it is comm0n to ossume on overoll system efficiency 0f

0.5 to 0.6. However, it moy be os low as 0.3 lor very smoll

instollotions ond os high os 0.7 f0r lorger schemes. Therefore ot

detoil€d desiqn stoge it is imponont to recolculote the power

output bosed on the octuol design 0nd monufocturcrs' doto for

the proposed equipment.

F i g , . r p l l H c o d . r h e \ e r t o l h . g l . l r h r c u ! h w h . , l | , h d r p r d r o p .

l rap/^ / )

a'/'/

z\{],,'<\,

l Anchq

2. Site selectionond planning

2.1 0verview

Th€ selection 0fon 0ppropriote sjte in m0st micro-hydropower

schemes is on iterotive process. In the Nepolese context, usuolly

some community members rvho hove hod previous exp0sure to

micro-hydrgpolver tcahnology oppiooch fundrn g ogenIies.

consultqnts or monufocturers dependinq upon their f lnonciolps0urces ond the size 0fthe scheme. Thf r€chnicions ofthe

ogency concemed undertoke o sire visit to ossess whether the

site is feosible f0r a micro hydro irstollotion. Bosed on the

feosibil i ty report submitled by th€se tecirnicions, th€ commu.

nity members ond others involved ln the process decjde

whether t0 pr0ceed f.rf l l ief with I ne di\ / lJpmpnr of rhe

scheme.

0nceth€ decisi0n is mode to proceed wjth the scheme,

ond if it is in the upp€r ronge 0f Dicro hydro (soy obove 20 kw)

then 0 detoiled survey ofthe protect or€q is undcrtoken ond a

detqiled design rcpon is prcpored. Th€ sor)cti0n oi loons,

subsidy ond grcnts by funding crgencies ond bonks ore bosed on

this repoft. Thrre ore frequent m€etings between the concernedporties during this stoge. F0r the lower el]d oi micro hydr0 (soy

iess thon 20 kW). usuolly the monufocturers undertake both the

design ond instoLlotion.

Apon from socio econornic foctors such cs the need 1br

electricity, 0lI0rd0bil ity, ond supply 0nd demond, technjr0lly

the selection ofon 0pproprioie site depends on the foll0wing

two foctors:

. Streom ilolv

. Topogrophy

As mentioned in Chopter I, the power ovoiloble from o

micro'hydroporver scheme is o functjon 0fboth the flow ond

the heod. The heod depends on the topogrophy i\,ficro'hydro

becomes technic0lly vioble oniy ifthe combinotion ofhead ond

flow ore such thor the demond of the rorgeted conrnrunity con

be met. Urdsr n0rmol circumstqnces. Ihe low scoson florv r,i the

III

nv( rs l r0u ld be u5ed wh i le (01 ,u l l l rng Ihepowpr 0 - lpu l I l

should be n0ted thot designers hove ll le c0ntrol over the l low

ovoiloble in the streonl. Horveve( they h(ve s0me conlr0lover

lht'topogrophy. They con choose dil lerent olignnents for lhe

intoke, heodroce ond penst0ck. l hey con olso modify the locol

topogrophy through excovotion, building 0fstructures ond by

undertqking s0il stobil ity enhoncemenl meosures.

Although the plonning ofDricro hydro civil works does

not rBquire the detoiled work oflorge projects, the principles orc

tht s0De 0nd core needs to be token to foll0w some bosic rules.

Proper plonning ond co-0rdinoti0n in th€ init iol stoge ofthe

proj€ct will keep costs to o mirrimum ond reduce deloys.

Meosurement ofheod ond flow ore beyond the scope of

thpse guidelines but full desc ptions 0fthe methods used con be

found in o number oftexts including Rei 1.

2.2 Principles of site investigation

Site rnvestigotion is the preliminory work c0rried out t0

estoblish the suitqbil ity for construction ofthe vori0us options(or the most fecsible option rI rt is opporentr t lrrough the

rnvestigotion of soils, slope stobjl ity, f lood l€v€ls, surfoce woter

movenent qnd subsidence. This is discussed loter in this

chopter

In most civil €ngineering work, the unexpecred hcppens.

Sit€ inv€stigotion oims to predict whot this might be so thot the

engineer con prepore o design thot wil l deol with it.

It should b€ noted thot th€ meosurement ofheod ond

flow serves to estoblish the 0pti0ns ov0iloble for development of

the site f0r micro'hydro. The site investigotion then qssesses the

suitobil jty ofthe site f0r eoch olternotive. The site invesrigotion

process helps to choose the optinlunr loyoul where more thon

on€ opti0n opp€ors to be teosible. Site condrtions ore ols0

recorded during the site investigqtion stoge so thot there is

odequot€ informotion for the detoiled design phose.

Ther€ is usuolly o limit t0 th€ time ond funds ovciloble

for site investigotions. lt is olwoys dimcult to know wh€n

odequote work hos been comp)eted. Thekeyistowork

efficielltly ond to think corefully 0bout where mor€ thorough

invesiigqtion is required. The principles ofsit€ investigotjon 0re:

. Take your time and be thorough. A return visit to coll€ct

informotion missed th€ first time is costly, ond inod-

equote civil d€sign ev€n morc so

. walk oll over the sire. Goin o fulloppreciotion ofthe

options ovoilqble.

. Tolk to local peopla especiol)y those who hove corried

out construction work in the or€o. Since most ofthe

riv€rs in th€ mountoins ond th€ middie hil is ofN€pol

hove not been gouged, streom flow dqto ore not usuollyqvqiloble. Therefore, it js imponont to tolk to l0c0l

people t0 get o l ir€l ofth€ flo0d lev€Ls for rore l lood

everts (soy 20 yeors t0 50 yeors return period).

. Overoll, oim to rqise the understonding ond oworeness

ofchonges in the site over time.

2.3 Selection of olternotive lovouts

2.3.1 AN OVERVIEW OF THE SITE

This will involve viervlng the site from o physicoLvontoge point

os shown in Figure 2.1, ond toking tim€ to consider the procti-

coldesign qnd construction ofthe olternqtive loyouts (i.e.

selected potentiol sites). Eoch possible loyout will require

construction work on diflerent pqrts ofthe potentiol site ond

the surveyor should th€rcforc note on which pon eoch compo-

neni ofthe scheme will be locctsd. The overview should note

feoturcs thot moy 0ffect the d€sign ofth€ scheme, such os slope

stobility, ond lond us€ ond ownership. A sk€tch mop of€och site

plon should be mode os shown in Figurc 2.2.

23.2 LOCATION OF COMPONENTS

For eoch ofthe olternotive loyouts selected du ng ihe site visit,

locotions ofeoch component should be identif ied ond th€n

included in rhe site plorl os shown in Figure 2.2. Nore thot

generolly the locotion of th€ intoke is the key cornpolrerlt in

determining the site loyout, sinc€ th€r€ is usuolly only one most

oppropriote intoke locotion. Ther€fore the intoke lo(otion moy

determine the locotions qnd qligrlments ofother components.

lntoke selection is covercd in Chopter 3.

once oll olternotives hove been identif ied, the most

suitnble loyout shou)d b€ chos€n. Ap0rt from the project cost.

the followirrg ore (he nlqLo criterio thot should be used to select

the most suitoble loyout:

. The combinotion ofheod ond flow ofeoch olt€rnotive

should b€ such thot the required minimum power

output is feosjble.

o Preference should be given to the simplest loyout in

terms ofdesign ond construction.

. The shoner rhe qlignment ofthe scheme is, the less the

requirement for construction moteriols. H€nce, such q

scheme con be constructed f0ster ond ot o low€r cost.

. The powerhouse should be os close os possible to the

lood centre. It is odvisoble to keep the tronsmissiol line

length less thon 2 kilometrcs.

. Finolly, techDic0l porometers such os overo)l slope

stobil ity, f lood risks, ond other site-specific issues should

be consider€d.

Y'r.{ t l u f t\ l \ ,

[ ..r

f d 6dr.-

##a.-)\ ,

r)n k t 1 /

4Flgurc 2.1 Viewing the site frotn o vontoge point glves the opportunity t0 ossess the options for the loyout ofo scheme

Y i l l q g eoo

q reqar o Ea a

Trqnsmiss ioa l j

PoWerlrouse- Qve\oc,F, Q,li!n

Rive r tzr rq.a spillrrzo

l r r i q q { i o a c - q n q

Tqi lrq.'

. ! Fore-bqv

Corn f isld

Corn F i

Sgt t t : "_g !SS;n

S P i l l w a

l leqdrc<.e. C-qnqlG r a v a - l { t

Figur€ 2.2 Atypicol site plon

_5lT E Pt,qN

r l

2.4 Geotechnicol considerotions

2.4.7 GEOLOGY

The geology ofthe site is crit icol to the design, costs ond future

performonce of the civil works of micro-hydro schemes.

Geologicol mops ofcertoin qreqs ofNepol ore qvoilqble qt the

Deportment of Mining cnd Geology or Tribhuvon University's

geologicol librory. It is worth checking whether such o mop is

ovoiloble for the oreo of interest since this will indicote the

generol geologicol condition ofthe site.

Geologicol chorocteristics ofo site con be grouped in the

following woy:

c Major weakness zones -Lorgeoreos ofgeologicol

instobility in the oreqs where the clvil structures ore to

be locqted.

o S/ope stability - The degree ofstobility ofthe hillsides of

the site.

. Sorl and rock fypes - Foundotion conditions ond liobility

t0 seepoge undermining ond subsidence oround

structures plonned for the site.

2.4.2 MAJOR WEAKNESS ZONES

The moin tectonic zones of the Himcloyos generolly correspond

to the physiogrophic divisions ofthe country ond run in

northeost-southwest direction. Mojor weokness zones such os

thrusts or fqults seporote these zones from eoch other. Inqddition there ore mony other "minor" weokness zones which

could significontly impoct the project. If qvoiloble, o geologicol

mop of the oreo where the micro-hydro scheme is proposed

should be consulted to ovoid plor:ing civil stmctures 0n these

mojor thrusts ond foults. If circumstonces dictote the inevitobil-

ity ofplocing the scheme in such zones, expert help from o

geologist should be sought.

2.4.3 SLOPE STASILITY

In geologicol terms, the hil ls ond mountoins of Nepol ore young

ond unstqble. They could be likened to o pile of sond in thot the

excovotion olong o slope eosily results in the sliding ofthe lond

obove, especiolly when o further triggering mechonism occurs

(porticulorly during the monsoon). Common triggering

mechonisms ore the followino:

. Surfqce woter

r Ground woter

r Undercutting ofslope by excovotion

The stobility of slopes will qffect the design of oll

components of o micro-hydro scheme qnd should therefore be

onolysed thoroughly, porticulorly in the following key oreos:

o Above ond below proposed conoi routes.

o Below the proposed locotion ofo settl ing bosin or o

foreboy tonk.

o Along the proposed penstock olignment.

r Above ond below the proposed locotion ofthe power-

house.

Threots in these oreos will either toke the form of

weokening ofthe support oround the foundqtions through lond

slipping owqy 0r collopsing, or domoge t0 structures through

folling debris, os shown in Figures 2.3 ond 2.4 ond Photogrophs

2.1 ond 2.2. tndicqtors ofslope instobii ity ore presented in

toDIe z. I .

figure 2.3 Threot to structures from below due to londslip

Figure 2.4 Threot t0 structures due to folling debris from obove

Photo 2,1 Tension crocks olong oslope Photo 2 2 Obstructions coused by debris follrng from on unstoble slope

tlbk 2.1 Indicotors ofslope instobility

sEcnoN 0F sroPE INDICATOR OF INSTABILITY

LJpper, middle or lower hillslopes Tension crqcks qlong slope (Photogroph 2.1), ground shelves shorply, trces leoning downslope

or bending upwords from the bose, woter springs or seepqge qt bose ofslope, displocement

of pqths, fence or posts.

Fresh rock foces exposed, presence ofsoft, weotheroble rock, openjoints in rock, tension

crocks, overhongs qnd loose rock, woter springs or seepoge ot bqse ofrock foce,

Frcsh d€bris ot bose ofslope, tree roots exposed,loose debris which moves underfoot,

profiles steepen towords bose ofslope, debris littered with deod or ovenurned woody plonts

ond oross clumDs.

Bpos€d foces of londslides

'lle followilg feotures ofthe slope or rock foc€ indicot€ slop€

stobilitf

. complete vegetotion cover, including trees stonding

verticolly

. Stroight, even, slope prolile

I Rock surfoc€s covered with moss, lichen or 0 weotheR

skin

. Hod, impemeobl€ rock

. Rock with no or fewjoints

. Closed mckjoints

. W€ll.pock€d d€bris, especiolly with fin€ moteriol

p0cked into voids between coorse moteriol

. Well-estoblished trees ond shrubs

. No octive gullying (olthough o stoble gully system

moy be present)

The incRosed Imowledge ofthe sit€ goined ftom 0 thorough

investigotion ofthe slopes will influ€nce the design ofthe

whol€ scheme, poniculorly the locotion ofprincipol

srruclurEs.

The recommend0ti0ns frOm thp rnvesligotion ofsl0pe

stobrlity 5hould iollo!\, rwo bcrsic rules:

. Never construct on fi l l , thot is, lond \,vhich hos beerl

builr up or f i l led using excovot€d moteriol.

. Avoid the locoli0D of structLrrcs close t0 londslide zones

2.4.4 SOIL AND ROCK TYPES

The surveyor should investigote whot locol a0nstrLrction

moteriqLs such os soil ond rock ore ov0iloble ot site. Possible

uses 0fsuch moteriols 0re preserted in Toble 2.2.

The type of soil or ro(k olso oflecls thf lourdotion oi

\ r f l r t u r e . 0 n d l l - p L u n 0 l t y p e . f o r p x o n r p l , . . f h e . o i ) t 1 p e , .

sondy loom, o lorger tbundoti0n depth is .equired. 0n the

oth€r hond, structures moy be built directly on hord rock

with0ut ony excovoli0r). Similorly, l ining nl0v not be requjred

for heodroce ccnol if rhe soil type is cloy HDw{rv€r, l ining wil l

be required ifthe oLgnmcnt rs through sondy soil.

Subsidence is coused by the locotion 0fqcid substonc€s

in the locol groundwoter octing on solubl€ rocks such cs

limest0ne. by the presence of rocks which ore l ioble t0 spli lt ing

ond l0liotioir, oi bV undcrEround cdverns \rhich cre prone to

coLlopsc. The presence of thick loyers of loo!c sqndy soil (Ioy

olso Leod to subsidence.

These chorocteristics qre identilled by coreful observo-

ti0n 0fthe site. Limesione 0utcrops, sinkh0les (holes of 2-10 nr

in diom€ter which lorrrl when the i im€storle beneoth diss0lVeJ,

cousing the s0ilobove t0 collopse), the oppeqronce olstreoms

or other seepoge from depressions or crocks in the ground

surfoce ore excmples 0l choroctri istics ro look for.

Undermining refers 10 the octj0n of surfuce woter on the

tbundqtions 0fsrrucrures. The iDtoke ofthe scheme ond the

penstock ore porticulorly prone to undcrminlng where surloce

woter threqtens the structures, but the h€odroce conol is olso

vulnerqble.

Toble 2.2 Possible use ofsoil qnd rock in micro.hydropower

2.5 Hydrology ond wster ovoilqbility

2.5.1 PRf,DICTION METHODOLOGIES

Hydrology dictotes the size ofvorioLrs micro-hydr0 conponents

like the turbine, chonnelond the penstock.lt olso hos gfeot

influence on the schene being designed over or under copocity.

The g€ncrol pro(tice jn Nepol tor mlcro-hydro sch€m€s is t0 visit

th€ sjte dufLng dry secson ond meosure the flo!v. The scheme is

then designed bosed 0n thjs flow This moy leod to situotions

wherc the l lows ore less thon the design flow ond consequently

turbines orp pr0ducing less porver thon expecled The foct thot

nro ny n lc ro hyd ro . h rnr?5 . rL Nepo l repon grnr ro r lon woy

below the iostolled copocity is strong evidence of this. It is

imperotive t0 understond whether the flow wos meosured in o

drier thon riyeroge yeor or in on overoqe yeor, becouse ofthe

influence th0t this hos on selecting the design florv. To be oble to

produce o design flow os occurqlely os possible. o prediction

study must be undertoken.

Most potentiol micro hydropower sites orc locoted on

ungouged cotchments where site specific hydrologic doto is

lo.king. To estim0te yield from ung0uged corchmerts, two

techniqLles qre currently ovoilqble to predict f l0ws. These ore

known os th€ WECS/DHM ond lhe MIP methods, and qre

present€d in the subsequent discussions to predict f lows in

ungouged cotchments in Nepol.

f iow€v€r, o( o rcgi0noi troining workshop on low flow

meosur€ment ond onolysls orgqnised by ICllr{OD in April 1999

in I(othmondu, Nepol, it wos reported thot both the WECS/DHM

ond MIP methods for estimotrng yield from ungouged cotch-

ments hod mojor drowbocks, ond use ofthese methods hod to

be ex€rcised with extro ccutlon- It was recommended thot rhe

WECSiDHM sludies be revielved, ond estimotion ofthe porom-

eters be updoted from time t0 time. In this regord, DHN'I is n0w

colloboroting with WECS Io rsview the pr€vious studies, ond

improve 0nd updot€ the por0nleters by using more stotions

with Longer records ofdcto. [t wos stressed rhot with Nepo]

focing blg problems in estimoting the d€sign low flows for o

N'IE OF SOIL

OR ROCK

POSSIBLE USE IN

Ii'IICRO.HYDRO CIVIL WORKS

TRIATMENT BI]FOR-L USE

Sond Concrcte

Ag!reg0te in concrete

Bed moteriolin droins

Cdbions ond masonrv

Conoll ining

Musr be selected or thoroughly woshed to be free from orgonic motter, fine

ponicles, cloy lumps 0Dd excessive mico.

Musl be corefully soned ond woshed.

Must b€ wosh€d.

N{usl be selected for c0rr€ct type of rock, density ond size.

Testing ofcloy content required to ensur€ thot it wil l serve os on

impermeoble loyer

crovel

Rocks

Clov

10

v0riety of opplicotions including micro-hydropower, o Ielioble

method wos urgently required. In this c0ntext, the lnstitute of

Hydr0logy, U.K. is undertoking 0 project titled 'Regi0nol Flow

Regimes Estimotion f0r Smoll-scole Hydropower Assessment

(REFRESIiA)" in coilcboroti0n with ICIIUoD ond DHII from 1999,

which oims to provrde o relioble method for estimoting the

hydrologicoiregime ot ung0uged sites in the Hrmoloyon r€giOn

0fthe country RIFRISHA is scheduled to b€ rtody in obout fivo

ye0rs trme.

WhcslDepotr|Jfjent of Hydrotogy and

Meteorolry pHMl method

The woter qnd Energ-v conlnrissi0n Sccretoriot (wECs) cud DHN{

(Rel4) method ls b0sed 0n 0 series of regression equ0tions thot

orc derived from onolvses ofoll the hvdrologi[ol records ir0m

Nepol. The findings ofthis l"gfession onolysis hov€ b€en used to

produce €quotions for predicting different hydrologic poronr-

eters such os the l0!v flols, flood flows qnd floiv durotion

rurves.lt js beyond the scope ofthis boQk to exploin in det0il

the WICS/DHIVI meth0d. Reodels ore odvised to consult the

Rfercnce. detoils 0f \\ hr.\ ore provrded in Chop'er I L Appen-

dix Adescribes this method with qn exomple.

lledium lrrigation Project method (MIPI

lh€ MIP method pre5€nts o technique ibr €slimcting the

distributloi, 0f nont hly ilows throuqhout 0 yeor'for ung0uged

l0t0tions. Th€ lvllP m€thod0lOgy uses o dut0hqse consisting of

DHM spot meosurenenrs. The 0ccosionol wddjng gougings

conducted by DHM include only 1ow llows ond these flows d0

not rPpresent the noturol c0ndjtions since they ore residuol

llows amoining ofter obsrroction ior different purposes like

iriq0tion. MIP pr€sents non-dimensionol hydrogrophs of meqn

rnonthly fl0ws for seven difierent physiogr0phic regi0ns. These

hydrogrophs present nonrhly fl0ws os o rotio ofthe flow in

April (0ssumed IOwest onnuol flow). For opplicotion to

ungoug€d sites, it is necessory r0 obtoin o I0w flow dischorge

e5tim0te by gouging ot a pofticulor site. Th€ m€osurcd flow is

then used with ih€ r€gionoL non dimensionol hydrogroph t0

synlhesise on 0nnu0l hydr0gr0ph for the site. Appendix A

describes this method rvjth on exomple.

Comryisons of the WECSIDHM s,,d the MIP opprooches

IIDCSIDHM: D€lio€otion 01 droinoge bosins qnd elevati0n(ontours oR oft€n distcfird on rhe cv0rlobl€ mops: olso

ngmsions wen derived 0n lhe bosis ofobserved 0ows for

c0tdlments ronging in size fr0m 4 up t0 54,100 kTn'. Therefore,

fol llows in smoller cotchments the results would prov€ to be

unnlioble.

MIP: The MIP method opprooch bosed on wodrng meosure.

ments tak€n 0n on int€rmittent b0sis connot be expected to

give 0 good estimotion oftot0l f low in the monsoon months, it

con, however, give o reosonoble opproximotion ofthe divertoble

flows in these months. In the rvet seoson months, NllP would be

expecred to underestimole WECS tlqures, which should more

0ccurotely represent totol f low In the dry seosor l i l lP ond

!VECS should both provide rotol f low estimotes. The MIP

prOcedure, which €xplicit ly odvocot€s the use 0floc0l doto to

odjust the regionol hydrogroph, should give r€osonobly

occurote estimotes through rhe dry seoson months thot ore

crit icol in ossessing micr0 hydro projects.

Not€ drot neither the WECS/DHM nor ihe MIP n€thOds

rvere derived from doto for high oltitude snow'fed cotchments.

F0r such cotchments, more weight should be given to the results

of site meosurem€nts.

It must be €mphosi5ed that one con get o fe€l for 0nnuol

i loods by meosuring f)ood lev€ls ot sjte. Silt ond debns depos-

ited olong the river bonks or l€veljust below th€ vegerction

growlh 0re irdicoti0ns ol l lood depths. By meosuring flood

deprh, width ond overoge gr0dient ofthe river ot the intoke

orco, it is possible to calculote the flood flow using I ' lonning's

equotion, described in 4.3.2. I l is beyond the scope ofthis book

to dcscribe the different methods ofriver gouging: pleos€ s€e

Re[. I or Rel. 2 fbr guidonce.

2.5.2 PROCEDURX TO ESTABLTSH fiE DESIGN FLOW

l. C0ndLr( | 0 flow n.eosurement ol srle during the dry

Jeo\on rNov( mber \1oyJ. Pr|.fcrobly rn February lor

snow-fed rivers ond li{orchiApril for 0ther rivrrs. Note if

the yeor is drier thon overog€, overoge or wettcr lhon

overoge This con be estoblished by tolkiog to rhe locols.

Consider ifthere orE sjgnificont obstroctions by 0ther

wqter users, such os jf igoti0n ond drinking woter

schemes upstreom ol the p0int where th€ gouging wos

conducted.

2. Colculote :

. Averoge nlonthly flows by using WECS/MIP methods.

. Flow durotion curve using WECs.

. lnstontoneous flood 0ows ofdifferent return periods

using WECS.

L compore the dry seqson rneon monthly flows obtoined

by IVECS ond N{lP method. lfthe tlow meosur€d ot site is

0bout overoge occordjng to the locol people, romp0re

the dry seoson meon moDthly flow obtoined by the

WICS method with thot obtoined by the lr'llP method,

ond use the lower volue. Ifthe fl0w wos meosured ot

11

sit€ du ng elther o wetter thon qverqgr yeqr or o drier

thon overoge yeor, then use the volue obtoined by th€

WECS melhod.

Use the llow durorion curve (FDc) to estoblish theprobobil ity of exceedonc€ ofthe volue fron step 3. The

FDC is useful becouse the power €quivolent ofthe flow

con be superimposed onto it, so thot it is p0ssjble lo reod

ofl the omount oftirne eoch ye0r thot certoin power

levels con be obtoired. This is o useful plonning tool,

oJlowing o choice ofsize ofturbine t0 be mod€, together

v,/ith 0n indic0ti0n 0frcquired vorioble flolv perform-

once ofturbine 0nd on indjc0tion ofthe plonl f0ctor

constroints which wil l result from ony portjculor choice

oftu.bine siz€. S€e R€f. l fordetails.

Decide on whct perc€ntoge ofthe l low es(qblished in

st€p 3 cqn be div€fted for power generotion. lfusing a

temporory weir ossum€ thot 50% ofrhe 1l0w corl be

divened. lfthe rive! preselts farmidoble dimculties,

ossume less thon 500/0. If using o permqnent w€ir

founded on bedrock ossume 954/0 ood for weir bosed on

olluvium foundotion, ollow for seepqge losses ond

ossume thot 90olo of the flow c0n be drvened.

Toble 2.3 cqnql seepoge losses

N PE OF SOIL SEEPACE LOSS, (lh/1000 n'

OF WETTED AREA)Rock

Impervious cloy loom

Medium cloy loom

cloy loom or silty soil

crovelly cloy loom or sondy

cloy or grovel cen€nted with cloy

Sondy loom

Sondy soil

Sondy soil with grovel

Pervious grove)ly soil

Grcyel wrth some eorth

<0.5

0.8 - 1.2

1 .2 - t .7

1 .7 ,2 .7

2 .7 ,3 .5

3.5 5.2

5.2 6.4

6.4 8.6

8.6 - 10.4

10.4 20.8

5.

6. c0lculote seepoge losses f0r the w0ter conveyonce

structures. Th€se iosses must be deducted fr0m the flow

estoblished jn step 5. Ssepoge colculotion is covered jn

Section 2.5.3.

7. Consider iftherc are other rvoter users such os jrdgotjon

ond drinking water dowlstreom ofth€ diversion works.

Estobiish th€ omount of flow that hos to be r€leased

downstrrom ond deduct this omount lr0m the 0ow

ifom st€p 6. This is the design IIow.

A design exotiple is inciuded in Appendix A.

2.5.3 SEEPAGE

It i. imperolive ro exomine lhe soil olong the r0ute o[the

proposed conol ond estimote the omount ofseepoge thot o

cqnol mqy suffer, on imponont issue thot is often overlo0ked by

Dicro-hydro designers. Thls is especiolly trut for micro-

hydropower schemes with long unlined conols. Toble 2.3 gives

conol seepoge losses for djffer0nt soil tvpes. By colculoting th€

wetted oreo for o given cross section ofthe conol, seepoge con

be colculofed using doto from the toble. [x0mpie 2.1 i l]ustrotes

this method.

2.6 Otherconsiderotions

2.5.I FLOOD RISK

In site investig0li0n, the concern is for the selection ofthe b€st

option for the desjgn ofthe scheme. Therefore know)edge of

flood levels is imponont ot the two extremes ofthe micro'hydro

scheme, the intoke ond the powerhouse, 0r ot other pons ofthe

A 500 metre lorlg unlined heodroce conol is to be con-

structed in sondy cloy to convey o design flow ofO.l m?/s.

A stondord tropezoidol s€ction is pmposed with o depth

of0.2 m, o bonom width of0.6 m ond side slopes of1:2(V:H). Colculote the seepoge loss in rhe conol.

Solution:

The wetted perimet€r (P) ofth€ ccnol con be colculoted

using the following equotion:p = s + 2 x H x {ifM(see chopter4)=o.o+zxo.2xVi iTZT= 1.49m

The wetted dr€o: P x L

= 1..19 x 500= 747 ml

From Tobi€ 2.1, seepage loss ir sqody clcy is 3.5 lA/1000

m'z ofwetted oreo. Th€ seepog€ loss is giv€n by:

q.,! = 3.5 x wett€d or€oi 1000= 3.5 x 747 /1000= 2.6 Vs

Which is 2.6% of the designed flow of the conol.

12

scheme thot moy be lulneroble to flood domoge from the river.

Flood l€vels moy be pr€dicted by hydrologicol colculotion

from ovoiloble doto to give the 20 yeor or 50 yeor 0ood level, 0r

by ronsulting locol people. ldeolly, both methods should be used

t0 give 0 relioble estimote. Alwoys cllow o morgin oferror so

thot o rore llood event is ollowed for, ond think rorefully obout

how the floods will olTect eoch ofthe prcposed loyouts for the

proJect. The locotion ofthe poweftouse higher oD o slope will

rcduce the ovnilobie heod ond therfore hcve on importqnt

unpoc on the.opoory ond the economrcs ofthe prqect.

2.5.2 CROSS DMINAGE

Sometimes, because 0fthe n0tur€ ofthe topogrophy, the

he0dmc€ conol ond/or the pgnstock olignments will n€ed to

cr0ss gullies ond smoll streoms. Note thot dry slopes ole more

stobl€ thqn soturoted slopes. Surfoce woter con be diverted by

conslructing v0rious t)?es of cross droinoge works. For

exomple, cotch droins con be constructed uphill from the

rnicro-hydro olignment to divert th€ surfoce runoff. Cotch

droins ore smoll chonnels thot divert surfqce runoff(thus cotch

it)qnd diveft it int0 neorby gullies or noturol drqinqge.

Another exomple ofcross drqinoge works is the use ofo

superpossoge. This is o covered heodroc€ conol orrongement

sudr thot the surfoce runoffllows over it whereos the design

flow is sofely conveyed in the conol.

2.6J WATER RIGHTS

Sometirnes there con be woter use conflicts betw€en the

pmposed micro-hydro sch€me ond other prior uses oFthe source

stnon. For €xomple, ifthep is on irrigotion scheme down-

stn0m 0fthe proposed micro-hydro intoke thot moy r€ceive less

wot€I {once the micro-hydro plqnt js commissioned), thelt will

be conflicts. Such w0rer righrs issues should be rcsolv€d beforc

inplementing the micro'hydrc sch€me.

It sh0uld b€ not€d thqt irrigqtion ord micro-hydro ccn be

c$ordjnoted ifon cgrc€ment with oll conc€rned porties is

Rodred in the initiol stoge. This is b€cqus€ inigqtiorL woter is

not ltquind throughout the yeor orld thercfore woter cqn b€

us€d for power production ot other times. This moy resuit in

less or even no power ovoiloble during peok irrigotion period.

fiow€ver, ifthe elertdcity users or€ olso owners ofthe irrigot€d

lond, they con prioritise their needs, such os by irrigoting in the

oftemoons ond nights ond producing power duriDg mornings

ond evenings.

2J.{ tiND OWNEnSHIP AND LqND USE

T1I€ surveyor should note down the issues conceming lond use

ond ownership. Ifthe olignment trqvers€s thrcugh o form€r's

poddy neld, the lond moy hove to be boughr by the prcj€ct.

Another €xomple is thot on open chonn€l heodroce moy be

technicolly feqsible but the designer m0y hove to choose o

buried pipe ifthe heodroce olignment is r.rlong cultivoted lond.

Similorly, sediment flushing ond spillwoy flows need to be

sofely diverted owoy from cultivoted lond. It is importont to

note down londowners whose lorld will be used for structures,

so thot ogreements such os leose orrongements cqn be negoti'

oted. These foctors will offect the design ofth€ schene.

2.5,5 HIGH AITITUDE SITES

These guid€lines ore g€n€rolly opplicoble to micro-hydropower

in Nepol, but some porticulor m€osurcs n€ed to be tok€n for

high oltitude sit€s to ovoid ill'efffects fmm fr€eziDg tempero-

tur€s.

To 0void frost dom0ge to concrele ond mosonry, th€

following meosurcs ore necessory:

. Keep the woter to cement rotio os low os possible,

pr€ferobly not mole thon 0.50.

. Avoid oggregot€ with o lorye moximum size, or o lorge

proportion of fl ot porticles.

. Use o woter reducirg oir entrqining ogent (plosticiser).

. Ensure good compoction.

. Do not build while night temperutufts ole below

freezing. Surfoces must be prevented from drying out

for ot leost three weel6 ifthe ombient temperoture is onqverog€ 5oC or less.

To ovoid ice domoge to conols ond structurcs, the woter

foce of wolls should b€ smooth concrete or plost€red mosonry

oDd inclined ot 0pproxrDotely l:1. The exponding ice con then

ise between the wolls, inst€od ofpushing the wolls aport.

Heodrqce c0nols should be designed for o minimum

velocity 0f0.6 m/s. Ev€n though the surfoce mcy frceze, woter

will flow under the ice.

The rop ofrroshrqcks should be below ony exp€cted ice

lev€1, to ovoid ice forming oround the troshrock bors. Timb€r

trsshrock bors moy b€ less lioble to icing thqn steel bors.

Th€ foundotion l€vel of structures should be below the

deprh of ground freezing. This is )ikely to be obout one metr€

depth.

2.7 Plonning

Th€ plqnning ofcivil engjn€ering works lor lorg€ projects is 0

complex process ond the skills Iequired ore considered to be o

seporote disciplin€ within the fi€ld ofcivil enginee ng. The

reqson thot plonning is given so much importonce ir th0t the

project construction cost con be significontly brought dowr by

13

emcient co-ordinqtion of lobou! €quipment ond mot€riols. This

eruur€s thot the Esources orc used ot their moximum prcduc-

tlury

As mentioned eorli€r. the plonning ofmicro'hydro civil

work does not rcquire the detoiled work oflorge prcjects-

However, the principles orc the sqme ond corc needs to be tqken

to follow some bqsic rules. The pmcess ofconstructing micro-

hydro civil works hos three ports:

. Unde$tandingwhot hos to be built

. Estoblishingthemethod, €quipment ond the p€ople

required

. Corr!'ng outthework sof€ly, economicolly ond to the

quolity r€quircd to sotisry th€ cli€nt.

"Ihe undentondingpqrt ofthe prcc€ss sounds stroightfor-

word, but it should not be overlook€d. civen the likely number

ofpeople involved, effective commumcotion ord cleor demqrco-

tion of responsibilities ore essentiql in plonning. Everyone

needs to lanow whot they ore occountoble for ond to whom.

There orc a number offoctors offecting hoq when ond in

whot order the work con be corried out. A checklist of these

foctors is os follows:

. Performonce ofstoff, €quipment ond moteriols.

. Avoilobility of stoff, equipment ond moteriols.

. Holidoys ond festivols.

. Access to the site.

. Weother, seosons.

r Avoilobility oftunds.

. Sit€ geology qnd topogrcphy.

. Existing use ofthe site qnd its boundories.

. Public relotions.

PRporing o "Project Implementotion Chort" in the

initiol stog€ is olwoys helpfr.[ since it will indicote whot

octivities ore in th€ criticol poth ond ollow for plonning qheod.

Undoubtedly, such o chort wiU undergo frequent revision

du ring the construction phose- However, it is stil helpful to

formulote o chort ord moke chonges os necessqry since it con

be used to monitor the progress of work ond plon for futurc

octivities such os procul€mellt ofconstruction moteriols ond

lobour orlqngements. A typico] implementotion chort is

showninFigure 2.5.

Activity Durqtion in months

1 2 3 4 5 6 7 8 9 10Public relotionsi oworeness roisino il D

Site survey including lowflow

meosurement & dotq processingI

Detoileddesign sFinoncing

Tendering ond oword of

construction contrqct @6weeks

A n

Fobricotion & supply ofsteel ports

(penstock, troshrocks, flush pipes etc.)

construction of heqdroce cqnql o N

Construction of settlino bosin & forebov N

Construction of mosomy wol & gully crossing s F T

Insto.llotion ofp€nstock & construction of

onchorblocks & support pie$

o E

Fobricotion & supply oftuftine. beh drive

ond otierelectrGmechonicol eouiDment

s

Instollotiol of tronsmission Iine N T A

Powerhouse construction T I

Electrcmechonicol instollotion qt powerhouse

Testing & commissioning A

Proj€ct hondover to the client L

Figure 2 5 A rwicol Prolect lJnplemcnlohon Chon

74

2.E Checklist for site selection

IAND OWNERSHIE LAND USE A,I!D WATER RIGIITS

H0ve 0ll issues conc€rning lond use ond owlership been duly

recorded during the srte visit? Does the olignment troverse

through o former's poddy field or is jt olong bqmn lqnd? Hove

woter rights issues such os irrigotion use b€en odequot€ly

oddressed?

INTAXE

Moke sure woter con be diverted qwqy from tie river ond

towqrds the heodroce. Does the river course oppeor stoble or

does it look like it will meonder? Think obout floods ond flood

levels. Does lhe riv€r corry l0rge boulders? Ifso, think obout

temporory diversion works r0ther thon o permonent w€ir.

GRAVU, TRAP

Does the river c0rry o sigflificont omount ofgrovel during the

monsoon? If so provid€ 0 grov€l trop os close to the heodworks

0s possible. Con rhe grovel be eosily flushed into the stl€om or 0

neorby gully from the grovel trqp?

SETruNG BASIN'this

stucture should be locoted qs close to the intoke qs

possible. The e0rlier the sediment is removed the less rhe

mohtenonc€ in the heodrqce. Ifthe source river is not for owqy

tle sedimenr c0n be dischorged bock into ir.

IIEADRAG

Il generoJ the heodroce olignment should be on level to slightly

doping ground. Ifthe olignm€nt is ste€p, corsider using o

h€odroce pipe insteod ofo conol. Try to get the olignment owoy

ftomtbe river os eorly os possible to minimis€ llood domog€.

Pmvide escopes upstreom oforeos where the conol might be

blocked by lorddides. tfseepoge fiom the heodroce cqnol con

trigg€r londdides, think obout hning the conol or using pipes.

FONBAY

Allowonce shonld be mode for finol settling ofsediments.

G€nerolly. this structurc should be locqted just uphill ofthe

tr0nsition 0reo whete the ground profile chonges from Ievel to

ste€p, ts th€Ie o possibility to sqfely dischorge the €nt[e flow

ftom o spillwoy in cose ofsystem m0lfunctiol?

PE{STffX

Tle p€Ntock olignmenr should stort where the ground profil€

gets steeper. An ideol ground slope would be between 1:1 ond 'l:2

lV:H). The Ilqtter the ground slope, the less economrc is rhe

p€trsto&.lt is dimcult to mqnuolly loy penstock, construct

support piers ond onchor blocks ifthe slope is greqter thon 1:1.

Also try to minimise bends since th€se will require odditionol

onchor block.

POWERIIOUSE

Moke sule thot ther€ is enough spoce for o powerhouse with the

requiftd dimensions (to fit the electro-mechonicol equipm€nt)

ot the loc0tion sel€cted. Excqvotion con be minimised by

locoting the powerhouse on l€v€l grcund. Think obout wher€

the toilwoter con be dischorg€d (i.€. tolhoce olignment).ls thepowerhouse high enough obove the river to be sofe from floods?

IAII,RACE

Moke sur€ thot th€ t0ilroce is protected fiom the streom into

which woter emerging from the turbine is dischorged. The

toihoce should be oriented downstreom to prevent floodwqter,

debris, ond bed lood from being funnelled into it toword the

powerhouse.

TR,qNSIItrSSION UNES

ls the vlllqge situoted owoy from the powerhouse site? lfso,

tronsmission lines 0re requipd. The cost oftronsmission lines

Photo: 2 3 A Stroight p€nstock run keeps costs to o mininum

15

qdds significondy to the overcli cost ofo scheme. Consult R€i I

for d€ioiis.

AVAII.IIBIIIIY OF COI{STRUCTION

MATERIALS AND IIAOUR

Constructiorl mdt€riols for micro-hydro schemes thot m0y be

fould at site ore sond, cagregote ond ston€s. Arc thes€ mcte -

ols eosily avoilobl€ 0t site or brought fronl outside? AIe skilled

lobourers such os mosons cnd carpenters ond ulskilled

lobourcrs ovoilabl€ at site?

The unit rotes for such construction moteriols ond lobour

should be obtoined while ot site for esrimoting quonritjes ond

cost ofthe scheme duing the design phose. It is more Ielevontto use prcvail ing rotes rother thon distrjct rotes, which orenorrnol]y lower thon the prev0il ing r0tes.

STAB!UTY

Apon from the obove criterio, it is very impofiont for the entire

scheme to be 0n stoble ground. Ifonly o smc)l length ofthe

0lignment is unstobie it m0y be possible to stobihse ir. Refer to

S0ct ron 2 .4 0nd Choprer 9 ro 0sseqs lh is j ssue.

3. Diversion works

3.1 0verview

The div€fiion works for o micro-hydropower sch€me control

the flow 0fr{oter frcm the source river into the heqdroce.

ThE c0mp*€ o diversion weir (usuolly). on intoke, ond

s0metunes nver troiDing works. The diversion works ore pqrt

oftheheodworks, qnd serve the foLlowing functions:

. m0intoin the design 0ow with nominol heod losses

during both monsoon ond dry seosoDs;

. !rcv€nt, or 0t leost minimise, th€ bed lood ond other

flo0ting moteriols (ice, timber, leqves etc.) entering th€

conol;

. sofely cont0in pe0k flows ir the iver ond owoy from

th€ micro-hydro syst€m so thot domoge is not coused

to th€ structures.

'Ihe principol mointenonce t0sk ossocioted with cjvil

works is oftenthe removql ofsediment orld debris conjed by

$e incoming woter, which con couse domoge to the turbines

should itbe pemifted t0 enter rhe penslock. It is therefore

tlsgltiol th0t the odapted intoke design prevents sqnd, bed

lood ond debris irom entering the intoke os much os possible.

one ofthe p ncipol couses ofproblems in the operotion

ofhydroporver schemes is o poorly designed intake which moy

permit oper0tion ofth€ schem€ in the shon'term but beyond

thot. cous€ serious domoge to the system. The design ofon

oppropriote intok€ structure for micm-hydrc in Nepol requires

on odequoi€ understonding of Himoloyon riven since theyh ' v , < ^ m , , , n i . ' , , f , n r ' , r , c

3.2 Generol principles forselecting intqke locqtion

The mojor considerqtions requir€d to select 0ppropridte intok€

locotiols ore disaussed in this section. It is imponqnt for the

design engine€r to r€olis€ thst much con b€ l€omed from

observing the irrigotion intoke sites selected by locol formers.

The forDers ore fomili0r with the rivem ond hove the odded

odvontoge thot they hove observed them over c long period of

tine. In foct, some of the former monoged irrigoti0n schemes

in Nepol or€ more thon 100 yeors old ond the intokes ofsuch

1 7

sites hove foced most problens brought qbout by Himoloyon

rivers.

The following princrples should be considered whiie

selecting oppropriote intoke locotLons:

Minimol disturbs,ncc to the nstursl stste ofthe iver

Construction ofhigh ond permonent weirs 1lo!g€r thqn 1'2 m)

ocross the totol width ofthe dver is g€nerolly ufldesiroble,

becouse domming hos the eflect 0fropid sedim€nt deposition

ond chonge ofpresent river course,leovlng the lntoke dry ond

useless. The design ond construction of weirs requires coreful

considerotion to qvoid preserltinq on obstocle to flood flow in

the roiny seoson. F0r diversion from o noturol pool, no weir is

required ond woter con be conveyed through HDPE pipes 0r o

covered mosonry flume t0 o heodroce conol.

For this reoson, ottempts should be made to locote

intokes such thot the noturol woter level ot low flow in the

strcom is suitoble for the intoke level ofthe con01. This will

ollow the conol intok€ structure to be built ot stream level ond

the onJy meosures nec€ssory within the streom or river bed

itselfore meosures for th€ stobilisoti0n ofthe present stote of

the streom.

Locotion in on srea which offers nsturol prctection

When withdrowing wot€r from o streom whose level moy

increose morkedly dudng roiny periods, it is desiroble to locote

the intoke behind or under lorge, permonently ploc€d boulders

or rcck, these limit the woter thot con enter the intoke, ond

deflect flood flows ond river borne debris owoy. Advontoge con

olso be roken ofstoble bonl<s 0nd rock outcrops.

Lnation on the oubide ofo bcnd

Therc is o noturol tendency ofthe ver to deposit sediment on

the inside ofbends olong th€ ive. At bends, the direction 0lrh€

flqw clos€st to the river bed chonges compored wjth the sudoce

flow. A spircl flow forms, which tronsports the bed 10od to the

inner side ofthe river bend. On oll streoDs ond rivers it c0n be

observ€d thot grovelond sand bonks form ot the inside bend,

i.e. the bed loqd is dive(ed from the deflecting bonk. As o rcsult

ofthis when the river flow d€creoses, the river width decrcos€s

from the inside ofthe bend. Therefore cn intoke should not be

sited on the inside ofo bend. To minimise sediment loqd ond to

ensure flow (tvoilqbility during the dry season, on intqke should

be sited on the outside ofo bend. The best location is about 2i3

t0 3/4 ofthe distonce oround the bend or lhe outside qs shown

in Figur€ 3.1. Shorper bends orc more effective in preventing

ihe entry of sediment, and the omount 0fbed lood tronsported

into the conol decreoses os the diverted proponio[ ofthe totol

flow ln the dver decr€oses.

FLgure l-1 Locoting intoke oround o b€nd

other considerations

In stroight sections of0 iver, the water flows poro)lel to the

bonks qnd the bed lood is transported olong the bottom.

Thefelore iIl stroight sectians the locqtion of the intoke is

governed by foctors such os bcnk stability and heodroc€

ollgnment.

Ih€ locqtion ofqn iltcke structure must be so chosen

thot th€ lorgest p0ssible ponion afrhe bed load remoins in the

river ond is not dive(ed into the hecdrcce. How€vec even c

good intoke lvill not exciude oll sediment; lhe grovel trqp cnd

seltl ing bosin [unher olong the conql (ompl€te this.

3.3 tntoke locqtion in relotionto river chqrocteristics

3J.1 CHARACTERISTICS OF HIMAJ.AYAN RIVERS

In Nepol, most micrc'hydropower schemes ore locoted in the

foothills ofthe Himolqyon Ronge. This includes the High

Mountoins, Middle Mountoins ond the Siwqliks os shown in

Figure 3.2. It is essentiol to hqve q cleor understonding ofthe

chorocteristics of these Himolqyon rivers beforr opprooching

tbe design ond construction ospects ofdiversion works. These

rivers flow in geologicolly young mountoin structuEs ond con

be choroctedsed os follows:

steep river grodient ond steep slopes olong both river

bonks;

High degrce ofcontinuing ercsion 0nd sediment

rr0nsporT;

Sm0ll€r streqms of steep ond unstoble noture with o

bouldery ol)uviol bed;

Ii0ble to tronsport consideroble quontit ies ofsedirnent

rnc lud ing bou lders dur ing lhe monso0n; .

A significont flow ond s€djment incrcose in the rivers

du ng the monsoon.

Due to these u!ique choroct€ristics, development of

hydropower from the Himoloyon rive$ pr€sents grcot chol

Figur€ 3.2 Feosible locotions of mrcro-hydro schemes in Nepol

lenges. Design ond c0nstruction ofoppropriqte structures to

cope with movement 0f lorge boulders qnd high sediment

loods ore two ofthese chollenges. River intokes used elsewhere

in nlotively flot ond stoble rivers including the Teroi ore

inoppropriote in the cose of mountqin rivers of Nepol.

Ioble 3.1 Cotegories of Nepolese rivers

Rivers in Nepol con be categorised occording to the woy

in which they ore influenced by vorious chorocteristics. The

types of river thot sre mostly utilised in micro-hydro ore shown

in Tqble 3.1.

TYPE GMDIENT

(MArN LOCATToN)

VALLEY SHAPE BED MATERTAT CHANNEL PATTERN SEDIMENT MOVEMENT

(N: NORMAL, F: FLOOD)

1A very steep(Mountqins)

Norrow volley no

flood ploinsRocks, very lorge

boulders

Single N - Sond in suspension

F - ravel. cobbles qnd boulders

IB Steep (Mountoins

ond hill regions)

Norrow volley,

irregulor norrow

fiood pioins

Rocks ond bouiders,

grovel ond cobbles

in shools

One moin plus flood

byposs chonnel

N - Sond ond grovel

F - Includes cobbles qnd smqll

boulders.

ic Steep (Mountoins

ond hill regions)

Norrow volley,

irregulor norrow

flood ploins

Rocks ond boulders,

grovel ond cobbles

in shools

Severol octive chqnnels

os well os floodwoys.

N - Sqnd ond grovel

F - Includes cobbles ond smqll

boulders.

A

,${

ry Intermediote

(Hill regions)

Outwosh river,

confined by

volley sides

Some boulders,

moinly grovelqnd cobbles

Single plus limited

floodwoys

N - Sand ond fine to medium

grovel

F - Includes coorse grovel,

cobbles, perhops smqll boulders.

28. Intermediote

(Hillregions)

Ditto but less

confined volley

Some boulders,

moinly grovel

ond cobbles

24 octive chonnels

with floodwoys

N - Sand qnd fine to medium

grovel

F - Includes coorse grovel,

cobbles, perhops smoll boulders.

2C. Intermediate

(Hill regions)

Ditto but wider

volley

Some boulders,

moinly grovel

ond cobbles

Broided, severol octive

floodwoys.

N - Sond ond fine to medium

grovel

F - Includes coorse grovel,

cobbles, perhops smoll boulders.

Soune: Ref.5

19

33.2 EXAMPLE INTAXf,S'typicol intoke locotions for some ofth€se rivers ore shown in

Figures 3.3 ord 3.4. It should be noted thot these ligures

illustrote only possibl€ locotions for iltok€s, not the prefened

rype ofintoke.

fijver type 1A

Mountoin rivers of Type 1A prcvide fovouroble conditions for

intokes in t€rms ofpermonence qnd lqck ofinterference from

s€diment irl normol conditions.

Iigure 3 3 Slung ofinlokes rn mountoin rive6 ofType lA(Soufte: ReL 5)

Nver We 1B

Int0kes on Type 1B rivers con olso be locoted similor to 1A.

However. these riv€6 provide o greoter choice ofintoke site, ond

p€rmit more permon€nt irtok€ structurcs, either ftom the side

ofthe chqnnel or os qn ongl€d or frontol inroke built inro the

chonnel It is often possible to protect the intoke behind o rock

0utcr0p.

fjver We lC

Intoke selection in these riv€n differs from 1A ond 18 oDly in

rcqui ng contrcl of one or more of the chonnels in order to

ensur€ thqt sumcient flow reoch€s the intoke. A possible

orrong€ment is shown in Figurc 3.4.

Figure 3-4 Siting ofintoke in mouDtoin or ste€p hill rivers ofType lC.(Soufte: Ret. 5)

crsvel bed rtvers

These or€ cotegory 2 rivers (2A, 28 & 2C) which hqve less steep

chonnels compor€d to cotegory 1 types. The riverbeds ore

moinly ofcobbles ond grovel, tog€ther with some boulders.

Intoke siting follows the some generol principles os in cotegory

]. However, these vers provide more flexibiliry For exomple, it

is posslbl€ t0 use morc permonent river control structures such

os concrete or mos0nry werrs ond liver rroining wolls.

Post,ua

l

t_tr00d I

' \

Flow dircdim

R o c l c l i f f ,loce

Route offeeder cqlol O

Phoro 3 I Ar?o olrnrole in o rype 28 river (Dhoding)

20

3.4Intqke types

3.4.1 DESCRIPTION

lypes 0fintoke structure ore chiefly distinguished by the

method used to divert wqter from the river. In micro-

hydropoweq moinly two types of intoke qre used os follows:

r Side intqke

o Bottom intoke

Toble 3.2 Selection criteriq for side und bottom intoke

Aport from the obove types, qn innovotive intqke colled"Coqndq intoke" hqs olso been field tested in o micro-hydro

scheme in the UK. This is discussed in Chopter 10 (lnnovotions).

3.4.2 SELECTION CRITERIA

Tqble 3.2 oids the choice between side ond bottom intokes for

grven conditions.

SEI^ECTION CRITERIA SIDE INTAKE BOTTOM INTAKE

Amount ofwoter: Fqvouroble site selection necessory

(outside ofo bend, or qn qrtif iciol bend

by groins) if the omount of diverted

woter is greoter thon 50% of the woter

supplied.

The bottom screen drqws off the river wqter up to the

copocity limit of the screen (i.e. oll river flow if

screen is lorge enough).

Grodient ofriver:

r very high (i > 10%)

tohigh(1070 >i >10lo)

o meon grodient

(tVo >i > 0.0170)

Fovouroble: mointenonce free operotion

ol'the intoke structure should be ensured^ ^ f ^ - ^ ^ ^ ^ - ^ : L t ^u ) l u l u ) P U 5 ) l u l ( .

Fovouroble

Fqvouroble for very high grodient; con be

mointenonce-free, if properly designed.

Unfovouroble ifi < 10o/o.

Unfovouroble: fine bed lood into the initiql heodroce

conol results in difficulty in flushing.

Plqn of river:

o stroight

r winding

o brqnched

Possible

Very fovouroble ifthe river chonnel is

stoble; when orronged on the outside

bend.

Unfovouroble; donrrning of the river

is required.

Very fovouroble, qs bottom screen is uniformly

looded.

Unfovouroble, os bottom screen is not uniformly

looded.

Unlovouroble.

Suspended sediment

c0ncentr0ti0n:

r high

o low

Suitoble in combinotion with very

ell lcient settl ing bosin.

Well suited

Less suitoble

Well suited

Bed lood tronsport:

. strong

r w€ok

Suitoble os long os sulflcient qmount of Less suitoble

woter remoins in the river for flushing.

Well suited Well suited

Nopted fromRef. 3.

z l

3.5 Side intoke

3.5,I DESCRIPTTON

Side intokes ore simple ond less exPensive thon oth€r tyPes of

intqk€. They ore eosy to build, operqte ond mointoirl Side

intokes ore similor to formers' troditionol intokes for irrigolion,

ond hence the form€rs con qurckly leorn the principles of

operotion ond mointenonce ofthese intokes The slde int0ke of

the 50 kw Golkot micro-hydro scheme con be seen in Photo-

groph 3.2. Note thot to mintmise flood flows in th€ conol, the

intoke is design€d os on extension of the heodroce conol lt wos

felt thot the intoke could be vuln€roble to flood domqge ond

therefore the coorse troshrock is locoted further downstreom

Phoro I2 Srde intote ofthe Coltot mrcro hydrc s.h€me Boglung NPpol

{se€ Appendrx C for lh€ dro!t'ing)

side intokes must be s0fe ogqinst boulder impoct ond

floodwqter entry. They ore m0sr effective when built on the

out€r bend 0fthe river (to minimise the omount ofsediment

drqwn inro the inrqke), neor norurol Pools or sit€d ln such o

wqy thot they ore protecled os much os possible from river

floods (e g behind o permoDent rock outcrop) Side intokes con

b€ used with or without o w€ir

side intoke without web lnotursl Pondl

I[ some coses, orl €xposed intoke structure moy be ovoided by

exrrocting woter ftom behind the shelter ofo r0ck outcrop ln

other coses, therc moy be 0 notur0l cleft ln o rock spul 0r on

opeling b€tween o very lorge boulder 0nd o rock woll' thot c0n

be used os o notur0l intoke. wherever Possible, this type of

intok€ should be preferred, slnce it is the most economlcol one,

ond scfe from the domoge offloods ond debris moteriols. It olso

mointoins the principle of "minimol disturbonce to Ih€ nqturol

stote of ver".

A side intoke withour 0 weir is unLkely to be suitoble for

river lypes 1C, 2B ond 2C, due to the strong possibil i ty ofthe

river course shifting in the future.

side intske with weir

The function ofo weir is to rolse the woter level in old€r to

ensule o constont minimum depth ofwqter uPstreom ofthe

weir This ollows the required flow to be div€rted to the

heodroce os long os there is sufncient woter in the river' Types

ofweir ore desc bed in Secrion 3.6.

3.52 TMSHRACKS FOR SIDE INTAXES

The troshrocks for side intqkes con be mo[ufoctured from flot

steel, ongles, tees or rould bors welded together ot flxed

intervols. The trqshrock qt the intok€ is qlso }clown os'coorse

troshrqck" since the bor spocing is wider hele compored to the

troshrqck ot rhe foreboy. For side intokes, Ihe functiol ofth€

troshrock rs to stop boulders, cobbles, flooting logs ond

bronches from entering the heodroc€ Coorse troshrocks for side

intokes ore Dot designed to exclude grovel ond sedrm€nt This is

thejob ofthe grqvel trqp ond the settl ing bosin.

Th€ size ofthe troshrock should be such thot th€ woter

v€locity is opproximqtely 0.6 m/s (o lower velocity is uneco-

nomic, whereos o high velocity tends to ottroct b€dlood ond

d€bris, ond results in increosed heodloss)

Photo.3.3 wh€re on intoke is lioble to ottroct llooting debris

o troshrock moy b€ necessory (Sn t.onlo)

22

Since boulde$ con frcquently impoct the coorseuoshrock, it n€eds to be robust, i.€. thick steel s€ctions shouldbe used. Depending on the length ond width ofthe opening,notur€ ofthe sediment lood ond the required flow o cleorspocing of50 mm to 200 mm con be used. The side intokecoorse trcshrock ofth€ Golkot Micro-hydro Scheme is shown inPhotooroDh 3.4.

Ptoto3.4 Coors€ troshrock for 50 kW Golkor MHq Boglung, Nepol. 55 mm x l0nI! 00ts ot 75 mm centre to centlP. (S€e App€ndix C for rhe drowingl

3J3 ORItrCE DESIGN

Aside intoke normolly includes on orifice domstpom of theElihrock ot th€ riverbonl, thrcugh which woter is iniriolly

d$wn hto the heodroce. Sometimes, the side intoke isjust ocontinuotion ofthe heodroce conol up to the riverbonk.

However, 0s for os procticoble, on orifice should be incorporotedto limit excessive flows during floods. with qn intoke thot isjust o continuotion ofthe heodroce conol to the riverbonl,€ress flow connot be controlled during floods. Such excessfow col domoge the heodroce conol ond other structurestlowastreom. Howev€r, the orifice need not be 0t the intoke0n0{i.e.0t the riverbonk). If it qppeors th0t rhe intqke is or o

ploin or susceptible to domoge from boulders, then thefiiEce con b€ locqted downstr€om. In such coses the conol

ofthe orilice ond the intoke would be temoororv ondnoy ltquft repoir ofter every monsoon.

An orific€ is on opening (Figure 3.5) ir the intoke from

which the river woter is conveyed towords the heodroce. Theorifice ollows the design flow to poss thrcugh it under normolconditions (i.e.low flow) but restricts higher 0ows duringfloods. The dischorge through on orifice for subm€rgedcondition is:

q = nc fi(r'; rt)

v : c \E(4-hJ

where:

Q is the dischorge thmugh the orilice in m3/s

V is the velocity thmugh the orilice

A is the oreo oforifice in m,

dotum.hh is the woter Ievel in the heodroce cqnol meosured iiom thesome dotum os h,.g is the occelerotion due to grqvity = 9.8 m/s,

Figure 3.5 Side intoke

C is the coemcient of dischorge ofthe orifice ond isdependent on th€ shope of orifice. The volue ofC decrcoses withthe omount ofturbulence induced by the intoke. For o shorp

edged ond mughly finished concrete or mosonry orilice

structure this volue is 0s low os 0.6 qnd for corefullv hnishedoperture it con be up to 0.8.

(h, - hh)will vory occording to the dischorge in the river

since o higher woter level in the ver will produce o gr€oter

heod ot the orifice.

The moximum velocity for o well constructed concrete/mosonry orifice is 3 m/s: ifthe velocity exceeds this volue. theorifice surfoce will be scour€d. For micro-hydro, the recom-mend€d velocity (V) through the orifice during normol flow is1.0 - 1.5 m/s. Stortirg with o smoll orince opening for normolflow (i.e. high velocity) will limit excess flow during floods,

since th€ dischorge through th€ orifice is proportionql to the

hh

h n

23

squore root ofthe difference between the wcter level in the river

ond the heodroce conol (h. - hn). However, if the orilice is

directly ot the river (without o troshrock) the velocity should be

less thon 1.0 m/s to ovoid drowing bedlood into the intoke.

The size of the orifice is colculqted qs follows:

r Assuming o moximum velocity of 1.5 m/s through the

orifice, colculote the required oreo of the orifice opening

u s i n g Q = V x A .

r Fororectonguloropening,A = WxHwhereWisthe

width ond H is the height ofthe orifice. Set H occording

to the river ond ground conditions ond colculote W.

. To ensure submerged condition, orronge the orifice

opening such thot the woter surfoce level ot the

heodroce conol is ot or slightly higher (scy up to 50 mm)

thon upper edge ofthe orifice. Note thot the design of

heqdrqce cqnol is covered in Chopter 4. Hence the

design of different micro-hydro components ore interde-

pendent.

Now colculote h, for the design flow conditions.

The h, is the woter level thot needs to be mointqined in

the river during normol conditions. If the octuol level in

the river is less, repeot the colculotions with lorger

width qnd smqller height of the orifice. If the sctuql

river level is still less provide o weir with weir crest level

ot h,

o Cclculote the flow through the orifice for flood condition

(h, = design flood level). The excess flow (i.e. flow

during flood less the design flow) will hove to be spilled

bqck into the river or neorby gullies in the initiql reach

ofthe heodrqce. This is discussed in the next Chqoter.

An exomple of on orifice sizing is shown in Exomple 3.1

ii,l lIi'l.I

I,ll

ffI;I r

II

Choose c suitoble size of on orifice for o design flow of 250 l/s. The normol woter level in the river is

0.8 m obove the bed level. The design flood level is obout 0.7 m obove the normol woter level. Whot

is the dischorge through the orifice during such o flood?

Q = 0.250 mr/s

Set V = 1.2 m/s :

- o 0.25Orifice oreo (A) =

i: LZ = 0.21 mz

set orifice height (H) = 0.20 m oni'*iArn of orifice (U =* = ** = t.os m' H 0.20

Set bottom of orifice 0.2 m obove the river bed level. This will minimise the bed loqd. Also, set the

dotum ot the river bed level.

Set wqter level ot heodroce conol, hn = 0.5 m with respect to the dotum os shown in Figure 3.6 (i.e.

100 mm above the upper edge of orilice to ensure submerged condition). Note thot loter the heodrace

canol will hsve to be designed occordingly.

q = 6g \Dsq- hJAssume C = 0.6 for roughly finished mosonry orifice.

Q = 0.2t x 0.6ffi3466- ss)= 0.31 m3/s or 310lls

Q *ouioo = 250 l/s: Therefore orifice size is 0K.Discharge through the orifice during flood flow:h, - hn : 0.8 * 0.7- 0.5 = 1.0 m;

Qn*o = 0.21 x 0.6 {2x9.8x1.0 = 0.56 mrls

Qn*o = 550 l/sThe dimension of the orifice ond the levels cre shown in Figure 3.6. Note thot the excess flood flowcon be dischorged vio o spillwoy st the grovel trop or onother suitoble locotion. A second option is toinstoll onother orifice {double orifice system) downstreom.

24

Flood level (1.50 m)#

Oriflco

Not to scalo

Normal wator levol (0.80 m)s

0.40 ms7

0.20 m

Rlver bed lsv€l (0.00 m) / Datum

Fioupl6 Dimensions ofth€ orillce ond levek

Plloro 1.5 Timber plonks ploced horizonrolly in grooves pmvide o low-cost gote in o chonn€l In this cose,

th€ dnb€rs hove b€€n lift€d to oct os o restricting orillce (Mhopung)

whether the river is eroding (o generol lowering ofthe river-

bed), oggroding (o generol building up ofthe riverbed), or

shifting its course. The heodworks design, ond in pqrticulor the

choice of weir, must toke occount ofpossibl€ future chong€s.

When it becomes qpporent thot o weir is required, the

following foctors should be considered for both permonent ond

temporory weirs:

. lf0 weir ocross port ofthe river l€ngth is sumcient, then

it should not b€ ext€nded 0crcss the €ntirc width. Aport

from 0dding extro cost it olso encourog€s sediment

d€position upstreom ofthe weir-

. The w€ir h€ight should be os low os possible (i.e. weir

cr€st l€vel = h,, just sumcient to m0intoin the w0t€r

level in th€ intoke). This mokes the structur€ more

stoble, less susceptible to flood domoge ond olso

minimises sediment deposition.

3.5.2 TEMPOMRY WEIRS

A temporory weir is typicolly con-

structed using boulders plcced octoss

pon or oll of the river width. A diqgonol

olignm€nt mcy r€duce the Rquircd

height ofthe w€ir obov€ the riv€rb€d.

This is the tr0ditional method used by

Nepoli formers to feed irrig0tion conols

or woter mills (ghqttos). ond is used

quite extensively in micm-hydro schemes

in Nepol. For micro.hydrc schem€s in the

lower ronge such os those used for ogro-

processing only, this type of weir is often

oPProPnqte.

Though q temporory weir is

simple and low cost, it hos o few

Iimitotions: for example it is not possible

to divert oll ofthe river f low even in the

dry seoson. Therefore this t]?e ofweir is

b€st suited to situotions where the dry

seoson flow ofthe river exceeds the plont's design dischorge.

3.6 Diversion weirs

3.5.I GENEMI.

A weir is Rquired ifthe flow cqnnot be diverted towqds the

side intole without roising the river woter level, especiolly

during the low flow seoson. Th€ weirmoybe oftemporory

semi-permonent or permonent construction, A temporory weir

is the prefened option for micro-hydro schemes.

In pl0millg o weir, ottention must be given t0 the

geomorphology ofthe river, ond ony chcnges tiot moy be

toking ploce. Alwoys consult with locol people ro esroblish Photo 3 6 A lemporory weirin o Type 28 river{Dhqding)

During the high flows, even if the weir is woshed owoy, it moystill be possible to divert the required flow towords theheodrqce since the woter level in the river is high.

A proposcl lor c temporory weir constructed ofstonemqsonry in mud mortor is shown in Figure 3.7. This isintended to ollow diversion ofo higher proportion of the dryseqson flow, but would still get woshed owoy during theqnnuol floods. Constructing temporory weirs with bouldersos lorge qs con be hqndled monuolly ond including cut-offwqlls and riprop con minimise flood domoge. As con be seenrn Figure 3.7, cut-off wolls ore downword extensions of theweir ct th€ upstreom ond downstreom foces thot reduce

seepoge post the weir. Riprop is on engineering term used todenote the plocing ofo loyer ofboulders for scour protection.

The omission of scour protection would result in scouring ofthe riverbed, eventuolly leoding to the foilure of the weir itself.

Once the river dischorge decreoses, o temporory weir

con be usuolly reconstructed ot l i tt le cost. The repoir ondmointenonce work on o temporory weir con be minirnised bybuilding the weir using rock outcrops, Iorge boulders ond

other noturol protection ofthe river. Good monogement ofcosh for the onnuol weir "rebuild" is required.

ln rnost coses, o temporory weir is suitoble only for thediversion of flows below 1 nrr/s. This fits well into the mrcro-hydro dischorge ronge, since the moximum flow in micro-hydro schemes rorely exceeds 500 l/s. For micro-hydro

schemes, o temporory weir is the preferred option over more

permqnent structures. This is becquse most rivers flowingthrough the mountoins ond the middle hil ls of Nepol corrylorge boulders during the m0ns00n ond therefore onystructure built ocross such rivers is not likelv t0 survtve.

3.6.3 GABION WEIR

Gqbions hove been used extensively in the post, for bothmicro-hydro ond irrigotion intoke weirs, but the result hosnot been very encouroging. The gobion wires ore vulnerobleto domoge by boulders moving during floods, ond ofter o fewqre broken the entire gobion structure moy collopse.Gobions ore therefore unsuitqble in river Types 1B qnd 1C.

However, if there is no significont boulder mov€mentolong the river stretch ot the intqke oreo o gobion weir moybe possible. Ifproperly designed qnd constructed, theodvontoge ofo gobion structure is thot, unlike concrete ondmosonry structures, it con tolerote some ground movementwithout significont domoge. TheJhonkre mini-hydro weir ison exomple of o gobion weir structure (see Figure 3.8 ondBox 3.i). The weir design should include checking:

o sofet! ogoinst scour (by founding 0n rock or lcrge

boulders, or by constructing o 'counterweir' down-

streom to lorm o stilling pool)

seepoge control (by using on impermeoble mem-

brone)

st0bility ogoinst overturning ond sliding

sofety on beoring copocity ofthe foundotion.

a

a

Temporcyweir, stone

Locolion of-0225-cb-ssT--rc

All dimensions ore in mm.

Figure3.7 AtempororyweirpfoposedforthelSkWThorongphedi micro-hydroscheme,Monong.NepolNote the cut'olfwqlls ond ripr(p at downstreom foce.

LO

@o(9

o{(ot \o

M M O M S

HDP f lush o i

140fflnfr HDPEfor irrigotionFore b

G rovel t ro

I n t oke

Poo lG ob ion we i r

i i i g u r e 3 ' 8 [ l e o d w 0 r k s o f r o n g c n ] e n t 0 | t h e 5 0 0 k W J i l 0 n k r e n l i n j I t y d r o s c 1 t e m e , N e p o l . N o t e t h o t t h e i n t o k e , s e t t l i n g b c s i n

structure ond there is no hecrdroce. the topogr0phy is such thct 0 pel)stock olignnlent could be storted ri itht 0t the heodworks.

II

I

, \€r\

Qt

lti7/

4,

27

Figure 3-9 Cross section ofJhonke Mini'hydro drversion welr

ll tr rl E&(

Photo 3.7 Diversion weir of rhe Jhonlce Mini-hydro Sch€me

The 500 kW Jhonlar Mini'hydropow€r Sch€me, locot€d 0n theJhonlqe river, Dolokha, Nepol, wos designedjointly by BPC

Hydroconsult qnd Development ond Consulting Services (DCS). The construction wqs undertoken by DCS. As con be seen in the

section through the weir, to minimise seepoge in the dry seoson, o heovy grode polFhene sheet hos been fixed qt the upstEom

foce of the gobion w€ir' T0 pr€v€nt the sheet ftom being punctured by boulders ond other debris, stone bockfll hos be€n

incorporoted in front ofit. Also to prevent the gobion wires from being nicked by rolling boulders, 150 mm ofploin concrete isploced olong oll exposed surfoce ofthe w€ir.

Dudng o 1995 monsoon flosh flood (esdmoted to b€ o 1:30 yeqr return period flood), this weir wos portiolly domoged. It wos

then repqired. Since then, the weir hos foced two onnuol floods without ony repoirs. occosionql repoir ofthe concrete topping

ondtlle gobionwires oreexpected (i.e. during the onnuol mointenonce period.

2 8

3.6.4 PERMANENT WEIR

Sometimes if there is o scarcity 0f woter, especiolly during the

low flow seoson, ond the river does not corry lorge bouiders, o

permonent weil moy be built ocross the river. Micro-hydro

schemes in the higher ronge (50 kW or obove) ond mini-hydro

schemes (100 kW to 1000 kW) often hove permonent weirs.

Permonent weirs ore generolly c0nstructed of moss

concrete (1:1.5:3 with 400/o plums), or stone mosonry in 1:4

cement mortor. A reinforced concrete surfoce loyer moy be

considered to protect the weir from domoge by boulders moving

in flood. A permonent weir should only be considered if oll of

the following conditions ore met:

r Lorge boulders do not move in the river ot the weir site.

r The river bed is stoble (not eroding, oggroding or

shifting course)

o There is o scorcity offlow, especiolly in the dry seqson.

r Skilled mosons ore locolly ovoiloble for both construc-

tion ond mointenonce.

r There ore suflicient funds for both construction ond

future mointenonce work.

Even if qll of the obove conditions ore met. further

considerotion should be given for remote sites (3-4 doys wolk)

becouse of the cost ond difliculty involved in tronsporting

cement ond reinforcing steel. Besides considering the foctors

mentioned eorlier (use of lorge boulders, weir ocross port 0f the

river if possible ond low weir height), lor permonent weirs

scour protection should olso be provided. The toe ofthe weir

(i.e., downstreom foce of the weir) is most susceptible to

scouring since there is o drop from the crest ofthe weir.

Protection ogoinst scour is provided by cut-offwolls ond

plocing boulders (such os stone soling) or riprop downstreqm of

the weir cs shown in Figure 3.10. The cut-offwolls olso reduce

seepoge under the weir, which con increqse the flow ovqiloble

t0 the intoke during the dry seoson. Figure 3.11 shows onother

option for 0 permonent weir in cose bedrock is found qt the

proposed site. When the weir is on bedrock, deep cut off wolls

ond riprop ore unnecessory. As shown in Figure 3.11, shollow

cut olf wolls ond onchor rods con be used to fix the weir on the

rock surfoce: the anchor rods should be grouted into the rock.

An ulternotive design is described in Box 3.2.

200rhk. Rc cT 12 @ ZOOdc tbothways

12C-V

-2.OOV

o.45v

I lmo I 3560 | tooo I

Note: All dimensions ore in mm. levels ore in m.

Figure 3.10 A stone mos0nry permonent weir proposed for Ghomi microtydro scheme, Mustong, Nepol. The 1:3 slope ollows rolling boulders to tr0vel dOwnstreomthroughthewcirondtheRCCblonkethelpstostrengt l ientheweirsurfoceogoinstobrosionduetorol l ingboulders. Alsonotethecutol fwol lsondr ipropotdownstreom foce.

Stone cement mosorry (

29

Figure I 11 A plum concrete permonent weir proposed for chdmi micro.hydro scheme The lil slope ollows rolling boulders to trov€l downstreom rhrough thew€r ond th€ RCC blonket helDs Io str€nath€n Ih€ weif surfoce oooinsr obfosion due to rollino boulders

Ph.rm concrele ( | : 3 : 6, 4OoloPlums)

2OO lhk RCC (t : 1.5:t500,r-1

Tl2 @ 2OOczc bof hwoys

€A.,.-3-v

t20v

o.@

16 onchor rodlonS @ 3 OOc,t,gortedwith l : I :O.4(cement,sond

Note: All dimensions ore in mm, levels ore in m.rvoler) qrot | .

lnPeru, rTDG hosbeenusing on opprooch to design

ofintokes which uses plonks slotted in piers

perpendiculor to the dil€ction offlow ofthe riv€r

Short reinforc€d con(ete piers or€ constructed ot o

spocing of2 metres. Eoch pier hos verticol grooves

olong its full depth. Then timberplonls ore ins€fted

betweenthe pi€rs by inserting th€ ends ofplonks

onto the slots. During the roiny s€oson, one or more

spons con be removed to regulqte the flow ot the

intoke orilice qnd to ollow river-bome debris to llow

olong it without cqusing domoge to thewhole

stntcturc.

Photo 3 8 slort€d conrrere piers

3 0

I

3.6.5 HEAD OVER WEIR

As stoted eorlier, plocing q weir ocross the river roises the woter

level. Any excess flow thqt is not withdrown into the intoke

flows over the weir. The dischorge over the weir is given by the

iollowing equotion:

Q = C* x L *., x (hou.noo)t t

where:

Q = Dischorge over the weir in mr/s

L *", = Length of weir in m

hou.nop = Heqd over the weir crest level in m

C* = Weir coeffrcient which vories occording t0 the weir profile.

C* for different weir profiles is shown in Tqble 3.3. In micro-

hydro, the weir is usuolly brood with round edges qnd therefore

C* is 1.6..

Table 3.3 C... for different weir profiles

The weir equotion is olso useful in colculoting the flood

levels ot the intake ifthe flood dischorge is known or cqn be

calculotedbosed on the river hydrology. Once the flood levels

ore known, the flood protection wolls ot the riverbonk con be

designed. For hrown dischorge over the weir, the heod over the

weir (ond hence the woter level ot the intoke) con be colculqted

by rewriting the weir equotion os follows:

. lQ f " '! : I - - l"ovef,op

\ c* x L*",, I

Colculotion of heqd over o weir con be seen in Exomple 3.2

3-Z Bottom intokes

3.7.I DESCRIPTION

The bottom intoke, qlso known os o Tlroleon or trcnch intoke, is

o grille-like opening thot coptures woter from the b€d ofthe

river ond drops it directly into the heqdroce. The flow generolly

posses through on opening in o wing woll of the intqke

structure ond owoy from the river. in some coses the grille moy

cover o smsll chomber, but generolly the bottom intqke is

designed os o trench, perpendiculor to the direction of the river

flow.

The bottom intqke is most oppropriote in Iocotions where

there is no opprecioble sediment movement olong the riverbed,

becouse it withdrows bottom woter in preference to surfoce

woter. This type of intoke wos first used for smoll hydro ond

irrigotion systems eorly this century in olpine oreos ofEurope.

Ptofile of crest of welr cw

nlnA

_rh

broad; sharp edges

broad; round edges

round ovedall

sharp-edged

rounded

rool-shaped

1 . 5

1 .6

2.1

1 .9

2.2

2.3

A brood crested weir hos been ploced ocross o river for a

micro-hydro intqke os shown in Figure 3.12. The weir

height is 0.5 m snd the length 5 m. How high should the-flood protection woll be for o 20 yeor return flood of 11

*,/j?_ ,C* = 1.6 for bmod crested weir

Flood level

Figure 3.12 Brood crested weir

h -/ a J*'"ovenop \ c. x Lr.o ,

Note thot C* is 1.6 for brood crested rveir

t 7l \0'657h"""n"o =(--i;Fl = 1.24 m

Height offlood protection wolls from river bed level = 0.5

m + ho",noo * 0.3 m (ollow 300 mm of freebootd) = 2.Oa

31

Worldwide proctice shows thot it is 0pplicoble in smollrivers in

mountoinous ond hil ly regrons, where the followrng conditjons

exlst:. steep river bed ofbore rock or boulders whjch ror€ly

move (they or€ suitoble for f low velocil ies €xce€ding 3

m/s);

. Minimol bed lood ofsond qnd grovel:

. surplus Ilow ovoiloble for continuol flushing To dote

oniy o few bottom intokes hov€ been constructed in

Nepol, s0 Nepqlese formers ore not lom ior with them.

The d€sign ofbottom rntokes must be done corefully to

ovoid becoming blocked with sediment. Bottom intokes

for Thome ond Jhong micro-hydro scheme ore shown ill

Photogroph 3.9 ond 3.10.

3.7.2 TRASHRACKS FOR BOTTOM INTME

Srmilor to side intokes. the troshrocks of bottom intokes con be

monufqctured from flot st€el, ongles, tees or round bors welded

together ot intervols. The sectlon chosen must be strong

enough to withstond impoct by ony bed lo0d moving dunng

floods. lrs shope is olso very imponont, stnce this qff€cts the

chonces ofclogging. Round bors, for exqmple, ore more Prone

to clogging, b€couse the opening in the middle ts smqller thon

on the top. From the point ofview ofclogging, th€ secti0ns

listed below ore orronged in the order ofbest to worstl

Tees

Angles

Chonnels

Flots

Round bors

The recommended cleor spocrng between these flots,

ongles or bors is 6 to 15 mm ond o commonly used sPocilg is

12 mm. The rcoson why these bors ore closer thon those ofthe

side irltoke troshrock is thqr grovel olso needs t0 be exc]uded

from the bottom intake. Since the init iol heodr0ce for this type

ofintoke is covered, it would b€ dimcult to r€move ony grovel

thot obstructs the flow. It should therefor€ be excluded The

spqcing ofthe flots or qngles dep€nds on the prtdominont

porticle siz€ ofthe sedlm€nts coffied by the river flow (i.e. bed

lood) ond the provision for o settling bosin ln the conol

syst€m. The lorger the spocing (oPening), the lorger the

pofticl€s thot will enter the heodroce. on the oth€r hond, if

the Openilgs ore too norrcw, theP is o high chonc€ of

clogging necessitoting frequent cleoning ofth€ troshrock. It

is 0lso importont to ploce rhe troshrqcks such thot the bors

or€ olong the dircction offlow This mlrumises the risk of

clogging.

Phoro 310 Bottom intok€ wrth the gnu rPmoved (Jh0n9)

on€ ofthe drowbocks ofthe bottom intoke is the

clogging oftroshrock by pebbles ond dry leov€s. EsPeciolly

during the dry seoson, the river moy corry q lot ofl€oves,

which become tropped in the trqshrqck ond reduce the flow

through lt Therefor€ the troshrock needs to be cleoned

periodicolly during the dry seoson During morlsoon, this is

not o problem; the river Ilow sweeps the grqvel ond leoves

before th€y con clog rhe troshrocks.

3.73 DESIGN OF BOTTOM INTAJG

The foilowing equotion is used for the design ofo bottom

intok€:

cpbr.fih

where:

Q^ = design dischorge into the intoke in mr/s,

b = width ofthe bottom intoke in m.

L = l€ngth ofthe rroshrock in m. ln proctice, it is recom-

mend€d thqt the troshrock length (L) be incEosed by 20%, i.e.,

L=1.2xL.".,r,,.d. Thiswil l ensur€ thot there wil l be odequc te

flow when the troshrock is portiqlly block€d by wedg€d

stones ond brcnches.

2

w

Photo I9 Botronr intoke ofThome mkro hydro schem€, N€pol

Bottom intok€ with the griu rPmoved (Jhong)

32

.>L -

" , k

1 "Tqble 3.4 1 vclues for p

ho = Initiol woter depth in m in the river upstreom of the

intqke.

h, = ho * vo'/29. Note thqt os con be seen in Figure 3.13 h, is

cctuolly the initiol woter depth in the river plus the velocity

heod ofthe river (v"'/2g). For steep rivers, the flow velocity

should be meosured since the velocity heod con be high.

X, = 0 function ofthe inclinotion ofthe troshrqck (p) cs shown

in Tqble 3.4.

c = Conection foctor for submerced overfqll.

0 = cleqr spocing of the troshrock bors in m.

d = centre t0 centre distonce between the troshrock bors in m,p = ongle ofinclinotion ofthe troshrock with respect t0 the

horizontol in degrees.

p = c0ntroctiOn coefficient for the trqshrock, which depends on

theshope ofthe bors os shown in Figure 3.12. Also in the figure,

Q is the river flow upstreom of the intoke ond Q. is the excess

flow in the river downstreom of the intoke.

Note thot to solve the bottom intoke equotion, either thelength or the width ofthe intoke opening needs to be set qnd

the other dimension con then be cqlculoted. The selection of

one ofthese dimensions depends on the site conditions. For

exomple, if the length of the trashrock is too smqll, the

heodroce ccnol will require deeper excovqtion in the riverbed,

which moy be difhcult. Generolly, the length of the bottom

intqke should be equol to the width of the heodroce canol, ond

the width should motch the river chonnel.

It is importont thot the culvert beneoth the trosh rock is

steep enough t0 convey the moximum conceivoble sediment

lood to the grovel trop: o grodient ofot leqst 1:20 is recom-

mended. The grovel trop moy require continuous flushing,

which meons thot sufhcient heod ond surplus flow hos to be

ovoiloble. The design must be oble to corry ond spili bock to

0o

20

40

6o

8o

100

720

1.000

0.980

0.961

0.944

0.927

0.910

0.894

140

160

180

200

220

240

260

0.879

0.865

0.851

0.837

0.825

0.812

0.800

= 0.6 , cosrj20

l l l o.zs-o es

\ t ???loso_oeofooz-

ooa t

J o 6s gqg o ?o-o esconlrrctlon corf f lcirnt g

fin'IIITTTITI

Figun 3.13 Symbols used in the bottom intoke equ0tions

the river the moximum flow entering the intoke r.rnder flood

conditions.

Enoineers desioninrt o botton intoke should refer t0

References 3 ond 5 for further informotion.

A suitoble site hos been locoted for o bottom intoke. The river width ot this oreo is 5 m ond the depth is 0.5 m (i.e. h. :

0.5 m). A velocity of 3 m/s wos neosured ot the intoke site. The design flow (Q^) required for power generotion is 0.40 mr/s.

Select on qppropriote size for the bottom intoke.

Design cqlculotions

Choose 20 rnm diometer round bors for th€ troshrock.

p = 0.85 for round bors (from Figure 3.i2) Set the cleor spacing between the bors,

o = 1 2 r n m

Centre t0 centre distonce between bors,

d: 32 mnt

Set the inclination ofthe trcrshrack 0 : 8" (The inclination ofthe troshrock should be equol to or slightly greoter thon ther i r t o r n r n A i o n l \

For p = 8u,X =0.927

2h -_ .y .h

3 ' " t '

h, = 0.5 + 3'z129 = 0.96 n'-

20rh -- x0.927 x0.96 : 0.59 m

3

oc : 0.6 ;* cos'tf)

0

I 0.012 \c = 0 . 6 x 1 _ l x c o s ' j ( 8 ' 1 : 9 . 2 2

\ 0.032 I

Now use lhe bot tonr in toke equot ion:

2n - - - , , k r E - , -Y a -

3 L f t u L \ l g n

2Q. : ^ x0.22x0.85xb*L . ,E igS*OSS\ 4 3

Q ^ = 0 . 4 2 x b x LWith QA = 0.40 Inr/s:

0.40b x l = 0 . 9 5 m r

0.42

0,95^ F I - -u t L *

rD

Select the width ofthe troshrock, b = 2 m L = 0.9512 = 0.48 m.

Increose the length by 200/o: L= 0.48 x 7.2 = 0.57 m. The

proposed dimensions of the bottom intoke ore os follows:

Width of the opening, b = 2.0 m (0t right ongles to the flow)

Length of the opening, L = 0.6 m (porollel to the river f low)

Troshrock bor size = 20 mm diameter round bors

Bor sPocing = 32 mm centre tO Centle

The plon of this proposed bottom intake is shown in Figure 3.14.

ffi ----1 rBot f c rn i n t r ke-

u Do rs qf p iTtri c,'c

Figure 3.14 Dtnreusions for th0 bol torn intoke of t ix t rmple 3.3

t /

Note thot in this exqmple the width ofthe troshrock is less

thon the river wrdth, which is occeptoble becouse only 50lo 0fthe

river flow is required. Where most of the flow is to be diverted,

the troshrqck width should be €quql to th€ mv€r width.

3.8 River troining works

A flood protection woll olong the riverbonk moy be required if

there is c high probobrhry offlood domoge to the inrliol heqdroc€

ond 0ther structures such os th€ grovel trop ond settling bosin.

Such wqlls ore qlso cqll€d river lroining structurcs since they

confin€ the river chonnel. The woll height should be gr€oter

th0n0rot leost equol lo the design flood level.

The foundotion ofony ver troining wolls must be

protected from undermining by the river. This con be done by

one ofthe foilowing methods.

(o) Founding the wqll on rock or lorge boulders. For gobi0l

wolls it mqy be necessqry to first build up o level bose

using stone mosonry or moss concrete.

ft) Founding the woll below possrble scour depth.

(c) Using o gobion mottress olong the dver side ofthe woll.

This method is not opprcp ote in dv€rs corrying o he0vy

bed lood, becouse the gobion wires will be domoged by

boulders moving during floods.

0n olluviol dvers (i.e. deep deposition ofsond ond cobbles),

gobion flood protection wolls ore usuolly more oppropriote for

micm-hydro sch€me. This is becouse the grould ofolluviol fivers

tends to chonge ond fl€xible structures con cope better in such

conditions Gobion wolls moy require onnuol mqintenonce

(especiolly ofter monsoon) therefore skilled mcnpower should

either be qvoiloble ql site 0r some locol peopl€ should be troined

du ng the consrruction phose.

Gobion wolls con olso seNe the function ofretoining wolls

ond stobilise the slopes behiDd it. Ifslopes ot lhe olluviol

riv€rbonk ore unstobl€, th€n gobion wolls con olso be designed

os ntoining wolls. Photogroph 3.11 shows the use ofo gobion

woll to stobilise the bonk slope. Refer to Section 9.4 for rctoining

woll design.

on stqble riverbonks, such os exposed bedrock, o mosonry

woll cqn be built provided thot rhe river do€s not corry lorge

boulders thot could domoge mosonry structurcs. In lorge

hydopower ond irrigotion projects even concrete flood boder

w0lls ore used but usuolly such solurions ore economicolly

unjustifi obl€ for micro-hydro schemes.

Figure 3.15 shows the use ofo gobion woll to prevent the

riverbypossing the diversion weir ond domoging the heqdroce

pipe during floods.

Photo 3.11 Gobion wqlls ot $e heqdworks ofthe 30kwJhorkor micro-hydroscheme, Mustong, Nepol

3.9 Checldist for diversion works

Refer to Toble 3.1 qnd find out whqt cotegory the

source river folls in.

Refer to Tqble 3.2 ond decide on whether o side intoke

or o bottom intoke is suitoble.

Is o weir r€quired or is it possible to divert the dver

wot€r without one? Remember the concept of"minimol disturbqnce to the nqturol stote ofthe

wot€r".

Does the river course opp€or stoble or does it look like

it will meonder? Think 0bout flood ond flood lev€ls.

Also, ifthe river cqrries Iorge boulders during the

floods, qnd o weir is requiEd, think obout temporqry

diversion works rother thon o permonent weir

To minimise flood dqmqge the intoke locotion should

be such thot it is possible to set the heodroce olign-

ment immediotely owoy from the ver course.

Ifo side intoke hos been selected qlong o river bend,

Iemember to locote it on the outside ofthe bend.

Hove the flood levels ond history ofthe river course

been discussed with the locol community members?

Firlolly, consider th€ cost ofdifferent options. Is it more

economic to construct temporory diversion works qnd

incur some onnuql lobour chorges or to choose more

permonent diversion works?

35

- Efiq. . t ]l Ii , l

Weir

lntoke

GobionFro

@ 4oOnrn closs II

Figure3. lS Heodworksorrongement0f the80kWBhujungMHP,underconstruct ioninLomjung,Nepol . Not icethef loodpmtect iongobionwol lsondr ipropot

downstrcom foce of the weir.

36

4. Hecdrace

4.1 Overview

The heqdroce ofo micro'hydropower scheme is o conol or opip€ th0t conveys woter from the inloke to th€ foreboy. The

heodroce olignment is usuolly on even to gendy sloping ground

ord the flow is coused by grovity. A h€0droce pipe is generolly

not subjected to significont hydr0uhc pressurc.

Since c0nols ore generqlly less expensiv€ th0n pipes, they

on used more often for heodroces in micro-hydro schemes. The

generol rule is to use conols os ofterl os possible ond ro use pip€s

ordy for the dimcult stntch ofth€ heodroce olignment, such os

t0 n€go(i0te cliffs or unst0ble oreos.

Micro.hydro heodroce conols qre similor to fqrmer

m0n0ged smoll irrigotion conols in thof they ore designed to

keep s€ep0ge, friction ond erosion to q minimum. Howev€r,

thett 0r€ olso some bosic differrnces os follows:

. lnigotion conols ore used only 3-6 months in o yeor

whereos micro-hydro schemes rcquire woter throughout

the yeor

. In inigotion conols, some voriotion in flows does not

crcote problems, ond temporory repqirs (e.9. plocing of

bronches ond leqves ot o leoking section ofo conol) con

be mode, The heodroce conol in o micro'hydro scheme

needs to be mol€ relioble.

r The loss ofheod ov€r th€ l€ngth ofthe heqdroce should

b€ minjmised so thot power output cqn be optimised.

Some micro-hydro texts use lhe term power c0n0U

conduit for €ither the length belween rhe intoke ond the

sdtling bosin (when thrs structure is seporote from the foreboy)

0rfor the €ntire heodroce. ln this rext the term heodroce is used

in ollcoses.

The velocity in th€ iniriol heodroc€ l€ngrh r€eds to be

high enough to corry grovel ond sedimert up to the grovel rrop

ord settling bosin respectively. where thel€ is o s€porote

seftling bosin ond for€boy, the velocity in the heodroce between

these structures con be lowered since it will corry sediment free

Ilow.

Photo: 4 1 Eorth Chonnel(Dhoding)

4.2 Conol types

Heodroce cqnols con be clossified occording to the moteriols

used to construct them. Vorious types ofheadroce conol used

in micro-hydro schemes ore os follows:

4.2.1 EARTH CANAIS

Th€s€ ore constructed by simply excovoting the grcund to the

required shope. Such conols ore used on stoble ond gently

sloping ground. seepoge con be high in such conols depending

on soil rype If therc ore signs ofinstqbiliry in o heodrace

section, or ifseepoge from the conol is Iikely to contribute ro

slope instqbilily such os londslides, this type ofcqnol should not

b€ s€l€cted. However, for heodroce olignm€nts on stoble ground

where seepage is not likely to couse instobiliry eorth conols ore

the most economic option.

Where cloy is locolly ovoiloble it could be considered qs q

lining to reduce seepoge from eonh conols. How€ver, o scheme

in Syongjo successfully used o cloy Iiring protected by sronepitching for the peoking reservoir (which wos fenced off) but in

th€ heodrqce cqnol the Iining wos destrcyed by cottle.

4.2.2 STONE MASONRY IN MUD MORTAR CANAIS

Ifon eorth c0nol does not oppeor to be feqsible, the s€cond

option to be considered should be stone mosonry in mud monor

type. Compored to 0n €onh conol, there will be less seepoge

from this type ofconal. For similor llows, the cross s€ction of

this type ofconol c0n be smoller thon the eqrth con0l becouse q

higher velocity is occ€ptobl€ (without cousing erosion) os will

3?

be discussed lqter An exomple ofo stone mosonry conol in

mud monor con be seen in PhotooroDh 4.2.

4.2.3 STONE MASONRY IN CEMENI MORTAR CANAIS

In terms ofcost, this is usuolly the leost preferobl€ option for o

heodroce conol. Th€ odvontqge with this type ofconol is thot

seepoge is minimol (i-e. significontly l€ss th0n stone mosonry in

mud mortor conols). A stone m0sonry in cement mortor conol

should be used ot locqtions where the soil type is porous

(leoding to losses ofunocceptoble omounts offlow) ond/or

s€epoge is likely to trigg€r londslides. For micro'hydr0 sites

locoted 3-4 dqys wolk from the roodhe0d, the need for o long

cement mortor conol con mok€ o micro-hvdro scheme uneco-

nomic due to the high cost ofcement.

An exomple of o sron€ mosonry in cement mortor

heodroce conol con be seen b€low ilr Photo0roDh 4.3.

Photo 4-4 Reinforced concrpte cover dobs provide protection from folling debds(Eol iv io)

4.2.5 OTHER TYPES OF CANAI

ln certoin or€0s there moy olso be other typ€s ofconol thon

thos€ mentioned qbove. For exomple, on irrig0tion c0nol in

Ecuodor construct€d ofused oil drums cut into two semi-

circulor holves con be seen in Photogroph 4.5. Such o conol moy

be useful for short ond diflicult sections or for oqueducts where

used drums ore €0sily ovailoble ond economicol.

Another exomple is the use oftimber conol os con be

seen in Photogroph 4.6. This requir€s the use ofhordwood ond

skill€d lobour Similor to oil drums, timber cqnols con bepossible for shon crossings ond oqueducts or where timber is

obundont ond inexpensive.

Exompies ofother types ofconol or€ pEsented in Boxes

4.1 to 4.5.

4.2.4 CONCRETE

CANAI.s

Most micro-hydro

schemes do not hove

heodroce conols

construct€d of

concPte since they

orc very exPenslve.

Th€re is virtuolly no

seepoge through

such conols. some-

times, rcinforced

concrete conols ore

used for short

crossings. Generolly,

HDPE heodroc€ prp€s

ore more economlc

thon concrcte conols.

Photo 4 3 Stone mosonry in cement mortorheodroce conol ofthe 50kw colkot MHBColkot, Boglung, Nepol

Photo 4 2 A rorsed mosonry chonnel supplying o mill (Mustong)

38

Photo 4 5 An oil drum rrrigotion conol, Ecuodor Photo 4 6 Timber conol with brocing supporting the sides, Thuptenchuling

39

Ferrocement pilot projects hove been promoted by the

Andhi Kholo Idgotion Pmject (A(IP) ond the Internotionol

Lobou Orgonisotion (lLO). Fefiocemetrt structures ore

mode of thin cement sond mortor (1:2 to 1:3)with thin

steel mesh os reinforcement. ILO hos used ferrocement for

Iining frigotion conols in th€ SindhuD nood Rehobilitotion

Proj€ct.

Th€ ILO ferrocement conol cost wos US$ 31 per lineor

meEe ond the cement mosonry desigl of similor copocity

wos US$ 28 (1989 prices). The tlo justifies the odditionol

cost by ottributing it to befter durobility snd little

mointenonce whidr fe[ocement conols requA€. other

odvontqges ore smooth finishing which reduces heod

losses, resistonce to obrosion, ond very low seepoge

Iosses.

The f€rrocement flum€ used in AKIP (designed by BPc

Hyftoconsult)is shown in Photogroph4.6 ond Figure 4.l.

colvonised sh€ets with intermediote steel fromes werc

used for the formwork. Multiple loyen of 10 mm to 15

mm thick, 1:3 cement sond mortor were ploced onthe

formw0rk. The Enol inside loyer (i.e. woter retoidng

surfoce) wos prepored using o mix of 1:2 cement sond

mortor. Golvonised thin wiE mesh (olso }amwn os chicken

wire mesh)wos ploced between ecchloyer os

reinforc€m€nt.

The Andhi Kholo ferrocem€nt flume hos been functioning

w€U since its commissioning in 1993. This design wos

more economicol thqn the conventionql stone mosonry in

cement mortor co[ol with drop structufts. However, it

should be not€d thot the construction off€nocement

conols requir€s skilled ond well troined monpower

(mqsons) to ochi€ve the requir€d quolity of work ond

therefore moy only bejustified where o very long ccrol is

to be instolled in poor soils. Furthermore, ifskilled lobour

is expensive, ferrocement conols moy cost more thon th€

conventionol design, osinth€ cose ofSindhuli Flood

R€hobilitqtion Proiect.

Fioure 4l Andhi Kholo Proiect fermcem€nt llume

I:2 CEMETTT SATO, MORTAR

Y ' 3 . 5 X 2

40

ln the Andhi Kholo ldgotior Project (AKIP) designed by BPC Hydroconsult, soil-cement wos tested os on option for ir gotion

conols. Th€ soifcement wos pr€pqred using o mix ofone pon cemelt ond one port sqnd to ten ports oflocol red coloured

cloyey silt soil. The red colour of the soil indicotes o high iron content, which r€octs with cement to form o hord loyer on the

excovoted surfoce ofthe conol.

1^,/o opplicotions of soil-cement werc tested in 1990 ond 1991. The first test used sorl which wos grqded using o 4-mm

sleve, with l0rg€r lumps ond soil broken up with o tomper After mixing the dry ingredients ofcement, sond ond soil, woter

wos odded ond rnixed thoroughly until the mortor reoched the desired consistencyforplostering. The excovoted surfoce ofth€

corol which contoined permeoble soil ond grovelwqs first modemoistby sprinkling woter ondthen the mix wos opplied

firrr y to o thicleess of

40 mm qnd pocked

tightly to eliminot€ oir

pockets. The surfoce wos

trowelled smooth qnd

therl cured for q week.

In 1991, o 15 mm

si€ve wos used to grode

the soil over o test

section of 140 mu Loter

moredemonding

conditions were used for

o furth€r test over o

section of25 m length, o

grcdient of 1:20 qnd q

velocity ofopprox. 1.3

m/s. A section of the

Andhi Kholo soil cement

conol ccn be s€en in

Photogrqph 4.10.

To dqte, the

performonce ofthe soil-cem€nt linilg ot Andhi Kholo hos been good. The 1990 test section developed some crocks ofter o

week. oppor€ntlydueto on excess ofwqterin the mix, whichthen coused crqcking qs the soil-cement dried up ondhordened.

These crocks hove not worsened. The 1991 section hos not shown oly crocking. The lining inst0lled irl th€ st€ep conol section

hos olso been performing well.

Th€ odvontqge ofthis technique is thqt it is low cost. Befween 20yo ond 40% ofthe cement requted for o conventionol

concrete mix is reploced by soil. The procedures qre eosy to leorn oIId ore similor to those used for troditionol houses con-

structed in the Andhi Kholo oreo. How€v€r, one pr€pquisite for this typ€ ofcorol is the ne€d for high iron content ir the soil

usedto pr€pore the mix.other soils will not perform well. Arother conclusion thqt hqsbeen drown fiom th€ Andhi Kholc

expeience is thot soil-cement conols ore not oppropriote for turbulent flows. Th€y ore suitobl€ where seepoge controlis

required ond the grodient is gentle {velocity limited to -1.0 m/s.)

Photo 410 Soil c€m€nr lined conol s€ction ot AndhiKholo, Nepol

42

The method developed by IT Peru ond d€scribed here is generolly known os th€ 'formers m€thod' for constructing conols,

The formers method p€rmits sovings in time ond moteriql in constructing concrete chonnels by reducing the need forpouring concEte into conventionol formwork. Precis€ plocement of formem ond lines tied betwe€n them enoble the

concrpt€ to be ploster€d to the insides ofthe trench ond lirished with o trcw€l {se€ Figup 4.4).

Th€ method involves plocing o loyer ofconcret€ on the bottom ond sides ofthe conol to form o uniform thickness ond

o smooth finish. L€v€llirg ond finishing th€ surfoce is done occording to th€ former.

Procedutt

. Setting out for the forme$.

Locqte pegs €very 10 metrcs ul

stroight sections ond every 5

metPs in curv€d secttons, toking

into occount the slope ofthe

d€sign. It is preferoble to use o

builder's level to ochieve the

Iequircd precision.

. Fixing the formers. Locote formeE on eoch peg ot right ongles to the centreline ofth€ conol, verticol ond exoctly in line.

They or€ fixed to th€ pegs using No. 16 goug€ wil€ ond noils, ofter which intermedidte formers oI€ locot€d every 2.5

metr€s in stroight sections, the requir€d slope b€ing checked with d pipe lev€l to give 5 mm drop ev€ry 2.50 metres (o slope

of 2 ir 1000). Eoch former is checked for lin€, Ievel, thot it is p€rp€ndiculor to the conol centreline ond fixed firmly.

. Lining the conal. PRpore o 1:1.5:3 concrete mix

After mokirg the dry mix, tuming the mix o minimum of thrc€ times to mix thoroughly, odd woter, which should

hqve o quontity no gRoter thon on€'holfof th€ totol weight ofth€ c€ment (i.e. for mix with 1 kg ofcement put % litre of

woter). Next the sides ofthe conol ore plosteRd ond compocted. The pegs ore tok€n out ofter the linish is completed.

TheB Iine sond is sprinlded with cem€nt to give o mix of 1:3 ond o plosterirg bo0rd is used to give o smooth, impermeoble

firish to the lining. When the sides ofthe conol ore completed the some procedup is followed for the bottom. To finish the

€dges, corc is r€quired to ensure thot the formers rcmoin in line, They should be checked using o cord or rule.

. L\trscting the foBn€rs. Form€rs sre tsk€n out oft€r 24 hours io cold climotes. To moke extroction eosy, o loyer of oil or

petro) is ploced 0n the formers before c0rrying out the Iining. This olso 0ssists with the pRservotion oftbe formers. CoIe

should be token to ovoid domoge to the €dges ofthe lining when the formers ole token out.

. Curing the concrefe. To r€och the required strength ond durobility, fresh concrete should be cured. This is ochieved by

filling rhe suffounds with woter so thot the linings remcin sooked for o p€riod ofo minimum of 10 doys. Thisiseosyto

c0rry out by locoting runs or eorth bonks ot eoch end, which retqin the woter. During r0iny periods 0 spjllwoy con be

formed to ollow excess wot€r to €scope, which will olso offer o check on the slope. The curing of concrete is very impor-

tont ond should not be overlooked.

. Exponsion joints. Exponsionjoints ore required i[ the spoces thot or€ left when the form€rs or€ tok€n out - €very 2.5

metrcs in sroight sectiOns orld vorioble in curved sections. Thes€ permit the concrete to expond ond controct without

crocking the linings. To fill th€joints the following work is required:

o) Cleon thejoints ofdebris ond unwonted moteriols with on ongulor polette whose dimensions ore suitobie for the

width ofthejoint.

b) Prime th€ iBside surfoce 0f th€ joint with o solution of tor with kerosene ln propc ions l:3 so thot it hos the

viscosity ofpoint. This solution should be opplied with o brush.

c) Ploce o hot mix oftor with line sond, in proportions ofl con oftor to 4 cons ofsond. First heot the tor ond then

groduolly odd the sond while mixing until it hos rhe consist€ncy ofblock sugor This mixture is pldc€d first ot th€

sloping sides ofthe chonnei ond then ot the bottom. lt is plqced in loyers ond compoct€d with th€ angulor pol€tte.

The finished level ofth€joint should not exceed the level ofthe conol liring.

Figure 4.4 Formers method oflining conols

{I .{ l il t j

iIl i ,; ti,r i f r' {'t

i l il i

4.3 Conoldesign

{.3.1 DESIGN CRITERJA

The following criterio ore used for the design ofheodroce

ccnolsi

Cspocity

The heodroce c0Dol should be oble to corry the design flow with

odequote freebocrd. Fr<ebood is th€ dillsrerce in elevotion

between the conol botlk t0p ond tir€ d€sigr wcter l€vel.

During monsoon, the river woter levelis high ond

therefore l lows higher thon the design l low con enter the

intoke. Spillw0ys and €scopes cr€ required to dischorge the

excess flows. Similorly if fqll ing debris or other obstructions

block the conol, the entire flow needs to be soleLy dischorged

into o neorby gully or stl loIn before it induces funher jnstobjl

ity problems.

Velocity

The velocity shou)d be Iow enough to elsure th0t ths bed ond

the wqlls 0fthe conoiore not eroded. The rec0mmended

moxlmum velocity f0r different types of conol is shown in Tcbie

4.1. Ifthe velocity is too low 0quotic plonts ond moss wil l stort

i0 grow on the conol ond reduce the cross sectiono) 0reo. A

mininum velocity 0f0.4 m/s should be mointqined to prevent

the growlh ofoquotic plonts. Also, the veiocity in the heqdroce

coaol up to the settl ing bosin needs to be high enough to

pr€v€nt sedirnent depgsition.

Eeodloss ond seepsge

As meotioned eorlier he0dloss ond seepoge need to b€ mini

mised. Heodloss is governed by the conal slope. Seepoge cor be

controlled by choosing the construction nloteriois (eorth, mud

or cement monor conols etc.) oppr0priole for rhe ground

conditions.

Side slopes

Theoreticolly, the optimum cross sectionol shope for o conol is o

semi-circle, since it ccn convey the moximurn flow for o given

tross sectronol oreo. Since lt rs dlmcult (o (onstruct o 5€nli.

circulor conol. in proctice, o tropezoidol sh0pe (which is close to

o semi-circ)e)is used. F0r mosonry conqls in cement moftor or

ploil concere concls thot qre continuous, Iertongulor shopes

(i.€., verticol wolls) ore rccommended unless the bockfill con be

well compocted or excovoting the required tropezoidol'shope is

possible. This is becouse tropezoidol cement mosonry ond pioin

concrete conqls'sid€ wolls wil l hove to depend on the bockfl l l

for support. The wolls moy crock 0t lhe conoi b€d level

(cousing seepoge) since it moy be difncuh to conpoct th€ .

F L r r r . l s l d J J r | " u l ) , o c h r r l i . r o r f l g ) d l . L l p T . r d u l o n o l s

bockfi l lproperly behind the wqlls, os showr in Figur€ 4.5.

Recommended side slopes for different conol types 0re shown

in Toble 4.2.

Stobility

Not only should the conol be on stoble ground but the or€os

obove 0nd bel0w the olignment 0lso !eed to b€ stoble. when

det€rmininq theconcl route ot site, the signs ofstobjl ity ond

instoirility discussed in Chqpt€r 2 should be referred to.

The conol design should qddress stobility issues such

os prot€ction ogoinst rocl'folls, londslides ond storm runoff.

covering conols by plocing concr€t€ slobs (or flot ston€s) ond

some soil cover (to obsorb the impoct offolling rocks) con b€

on oppropriote solution ifo smoll length ofthe conol is

vulneroble to rocHolls. Exomples of concrcte slobs con be

seen in the superpossoq€ drowings ofthe colkot sch€me in

Appendix C.

Economics

similor to ony orher engin€edng strucrure, the design ofth€

conol should be such thot th€ cost is minimised. This is

especi0lly importont in the cose of o long heodroce conol

sinc€ optimising the design wil l result in substontiol soving

in the totol project cost. Design optimisotion or minimisirtg

costs requires k€eping lhe conol olignmelt qs short ospossible lunless longer lengths ore needed to ovoid unstqble

oreos ond crossings)os w€ll ds minimising excovotion ond

the use 0fcorstruction moteriols, €speciolly cement ond

stones. FOr exomple, in 0 mjcro-hydro schem€, cement

masonry canol could be used only ot sections where the sojl

is porous ond/'or s€epoge is likely to trigger landslides. ln the

sqme scheme, eorth ond stone mosonry in mud monor

conols could be used ot sections wh€re probl€ms qssociot€d

with seepoge oI€ not expected.

43.2 MANNING'SEQUAIION

The design ol 0 heodroce conol is bosed on Monning's

equqtion. Monning's €quotions for flow ond velocity ore os

follows:

' . 1

l ;

l ,

AR4'VS

wher€:

Q is the flow in th€ conol in mr/s

V is velocity in the conol in m/s

is the roughness coeflicient ofthe conol (olso colled

Monning's n)which is d€pendent 0n the moteriols ofthe

cqnol. The vqlue ofn for differ€nt typ€s ofconol is given

in Toble 4.1.

is the cross sectionol oreo up to the woter surfoce l€vel

in m'?.

is the slope ofthe energy grode line. The invert slope of

the conol is used for s since it is porqllel to the energy

grod€ lin€ 0t loog€r lergths. For exomple i:500 (1 in 500)

irv€rt slope is I m ofdrop in l€vel in 500 m ofhorizontol

conol length.

Sometimes percentqge (0/o) or froctions orc olso used to

denote the slopes. For exomple o slop€ of 10lo meons thot th€r€

will be o difference in lev€l of I m every 100 m of horizontol

distonce.

The equivolents ofthe slop€ in froctions or decimols ore

given by the following exomples;

2 % = 2 l 1 O O = 0 . 0 2 = 1 i n 5 0

2 in 1000 = 2/1000 = 0.002 = 1in 500

1.50 ,6 = 1 .5 /100 = 0 .015:1 in67

3.5 in 1000 = 3.5/1000 = 0.0035 = 1 in 286

is the hydroulic rodius. R = A/P

is the w€tted p€rim€ter in m. This is the totol length 0f

the bottom ond th€ two sides ofth€ conql up to the

woter surfoc€ level.

n

R P l FI1

R

P

{3J SEDIMENT DEPOSMON IN CAI{AIS

The velocity in eoch s€ction ofthe heodroc€ conol should be

high enough to trcnsport ony sediment entering thot section.

Betwe€n the intoke ond the grovel trop o velociry of 1.5 - 2.0 m/s

is recommended. Between the grovel trop ond the settlipg

bosirl o lesser velocity is possible, but the sediment tronsport

copobility should be checked usirg o simplified version of

Shield's formulo: d= 1lRs

where:

d is the size ofporticle tronsported in o conol, in m

R is the hydroulic rodius, in mc i c r h , . n h ^ l h d < l ^ n ,

Ifthe grovel trop is designed to settle porticles lorger

thon 2 mm, then th€ conol downstftom ofthe grovel trop must

b€ oble to tronsport pofticles up to 2 mm.

Tqble 4.1 Roughness co€mci€nt qnd o-llowqble mqximum velocity

See note below for advice an chanftels where the water dcDth is less tha7 one metrc.CHANNELTYPE DESCRJPTION MA)C

vELOcITY (mlslEorth chonnel Clay, lvith stoles ond scnd. ofier ogeing

Grovelly or scndy looms, mqintoined with mtnimum vegetotion

lired wjth coors€ st0nes, mointolned with rninlmun vegetotj0n

For cqnols less thon 1 metr€ deep, use the equotion in N0te '1.1 for n e.g.:Vegetated (us€ful to stobil ise soil); woter depth 0.7 nl

rvoter depth 0.3 m

Heoviiy ov€rgrown, woter depth 0.1 metrcs

0.020

0.030

0.040

0.050

0.070

0.150

0.8

0.4

1 . 0

0.8

0 .8

1 . 0Rock cut 0.015

0.045

0.060

Smooth ond uniform

Jogged ond irregulor

Very jogg€d ond ifngulqr

1 .5

1 .5

1 . 5Mosonry qnd

concreteStone mosonry in mud morto( dry st0ne mosoory

Stone mosonry in cement mortor using rounded ston€s

1:4 cement scnd mortor

1:3 cement sond mortqr

Stone mosonry in cement rnort0r using split stones (drcssed)

1:4 cement scnd mortor

1:3 cem€nt sond mortor

wlth l:2 pointirlg

Concrete (occording to finish)

1:3:6 ploin concrete

1i2:4 ploin concrete

1:1.5:l reinforc€d concrete

1:l :2 reinforced concrcie

Cement pl.rster

0.015

0.030

0.020

1.0

l . l

2.0

3.0

5.0

1 . 5

2.0

1 .0

5 .0

3 .0

5 .0

0.013 - 0.017

0.013

1 : l

1:2wooden conols Ploned, well jointed boords

I l n h l n n p a h ^ ^ r / (

Older wooden conols

0 .011

0.012

0.015

3.0

3 .0

1.0M€tol conols Ail types

Mountoin str€oms DominoDt bed moteriol :

Crovel (up to 60 mm)

Cobbl€s {up to 200 mnr)

Boulders (up to 600 mm)

Lorge boulders (> 600 mm)

Note 4.I Roug,ilrl€ss efi:ct [or shoi]ow channels

Resecrch ot Wogeningen University in th€ Netherl0nds demonstroted thot the roughness is increqsed for chonnels under 1 metrc in

depth, becouse oi rhe turbulence creoted by the side ond b€d suifcces. The rcsecrch showed thot the follorving equotions con be

used to hnd rhe roug\ness coriirii.,r. i.\i\\,i dt!'.f. cl\cler

0.020

0.03

0.04

0.05

0.07

3.0

n - o . o 3 i \ E H < 1 mn = 0 . 0 { / \ F H < 1 n rn = 0 . 0 8 / { F H < l m

well tnointoinrd channels u'ith l i tt le veget{rtio!:

Chonnels with siron vegetotlorl:

Heovily overgrolvn chonnels:

Ii,l,

In proctice it is sensitrle t0 l l lointoin short veg€totion ir o er t0 protect the bonks of conols.

Toble 4.2 Re(omm€nded sidc slopes for heodroce conolsCANAL MATERIAI stDE sLoPE (N = h/vlR0ck/conglomerqre (hord t0 loose)

Iirm cloy

Loom

Sondy cloy, scndy locnr

Silty sond, sondy eofth

loose sordy €orth. porous eorth

Grovely e0rth, sri lTor loose conglomercte

Grovelond boulder mixed wIh eonh (soft ond Ioose)

Stone mosonry in mud rnortor

Stone mosonry in cement mortdr

P lo in Ionr rP ie

Notesl

1. These volues orc for conols excovoted in s0il ofl0w nl0isture cortent with woter toble below conal bed. slopes need to beflottened ifthese condirions or€ not ochiev€d.

2. The sides ofl ined conols rtlcy b€ v€nicol (designed qs r€tcining wolls)or ot the slop€ reronmended for the uDderlying so)l

0 (verticol) to 0.5

0.25 rc 4.5

1 .0 to 1 .5

1 .5 to 2 .0

2.0 to 2.5

2.5 to l

0 .5 to l

1..5 ro 2

Sec Not€ 2

S€e Note 2

5(e Note 2

43.4 DESIGN PROCEDUR"E

the heodroce canoldesign procedul" is os follows:

L Decide on coDol type os per sile condrtious ie.g. eorth

corol, st0ne mosonry in mud monor or stone mosonry

rn cement mofior).

2. Choose o suitqble velocity (V) such lhot it is less thon the

mcxinurn velocity given in T0ble 4.1. N0te lh0t

unoccept0ble heodl0ss moy result ifchosen velocities ore

close to m0ximum velocity Also choose the correspond

ing roughness coell lcient (n) fron Tobie 4.1.

lhen colculote cross sectionolorpo (A) from theo

following equotion: A =f

Free boord

lel

Figurp 4.6 Symbols used rn conol sizing

3. Using Table 4.2 decide 0n the side slope (N). Note rhot N

is th€ ratio 0fth€ horizontol length divrded by th€

verticol height of tbe sjde woll (i.e. N = h/v os sholvn ir)

Figure 4.6).

Colculcte the optin]um conolheight (H). conol bed widrh

(B), ond th€ conol top widrh (T)using the iollowing

equotions:

x = 2 \ ' [ + N j 2 N

r - A, , V X + N

B = H X

T = B + ( 2 H N )

Note thot in cose of o rectongulor conol, N = 0 ond

X = 2 , s 0 :

i ^H = / , ! o n d T = t = 2 1 H

\ 2

I{ence, for o rectongulor conol the hydroulicolly

optimum shop€ is wh€n the width is twice the height.

These symbols ore schernoticolly shown Ln Figure 4 6

lfon optimunl cor)ol shope is not possible due to

site specil ic conditions (such os norrow width olong o

clif l) then either the width or th€ height should be

selected to 5uii the sit€ conditions. Then the other

dunension con be colculoted.

To ensure stoble ond uniform flow in o long conol, the

velocity must be less thcn 80% ofthe "crit icol velocity

l ^ "l imir" V, =J '=

, where V. rs lh€ crit iLclvel0ciry

thot for o rectongulor cqnol V. = fit

Ifthe conol vrlocity js greoter thon 0.8V then rcpeot

colculqtions with Low€r velocity.

6. Colculote the wetted p€rimeter (P)using rhe following

equotion:

P = B + 2H .', i1 1,11 , note thot for recrcngulor conol,

P = B + 2 H

7. Colculote the hydroulic rodius (R)os fo)lows;

8. The slope (S) cot now be found from Monning's equo-

tion:

/ n t \ 'S = I I

Now oll dimensions required f0r the c0nstruction ofthe

ranol ore knorvn.

9. Heodloss = L S (L is the length ofthe conol section).

Sometimes S is f ixed by th€ conolroute, which hos

oireody been decrded ond surv€yed. Another €xornpie of

fixed slop€ (S) situotion is when on existing inigoti0n

conol is proposed to be used for o miclo hydro scheme(ond higher flows 0s well 0s l€ss leokoge orc requir€d).

In such situotions different cr0ss sectio!l01 0reos should

be ossumed (i.e. triol qnd error) such that the v€locity is

less thon the ollowoble moximum velocjty for the

design flow ond ihe type 0fronol proposed. This con be

done by r€writ ing Molroing's equotior) os follows:

^ (BH + NHl" \!v - r - x l

n [(B + 2]r \ (r +N1 I

with o known design flow (Q), select the oppropdote

side slope (N) 0ccording to the typ€ ofconol chosen.

Then fix either B or H ond colculote the 0ther using the

dbove equotion. Finolly from Tobl€ 4.1, check thot thevelocity (V = Q/A) is l€ss thon lh€ moximum velocity for

the conol type.

10. Col(ulqte rhe size of the lorgest pq(icle rhor wil l betrqnspolted in th€ conol:

d = 1 1 R S

Ifthis is less thon the possible size in the conol, repeqtthe design using o higher veLocity.

11. AlLow o freeboord os follows:

300 mm for Q < 500 lis

400 mm for 500lls < Q < 1000 iis (such flows oreunusuol ior micro'hydro schemesJ.

Such freeboord ollows for:

. Unc€rtojDties in the design {e.9. the vo)ue of n'moy

diff€r by 5olo to t0% from estimote).

. Woter level being obove the design level due to

obstructlon rn the conol or durrng emergenr ies.. D€t€riorotion of th€ conol embonkment.

12. Check thqt possible flood flow in conolcon be occommo'

d0ted without using more thon 5070 ofthe freeboord.

13. Find the totol h€od loss. If this is too high or too smoll,

repeot the colculorion( with o dlferenr velocLty.

Consider using different typ€s ofconol keepiug the

overoll cost in mind.

Avoid o conol width ofless thon 300 mm os n0rrow

c0n0ls con b€ eosily blocked. Also fbr stone mqsonry conols,

smoller sizes ore diff icull Io construct.

Th€ existing irrigotion conol ot Colkot needs to be modilled qs o heodrace conol for o pow€r outpur of 50 kW The exist inginigotion conol's cornmond ol€o is 20 hectots. The community hos requ€sted thot the conol be sized such thot it would b€possible to ir g0te the fi€lds ond produc€ 50 kW simultoneously.

The following informotion wqs coll€cted through site inv€stigqtion ond d d€toiled survey:

Gross heod {h) = 22 m {forebgy to powerhouse)

lntoke to 130 m downstreom: 1:50 slope (s) with on€ drop srructur€.

131 m to 231 m downstreom: 1:92 slope.

232 m to 405 m downstreom: 1:365 sl0pe.

406 m to 730 m downstreom: l:975 slope with 3 crossings.

731 m to 1119 m dowostredm {for€boy)r 1:400 slop€ with on€ crossing.

48

site conditions dictote thot the entire heodroce olignment be constructed out ofstone mosonry in cement mortor_Note thot I m goP hos been provided ot chonge o[slopes. This is the tronsitionol length thot connects the rwo diflerertslopes.

ln this exomPle, the lequired design 0ow will be colculoted 0nd the heodroce conol from chojnoge 406 m to 730 m will b€slz€d.

D€sign fl ow colculotions:

Assume 550/0 overoll €mciercy (e" = 0.55)P = Q g h€, (power equotion)

Q = P / ( s h e " )= s0l{9.8 x 22 x 0.55) = 0.421 mr/s

Therefore flow required for pow€r gen€rotion is 421 l/sAssum€ on ir gotion rcquirement of1.5 i/s/ho for existing i lr ig0t€d lond.kdgotion d€mond (Q) = 1.5l/s/ho x 20 hq

= 30 l is

Tot0i d€sign flow for the hecdroce cqnol = 4zl Us + 30lls = 451 lls. Thertfore use o d€sign llow of455 lls to size tlleheqdrqce conol.

conol sizing

c0n0l type: srone mosonry in cement mortorn - 0.020 for dRssed stone mosonry {from Toble 4.1)

Q = 0.as5 mr/s

s = l/975

From Toble 4.2 choos€ N = 0.5 (1h/2v)

Set lh€ botlom widih {B) = 0.450 m which is the size of the existing irrigotion conol. This miDimises excovotion works.Now use the foll0wing form ofthe Monning's equotion where only the woter depth, H. is unknown:

^ (BH+NHz)5',\ i;Y r , - t r 3

n l (B+2H! ( l +N1 l

10.450ii +0.5H11 rx\tiE75u,r')) = - -=-

o.o2o[o 4so+2H ''(r +051 ]"By triol ond €rror meth0d, the obov€ equotiot is bolonc€d when H = 0.268 m for o flow 0f455 lh.Therefore, the wqter depth will be obout 768 mm. N0w check thot rhe velociry is less thon the moximum ollowoble velocityof 2.0 m s ffom Toble 4.t.

v= Q/n \

0.455

(BH+NH1

0.455(0.450x0.768 + 0.5x0.768')

or V = 0.7 m/s < 2.0 mis OK.

The drowing qnd dimensions for this concl sertion con be se€n in Drowing 420/04/2A01 (Conol type B) ofAppendix C. Not€thot the originol design wos bqsed on on ossurned volue of0.()17 for Monning's n, giving o woter depth ofZ05 mm, rhereforeoctuol fr€eboord mqy be less thon recomm€od€d. The oth€r conol s€ctions ofthis scheme con be verilled by simiior colculo-tions.

3.4.1 IOCATION OF SPIIIWAYS

As mentioned eorlier, spillwoys ore required in heodroce conols

to spill excess flows during the monsoon ond in cose ofobstruc.

tion in the conols. Similorly, spillwoys ore olso requir€d ot the

foRboy to spill the entire design flow in cose ofsudden volve

closure ot the Dow€rhouse.

Note thot when the conol olignment hos oL€ody been flxed (i.e. fixed conol b€d dope, s) os in the c0se of the C,olkot schem€,there is little control in the velocity. The velocity con be slightly modified by chonging the cmss sectionol oIPo but it will b€difficult to moke significont chonges. For exomple, the velocity in the U92 slope conol section ofthe C,olbt scheme is obout2 m/s. However, this wos found to be mol€ economicol (i.€. reshoping the existing conol) thon r€oligning the conol olignmentto reduce the slope. This impli€s thot the steeper sections ofthe conol moy require more mointenonce work thon the gentlersections. This is one Eoson for plostering the inside surfoces of th€ conol.

Also, note th0t earth inigotion conols or€ gmerolly ste€per since lf (mughness coefficient) is higher. when such conols or€

modified os heodroce, they become smoother (use ofcem€nt mortor, ploster, better shope, etc.) ond hence con hove highervdocities.

3.4 Spillwoys The exc€ss flows rhot ore dischorged vio o spiliwoy

should be sofely diverted into the streom or neorby gully such

thqt they do not couse ony ercsion or dqmqge to other struc-

tures. Sometimes, this moy requiR the construction ofo

chonnel to the noturol woter cou$e. Locoting spillwoys close to

o gully will sove the cost ofchonnel construction os con be seen

in PhotooroDhs 4.11 ond 4.12.

Photo412 spillwoyon o crossing where the excess llow is dischorged intoogully, Colkot micm.hydro schem€, Boglulg. NeDol

4.4.2 SPTIIWAY DESIGN

Where woter is ponding ot o downstr€om regulotor such os in o

foreboy, the design ofspillwoys con be bosed on the weir

equotion discussed in Chopter 3.

0 = C t . . ( h ) ' sPhoto4.1l overflow from the forpboy dischorc€d overo rockdiff, Dhoding

micro-hydrc, N€pol

50

where:

Qpir.oy = dischorge over the spillwoy in mr/s

L,pir*oy = length of the spillwoy in m

hou.noo = heod over the spillwoy in m (i.e. height of wcter

over the spillwoy)

C* : o coefficient (similor to weir coeflicient) which

vories occording to the spillwoy profile. C* for different weir

profiles is shown in Toble 3.3 (Chopter 3).

The design steps qre os follows:

o Colculote the flow through the intqke during floods os

discussed in Chopter 3. The spillwoy should be sized

such thot the entire flood flow con be diverted owoy

from the conol. This is becquse the micro-hydro system

could be closed during flood or there could be on

obstruction in the conol.

r Choose o spillwoy profile ond determine C*. In the

Nepolese context, o brood, round edged prohle (C* =1.6)

is suitoble since it is eosy to construct.

r Spillwoy crest level should be 0.05 m obove normol

cqnol woter level. No more thon 500/o of the freeboord

should be used. Therefore, with o generolly used

freeboard of 300 mm, the ovqilqble hou"no, is 0.5 x 0.30 -

0.05 = 0.10 m. The required length con then be colcu-

loted for the chosen hou.noo ord flood flow.

Where there is no ponding immediotely downstreom,

such os in the heodrqce conol, the spillwoy length colculoted

using the weir equotion should be multiplied by 2: this occounts

for the groduol decreqse in heqd over the spillwoy, until the

required level is reoched at the downstreqm end of the spillwoy.

ln this cqse only the excess flow (Qn"o, - q.,,nn) should be used

for Qp,u,oy. Note thot in such coses, locoting the spillwoy

immediotely upstreom of on orifice will increose the flow

through the weir. The design of o spillwoy is presented in

Exomple 4.2.

Design o heodrqce conol to convey o flow of 285 l/s. Site conditions indicqte thot the conol would be stoble if stone mosonry

in mud mortor is used. The expected flow through the intoke during o Z0-yeor return flood is obout 480 lis. Design an

odequote spillwcy.

Design procedure:

Ccnol type: stone mosonry in mud mortor

Q = 0.285 m3/s

From Toble 4.1:

Roughness coeflicient n = 0.035

chooseV = 1.0m/s

From Tqble 4.2, for grovelly eorth, select side slope, N = 0.5, (1h/2v).

Cross sectionol sreo, A = 0.285/1.0 = 0.285 mz

x = 2{ff i -2*X = 2{ i1"r-gfr) -2x0.5

X = 1.236

Cqlculcte the woter depth in the cqnol, H:

,r= fT-." { ( x+N)

u = f__Q285_" { (1.236+0.5)

H : 0.405 m

Calculote the bed width, B:

B = H X

' I

i

B = 0.405 x1.236

B = 0.50m

Colculcte the top width up to the design woter level, I

T: B + (2HN)

T = 0.50 + (2x0.405x0.5)

T = 0.905 m

Check if V < 0.8 V,

.. tTo- | o285xe3-v I r

- = r -c \ i T v 0 . 9 0 5

V, = 1.76 m/s

0.8 V. = 1.41 m/s > V : 1.0 m/s OK

Colculote the wetted perimeter, P:

P: B * ZxH{ f f iP = 0 . 5 + 2 x 0 . 4 0 5 \ F + O y )

P = 1.406 m

Colculote the hydroulic rodius, R:

A 0.285R = _ - = - = 0 . 2 0 3 m

P 1.406

Colculote the required consl bed slope, S:

/ nv \ 'q = f - l- \ R0f67 I

/ 0.035x1 \'s - | _ t\ o.2o3o*' I

S = 0.0103 or 1:97 (i.e. 1 m ofdrop in 97 m ofhorizontol

ccnol length)

Finolly ollow 300 mm of freeboord. The cancl dimensions

con be seen in Figure 4.7.

Check the flow depth for maximum flood flow in the

canol.

(BH+NH1t3{;a-

n[to+zHr4r+r.r1 ]"'

0.480 =(0.sH+0-51x3 xfi-Oto:

[ , - I2 , ro.o3s [o.s + 2H v(1 + 0.51 J

By triol ond error method, the obove equotion is balanced when H = 0.55 m. Therefore, the flood flow occupies 500/o of thefreeboqrd (the moximum qllowed, os discussed eorlier) ond the heod 0n the spillwoy (hou,noo) wiil be 100 mm.

Check the size of porticle thot will settle in the canal ot o velocity of 1.0 m/s.

Figure 4.7 Proposed internol canol dinlensions for Exomple 4.1

52

D = 1 1 R S: l l x 0.203 x 0.0103= 23 mm

I.e. porticl€s lorg€r thorl 23 mm would settle in this heodroce cono]. Therefore, to ovoid deposition upstrcom ofthe settling

bosin, the grovel trop must be designed to remove oll porticles grcoter thon 23 mm.

Design of spillwoy

Note thot 2 conditions need to be ch€cked os follows:

1. The spillwoy must be oble to convey the entire flood flow of480l/s in cose the h€odroc€ conql downstrcom gets obstmcted

{ponding cose).

2. The spillwoy should be obl€ to spill the excess flow (48014 - 2851/s) when there is no obstruction downstr€om.

The colculoted m0ximum spillwqy length should be used in the design.

cqlculotions

Choose q bro0d crested weir with round €dges profile, so C, = 1.6

Cose 1: qe,[*"y = 480 l/s

h",.""e = 100 mm colculoted eorlier

Now colculote lhe length ofthe spillwoy,

. Qp'rr*vL,p,rr*oy = [1fr--p

. 0.480"rpr [eoy l .6x{0.1)rr

Cose 2: qoijr""y = 480 - 285 = 0.195 lh

20

c x{h

2x0.195l.6x(0.1)r5

LTherefore o spillwcy l€ngth 0f9.5 m is requiEd for the

obove conol {Cose 1).

Pholo 4 l3 HDPE prpes provide 0n overflow from o timber chonn€l (Mhopung)

4.5 Crossings

Sometimes the heodroce or rhe penstock olignm€nt mqy n€ed to

cross guli ies ond smoll slreonrs. Crossings ore such structur€s

thot conv€y th€ flow over streoms, gullies or qcross unstoble

te oin subject to londslides qnd erosion

The cqlkof crossing wirh o spil lwoy wos shown in

Photogroph 4.10. This is o 1.2 m long oqueduct thot is con'

structed from reinforced concrete. Its size ond slope ore similor

to the upstreqm heodroce conol. In micro-hydro sch€mes,

reinforced concret€ crossings moy be feosible ifthe l€ngth is

short. Such structures ore expensive ond complicoted for longer

lengths.

53

The Jhonke mini-hydro penstock crossing cqn be seen in

Photogroph 4.14. ln this cose the penstock olignment hod to

troverse o 12.6 m wide gully This gully is octive only in the

monsoon ond 0t other times it is dry. A series of mosonry wolls

wele designed to support th€ penstock (similor to the suppon

piers) olong the gully. All ofth€se wolls rest on o continuous

foundotion pod. During the monsoon, the surfoce runoffflows

between the wqlls.

Photogroph 4.15 shows the chondruk cmssing. The 50kw chondruk micro-hydrc scheme hos o long HDPE heodrocepipe (see Box 4.6) ond ot one locotion, the olignment hod tocross o gully. As con be seen in the photogroph. 0 mild steel

Phbto415 Chondruk micm-hydm heod roce crossmg.

chondmk, N€pol

pipe wos used for the crossing with onother verticol pipe

supPorting it.

Aport from the types ofcrossings discussed obove,

inverted siphons ole olso sometimes used ocross gullies,

Invert€d siphons qre pipes thot ore buried ocross the gullla They

trqverse down to the lowest point ofthe gully ond then come

up ot the other side (hence the nome inverted siphon). As long

os there is suflicient heod ond the pipe is below the hydroulic

grqde line, the flow con be conveyed through such siphons. A

Ilush out volve must be incorporqted ot th€ low point ofthe

siphon (since sediment con be deposited ot the low poinr).

4.6 Heodrcce pipe

4.5.1 GENERAL

Pipes moy be rcquipd olong the heodroc€ olignment where

slop€s ole unstoble ond wher€ londslides moy occur Although

mosonry ond concrete conols con minimise seepoge induced

londslides. they ore rjgid structures ond in the event ofslope

foilures, such conols con be swept owoy- These conqls will olso

crock ifth€re ore sm0ll slope movements. Where soil instobility

prcblems ore expected, flexible pipes moy be 0n oppropriote

solution prcvided thot the required pipe length is not too long

(s€e Box 4.6). Anotherc0se for the use offlexible pipes is when

the entip hillside is slowly sliding (i.e. moss movement is

occurring)ond port ofthe heodroce olignment needs to

troverse it.

In Nepol HDPE pipes ore often used to oddress th€ obove

pmblems. These pipes ore flexible enough to occommodote

some ground movement ond con bejoined by heot welding,

which is described in Box 4.7. HDPE pipes should be buried to

protect them from sunlight, cottle ond vond0lism.

The reoson why PVC pipes hcve not been used for

heodr0ce in N€p0l is b€couse olthough they ore eosy tojoin

(with o PVC c€ment solution), they ore olso very gid. Therc-

fore, they connot occommodote ground movement.

Appendix B includes doto on stondod pipe sizes ovoil-

oble in Nepol.

4.62 DESIGN CRITERIA

The design criterio for heodroce pipes ore similar to those of

heodroce conols. specificolly, the design should oddress the

following issues:

. The pipe diometer should be such thot for the ground

slop€ ofthe olignment, it should be oble to convey the

design flow. Ifthere is o possibility offlood llows

entering into th€ pipe, moke provision for spilling srlah

exc€ss flows.

Phoro 4 14 Jhqnlce mlni hydro penstock crossing, Dolokho, Nepol

54

The inlet to eoch section ofheodroce

pipe should be protected with o

troshrock, so thot debris does not get in

ond block the pipe. The spocing ofthe

troshrqck bqrs should be no more thon

one third ofthe pipe diometer, ond the

velocity through the troshrock should

not exceed 1 m/s.

Wherc o section ofheodroce pipe ends

in on unlined conol, o mosonry

tronsition strucNr€ is recommended, to

ovoid scour by the high velocity flow.

Heodroce pipes qI€ emcient when they

orc flowing full, but ifthe heod on the

pipe exceeds the roted pipe heod (i.e.

ollowoble heod on the pipe) breok

pressur€ tonks ne€d to be provided. Such tonl6 dissipote

the heod over the pipe ond ovoid the need to use o

higher pipe roting. Howeve4 in proctice, repeoted use of

bEok pEssure tonks hos sometimes induced cyclic surge

(i.e. periodic chonge in heod ond hence the llow).

Another option in such coses is to sel€ct o lorger pipe

diometer such thqt open flow condition prcvqils. Br€ok

prtssule tonls should be provided with lockoble covers,

so thot debris connot g€t in ond block the pipe.

Photo 4.15 BlPoI prEssuR tonk with ice orcund lhe wols (Jhonq)

o As for os possible, th€ pipe olignment should be such

thot it is olwoys sloping downhill. This ensures thot

therc is olwoys o positive heod ov€r the piPe qnd the

chonce ofit being blocked is olso reduced.

. Ifthen is o need for inv€rted siphons (or the piPe ne€ds

to go uphill for some length due to the gmund profile),

oir Eleose volves should be provid€d qt high points

olong the olignment. similorly, flush volves should qlso

be pmvid€d 0t low points to flush sedim€nt from the

pipes qnd henc€ pr€vent them ftom being dogged.

Photo 4 l7 Flush-outs should b€ provided ot low points in pipeliner sothot hedvy debris cdn be p€riodicoly rEmoved (Siklis)

Note thot the setting out ond preporotion ofthe bendl for

heodroce pipe is similor t0 the heodroce conol discussed in

Section 4.4. As mentioned eorlier, HDPE pipes should olwoys be

buried. A minimum buried depth ofl m with sieved soil

150 nun t0 300 mm oround the pipe is Ecommended os shown

in Figun 4.8. The use of sieved soil ensuRs thqt the pipe is not

punctuEd by pointed rocks during compoction, distributes the

loods evenly ond prevents futurc diffeftntiol settlements obove

the pipe. The 1 m depth minimises the overburden loods over

the pipe such os when people or coftle wolk over it. Also, in

ol€os wher€ freezing is expected during mid-winter, 1 m is

usuolly sumcient to be below the ftost line.

At inlet ond outl4 sections ofo heodroce pipe, it is

Rcommended to provide ir et ond outlet structur€s ofstone

mosonry or conc€te.

55

The 50kW Ghondruk micro.hydro scheme wos one ofthe first micrc-hydropower projects thot fmc Nepol wos involved in

HDPE pipe hos been used successfully for the long heodroce through forest, but lessons shouldbe leomed from the Problems

exP€n€nced:

. Sticks ondleoves entering the piPe qt the heodworks

get wedged ot the weld beods, cousing pipe blockoge.

. Vondols thrcwing stones into thebreokprcssul€ tonks,

. Pipe collqpse du€ to negotive pressure ot o high point

(where th€ pipeisbelow the hydroulic grode line).

. Surging flow due to oirbeing drown intothe pipe ot

breok pressure tonks.

At one short locotion, th€ hillsid€ wos not very stoble qnd

the HDPE pipe hos been supported by golvodsed wires tied

to trees os con be s€en in PhotogroPh 4.18. A.lso notlce

thot the HDPE pipe con be bent wher the bend rodius is

loJge. However, it would hove beentechnicolly sounderifo

gobion woll hod beer built downhill of the PiPe 0lignment

ond the pipe covered with soil qs shown in Figure 4.8

Photogrqph 4.19 shows o mitred b€nd on the chondruk

HDPE heodroce pipe. This wos mode by cutting piPe

sections ot on ongle ond them by heot welding. It hos storted leo]cing ot the bend ond the villogers hove wroPPed it with

plostic sheets ond golvqnised wire. Bends tiot ore constmcted by cutting ond welding pipe sections require core during the

?hoto 4 18 IIDPE heodroce pipe olong unstoble oligrunmt, Chondruk

mrcro-hydro scheme, Nepol

joining process (i.e., the more joints, the higher

the likelihood ofleotoge). fthere is some

h€qd over the heodroce pipe, then there con be

significqnt forces ot the bend os will discussed

in Chopter 7. Such forces cqn weoken the

joints ond couse leol<oge. Also note thot tI€

pipe section shown in the photogroph should

hove been buried.

Photo 4 19 B€nd prepored by cuning ond welding

the IIDPE h€odroce pipe ot Ghondruk

IIDPE pipes ore ovoiloble in th€ mqrket in fixed lengths (e.g.46 m pieces)qnd need to be joined ot site. Unlike pvc pipes, thereis not o liquid solution thot con be used to join HDPE pipes. The only economicol method ofjoining thes€ pipes is by heotwelding them. This involves heating the ends (thot need to be joined) sucl thot they become soft ord molleoble ond then

ioining them by applying force from close to both ends ofthe pipes, This joining temperqture is reoched qt obout 200"C. Thefollowing steps orer€commended whenjoining HDPEpipes otslt€:

. First heqt the welding plot€ until the required temp€roture

is reoched. The welding plote (olso lglown os the heotingplote) is o mild steel disc with o rod welded ot the edge ondq wooden grip ot the end ofthe rod. Heoting the w€ldingplote con be done by either using o kerosene burner (os

shown in Photogroph 4.20) or by heoting the plote over ochorcool fire. A speciol chqlk colled tiermo-croyon con b€used to ensure thot tlrc plote hos reodrcd th€ requiredjoining temperoture. A few lines should be mork€d on theplote while it is being heated. When the plote reoches thejoining temperotue the dlolk colour tums blue t0 blockwithin one second.

. The welding Plote should then be removed and ploced inside o Teflon bog (the bog con be mode by stopling Teflon fobric).The Teflon bog ensults thot the heoted I-IDPE pipe ends do not stick to the heoting plote ond distort the slnp€ ofthe pipe.Teflon is o speciol fobric thot cqn withstond higher temperotuj€.

. Th€n with the heoting plote inside the T€flon bog, the pipes should b€ pushed together until thet is o uniform beod oroundthe outsideioint surfoce. The heoting plqte olong with bag should then be removed ond the pipes quickly pushed ogainsteoch other. This Pquircs ot leost thr€€ people (one t0 hold the plote ond two to push the pipes.) os shown in Pbotogroph4.21. once the plote is placed betw€en the pipes. the entire process should be completed within 15 minutes since the plotetemperoture will stort decreosing. One prcblem in ttris metlod is thot th€ two pipes moy not be straight sinc€ it will bedifficult to opply uniform forces orould the pipe circumf€Enc€ monuolly- An olt€rnotive is to use collot flonges os shown inPhotogroph 4.22 These flonges ore mode in two ho.lves such thot they fit on the outside circumference ofthe pipe. In thismethod, th€ collo$ ore fitted obout 50 mm to 100 mm from the heoting mds ofthe pipes, b€fore inserting t}re heoting

Plote. As soon os the required temperoture is met, the heoting plote is tolen out, ond bolts ore inserted olong the flongesond tighten€d everdy. This ensures thot the two pipes oft stroight. Once thejoint cools, tle collors ore removed byunbolting them. As Gn 0lternative to tlle obove methods, o mechonicol j ig is commoDly used, which serves both to olign thepiPe ends ord to opply the requiredjoining force. The pipe monufocturers con odvise the requir€d force for different pipediometers ond grodes.

Refer to Oopter 10 (lnnovotions) section 10.3 concerning o de-becder tool to ftmove the ctcumfer€ntiol beod corrsed by heotwelding. photo 422 Collors used rojoiD ItDpE pipes

Phoro 4.21 JoiningHDPE pipes by pushingthem while hot- Noticethe Tellon bog.

Ph0t0 4.20 Heotitrg the w€iding plote

Generol bockfi | | cornpoctedin 25O mm loyers

Sieved bckfill morirnm srze 5mm)conpocled In mm hyers

Pipe

Drystone mosonryto retoin bockfil l

I

\z

cEooI

II

I

[5dmn-Tr

Generol bocKill

Sieved bockfil l

Pipe

hsd mn-1-l--

58

i

{I

4.63 DESIGN PROCEDTJRE

The design procedure (i.e. selection ofon oppropriote pipe

diometer) for o heodroce pipe is os follows:

1. Choose o stondord pipe size from Appendix B, such thqt

the velocity V is less thon 3 m/s (to minimise woll

obrosion ond to ovoid excessive heodloss) ond greoter

thon 0.5 m/s (to ovoid sediment being deposited in the

pipe). In generol, for HDPE pipes o velocity of 2.5 mls to

3.0 m/s is found to be economicol.

2. Colculqte the octuol velociw:

40r t - . -

rId,

where:

V is velocity in m/s

Q is design flow in m3/s

d is the pipe internol diqmeter in m.

3. At the entronce ofthe heodroce pipe set the submer-

gence heod os follows:

. 1.5v'zn ) -s - 2 9

where h, is the submergence heod in m os shown in

Figure 4.9. Note thot this is the heod from the crown of

the pipe. If the submergence heod is less thqn required,

then the pipe will not be oble t0 convey the design flow

(Q becouse oir will be drown into the pipe.

Figun 4.9 Submergence heod for o pipe

4. Cqlculote the heodloss in the pipe length bosed on the

inlet, woll friction, bends, volves ond exit losses os

follows:

Totol heod loss = woll loss * turbulence losses

The woll losses result from the friction between the flow

and the pipe woll. Woll losses ore colculoted os follows:

First determine the roughness volue, k in mm from Toble

4.3. Note thot the values of k iq this toble ore bosed on

normql oge (5-15 yeors) or condition.

Then use the Moody Chort in Figure 4.10 to find

the corresponding friction loctor ffor the selected pipe

mqteriol, diometer ond the design flow.

The wqll loss cqn now be colculoted from the foilowino

equotion:

LV2h = f _"woll loss

dX2O

In terms of the flow, diometer ond length, this equotion

con qlso be rewritten cs:

, fLQ.n ='^wqll loss 12d5

furbulence losses qre colculoted os follows:

h = V ' z l 2 s ( K + K + K + K )tu rD lo \s I v ' en l ron(e Dand (on l rocuon vo lve?

where heqd loss coeflicients, K, ore qs shown in Tqble 4.4.

Note thot HDPE pipes cqn be bent (by hond) without

cousing ony domoge if the bend rodius is qt leost 50

times the pipe diometer. This should be done wherever

possible, becouse:

o) it ovoids the need for mitred bends;

b) it ovoids the need for onchor blocks to restroin bend

forces (discussed in Chopter 7); ond

c) ot such Iorge rodius, \"n, becomes negligible.

Where o long rodius bend is not possible, o shorper bend

is required, ond the volue of \.no should be tqken from

Toble 4.4. Mitred bends will normolly be used for steelqnd HDPE pipelines: these qre fobricoted by cutting the

pipe ct on ongle (moximum 15") qnd then welding the

ends together to creote o bend ofup to 30". For bends of

more thon 30", two or more mitre joints ore required.

Check if the totol heqd loss for the design flow is less

thon the loss in heqd due to the pipe grodient (S) ond

thot the pipe profile is below the,hydroulic grode line

everywhere. If not, repeot cqlculotion with lorger pipe

diometer.

Determine the woter level ot the control structure ot the

end ofpipe such os the breqk pressure tonk, grovel trop

III

II

6.

59

or the settling bosin. Allow 100/0 morgin by ossumingthot the totql heod loss is 10%o higher thon colculoted(i.e. woter level is l0%o lower thon colculoted). This is toollow for uncertqinties such os the woll losses beinohigher thon ossumed.

7. Repeot colculotions with higher submergence heod dueto flood flows ond colculote the corresponding losses ondpipe flow. The excess flow will hove ro be spilled from ocontrol structure (grovel trop, settling bosin etc.) ot theend ofthe pipe.

Tqble 43 Roughness volue for differrnt pipe moteriols

MATERIAT ROUGHNESS VALUE, k (mm)Smooth pipes

PVC,HDPE, MDPE. Glqss fibreConcrete 0.15Mild steel- Uncooted- Gqlvqnised

0.06

0.06

u . l )

(I

i

i

I

;

I

1 . 2 O / m 3 / s , r

; \ , " /. 2 . 5 t 2 l 0 20 5 0 1 0 0

6(o

't()

ll_

0 l

. 09

.08

. o7

U O

. 05

.04

.03

.025

.o2

.0r 5

0. I

.09

.08

0 7

.06

.05

.03 s.9

.02s 6LL

.02

.01

.o09

.008

.01 .02 .05 . t .2

1 .2

.5 I

*(#)2 s / r o \ z o s o roo

rvd - 000.00t ud-.999.005

Figure4.l0 Moodychort

60

Tqble 4.4 Turbulence losses in pipes

Heod loss coefficient for intokes lK-*jEntronce prohle

z7

kvK-c** 1.0 0.8 0.5 0.2

Head loss coeffici€nts for bends (Ko..of

Bend profile

r/d MITR-ED-

{o l0 = 20'lk-o l0 = 45"1k".", l0 = 90"|

Q.20

0.400.75

0.15

0.30

0.50

0.120.250.40

0.10

0.20

0.30

0.100.220.45

.Mitred bends with 4d : 1.5, maximum 30 per mitred joint

Heod loss coemcients for sudden controcrtions lK_.*.*lControction profile

5.0) \2.01 .51.0d,ld,0.500.400.35

Heod loss coefficients for volves (\",.f

K .

SPHERICAI.

0.1

o t

BUTTERFLYTYPE OFVALVE GATE

Ii

I

Flood lrvcl

J$.m3BodioHDpE160 Us in 2r?8O

GRAVEL TR.Aq

l{ol fo rcolc

rivcr levrl

Figur€ 4.ll Heodworb of the tffi kW Siklis micro-hydm scheme (Siklis. Nepoli

A sketch of the heodwork of the existing 100 kw Siklis micro-hydropower scheme is shown obove in Figure 4.11. colculorethe following:

1. Heodloss in intoke pipesZ. Design woter level in grovel trop3. Flood flow through intoke pipes4. Spillwoy length ot grovel trop

l. Hecdlocs in lntake pipes ct design 0ow

nl Pinp frictinn

For 280 mm di0'meter, Closs II HDPE pipe monufocturcd in Nepal, internal diameter = 262 mmFIow perpipe (Q = 160/2 = 80 l/sFrom thble {.3, sssurne k = 0.06 mm

k 0.06mm't;-=Em;- = o'ooo23

l.zQ 1.2x0.08;--= fll6z

=0.356

.'. f = 0.0166 (from Moody Chort, Figure 4.10)

. fLtr" h m u r o s : l 2 d i -

_ 0.0166x40x.0.08, = Ol9 m

12x0.2625

b) Inlet heodloss

K** = 0.8 for this cose (Tcble 4.4)

62

I

I

I

I

v2. ' . h . . - K xror( toss emmftc

29

Check velocity;

40 ,1x0.08V = i - = - = 1 . 5 m r s-

fld2 nx0%t

0.8x1.52of hintnl., =

Z*9f = 0'qLE

c) Exitheodloss

- \lzh . = l ( . 1 -

srr6r &t Zg

1.0x1.5'zz-9f

= o'11 m

.'. Totol heodloss tn intok€ pip€s= 0.29m * 0.09m * 0.11 m = 0.49 m

2. Ilesign water levd in grovel trcp

This should be ot leost 0.49 m * ltl% (sofety mcrgin) i.e.0.54 m below the low river level ot the intoke, or "o" = 0.54 m inFigure 4.11.

3. Flood flow through tntala pipes

Flood level is 1.5 m obove low river level.Allow 0.2 m heod over grovel trop spillweir (i.e. b = 0.2 m in Figure 4.ll).Then net heod on intoke pipes = 0.54 + 1.5 - 0.2 = LE4_8., or 'c" = 1.84 in Figure 4.11.

fiol ond error solution for flow:

o) TrY Q = 200 l/s in eoch pipe

7.20 7.2x0.2-

a : i .262- =o'916

+ f = 0.0152 (from Moody Chort)

0.0152x40x0.20'?t i-^...^,,,-.:-::--:-:-::--- = 1.64 mwour*s 72x0.2625

v = 4Q - 4xo'2 = 3.71 m/slld'z llxQ%:t

Inlet & exit losses (0.8 + 1.0) + = 1.26 m' 2 9

Totol heod loss = 2.90 m

This is more thon 1.84 m (net heod on intoke pipes for flood level), .'. ossumed flow is too high.

Try interpolotins: 2oo U, - (# )"= ,r, U,

OJ

b) Check for Q = 159 l/s in each pipe.

l.zQ 1.2x0.159*a =Tff i ' - =0.?30

-+f = 0.0i54 (from Moody Chort)

0.0154x40x0.15fJh*otrrorr=

l17p1AZG2t =l'05m

40 4x0.159v=fr, =

;oo%z, =2'95mls

Inlet ond exit losses (0.8+1.0) *

: *rn

Totqlheodloss = 1.E5 m

This is neor enough to 1.84 m

Therefore flood flow through the two intoke pipes is: 2 x 159I/s = 31E Us

4. Spillwcy length ot grovel ftop

Weir equotion:

Qpimoy = C* x Lrpitt*oy x (ho"rno/t t

Required spillwoy weir length,

- Qoittwovl _ =-spuwoy

c*x(ho""noo)rt

Toke C* = 1.5 ond Qp'rwoy : 318 Us to ollow the entirc flood flow to be spilled over in cose the turbine needs to be closed

during such floods.

hou.noo = 0.20 m (heod over weir, ossumed eorlier)

0.318. . . L . . = -=2 .22m

spurwoy 1.6x0.20,.t

or'd" = 2.22 m inFigure 4.11.

Note the following:

1. To limit the inlet velocity, two porallel pipes hove been used from the intoke to the grovel trop. Downstr€om of the

grovel trop there is only one pipe and the veiocity is doubled. The rroson for using a lower velociry in the initiol pipe

length wos to lower the submergence heod so thot excovotion work ot the intoke could be minimised. With lower inlet

velocity there less chonce of ottrocting flooting debris which could block the inlet.

2. The spillwoy weir length is reosonoble, but note that on olternotive ossumption for heod over the weir would give o

di{Ierent onswer. The wolls oround the grovel trop must be high enough to contoin the flood flow over the spillweir.

3. The grovel trop hos to be locoted sufliciently for downstreom ofthe intoke to ensure thot the grovel trop spillweir isqbove the moximum river flood level ot thqt point: in this cose the 40 m intoke pipe Iength is more thon enough to meet

this criterion.

4.7 Construction of conols

4.7.1 DESCRIPTION

Once the conol type hqs been selected ond the design corriedout, there qre four stoges in the octuol construction os follows;

. setting out ofthe course ofthe conol,

. preporing the bench for the conol,

. excovoting the conol, qnd

o lining the conol.

These secticns describe 0 g€nersl nethod 0lc0nclconstruction ond offer exomples of other proven methods thotmoy be suitoble under certoin conditions.

4.7.2 SEIIING OTII

Setting out the conql requires the following equipment ond

sto{I

r Bosic equipment:. Level mqchine (or Dumpy level). Meosuring tope. Tripod. Wooden pegs. Mqchetes. Mqllet. Pick. Hoe. Point. Pqintbrush

o Stqff:. Surveyor. Chcinperson (ossistont to surveyor). Helper to cleqr vegetotion qnd pr€pore pegs

The setting out ofthe cqnql is done by plocing pegs olong

the olignment. Depending on the topogrophy, such pegs shouldgenerolly be ploced ot 5 t0 20 m intervols olong the olignment.

Pegs should olso be ploced qt bends, structures such os drops,

ond the beginning ond end of crossings ond superpossoges.

Some intermediote pegs or reference pegs should beploced just outside the conql olignment using o level mochine(or o Dumpy level). With the use of the level mochine, the

difference in levels between these pegs con be cqlculoted. Suchpegs will serve os reference levels for the excovqtion work. An

olternqtive to this is to point morks ot exposed rocks just

outside the olignment ond colculqte their levels.

4.73 BENCH CUT

The bench of q conol is like o rood of uniform width ond slope,see Figure 4.12. The bench is prepored by excovoting o strip oflond ofeven width olong the pegs ploced eorlier on the conqlolignment.

The bench width should be the top width of the conqlplus on ollowonce for berms on eoch side of the conol. On thehill side, q berm of 300 mm is recommended. so thot moteriqlwoshed down by rqin from the slope obove is not depositeddirectly in the conol. A 1.0 m wide berm is recommended on thentt tSlde nf thq henrh tn rpdrrCp sppnnnp thrnrrnh thp rnnnl hnnlz

! r . r v g 5 ^ ^

ond to provide occess for construction ond mqintenonce. Alesser berm should only be used in conjunction with verticolcement mosonry wqlls founded on rock. Note thot q bermwidth less thon 500 mm is diflicult to wolk olong.

The slope ofthe bench should be the some os the slope (S)ofthe conol section. Therefore, where there is o chonge in theconol slope (in the design) the bench slope should olso chonge

occordingly. The levels of the cqnol ond the bench ot differentlocotions con be verified using o theodolite or o level mochineqnd the intermediote pegs thqt were ploced outside the conololignment eorlier.

Once the initiql level ot the intoke is fixed, the subsequentlevels cqn be colculqted bosed on the slopes. The initiol level

con be estimoted bssed on the contour mops of the oreo or byon oltimeter. Another method is to use the trigonometric points

estqblished by the survey deportment, but this moy toke longerond require more resources.

The initiol level does not hove to be very occurote (i.e. theexoct elevotion from the seo lwel) but the differences betweenintermediote pegs should be occurote, since it is these differ-ences thqt determine the slope ofthe conol.

An exomple of o level colculotion is presented below:The designer hqs recommended o slope of 1.520 for o

certoin cqnol section. The topog rophic mop of the oreo

indicotes thqt the elevotion ot the intoke is qround 1600 m

obove meon seo level (MSL).

In this cose the first peg thot is ploced ot the intoke oreocon be ossumed t0 be ot o level of 1600 m qbove MSL. Ifthesecond peg is to be ploced 20 m (horizontol length) downstreqm,the bench level here should be:

20 m x 1.5/100 : 0.30 m down from the intoke or 1600 m - 0.30m = 1599.70 m obove MSL.

The subsequent reodings between intermediote pegs (i.e.

reference points) con be noted in sequence with similorcalculotions.

65

a

{

exceeding the top width ond meeting the bottom width ot the

required depth. Thus, the required tropezoidol shope con be

orrived ot. This method of excovotion minimises the use of

construction moteriols ond the need to bqckfill. Note thot, os

mentioned eorlier, the side wolls of o tropezoidol cement

mosonry conql ore more likely to crqck if constructed on

bocklill.

It is qlso helpful to prepore q wooden "former" to check

the cross sectionol shope ofthe cqnql for tropezoidol shopes.

This involves constructing o wooden frome (using rectongulor

sticks) ofthe required tropezoidcl shope.

The cqnol invert slope should be constontly checked

using o level mochine. Note thot on inqccurote slope con be

very costly: if the slope is less thqn required, the conol will not

hove the copccity to convey the design flow; ifthe slope is

steeper thon required, the velocity moy exceed the mqximum

vqlue for the conql type ond stort eroding it.

4.7.5 CANAI. UNING

Once the excqvotion work has been completed, the octuol

construction ofthe cqnol con commence. The construction of

the cqnol depends on the type thot hos been chosen. For- . . ^ * - l - : f ^ - ^ ^ + L ^ ^ - - l L - - L ^ ^ - - L ^ ^ - * ^ t l . L - . : - - - ^ - - : - - jcxul l lp l t , l l u l . l tu lL l l Lul lur l luJ uccl l L l ruscl l , u l l urur , t5 lcqut lcu

is to trim the side wolls qnd bottom width qt some ploces where

the excovqtion work hos been poor. However, if o mosonry

cqnol hqs been chosen, then this will require collecting stones,

dressing/sizing them ond then plocing them ot the excovqted

surfqce occording to the design.

For stone mosonry in cement mortor, the following is

recommended:

o The minimum thickness for bed ond side wolls should be

300 mm, since thinner wolls require more stone work

(dressing ond sizing) ond moy not hove the required

strength. This olso opplies to stone mosonry in mud

mortor conqls. Recommended designs ore shown in

Figure 4.13.

r Sond used for preporotion ofthe mortor should be clean

I

I

1

Figurc4.12 Conolbench

4.?.4 CANAL EXCAVATION

0nce the conol bench hos been prepored, the excovotion lines

need to be set out os follows:

o Plqce pegs olong the centreline ond the top ond bottom

widths of the conol. The centreline is on imogincry line

thot posses through the centre ofthe conql ond porollel

to the sides. Note thqt the top ond bottom widths should

include the side woll thickness os well (i.e. outside edges

ofthe finished cqnal).

r Join the pegs using thin ropes. Then mork seporote lines

for the top qnd bottom widths (for tropezoidol sections)

using powdered lime or qshes so thot they ore indicoted

on the ground. Note thot for rectangulcr sections, the

top ond bottom widths ore equol ond two porollel linesqre suflicient for the excqvqtion work.

o Check the dimensions ogoinst the design specificotions.

Once the excovotion lines hove been prepored the conol

should be excovoted to the required shope ond slope os per the

design. For o rectongulor conol, the excovotion should stqrt

from the sides down to the required depth. For tropezoidol

sections, the excqvotion should stort ot the centrql port without

exceeding the bottom width lines verticolly down t0 the

required depth. Then the sides should be excqvqted without

1.00

h>

0

min,

' o ) Woll height <0.46

Note: All dimensions ore in metres b )woll heighr >0.46

Figur€ 4.13 Conol lining with stone mosonry in cement mortor

66

ond free from orgonic moteriols qnd fine porticles. Thesond porticles should be gronulcr (like ordinory sugor)ond not floky. Sond mixed with fine porticles should bethoroughly woshed before use.

The rotio ofthe mortqr should not be less thon 1 portcement t0 4 ports sond by volume (1:4 cement/sondmortor). This opplies to qll wqter retoining structuressuch os the settling bosin ond the foreboy tonk. Thestones should be wetted before construction (dry stonesobsorb wqter from the cement mortor, stopping it reochfull strength).

1:3 cement sqnd mortqr moy be used for plosterwork inthe heqdroce conol ond other wqter retoining structuressuch os the settling bosin ond the foreboy. plostering theconol lining is normolly unnecessory, but could be usedto reduce hydroulic losses (refer to Tqble 4.1) or whereseepoge is occurring in bodly constructed mosonry. Thethickness of the ploster should be obout 12 mm (1/2

inch).

Immediotely ofter the construction of o cement mo-sonry portion ofthe conol length, it should be kept moistfor ot leost four doys. This is colled curing ond is doneby gently pouring woter on the wolls of the conql. Theuse of hession (wet socks) to cover the mosonry helps toretoin moisture cnd cures the cqnql structure better. Anuncured conol will not goin full strength. During hotond dry weother pouring woter on the mosonry conolwill be required frequently to ensure thot the conol wollsremqin moist ond reoch their full strength. Curing ismore importont for plosters since they ore thin surfqcesond con eosily crock ifthey dry up quickly. Note thot ifthe ploster is done ot o loter stoge (ond not immediotelyqfter the mosonry work), it will require further curing

for ot leost onother 4 doys. Also, the mosonry should be

wetted before opplying the ploster.o For ploin concret€ lining, use 80 mm thickness. A

minimum curing period of Z doys is recommended.o For reinforced concrete see Section 8.5.2.

4.8 Checklist for heodrqce works

o Check the heodroce olignment for stobiliry. Is the oreaobove ond below the heqdroce olignment stoble? Referto Chopter 2 for signs of instobility. Remember thoteorth conols ore the most economic option where theheodroce olignment is on stoble ground ond seepoge isnot likely to contribute to slope instobility.

o To minimise costs, stone mosonry in cement mortorcqnals ond heodrqce pipes should only be used clong thedifficult stretches of the olignment.

e While fixing the heodroce olignment do not moke theinvert slope steeper thon necessory since ony loss inheqd here leoves less heqd for power generotion.

Minimise the length unless longer length is required toovoid costly crossings. \ different options so thedesign is economicql ond the construction is procticol.

r Hqs the heodrqce cqnol or the pipe size been colculotedbqsed on the ovoiloble site doto? Ifon inigotion conql isbeing refurbished into o heodrqce, note thot there moynot much control over the invert slope. Decide on therype ofconol by trying different cross sections ondcolculoting the corresponding velocities such thot theyqr€ within the limit shown in Toble 4.1.

r For HDPE heodroce pipes, be sure to follow Figure 4.g forpipe buriol detqils. HDpE pipes should not be exposed.

r For the construction work refer to Section 4.7.

+ -

b l

5. Grovel trop, settlingbasin ond foreboy

5.1 Overview

5.I.1 THE SEDIMENT PROBLEM

Most rivers corry o substontiol quontity of sediment in the

form ofgrovel, sond or f iner rnotericl depending on the river

chorocteristics, geology ofthe cotchrnent oreo ond the dis-

chorge. Steeper rivers such qs those thot originote from the

Iiimoloyos corry cobbles ond even move lorge boulders during

onnuol f loods. Intokes ore locoted ond designed to l imit the

omount of sediment entering the micro-hydr0 system, but such

sediment connot be entirely eliminoted. Intokes con only

prevent boulders ond cobbies from entering into the system

ond minimise the influx of grovel ond finer sediment.

l-orge porticles con block the heodroce ond reduce its

copocity. Suspended sediment con couse severe weor on the

turbine runner, seols ond beorings, since the flow velocity ot

the runner is high. Such weor couses o reduction in the

efhciency of the turbine ond eventuolly leods to its complete

foilure. In either cose, mointenonce is necessory, requiring

high expenditure in terms of reploced ports, mon-hours ond in

loss ofpower production. There ore obundont exomples of

turbine runners completely destroyed within o few yeors ofter

instollcrtion ot micro-hydro plonts thot locked settl ing bosins.

The rote of weor of turbine ports due t0 sediment

obrosion is governed by the following foctors:

o Concentrotionofsuspendedparticles

r Hordness ofporticles

r Size of porticles

o Shope ofporticles

o Resistonce ofturbine runner

r turbine heqd

It is not necessory to exclude oll sediment ot the settling

bosin. This is virtuolly impossible ond would not be economi

colly vioble, especiolly for micro-hydro schemes. A smqll

concentrotion of fine sediment is often permissible os will be

discussed lqter. The design should be such thot the size ond

concentrotion of sediment possing the settiing bosin qre within

occeptoble limits.

5.1.2 FUNCTION OF THE STRUCTURES

Grovel trcps, os the nome denotes ore designed to trop grovel

thot enters the intoke olong with the diverted flow. If o river

only corries fine sediment ond not grovel (even during floods),

then this structure is not required. However, most mountoin

rivers in Nepol corry grovel, especiolly during floods. In the

obsence ofo grovel trop, grovel wil l settle olong the gentler

sections ofthe heodroce or in the settling bqsin, where it is

difficult to flush out.

A settling bqsin is o bosin whose function is to settle the

suspended porticles present in the diverted river flow. Since

rivers qre never free from sediment, oll micro-hydro schemes

should hove o settling bqsin. For smoll schemes, this moy

simply be a widened section of the conol. The flushing mecho-

nism moy be rudimentary, which is occeptoble provided thot

domoging sediment does not reqch the turbine.

A foreboy is o tqnk locoted qt the end of the heodroce ond

the beginning of the penstock pipe. It is o structure thot ollows

for the trqnsition lrom open chonnel to pressure flow condi

tions. The woter Ievel ot the foreboy determines the operotionol

heod of the micro-hydro scheme.

5.1.3 LOCATION OF THE STRUCTURES

Whenever possible the grovel trop, settl ing bosin ond loreboy

should be combined. This minimises the construction cost.

Sometimes, either the grovel trop ond the settling bosin or the

settling bosin ond the loreboy ore combined, but the topo-

grophic conditions ore rorely oppropriote to be oble to combine

oll three structures. The Jhonkre mini-hydro is q rore exomple

where it wos possible to combine oll three structures os

described in Box 5.1.

Selection ofon oppropriote settling bqsin site is governed

by the following criterio:

o The locqtion should be such thqt it is possible to flush

the sediment ond spill excess flow from the bqsin

without cousing erosion problems or damoge to other

structures. There must be suflicient heod to flush the

sediment qnd druin the bosin.

r The settling basin should be locoted qs close to the

heodworks os possible, especiolly ifit is seporote from

69

the foreboy. The eorlier the sediment is removed the less

the mointenonce of the heodrqce. Furthermore, the

heodroce olignment downstreom of the settling bosin

con be gentler (hence less loss in the cvoiloble heod)

since the flow will be sediment free. A locotion close to

the intoke ollows ecsy dischorge of sediment bqck to the

river. From on operotionol viewpoint, it will olso be

eosier for the operotor/helper to combine work ot the

intoke, such os cleoning the coqrse trqshrock, qnd

flushing ofthe settling bosin.

r There needs t0 be odequote spoce to construct this

structure os designed. Note thot it cqn be o relotively

wide ond long structure. Therefore, locoting this

structure on foirly level ground minimises the excovo-

tion costs.

The foreboy is locoted immediotely uphill of the

tronsition oreo where the ground profile chonges from

level to steep. The following odditionol foctors should be

considered before decidino whether o site is suitoble for

o foreboy:

r It should be possible to spill the entire design flow from

the foreboy without cousing erosion or instobiliry

problems. Ideolly if this structure con be locoted close to

o gully, it moy be possible to sofely divert the spillwoy

flows into it.

o Similqr to the settling bosin there needs to be odequote

spqce to construct this structure os designed. However,

the foreboy is usuolly smqller in size.

5.2 Grovel trap

A grovel trop is recommended for oll micro-hydro schemes in

Nepol. In the obsence of o grovel trop, the settling bqsin must

be close to the intqke ond qble to flush the grovel thot enters the

bosin. Grovel trops differ from settling bqsins in thot they

hondle coorse moteriql thot enters neor the bed, rother thon

suspended moteriql thot needs to be settled. The moin design

principle for o grovel trop is thot the velociry through it should

be less thon required t0 move the smollest size of grcvel to be

removed. The lorgest size ollowed to enter into the intoke con

be controlled by the spqcing of the coorse troshrock bors. In

generol grovel trops should settle porticles lorger thon 2 mm

diometer. Smoller sized porticles will be settled ond removed in

the settling bosin. The following criterio should be used for the

design ofthe grovel trop:

o To be oble to trop porticles down to 2 mm diometer, the

velocity in the grovel trop should be limited to 0.6 m/s.

o lfthe grcvel trop is hopper shoped, the floor slopes

should be obout 30" (1:1.7). Such on orrongement will

focilitote eosy flushing ofgrovel. Ifit is not possible to

construct such o shope, the floor should siope towords

the flushing end, with o longitudinol slope of 2-5%0.o JIq lgnglh of the grovel trop should be ot leost three .

times the width of the heqdroce colol or 2 m, whichever

is lorgg. With this fixed length ond o velociw of 0.6 m/s.

the required width of the trop con now be determined. .Note thqt this is o generol rule of thumb, but if a

significont bed lood con enter the intoke, then o longer

length moy be required. Since studies regording the

movement of grcvel in rivers ore rore (rorer thon

sediment studies), it is usuolly diflicult to estimote the

storoge required in o grovel trop. Note thqt the storoge

must be provided below the normol flow depth.

o To minimise blockoge of the heodrqce or domoge due to

obrosion in the heodrqce, grovel trops should be locoted

os close to the intoke os possible.

Crovel trops con be emptied vio flushing gotes or by

lifting stoplogs (i.e. wooden plonks). Since grovel enters the

intoke only during high flows, incorporoting stoplogs isgenerolly more convenient qnd economic.

The Golkot grovel trop is shown in Photogroph 5.1 ond in

Drowing 42010/.12C02 of Appendix C. Although o grovel trop,

this structure hos oiso been designed os o primory settling

bosin. This is becouse the heodroce conol is long (1.1 krn) ond if

significont sediment lood con be tropped in the grovel trop, the

mqintenqnce requirement will be less fqr downstreom in the

heodroce conol. Furthermore, once the sediment is removed.

the heodroce conol slopes con be gentler os discussed in Chopter4. Since this is o combined structure, the colculotions ore

presented ofter the discussion on settling bosins.

Note thot os con be seen in Drowing 420lCF.l2A0l(Appendix C), the Golkot grovel trop is locoted 35 m down-

streom from the intoke. This is becouse the initiol length of the

intoke wos felt to be vulnerqble to flood domoge. For the somereoson the coqrse troshrock is ploced qt the end ofthe orovel

Irop.

In the Golkot micro-hydro scheme, significont grovel lood

is not expected for the following reosons:

o The diversion weir is of o temporory noture ond does

not extend throughout the river width.

r The intoke is locoted on the outside ofo bend.

70

53 Settling bosin

53.T DESIGN CRITERJA

Suspended sediment thot is not settled in the grovel trop is

tropped in the settling bosin. The bosic principle ofsettling is

thot the greoter the bosin surfqce or€q ond the lower the

through velocity, the smoller the porticles thot con settle. A

settling bosin hos o significqntly lorger cross sectionql or€o

thon the heodroce conol ond therefore the flow velocity is lower

which ollows the settling ofthe suspended moterioJs.

A settling bosin must sotisry the following thr€e c terio:

Scttling copocity

The length ond width ofthe bosin must be lorge enough to^rr^Lr. r^mo noronr.^o ^. rh6 nno .o.r i .ne-t tC f0] loul Cfu ' w r r e r u r 9 ! l l l ! r ' r r u g L u . r r l r r u r l I u r

suspension ond be deposited on the bed. The sediment concen'

trotion pqssing the bosin should be within occeptoble limits.

The geometry ofth€ ir et, the width ofthe bosin ond ony

curvotur€ must be such os to couse minimum turbulence.

which might impoir the effrcienry

Stomge corcity

The bosin should be qble to storc the settled pqrticles for some

time ur ess it is designed for continuous flushing. continuous

flushing mechonisms ore however not incorporot€d in micro-

hydro schemes due to the complexity ofthe design ond the

sconity of woter during the low flow seoson. H€nce, the

stomge copocity must be sumciently lorge thot the bosin does

not require fr€quent flushing.

Flushiry cspcity

The bosin should be oble to be operoted so os to rcmove the

stored porticles from it. This is don€ by opening gotes or volves

ond flushing the sediment olong with the incoming flow in the

bosin. The bed grodient must be ste€p enough to cl€ot€

v€locities cqpoble ofremoving oll the sediment during flushing.

532 THE II'EAL SETruNG BASTN

The theory behind the design ofo s€trling bosin is derived onthe bosis ofon ide0] bcsin. Therefore, before proceeding tothe

design phose. the concept ofthe ideol bosin needs to b€ under-

stood. Such on ideol bosin is shown in Fioure 5.1.

tuint X Plon oreo A

FigurE 5.1 An ideol s€ttling bosin

Consider o porticle entering the'ideol settling bosin" on

the woter surfoce ot point x (i.e. beginning ofthe settling zone)

os shown ill Figurc 5.1. In this figure:

L = length ofthe setrling zone (m)

B = width ofthe settling zone (m)mpnn wntpr dpnth in thp <p t t l inn znno lm l n lcn

colled hydroulic depth

t = time for porticle to trovel the length L {s)vp = horizontol velocity component ofthe ponicle (m/s)

w: v€rtico.l velocity component ofth€ porticle (m/s), i.e..'foll velocity" which is discussed loter

Q: dischorge (mr/s)

Then the following equotions must hold for the pqrtide

to reoch th€ end ofthe seftling bosin (point Y):

y : w t ( o l

L = v p t ( b )

Q : B v p y ( c )

substituting for y, vpond t ftom (o) ond (b) into (c) Rsults

i n : q : 9 1 *

Phoro 5.1 Colkor grovel trop

71

Therefore, for o given dischorge Q, the plon oreo ofthe

settling bosin con theoreticolly be determined for sedimentotion

of o porticle with foll velocity w However, in prcctice, o lorger

bosin qr€o is required beccuse of the following foctors:

r the turbulence of the woter in the bosin;

o imperfect flow distribution qt the entronce; ond

o the need to converge (sometimes curve) the flow

towqrds the exit.

Therefore in 'reol bosins" the through velocity is limited,

to reduce turbulence, ond the required plon oreo is obout twice

the oreo colculqted for the "ideol bosin".

533 FAII VETOCITY OF SEDIMENT AND PARTICI.E SIZE

The foll velocity, w, chqrocterises the obility of porticles of

vorlous sizes to settle out under grovity. For o discrete pqrticle,

this volue depends on its size, density, ond shope, os well os the

temperoture of woter.

Figure 5.2 shows the foll velocity in woter, w, os o

function ofthe porticle diqmeter for reference quartz spheres.

This figure con be used to estimote w for the colculqtions

required in the design ofthe bosin. Note thqt the temperoture

effect becomes less for lorger diometer pofticles.

In micro-hydropower schemes, the settling bosin is

designed to trop 1000/6 ofporticles greoter thon o certoin size,

d,,,n. 0nly o proportion of smoller pqrticles will be tropped, but

d, ., is set so thot the smoller porticles possing though the bosin

will not couse significont obrosion domoge to the turbine.

For micro-hydro schemes the following procedure is

recommended for the selection of d,,.u:

r Low heod schemes, h < 10 m:

4,.n: 0.3 to 0.5 mm

o Medium head schemes. 10 m < h < 100 m:

d,,,, = 0.2 to 0.3 mm

r High heod schemes, h > 100 m

d,,, : 0.1 to 0.2 mm

where h is the gross heod.

The current proctice in Nepol is to use dr..., of 0.3 mm

regordless of the heqd of the scheme, which is somewhot

orbitrory. The opprooch outlined in this section is more logicol.

This is becquse for o given ponicle size, the higher the heod, the

more the domoge is to the turbine.

Th.4,-, ronge given obove os o function of heod ond

flow ollows the designer some flexibility in deciding the porticle

size to be settled.

J1ll tI I III z rrfI I

TT aII t vzv

1 _-Ternpelof--ilrn -C -7

r-//, .-/

2 7 7-

t o

aaoE=E.s3

e.Yoo l

oo l I lo looFo l l Vc loc i ty , In cent lnct r r pe lecond ( Rouse,1937 )

oo l o l rooo

Figun 5.2 Foll velocity of quortz spheres in woter

72

.II

ItIt

The following foctors should be used while deciding on

the volue of d,,.u:

o If most porticles ore highly cbrosive (quortz sond or

minerols), then the lower limiting volues should be used.

Ifthe pcrticles qre softer less obrosive substqnces, then

the higher limiting volues moy be occeptoble.r Crossflow turbines ore relotively less sensitive to soft

impurities such qs siit ond cloys. Other types such os

the Froncis turbines ore m0re sensitive to ony kind of

suspended motter. Pelton turbines ore intermediote.

r For exomple, d,,.u : 0.2 mm should be selected in q cqse

where: h = 50 m, suspended porticles are mostly pure

quortz or similor minerqls, ond o Frqncis turbine is

used.

5.3-4 SETruNG DESIGN

The oreo required for the settling bosin ond its plon shope ore

colculoted os follows:

1. Using the criterio discussed in Section 5.3.3, determine

what the ronge of the scheme is (i.e., low, medium or

high heod) ond decide on the corresponding minimum

porticle size to be settled, i.e. d,*,,.

2. Using Figure 5.2, for the selected d, n,,,, determine the fqll

velocity, w.

3. Colculote the required bosin surfoce oreo (A) using the

following equotion.

) i

A- -::w

Note thot o foctor of 2 hos been used to ollow for

turbulence in the bosin.

4. With the bosin qreo colculoted obove, fix either the

length, L, or the width, B, occording to site conditions

ond colculote the other dimension such thqt 4 < t/B <

10.

5. Check thot the horizontsl velocity (V

0.44 \q;, i.e. V < 0.24 m/s

=*," less rhqn

where d,,,, : 0.3 mm. If not, increose the cross sectionol

oreo (B or y) to meet this condition.

53.5 STORAGE DESIGN

The concentrotion ofsuspended porticles in the flow con be

expressed os lollows:

Concentrction (C) =kg of suspended motter

m3 of woter

Unfortunotely, there hove not been ony studies regording

the concentrotion of sediment in smqll mountoin rivers of

Nepol thot ore oppropriote for micro-hydro instollotion.

Therefore, in the Nepclese context, the designer hos to rely on

doto ovoiloble from lorge hydropower projects. The recom-

mended proctice in Nepol is to use C = 2 kg/m3 for the design of

settling bosins for micro-hydro schemes

The sediment storoge requirement in o settling bosin is

colculoted qs follows:

1. Colculote the sediment lood using the following equotion:

S , -o = QTCwhere:

S,*o : sediment lood in kg stored in the bosin

Q = dischorge in m3/s

T = sediment emptying frequenry in seconds

C = sediment concentrotion of the incoming flow in kg/m' .

A ressonoble emptying frequency (T) in the Nepolese

context could be obout once to twice doily during high floW

which results in less thon once q week during the low flow

seoson when the sediment concentrotion is low.

2. The next step is to colculote the volume of the sediment,

using the following equotion:

\l / _

- lood

' r e d r m e n t - S . X P -

oansnv tof,or

where:

V,.di..m = volume of sediment stored in the bosin in m3.

Sd"n,iry : density of sediment in kg/mr, obout 2600 kg/mr. Unless

other doto ore ovoiloble this volue should be used for So.*,r.

Prono, : pocking foctor of sediment submerged in woter.

When submerged in woter, porticles occupy mor€ spoce

thon when dry. This is meosured in terms of pochng foctor,

which is the ratio of unit volume of dry sediment to unit

volume of wet sediment (i.e. volume of 1 m3 of dry sediment

divided by the volume of this sediment when submerged).

Pocking fuctor for submerged sediment is obout 0.5 (i.e. the

volume of dry sediment is doubled when submerged).

Beiow the settling zone must be the copocity to store the

colculoted volume of sediment, \.ain.nt. This storoge spoce is

ochieved by increosing the depth ofthe bosin os follows:

t ioaoqa

-

Where Yuo,on.is the storoge depth in the settling bosin

below the hydroulic depth (y) discussed eqrlier, ond A is the

plon oreo. The hydroulic depth ond the storoge depth ore olso

shown in Figure 5.3.

53.6 COMPONENTS OFA SETruNG BASTN

The settling bosin hos three distinct zones; the inlet, settling

\/sedlment---;-

lt

i

i

i

\1l

1

It

Freeboord

TYPICAL CROSS-SECT lON

' tvPrcAL Lor{GrruotuL sEcrro}J I

lnlet zonc Sellling zonc Oulht zone

Freeboord

f low+

-!-

f l ow ' ,

N S.for.o99 zI

Figure 5.3 A typicol s€ttling bosin ond its components

ond outlet zones. These ore discussed below ond shown in

Figures 5.3 ond 5.4.

Inlet zone

This is the initiol zone where the tronsition from the heodroce

to the settling bqsin occurs ond there is o groduol exponsion in

the bqsin width.

The design of the inlet is importont to the efliciency of

the bosin. For high hydroulic efliciency ond effective use ofthe

bqsin, the inlet should distribute the inflow ond suspended

sediment over the full cross sectionol oreo ofthe settling zone.

Vorious reseqrch doto show thot horizontol velocity

voriotions qcross the width of q rectongulor tonk offect the

hydroulic efliciency considerobly more thon velocity voriotions

in depth. Therefore, ottention needs to be given t0 uniform flow

distribution in the horizontal plone. The following methods ore

used in the inlet zone t0 ochieve o good flow distribution:

o Grqduql exponsion of the iniet chonnel. This is the most

commonly used method in micro-hydro schemes. To

determine the length of the inlet zone, set the horizontol

exponsion rotio ot obout 1:5 (cr = 110) os shown in

Figurr 5.4. This will ollow on even flow distribution ot

the beginning ofthe settling zone. The verticol expan-

sion rotio con be higher ot qbout 1:2 (a = 27) os shown

in Figure 5.3.

o Another option is to incorporote o weir os con be seen in

the Golkot settling bosin (Drowing 420/04/3C01).

r ftoughs with slots or orifices in wolls or bottom.

. Bofile wolls

Note thot orifices or boffle wolls ore often used in woter

treotment focilities where extremely low velocity is required but

these methods ore rorely used in micro-hydro schemes.

In some schemes in Peru, o sliding gote is instolled in

front of the settling bqsin os shown in Photogroph 5.2. During

flushing, the gote is initiolly closed, impounding woter behind

it. When the settling bqsin is emptied, the gote is opened ond

the sudden rush ofthe impounded woter flushes out ony

sediment thot hos remqined inside the bosin.

a^

Fiqure 5 4 Exponsion ond controction rotio in s€ttling bosin

Settling zone

The b0srn rcoch€s the required width ot the beginning ofthis

zone. Pofticles or€ settled, stored ond flush€d in this zon€. The

length ofthis zone is longer thon th€ ir et or the outlet zones. It

should be noted thot long norrow bosins perfom better thon

shQft wLde bosins. A ronge of 4 to 10 is rccommended for the

r0 0 ofthe length Io width (L/B). Bosin shqpe con olso be

improved by subdrvision with q longitudinol divide wcll, since

thrs d0ubles the L/B rotio for q given bosin length. Also, the

longitudinol divide woll cqn ossist in the operotion ofthe

scheme. For exomple, the sediment in one sub-bosin con be

flushed while the oth€r is in operotion, producing holfthe

power 0utput. Without the subdivision, the pl0nt w0uld hove

to b€ closed during flushing.

Provision for flushing the stored s€diment should be qt

the end ofthe settling bosin. A floor slope of1:20 to 1:50 in the

settling zone focilitotes flushing.

Outlet zone

This forms the trqnsition from the settling zone to th€ h€odroce.

The tronsition con be more obrupt thqn the inlet exponsion (i.e.,

horizontolly 1:2 or P = 26.5"os shown in Figur€ 5.4, ond

verticolly 1:1 os shown in Figure 5.3). Note thqt ifthe settling

bosin is combined with the foreboy, then this zone is not

necessqry: the for€boy structure con be dir€ctly downstreom of

The operoting woter level of the settling bosin is gener-

olly contrclled ot th€ outl€t. som€times by o weir which moy be

design€d to operot€ 0s submerged in oder to conserve h€od.

53.7 FLUSHING ARMNGEMENTS

verticsl flush pipe method

There ore vorious woys ofremoving the stored s€dim€nt from

the settling bosin. An qppropriote method for micro-hydro

settling bosins is the'v€rticql flush pipe". This us€s o detoch'

oble venicol mild steel pipe over o hole in the bosin floor A

droin pipe is lued below the bosin floor to convey the flow out

of the bosin. when the verticol flush pipe is lifted, the w0ter

stored in the bosin ond the incoming 0ow olong with the

sediment ore droined through the hole. Aport from being

simple, th€ other odvontoge ofthis system is lhot it con spil l

some excess flow such os during floods when the wot€r lev€l in

Pno o 5 2 SIdrn9 gor p or \et lhng bosrn enl ionce, Peru

Figurp 5 5 nushino o settling bosin using the venicol flush pipe method

?5

the bosin is qbove the normol level. This verticol flush method

is shown schemoticqlly in Figurc 5.5. The colkot settling bosin

is bosed on this method os con be seen in Drowing 420/04/3C01

ofAppendix c- similorly, theJhqrkot micro-hydro scheme olso

uses this method for flushing os con be seen in Photogrqph 5.3.

Photo 5.3 Jhorkot settling bosin

The diometer of the flush pip€ is governed by the

following criteriol

o) overflow copocity

It needs to spill the excess flood flow thot enters the bosin os

shown in Figurc 5.6. This is governed by the weir equotion,

where the perimeter ofthe pipe is used for the length cs follows:

0" . : fI dC h^ .r1?

where:

Qn""d is th€ expected flood flow in the bosin

hn""dis the depth ofwoter obove the verticql pipe during

Qn*d This is the heighr between the top ofthe verticql flush

pipe ond the top ofthe settling bosin woll.

C" is the weir coemcient for o shorp edged weir, which is

1.9 (see Tqble 3.3, Chopter 3). The reoson for using the shorp

edged weir coefhcient is becous€ the pipe thickness is smollr^mnnrod r^ rh , h ' ^ ,1

In terms ofthe pip€ diometer, the obove equotion con be

rewritten os follows:0" .

/ i = 41.9nh_ 3i,

To ensure droining ofexcess flow ond to prevent spilling

ofthe design flow the height 0fthe verticol flush pipe should be

such thot the top lev€l is 50mm obove the design woter level.

Also note thot ifthe settling bosir is combined with the foreboy,

it moy be mole importont to size the flush pipe diometer such

thot it is oble to spill the design flow. This is becouse ifthe

turbine volve is closed during emergencies, the entire design

flow will hove to be spilled from the foreboy until the operotor

reoches th€ intoke or other control structurcs upstreom ofthe

forebola

b) Flushing cqpocity

The pipe should be obl€ to divert both the incoming flow ond

the woter volume in the bosin, thus emptying it. This is bosed

on the following equotionsl

l .s0. = c,c \6 + tL

or O. = CAril{6i9i

where:

Q.,in" is the design flow. q.,ir" is multiplied by 1.5 in the

first €qu0tion to ensurc thot therc is 0 drow down in the w0ter

Ievel inside the bosin during flushing {i.e., both the incoming

flow qnd the flow in the bcsin con be droined).

C is the orifice coefficient : 2.76 (oppli€s or y wh€re the

totol pipe length is less thon 6 m).

tL,t"is th€ depth ofwoter in the b0sin during the design

flow prior to flushing.

ho",n is the flushing heod when bosin is empty. This is the

diff€r€nce in level betwe€n th€ floor ofthe bosin ond the flush

pipe outlet os cqn be seen in Figurc 5.6

A is the oleo ofthe pipe section.

Th€ second €quotion ensures thot the design flow con be

dischorg€d through th€ system wh€n the b0sin is empry lt is

importqnt to check this condition especiolly ifthe hn",h is low.

Photo 5 4 Lifting the {lushing mec}onism 0hong)

76

In terms ofthe pipe diometer, the obove two equotions

con be rewritten os follows:

, - / 6a" ' . ' \ ' '"

- \ l lc.rG-+h /

^ . , - / 4 Q ' ' '

\ '" ' " - \ncVn I

Not€ thot these equotions 0ssum€ thqt there is free pipe

flow ot the outlet ond the plpe dtonteter is constont {verticolond horizonrol pipes ofthe system hove the some diometer).

All of the obove three equotLons should be used ro size the

drqmeter ofrhe flush pipe. The pipe should be siz€d using the

equotron rhot results in the lorgest diqmeter lfthe totol pipe

length is m0re thon 6 m, the flow should be colculoted using theguidelines given in Chopter 4.

Sluice gste

Another convention0l m€thod offlushing includes the use 0f

sluicing gotes. This is more common in minr- ond lorge

hydrcpow€r schem€s. In this system, gotes ore lifted either

monuol)y or mechonicolly, to droin the bosin. Th€ Solle

Chiolso mini-hydro scheme is bosed on such conventionol

flushing system os con be seen in Photogroph 5.6.

53.8 OTHER CONSIDERATIONS

Spillwsy requirement

Ifexcess flows con not be spill€d from the upstreom heodroce

portion such os du€ to lock of o suitoble oreo (or if o pipe is

used), 0 spillwoy should olso be incorporqted ot the settling

bosin. The spillwoy should be sized to spill the entire llow

expected during the high flow seoson. This is becous€ the plqnt

moy need to b€ shut during high flows for rrpoir work. The

spillwoy should b€ locoted upstr€om ofthe bosin to ovojd

excess flow (ond sedim€nt) through the bosin. Note thot the

design ofspillwoys w0s coveRd in Chqpter 4.

However, in the cose where there is o verticol flush pipe

sized to divert the expected high flows, o seporote spillwoy is

not necessory

Cover

Sometimes th€r€ con olso be site specific considerotions thot

need to be oddressed du ng lhe design ofthe settling bosin. For

€xomple, th€ Ghondruk sertlirlg bosin is locoted in o forest oreoqnd lorge tree leoves were constontly blocking the troshrqck.

This problem wos overcome by plocing wirc mesh over the

bosin os con be seen in Photogroph 5.7.

Phoro 5 6 Solleri Chroko serrhng bosin

Figure 5 6 venicol {lush pipe scction in o serrling bosrn

Photo 5 5 Sert lng bosrn or lhor l rot

77

7

Ploto 5 7 Chondruk serdrng bosin

The Golkot grov€l tropiprimory settling bosin is designed for q llow of455l/s. Noteth0t the gross heod ofrhe scheme (h)is 20m.

As grovel trop or y. the minimum dimension should be os follows:

crcss sectionol ol€o requircd for V = 0.6 m/s to trop porticle size down to 2 mm.

0 ' 0 .455A: - - - : = - =0 .758m2

v 0.6

With o flow depth = 0.5 m:

Width B = 0.758/0.5 = 1.52 m, soy 1.5 m.

Using L = 3 x heodroc€ conql width (B' = 0-6 m)= 1.8 m. Use 2.0 m minimum length.

Therefore ifthis structure werc designed hs o grovel trop only the dimensions would hove been os follows:B = 1 . 5 m

L = 2.0m

As o settling bosin, the dimensions r€quired ore os follows:

since 10 m < h < 100 m, the scheme is clossified os medium heod. Recoll thot the turbine is o cmssflow type. Therefore, d,-,: 0.3 mm.

With o meon river temperoture of15 0C during the high 0ow seoson. fiom Figup 5.2, the foll velocity w = 0.037 m/s for

78

rl .r, = 0.3 mm

LB = 2Q/w = 2x0.45510.037=24.6m2t

SetB = 2.5m

L = 24.61?.5 = 9.8 m, Set L= 10.0 m

LIB=+Inlet profile due to spoce constroints set o = 260,

B_B'I = _ --islet

2 ton(a)

2.5-{.6

(2 ton 260)

= 1,94 m. Set Lnr"t = 2.0 m

Check required depth ofsettling zone, y:

Msximum horizontol velocityv = 0.aa {Irr*

= 0.44i6-.3 = 0.24 m/s

a 0.445

" 'Y=Tt=--rE; ,T=0.76mSediment storoge r€quircment:

Assume sedimentconcentrotion,C = 2kg/mrg. = 2600 ko/m3qorny

P- = 0.5loaIor

Flushing frequency, T = 8 hours wos chosen for this scheme (but 12 hours is recommended). 8 hours = 28,800 s

S , * o = Q x T x C= 0.455 x 28,800 x 2= 26,208 kg

rr - Slooa

v sediment -

sd.nrny x Pfo.,o,

= 26,208 / (2600 x 0.5) =29.16 *3

Actuol bosin oreo = LB : 10 x 2.5 = 25 m2

Required storqge d€pth,Y,,o,on. = 20.16125=0.81 m

Requireddepthofbosin = Freeboord * Y * Yuo,n"= 0.3 * 0.76 + 0.81 = 1.87 m

Therefore, os con be seen in Drowing aZ0l0Al2C02 in Appendix C, the actuol internol dimensions of the basin sre os follows:

L : 1 0 . 0 msfiillng

B . = 2 . 5 mqruD9

79

Depthofbosin = 1.9mL** = 2.0 mLoou* = 1.25 m

Since the heodroce conol is long, o secondory settling basin has been incorporoted upstreom ofthe foreboy os con be seen in

Drowing 420/0413C01 in Appendix C. As con be seen in this drowing, the settling bosin hos the following dimensions:

L . : 7 . 8 msetutno

B*,,* = 2'4 m

Depth ofbosin = 1.7 m (ovJ

L,r., = 4.4 m including the weir length

Lou,r. = 0 m (outlet into foreboy)

Note the following:

Qesisn = 421 l/s in the secondory settling bosin/foreboy. Recoll from Chopter 3 thot the flow required for power production

wqs 421 l/s ond the heodroce conol wos designed for 455 lis to provide extro irrigotion woter.)

As discussed eorlier, o weir hos been incorporoted ot the inlet zone to ensurc on even distribution of flow. Since the settling

bosin is combined with the foreboy, the outlet zone hos been omitted. Also notice the submerged weir ot the end of the bosin

which controls the velocity through the bqsin and provides sediment storoge depth. Since the grovel trop is expected to

settle most of the sediment, there hos been o compromise in the rotio of L/B (3.25) in the settling bosin: in this cose the weir

ond porollel sides upstreom ofthe settling zone give o good flow distribution ocross the bosin.

As discussed eorlief, note the flushing orrongement where sediment is flushed by removing the verticol pipe. The sizing of

this pipe is os follows:

Since there ore o number ofspillwoys along the heodroce conol (upstream ofthe settling bosin/forebay), flood flow is not

expected. Therefore, the criterion is to ensure thot the flush pipe is oble to divert both the incoming design flow and the

woter volume in the bosin, thus emptying it during flushing

Check the flush pipe diqmeter using the following two equotions:

Note thot cs con be seen in the Golkot drowing $2010apC01) h*,,n = 1.3 m ond hnu,n :1.7 m

,_{ 6q.*n" l "d = \ R C . ,

= 0 . 4 1 0 m 0 r 4 1 0 m m

, - f 4Q. . " \ " 'd = t n111;- ,l

= o.rt6 m or 386 mm

Therefore, o diometer of 410 mm is required for the flush pipe.

The octuol flush pipe diometer thqt wos used for the Golkot scheme is 400 mm (slightly smoller thon colculoted). This wos

occepted becouse it motches the penstock diameter ond wos eosier to fobricote.

TheJhonke mini-hydro scheme is o rore exompl€ where it wos possible to combine the grovel trqp, settling bosin ond foreboyinto on€ structure os cor be seen in Photogroph 5.8 ond Figup 3.8 (Chopter 3). The intoke is locot€d ot the left bqrk of o widepool and there wos odequote spoce to combine qll three structures herc. Also, the topogrophy wos such thot it wos possible tostort the penstock olignm€nt right ot the intqke.

The grovel trcp is ploced ot the curved

section imm€diqtely behind the intoke.

The stroight s€ction behind the grovel

trop work os o settling bosin ond th€

tqnk behind this is the foreboy Since

the initiql penstock qlgnment is buriec

it cqnnot be seen in the photogrqph.

Also note tlot os discussed eqrlier, the

structure hos been divided into two

bosins so thqt th€ plont need not be

completely shut during flushing.

Plotforms hqve been incorporoted ot

the end ofthe grovel trop, settling

bqsin qnd obove the foEboy to

focilitot€ flushing os well os deoning

of the troshrock. The flushing system for both grov€l ond sediment is q modilicotion of th€ 'v€rticol flush pipe" method. As

shown in Figure 5.7, insteod ofo flush pipe o cylinder (top€red ot the bottom) is used which fits snugly into the hol€ on the

bosin floor. Since the woter depth is high, the cylinders ole lifted witl spindle wheels (thus gaining mechonicol odvortoge)thot rest on the slobs. However, note thqt with thls system, th€ excess flow cqnnot be diverted viq the cylind€rs since they oreclosed on top.

The troshrock qt the foreboy is cleoned by roking thrcugh th€

bors (flot plotes) with o speciql steel roke. To prevenr

vondolism th€ spindl€ wheels ore stor€d seporotely ond

instolled only du ng flushing. lnthe photogroph the

threoded ends (where the spindles ore insert€d)conbe s€en on

the grov€l trop ond settling bosin plotforms

Figure 5.7 nushing system ofjhoDke miln hydro

Photo 5 E Grovel trop, settling bosin ond for€boy ofJhonlae mini'hydro

n

8 1

5.4 Foreboy

5.4.1 GENEML

The foreboy ofo micro-hydro scheme serves th€ following

functions:

. It ollows for the tronsition from open chonnel to

pr€ssurc fl ow conditions.

. It regulotes th€ flow into the penstock, porticulorly

through the releose ofexcess woter into o spillwoy.. It releoses the surge pEssure os the wove trovels out of

thp npn(tn.k n inp

. It con qlso serve os o secondory/fnol settling bosin ond

trop some porticles thot enter the heodroc€ downstr€om

of the settling bosin.

. Although very rore in micro.hydro schemes, the foreboy

con olso provide woter storoge for use during peok

power demond period os discussed in Box 5.2.

Structurolly, the for€boy tonl is similor to the settling

bosin €xcept thot the outlet uonsition is reploced by o troshrock

ond the entronce into the penstock pipe

t i

Photo 5 9 A dry stone mosonryforeboy showing the connection with thepenstork

5.4.2 PIPE IJVEL

The foreboy ollows for th€ tronsition from open chollnel to pipe

flow by providing odequote submergence for the penstock pipe.

As discussed in Chopter4, ifthe submergence heod is nor

sumcient, the pipe will drow in oir ond be unoble ro convey the

design flow Similorly, r€coll from Chqpter 4 thot the minimum

submergence heod rcquired for the penstock pipe is os follows:1 qlrz

h > _i::' 2 9

whel€:

h, is the submergence heod, ond

V is the velocity in the penstock.

5.43 I'ESIGN OF A FOREBAY

If the length ofthe heodroce conol between the settling bosin

ond the foreboy is long. tlen sediment con enter the conol, such

os when debris folls from uphill ofthe heodroce olignment.

Similorly ifon eorth conol (or stone mosonry in mud mortqr)is

constructed between the settling bosin ond the for€boy,

sometimes high velocity in the conol, such os during the

monsoon, con couse emsion ond cqrry sediment to the for€boy.

In such coses the foreboy should olso be designed to sewe os o

secondqry settling bosin ond the design method used for sizing

o settling bosin should be used. However, o lower sediment

concentrotion (soy C = 0.5 kg/mr) con be used since onlyporticles thot hove escoped the s€ttliq bosin or those thot hov€

been eroded from the heodroce conol oIe exDected in the

foreboy

Ifthe heodroce upstreom ofthe foreboy consists ofHDPEpipe or ofcement mosonry conol ond the settling bosin is

functioning well, there will not be ony need for secondory

settling. Howeve! os o pr€coution, some storoge depth below

the pipe invert should be ollowed for. A depth 0f300 mm or

€quol to the pipe diom€ter, whichever is lorger is r€commended

for this purpose.

5.4.4 FOREBAY SIZE

The minimum size ofthe forcboy should be such thot o person

con get in ond cleon it. The minimum cleor width r€quircd for

this is I m. Even ifth€ sediment lood is not expected in the

foreboy, it moy sometimes reoch this structure such os when

the s€ttling bosin is filled in quickly during the monsoon or

there is 0 smoll londslide. lfo pe$on con get into the foreboy

ond deon it occosionolly or during the onnuol mointenonce

period,limited sediment occumulotion will not be o problem. A

storoge depth below the invert ofthe penstock should beprovid€d for this, os con be s€en in Figure 5.8.

lfpossible, the foreboy should olso be sized such thot 15

seconds ofthe design flow con be sofely storcd in the tonk

82

obove the minimum pipe submergence level. This is more

imponont ifthe scheme consists ofo h€odroce pipe insteqd ofq

conol. There con be smqll tronsient surges in the heodroce pipe

which r€sult in uneven flow. The 15 s€cond storoge copqcity

h€lps to bolonce such uneven flows.

0.6 m/s, but o moximum of 1 m/s cou]glgllgl-

It should olso b€ not€d thot the troshrockbors should beploced v€rticolly since horizontol bqrs ole dimcult t0 deon os

shown in Photogroph 5.11. The spocing between the troshr0ck

bors should be obout ho.lfthe nozde diomet€r for Pelton

turbines ond holfthe runner width for

crossflow turhine. This Prevents the

turbines from being obstructed by debris

ond minimises the chonces ofsurge.

Cl€qning ofthe troshrock con be

minimised by fixing it such thot it is

submerged during the design flow os in

th€ cose ofthe Soll€ri Chiolso mini-hydro

(Photogroph 5.12.). Here the top level of

th€ troshrock is below the d€sign woter

level. Any flooting debris such os leoves

orr woshed by the flow obove the

troshrock ond spilled viq the spillwqy

Although this type ofqrrqngement

focilitotes self-cleoning of the troshrock,

some 0dditionol flow (thon the design

flow) will be constontly required.

Photo 511 Cleoning con be d'fficult wirhhorizontol bors.

FigurP 5 8 ForPboy

5.4.5 TRASHRACK

The troshrock qt the foreboy should be plcced qt 1:3 slope for

both emcient hydroulic performonce ond eose ofcleoning (such

os by roking) os shown irl Frgure 5.8. To minimis€ heodloss ond

blockoge, the recommended velocity through the troshrock is

II

Photo 5.10 A cemenr mosonry chonnel ond foreboy ot the rop ofo st€ep dope (Dhoding)

83

7

5.4.5 SPilIWAY

As discussed eorlier, o spillwoy should qlso be incorporoted ot

the foreboy. The spillwoy should be sized such thot it con

releose the entire design flow when required. This is becouse if

the turbine volve is closed during emergencies, the entire design

flow will hove to be spilled from the foreboy until the operotor

reqches the intoke or other control structures uDstreom ofthe

foreboy.

5.4.7 GATE AND VENT

Incorporoting o gote ot the entronce of the penstock will moke

the mqintenqnce work of the turbine eosy. The gote con be

closed, thus emptying the penstock qnd work cqn be done in the

turbine. However, o ropid closure of this gote will creote o

negotive pressure (i.e. vocuum) inside the pipe ond could couse

it to collopse. Plocing qn qir intake pipe os shown in Figure 5.8

will prevent such o situotion since oir con be drown through

the oir intoke pipe ond into the penstock.

The required size ofthe oir vent is given by:

A 2 -

where:

d = internol diometer of oir vent (mm)

Q = moximum flow of oir through vent (l/s)= moximum flow of woter through turbine

E = Young's Modulus for the penstock (N/mm'z,

see Toble 6.2)

D = Penstock diometer (mm)

t.n.,iu. = effective penstock wqll thickness ot upper

end (mm) (refer to Section 6.6)

F = sofety fqctor,5 for buried pipe or 10 for

exposed pipe.

+(#lPhoto 5.12 Submerged troshrock, Solleri Chiolso mini-hydro scheme

Consider o 300 mm steel penstock of 3 mm woll thicknessconnected to o turbine thot con toke 250 lis. Thepenstock is obove ground.

Q = 250 l/sE: 2.0 x 105 N/mm'z(from Toble 6.2)D : 3 0 0 m mt = 3 m mt.r..tiu. = 7.27 mm (from Section 6.6)F : 10 for obove ground pipe

0r, d = 80 mm, i.e. the minimum internol diometer of

the oir vent should be 80 mm.Photo 5.13 0verflow weir for the senling bosin otJhorkot

84

Th€ d€sign flow ofthe 50 kW Ghqndruk micro hydro scheme is 35l/s but the dry seoson flow is 0nly 201/s. Hence during th€dry seoson the power output wos obout 39 kW untll o p€qkrng reservoir wqs bullt in 1994. Such q peqking reservoir b€comenecessory becouse ofthe demond for firll power (50 kW) ln the !'rllage during the morlings ond evenings. Th€re is nominolpower demond rn the ofternoon ond even less du ng night time.

A suitoble site for the reservoir wos iocoted on the te[oce immedrote]y downstreqm ofthe old foreboy. Photogrophs ofthepeoking reservoir dudng cnd ofter construction con be seen below.

The wolls ond the floor o[the reservoir were constructed ofstone mosonry in ceme[t mortqr. The reservolr hos been sized suchthot it cqn provide the design flow ol35l/s for ot leost six hours (3 h0urs in the morning ond 3 houn in th€ evening). Thecolcuiotions ore os followsl

Storoge volume required - (D€sign flow - dry secson flow) x 6 (hr ) x 60 (min/hr) x 60(s/min)= (35 20) x 6 x 60 x 60 - 324,000 litres 0r 324 mr.

Hence o reservoir wrth o minimum storoge copocity ofl24 mr is r€quired to b€ qble t0 provide 50 kW for su hours. The octuoldimensions ol the reservoir ore qs follows:. Length = 20 m

. Width = 20 m

. Depth = 1.2 m

Hence, the st0roge volume is 480 mr, obout 48rl0 lorger thon lhe minimum required voiume. Note thot th€ old foreboy hosnow bec0me redundont. Also, since the peoking reservorr is downstreom 0fthe old ibreboy, o ferv metres ofheod orc lost.This is cOmpensoted by slightly increosing the dcsign flow

Any sedrment deposifed in the res€rvoir is monu0lly cleoned du ng the onnuol moint€nonce period. A flushing focility wosnol instolled becouse 0fp0tentiol erosion ond londslide problems due to the lqrge volume ofwoter involved.

At preselt the power plont is shut when there is n0 demold for po',ver, then the reservoir is o]lowed t0 fill.

Ph0to 5 i4 Chondruk peohng reseruoir dudng construcrion Pho, 5.15 Chondruk ppoh. lg rcseryoir o l lpr con.rrucrron

8 5

5.5 Construction of woterretoining structures

Once the size ofthe grovel trop, settling bosin qnd foreboy hove

been colculoted, the type qnd dimensions of the wolls ond floors

need to be determined. For micro-hydro schemes, stone

mosonry in cement mortqr is generolly the most opproprioteqnd economic option. The construction detoils ond procedures

for this type of structure ore os follows:

o The ground should first be excovoted occording to the

bosin shope qnd then be well compocted using o

mqnuol rom.

o Since these qre woter retoining structures, 1:4 cement

sond mortor should be used for the wolls ond floors qs

discussed in Chopter 4.

r The wolls should be built such thot they ore o minimum

of 300 mm thick ot the top ond increose with depth os

shown in Figure 5.9. Note thot in this figure, the woll

surfoce 0n the woter retoining side is verticql. This

increoses the stobility ofthe structure since for o

cOnstont depth the woter pressure is Iorger thon the soil

pressure. Ifthe verticql foce is towords the soil, the

woter volume in the bosin will increose but structurol

stobility will be slightly reduced.

o The internol surfoce (woter retoining surfoce) ofthe

wolls ond the surfqce ofthe floor should be plostered

using 1 :3 cement sond mortor to o thickness of 12 mm.

This significontly minimises the l ikelihood of seepcge.

r Finolly, the wqlls ond the floor should be cured os

discussed in Chopter 4.

Another option is to use reinforced concrete for the floor

ond wolls. However this is more expensive ond olso requires

skilled lobour, so is not generolly recommended for micro-hydro

schemes.

5.5 Chechlist for grovel trop, settlingbosin ond foreboy work

r Con the grovel trop, settling bosin ond the foreboy or ot

leost two of these structures be combined together?

o Are these structures locoted such thqt excess woter con

be spilled sofely, without cousing erosion or stobility

problems?

r Is the settling bosin sized such thot the emptying

frequency is once to twice doily during high flows? Also,

does d,uun correspond t0 the heqd ond turbine type?

Refer to Section 5.3.3.

o Is secondqry settling required ot the foreboy? Is the

foreboy lorge enough for mqnuol cleoning ond is o

spillwoy incorporoted in this structure? Hos the

submergence heod been checked?

r Once these structures hove been sized, refer to Section

5.5 for the construction detqils.

lsoomtnn.iilf

Stone mosoni n ' l :4 cen ien lrDr to r

Compocted eorth

l2 inm th ick o losterl :3 cement morfor

figure 5.9 Wolls ond floors ofwoter retoining structures

86

5. Penstocks

6.1 Overview

A penstock is o pipe thot conveys the flow from the foreboy tothe lurbine. The penstock pipe stqrts wherc the ground profileis steep os shown in Photogrqph 6.1.

Phoro 6l Penstock olignm€nr ofthe 36 kWJhorkot micro-hydro scheme,Mustong, Nepol

The potentiol energy ofthe flow qt the foreb0y isc0nverted into kinetic energy ot the turbine vio th€ penstockprpe. Since the flow is conveyed under prcssure it is importontfor the pipe design to be sofe. Coses hove be€n reported whelethe penstock pipes hove burst. Since the pensrock is on steepground slopes, such pipe burst con instqntoneously couse

londslides ond other stobility problems. Furthermorc, penstock

instollohon is ofren chollenging ond requires sofe ond cqEfulwork os shown irl Photogroph 6.2.

Photo6.2 P€nnock o lig nment of the 5r0 kw Borpo} micrD-hydro scheme,C,orkho, Nepol

The penstock pipe usuolly constitutes o significontportion ofthe totol micm-hydro construction cost. Therefor€ itis worthwhile optimising the design. This irvolves o cor€fuIchoice of: pipe moteriol, such os mild steel or HDPE; on economi-col diqmeter such thot the heod loss is within occeptoble limits;ond woll thickness so rhe pipe is sofe for the design heod ondony surge effect thot moy result from sudden blockoge oftheflow.

6.2 Selection of the penstock clignment

6.2-1 SrTE WORK

Selection ofth€ penstock oliglment ot site should be bosed onthe following criterio:

87

r

Fottbsy fio{.otion

The penstock storts ot the foreboy, for which locotion criterio

ore given in Section 5.1.3. In oddition, the foreboy locotion

should be chosen to optimis€ the lengths ofh€odroce ond

penstock whilst ochieving the required power output from the

sch€me. Penstock pipe is generolly more €xpensive thon

heqdrqce conql, thereforc in most coses th€ for€boy locotion

should be chosen to give the minimum penstock length.

How€ver, sometimes o longer penstock moy be economic, to

ovoid the need for the heodroce to crcss 0n unstoble sloD€.

Procticol ground slope

An ideol ground slope for the penstock olignment is between l:1

ond 1:2 MH). The flotter the ground slope the less economic is

the penstock since o longer pipe l€ngth is r€quir€d for o low€r

heod.

Although o ste€p slope minimises the penstock length, it

will be difficult to.monuolly loy the penstock, construct suppon

pi€rs ond onchor blocks ifthe slope is greoter thon 1:1. There-

fore, for penstock olignments on slopes steeper thon 1:1, the

Photo 6-3 Excovotion to rEduce the cost of the p€nstock ond reduc€ the need fol

oncho$ (Siklis)

odd€d site instollqtion cost moy outweigh the sovings mode on

the pipe costs.

Avoid o penstock pmlil€ thot storts ot o gentle slope ond

then becomes steepe! becouse ofthe risks ofnegotive surgeprcssures cousing sub-otmospheric pressurc. See Section 6.5.

For micro-hydro schemes with l€ss thon 20 kW of

instqlled copocity, the ground prof e ofthe p€nstock olignment

cqn be meosured using on Abney Level os discussed in Miclo-

hydro Design Monuol (Ref l). For lorger micro-hydro schemes.

the use ofo theodolite ond o pmfessionol surveyor is r€com-

mended. This is becouse ifthe pRfobricot€d b€nds do not frt ot

site due to survey efiors, odditiono] cost ond time will be

required to omend these, especiolly ifthe sit€ is locoted for fmm

the roodheod ond the pipes ore flonged. Note thot som€ slight

odjustment con be mode ifthe pipes ore w€lded ot site.

Errors in the design heod colculotion (due to survey

elron)will result in eith€r oversizing or undersizing the electro-

mechonicol units, which will olso incrcose the project cost,

either in terms oflost power production or in €xtro cost for the

oversized units.

Minimum numfur of D€nds

Bends increose the heodloss ond require odditionol onchor

blocks. Th€r€forc the selected olignment should be os stroightqs possible, both in plon ond elevqtion. Note thot smoll bends

con be ovoided by vorying the support pier heights for the

exposed section ond the trench depth for the buried section.

Spoce for powerhouse qr"s

The chosen oligrment should be such thot it is possible to

construct o powerhouse ot the end of the penstock. A river

terroce w€ll obove the flood l€vel is ideol for the powerhouse

oreo. A route thot is otherwis€ suitoble for the penstock

olignm€nt but do€s not ollow for the construction ofthe

pow€rhous€ is inopprcpriote.

Stsbihty

since th€ penstock olignment is on steep ground slopes ond the

pipe is under pressure, it is importont for the olignment to b€

on stobl€ grcund. Any gmund movement cqn domoge the pip€,

support piers 0nd onchor block, qnd in cose ofpipe bursts

unstoble slopes will couse further emsion ond londslides. slope

stobility is discussed in detoil in chopter 9.

88

Photo6.4 Penstock instollotionis oft€n chollenging ond ftquir$ sole ondcorcful work

Other site qncifrc conditions

Aport from the obove criterio. there moy be other site specilic

conditions thot dictote the p€nstock olignment. For €xomple, if

the olignment cmsses o locol troil, this section should either be

buried or high enough obove the grcund such thot people ondcottle cqn wolk undemeoti.

Th€ Jhonlce mini-hydro penstock olignmenr is on

exomple where o site specific condition govemed the penstock

olignment. Th€re is cultivot€d lond between the intok€ ondpowerhouse ofthis scheme, so the penstock wos oligned mostly

olong the edge ofthe culrivoted lond. At on€ section this wosnot possible ond the olignment hod to troverse the cultiv0ted

fields. Since it wos not possibi€ ro bury the pipes ot this section

{due to downstr€om olignmenr), o few ofthe support piers were

sized to be 2 m high qs shown in Phorogroph 6.5. This rcsultedin q cleor spoce ofobout 2.5 m under the penstock, which

ollows formers ond cottle to w0lk undemeqth.

6.2.2 PROFII,J OF THE SELECTED ALTGNMENT

Bosed on the site survey. o plon ond pmfile ofthe penstock

olignment should be plepored ot the design office os follows:

The ground profile should firsr be drown using on6<-

oppmpriote scole. Some scqle should used for bothhorizontol ond verticol lengths so thot the bend onglesore true ongles, which minimises the likelihood ofermrs. Ifthe olignment olso hos horizontol bends, theno plon view should qlso be pl€por€d to show horizontol

bend ongles.

Once the grcund prcfile hos been prepored, the penstockpipe should b€ drown on it such thot the number ofbends is kept to o minimum. In g€nerol for oboveground olignment the support pier height should beminimised unless some ofthem need to be incnqs€d toovoid smoll 0ngl€ bends. Similorly. excovotion shouldbe minimis€d for the buried section unless deepertftnch€s or€ r€quired ot short s€ctions to ovoid smoll

ongle bends. Optimising the olignment will requiresome iterotions. An exomple ofo penstock profile isshown in Figur€ 6.1.

For obove ground penstock sections, o minimum ground

cleoronce of300 mm is r€commended ro keep the pipe

dry ond for ease ofmointenonce such os pointing.

For buried penstock s€ctions, o minimum soil cover of1

m is r€commended os in the cose ofHDPE heodroce pipe,

ond th€ trcnch detoils should be similqr to those shownin Figure 4.8 (Chopter 4).

Photo 5.5 ttnrtock olignmenr high obove th€ ground to 0llow oc(ess for peopleond (otrle, Jhonkl? mini-hydro

89

Trorhrock

nd lrvrl

mo3onrY lnl:.1 c.nont mortsr

3OO min. round c l rorcncr

d 3 mmlh l ck m i l d r t cc l p rn r toc t

Ponrhouse

- 2 O 2 4 6 m

Sco lc

io in l

A nc ho rbloc k

Figun 6.1 'l)rpicol penstock prohle

6.3 Pipe m0tefi0ls Peru (see chopter 10, Innovorions) cnd Sri Lqnkq, but hqs

not yet been used in Nepol. Toble 6.1 compores these three pipeIn Nepol the most commonly used penstock pipe moteriols ore moteriols.

mild steel qnd HDPE. Rigid or unplosticised PVC (uPVC) is

onother option thot hos been used in other countries such qs

lioble 6.1 Advontcges ond disqdvontoges of different penstock moteriols

MATERIAL OCCURRENCE ADVANTAGES DISADVANTAGES

Steel Most common o Verv widelv ovqiloble o Heovy, tronsport cost con be higho Pipes con be rolled to olmost ony size o Rigid, bends hove to be speciolly fobricoted oto Con go up t0 olmost ony thickness workshop

o Eosy to join ond con withstond high r Hos corrosion problems

pressure r Cqn be expensive

o Con hove high surge requirementHDPE Foirly common r Does not corrode o Diflicult to join (solvent not ovoiloble)

o Light ond hence eosy to tronsport r Avoiloble in discrete diometers, moximumo Flexible (occommodates smoll bends) diqmeter ovqiloble in Nepol is 315 mm OD.o Low surge requirement o Must be buried (due to ultro violet (W) ond

thermol degrodotion) ond corefully bockfilled.

Limited pressure rotings ovoiloble in Nepol (up to

10 kg/cm'Zwhich is 100 m heod)

More expensive thon mild steel for lorge diometers

ond high pressures

90

PVC common in

other countries

but not y€t used

in Nepol

Does not conode

tight

Eosy to instoll (solution ovoiloble

tojoin pipes)

Brittle, con b€ domoged during tronsportotion

Must be buried (due to W ond thermol

d€gr0dotion) ond coEfully bocldilled.

Unsuitoble in fl€ezing conditions

Not ovoilobl€ in diometers lorger thon 250 mm in

Nepol

Limited pr€ssure rotings ovoilobl€ in Nepol (up to

10 kg/cm'z = 100 m heod)

More expensive thon mild ste€l ot high pressures

The decision os to which pipe moteriol to use for the

penstock con be bosed on Toble 6.1, esp€ciolly in Nepol. When in

doubt, it is recommended thot the design€r undenoke prelimi-

nory designs for oll pipe moteriols ovoiloble ond compore the

c0sts.

To minimise costs, for long penstock olignments HDPE

pipes con be used for the upstreom length where the heod is

Ielotively low (see Box 6.1). Stondod couplings orc ovoiloble tojoin HDPE ond mild steel pipes os shown in Photogroph 6.6 0nd

Figure 6.2.

Photo 6 6 HDPE-mild neel coupling Note thqt exc€pt for rhe finol lenqrh. rheHPDE pipe isburied,Jhong micro-hydro scheme, Mustong, Nepol

Although steel pipe for micro-hydro in Nepol h0s

normolly been speciolly monuf0ctured locolly, stondord steelpipes moy be ch€oper in some cqses. Detoils ofsuch pipes olegiven in Appendix B.

6.4 Pipe diometer

Orce the penstock olignment ond pipe moteriol hove b€en

decided on, the design involves choosing the diometer ond pipe

thiclaress. Selecting on opprcpriote pipe diometer is discussed

in this section ond the woll thickness is discussed in Section 6.6.

Note thot with o few exceptions th€ sizing ofthep€nstock diometer is similor to thqt ofo heodroce pipe dis.

cussed in Chopter 4. For simpliciry the entip penstock diom-

eter selection Drocess is included in this section.

Choos€ o pipe size such thot th€ veiocity, V is between

2.5 mF ond 3.5 m/s. In gen€r01, o v€locity lower thon

2.5 m/s results in on uneconomicolly l0rg€ diometer

Similorly, ifthe velocity exceeds 3.5 m/s, the heodloss

con be excessive ond hence uneconomic0l in the long

run due to loss in pow€r output. Furthermore, higher

velocities in the p€nstock will rcsult in high surge

pressure os will be discussed loter.

Note thot compored to the heodroce pipe, higher

velocities con be ollowed in the penstock pipe since it

conveys sediment fite woter

For steel penstocks, it moy be economicol to

choose the diometer so thot ther€ is no wostoge fiom

stondord size steel sh€ets. For HDPE or PVC. ovoiloble

sizes must be selected. Pipes ole normolly specilled by

outside diomete! so 2 times woll thickness must b€

subtroct€d to obtoin the intemol diqmeter Stondod

pipe siz€s orc given in Apperdix B.

Colculote the qctuol velocity:

Figure 6 2 Typicol HPDE-mild steel pipe coupljng

4 it, _ --::-' - nd ,

9l

I

r t 2

where:

V is velocity in m/s.

Q is design flow in mr/s.

d is the pipe internol diqmeter in m.

Colculqte the heodloss in the pipe length bosed on the

inlet, woll friction, bends, volves ond exit losses os

follows:

Totol heod loss = wqll loss * turbulence losses

Wqll losses ore colculoted qs follows:

First determine the roughness volue,'k'in mm from

Toble 4.3 (Chopter 4).

Then use the Moody Chort in Figure 4.10 (Chopter 4) to

find the corresponding friction foctor ffor the selected

pipe moteriol, diometer ond the design flow.

The woll loss con now be cqlculoted from either ofthe

foilowing equotions:

LV2h = f - ^r"woll loss d X 29

"'

. f L x Q 'n ="woll loss

l}ds

furbulence losses ore colculoted os follows:

1 " -turD loss

t K + K . + K + K . ). entronce ueno conlrocuon votve,

where loss coefficients, K, ore os shown in Toble 4.4.

4. In generol ensure thot the totql heod loss for the design

flow is between 50lo ond 100/o of the gross heod, i.e.95o/o

to 90olo penstock efliciency.

5. Ifthe heod loss is higher thon 10%o ofthe gross heod,

repeot colculotions with lorger diometer. Similorly, if

the heod loss is less thon 50lo the pipe diometer moy be

uneconomic, therefore repeot colculotions using smoller

diometers.

Note thot in exceptionol coses o less efficient penstock

moy be more economic, such qs when the power demond is

limited, the penstock pipe is long qnd there is qbundont flow in

the river even during the low flow seoson. In such coses, o

higher flow con be qllowed in o smoller diometer pipe ollowing

o higher heod loss, which is compensoted by the flow. Hence

sovings con be mode in the cost ofpipes os discussed in Box 6.1.

However, this opprooch should be justified by o detoiled

economic onolysis.

29

The 80 kW Bhujung micro-hydro scheme (Bhujung, Lcmjung, Nepol) designed by BPC Hydroconsult for Annopurno Conservo-tion Areo Project (ACAP) is currently under construction. The design dischorge ofthe scheme is 150 l/s, the totol penstock

length is 860 m and the gross heod is 104 m. Since it is o long penstock, HPDE pipes ore used for the initiol length ond mildsteel pipe for the downstreom end os follows:

PENSTOCKTYPE IIIICT{NESS lmmf3

315 mm diometer. Closs III HDPE 16.1

300 mm diometer, mild steel 3

300 mm diometer, mild steel 4

Totql heodloss

% heodloss

Note thot the totol head loss is obout 120lo: though more thon 10%0, in this cose o higher heodloss wos found to be economic.

This is becouse the estimoted power demond for the villoge is 80 kW ond the source river (Midim Kholo) of the scheme hos

significontly higher flows, even during the low flow seoson (minimum flow of 0.5 m3/s in April) thon the required design

dischorge.

92

If the penstock pipe diometer wos sized for less than 10% heodloss (i.e. by increosing the diometers cnd decreasing the design

dischorge such thot power output = 80 kW), the pipe cost including loying ond tronsportotion would hqve increosed by 15%.

Similorly if mild steel wos used for the entire olignment (for heodloss = 72o/o), the pipe cost would hove increosed by about

30026. Note thot settling bosin ond hesdroce costs need to be included in the optimisotion.

6.5 Surge colculotion

5.5.1GENERAL

The thickness of the penstock pipe is determined by the gross

ond surge heods of the scheme. It is therefore importont to hove

some understqnding ofthe c0ncept ofsurge before colculoting

the pipe woll thickness.

A sudden blockoge ofwqter or ropid chcnge in velocity in

the penstock (or ony pipe thot hos pressure flow) results in very

high instontoneous pressure. This high pressure is known os'surge' pressure or often referred to os "woterhommer". Surge

pressure trovels qs positive ond negotive woves thrOughout the

length ofthe penstock pipe.

Wqter hommer occurs os the surge wove trqvels lrom the

source 0r the origin ofthe disturbonce, olong the pipeline until

it strikes some boundory condition (such os q volve 0r other

obstruction) ond is then reflected or refrqcted. Ifthe pipe is

strong enough to withstond the initiol surge effect, the pressure

will ultimotely dissipcte through lriction losses in the woter

ond pipe woll os well os through the foreboy. The speed of the

surge wcve (wove velocity) is dependent on such foctors os the

bulk modulus of wqter, flexibility of the pipe ond the rotio of

pipe diometer to woll thickness.

ln hydropower schemes, positive surge chorocteristics

ore different for different types ofturbines. Surge heod colculo-

tions for the two most common turbines used in micro-hydro

schemes qre discussed here. Note thqt these colculotions ore

bqsed on the initiol (i.e. undompened) positive surge heod.

In proctice there will be some domping of the surge

pressure os the wove trovels olong the pipe, ond whilst the

pressure fluctuotion is uniform in the lower portion it dimin-

ishes groduolly t0 zero ot the foreboy, os shown in Figure 6.3.

However, the pipe is normolly designed for stqtic heod plus

constont positive surge over the full penstock length.

Note thot the negotive surge con produce dongerous

negotive (sub-otmospheric) pressure in o penstock if the profile

is cs in Figure 6.3. Once the negotive pressure reoches 10 metres

the wqter column seporotes, ond subsequent rejoining will

couse high positive surge pressure sufficient to burst the

penstock. Sub-atmospheric pressures less thon 10 metres cqn

cquse inword collopse of the pipe wqll, so should olso be

ovoided. Ifthere is ony possibility ofnegotive pressure the pipe

wqll thickness must be checked for buckling (see Section 6.6.2).

To ovoid negotive pressure, move the foreboy to Point A

in Figure 6.3. Alternotively toke meqsures to reduce the surge

pressure.

"Bursting disc" technology could provide o reliqble meons

ofsofely releosing excess heqd in cose ofsurge pressure without

increosing the pipe thickness (which is the convention). This is

discussed in Chopter 10.

Figur€ 6.3 Surge pressures

6.5.2 PELTON TUNBINE

For o Pelton turbine use the followino method to colculqte the

surge heod:

1. First colculote the pressure wcve velocity 'o'using the

equotion below.

1M0m/s

f{elwnere:

E is Young's modulus in N/mm'z. The volue of Young's

modulus for mild steel. PVC ond HDPE con be seen in

Toble 6.2.

d is the pipe diometer (mm)

t is the nominql wqll thickness (mm), Dot t.n.,iu.

tL

93

2. Then colculote the surge heod (h,,*"), using the following

equotlon:

where:

n is the totol no. of nozzles in the turbine(s).

Note thot in o Peiton turbine it is highly unlikely for

more thon one nozzle to be blocked instontoneously.

Therefore, the surge heqd is divided by the number of

nozzles (n). For exomple if o penstock empties into two

Peiton turbines with two nozzles on eqch turbine.

n = 4

The velocity in the penstock (V) is:

. , 4Qv - -

no'

3. Now colculqte the totol heqd:

h : h + hlotol grc1s surge

4. As o precoution, cqlculote the criticol time, T., lrom the

following equotion:

T. = (21)/o

where:

T, is the criticol time in seconds,

L is the length of penstock in m,'q'is the wove velocitv colculqted eorlier.

lf the turbine volve closure time, T, is less thon T,, then

the surge pressure wove is significontly high. Similorly, the

longer T is compored to T , the lower the surge effect.

Note thot this colculotion is bqsed on the ossumption

thot the penstock diometer, moteriol ond wqll thickness ore

uniform. If ony of these porometers vory, then seporote

colculotions should be done for eoch section.

Also note thot when the T = T,, the peok surge pressure

is felt by the vqlve ot the end ofthe penstock. lfo pressure

gouge is not instolled upstreom ofthe volve, o volve closure

time of ot leost twice the criticol time (i.e., T > 2T") is recom-

mended.

The design engineer shouid inform the turbine monufoc-

turer of the closure time (T) so thot if possible the monufocturer

con choose the threod size ond shoft diqmeter such thot it will

be dillicult to close the vqlve in less thqn twice the colculoted

closure time. The operotor ot the powerhouse should be mcde

owore of this closure time ond the consequences of ropid volve

closure.

If the gross heod of the scheme is morc thon 50 m, it is

recommended thot o pressure gouge be ploced just upstreom ofthe volve. Compored to the cost of the turbine ond thepenstock, the cost ofsuch o device is low (obout US$50 in Nepol)

ond is worth the investment. When the operotor closes or

opens the vqlve, his speed should be such thot there is no

observqble chonge in the pressure gouge reoding.

6.5.3 CROSSFLOW TURBINE

In o crossflow turbine, instontoneous blockoge ofwoter is notpossible since there is n0 obstruction ot the end of the monifold(i.e. crossflow turbine hos o rectongulqr bore opening insteod of

o nozzle). Therefore, surge pressure con develop only ifthe

runner vqlve is closed ropidly.

For o crossflow turbine use the followinq method to

colculqte the surge heod:

1. Cqlculote the prcssure wove velocity 'c' (using the sqme

equotion os for Pelton turbine).

2. Now colculote the criticol time l, similor to the Pelton

turbine cose:

r. : (zr)/o

3. Choose o closure time, T (in seconds) , such thqt: T > 2T "

Similor t0 the Pelton turbine cose, the design engineer

should inform the turbine monufocturer of the closure

time (T) ond the operotor ot the powerhouse should be

mode owqre of this closure time.

4. Now cclculote the porometer 'K' using the following

equotion:

K: IColculote surge heod by substituting the volue of'K' in

the equotion below:

h 'u* ' = [ ; '

If 'K'is less thon 0.01 (i.e. closure time (T)is long

enough), then the following simplified equotion con olso

be used:

hru*, : hnr*{ K

Note thot ifthe vqlve is closed instontoneously, the entirelength ofthe penstock will experience o peck pressure os

o v lsurge g n

*i*r-l'

v.l

follows:

h,u,r. : ov/g (i.e., some os in the cose 0f Pelton turbine

with one nozzle).

However, in proctice it wiil take 0t ieost five to ten

seconds for the operotor t0 close the volve, therefore in o

crossflow turbine instontoneous surge pressure is not o

problem.

If the gross heod of the scheme is more thon 50 m, q

pressure gouge should be ploced upstreqm 0fthe volve to

control its closing/opening speed, os in the cqse ofo Pelton

turbine.

6.5.4 QUICK METHOD FOR SMALL SCHEMES

WITH CROSSFI.OW TURBINES

For smoil micro-hydro schemes using crossflow turbines (such

os milling schemes) where the power output is less thon 20 kW

ond the gross heod is less thon 20 m, this quick method moy be

used.

Add20o/o to the gross heod to qllow for surge heod, i.e.

h,u", : 1.2 x hq,.,. This results in o more conseryotive volue for

the surge heod but its contribution t0 the increqse in the

thickness would be insignificont since the h0.,, is iow.

6.6 Pipe wall thickness

6.6.1 POSITTVE INTERNAL PRESSURE

Once the surge heod hqs been determined, the nominql woll

thickness (t) con be colculoted os follows:

1. If the pipe is mild steel, it is subject to corrosion ond

welding or rolling defects. Its effective thickness (t.o..,,u,)

will therefore be less thon the nominol thickness.

Therefore, for mild steel, ossume q nominql thickness (t)

ond to colculot€ t.,T,,,,u, use the following guidelines:

o) Divide the nominql woll thickness by 1.1 to ollow

for weldina defects.

Divide the nominol woll thickness by 1.2 to ollow

for rolling inoccurocy ofthe flot sheets.

Since mild steel pipe is s_ubject to qoryo1ion,

for 10 yeqlr ofplont life: subtrocl 1 mm onq:_

for 20 yeors of plont life: subtroct 2 mm

The recommended uenstock desion life is 10 veors for

-lehemes up t0 20 kl^L+s yeors fo!$b9!Sgsa&9l9.IyLsld20-yeors for schemes of 50-100 tE.f!g!e_!S!-nes-mql.be odiusted -olglsygqgryfglonolys is.

For exomple the effective thickness of o 3 mm thick mild

steel pipe designed for o 10 yeors life is:

3t _ = - - _ 1 : 1 . 2 7 m meuec l rve

1-1 x 1 .2

From this exomple it is cleor thot if o mild steel pipe used,

the nominol woll thickness (t) should be qt leqst 3 mm.

Note thot this does not opply for HDPE pipes: their

effective thickness is the nominol woll thickness of the pipe. A

low temperoture c0rrection foctor moy opply to PVC pipes, refer

t0 the pipe monufqcturer: if the temperqtures ore sub-zero,

t"n".,iu" froy b€ os low os 0.5t. Aport from protection from ultro-

violet degrodotion, this is onother reoson t0 bury PVC pipes ot

high oltitude.

2. Now colculote the sofery foctor (SF) from the following

e0uoti0n:

2 0 0 x t x S5 f =

h,u,o, X d

where:

t,r.,,,u" is the effective thickness ond d is the internol

diqmeter of the pipe. Note thot some units (m or mm) should be

used for both t.n"oiu. ond d since they concel out in the obove

equotion.

S is the ultimote tensile strength of the pipe moteriol in

N/mm2. Volues of S ond other useful porometers ore shown in

Toble 6.2.

h,o,o, is the totql heod on the penstock os follows:

h ,o to , : hg . r r+h ru * .

3. For mild steel or PVC pipes:

IfSF < 3.5, reject this penstock option ond repeot

colculotion for thicker wolled option. However, SF > 2.5

con be occepted for steel pipes ifthe surge heod has been

colculoted occurotely ond sll of the following conditionsqre met:

o) There ore experienced stoffot site who hove

instqlled penstock pipes of similor pressures ond

moteriols.

b) Slow closing volves qre incorporoted ot the

powerhouse qnd the design is such thot o sudden

stoppoge ofthe entire flow is not possible.

Domoge & sofety risks ore minimol. For exomple

even if the pipe bursts, it will not couse londslides

or other instobility problems in the short run.

Coreful pressure testing to totol heod hos been

performed before commissioning.

b)

c,

d)

I,lr-

95

for f lrJt t DtDes:

HOlf pipes ore qvqiloble in discrete thicknesses bqsed on

the pressure rotings (kg/cm'z) 0r stotic heods. The designer

should set SF > 1.5 ond cqlculote t.r.,,u" (tot€ thot t : t.r.,,iu" f0f

HDPE). Then from the monufocturer's cotologue the qctuol

thickness should be chosen such thot it is equol to or lorger

thon the colculoted t.'.,,u,. Thc Sofety Foctor should then be

checked using the octuql thickness. For HDPE pipes, it is

recommended thot the Sofety Foctor olways be ot leost equal

to 1.5.

6.6.2 NEGAIIVE INTERNAL PRESSURE

Check the pipe woll thickness for buckling ifthe negotive surge

con produce negotive internol pressure in the pipe. N0te thot

the negotive pressure must not exceed 10 metres heqd, see

Section 6.5.1. The shope ofthe negotive surge pressure profile

Toble 6.2 Physiccl chqrocteristics of common mqteriols

connot be occurotely determined: ossume it is horizontol in the

lower half of the penstock, ond diminishes groduolly in the

upper holfto zero qt the foreboy, see Figure 6.3.

In order to provide on odequote foctor ofsofety ogqinst

buckiing, the minimum pipe woll thickness is given by:

/ p D t o l l

t ^ > d l ' ^ lerr€((ve - \ze I

where:

t"n.tiu. is the effective pipe woll thickness, mm

d is the pipe internol diqmeter, mm

F is foctor of sofety ogoinst buckling (2 for buried penstock ond

4 for exposed penstock)

P is the negotive pressure, N/mm'z(10 m heod = 0.1 N/mm'z)

E is Young's modulus for the pipe mqteriol, N/mm' (from Toble

o .z l .

MATERIAL YOUNG'S

MODULUS lEf Nfmmz

COEFFICIENT OF UNEAR

EXPANSION lctlfC

ULTIMATE TENSII^E

STRENGTH (S)Nfmm'z

UNIT WEIGHT lylkNlm'

Steel (ungroded)

Steel to 15226175

or IS 2062/84

PVC

HDPE

2.0 x 10s

2.0 x 10s

2750

1000

12.5 x 10 {

12 .5 x 10 -6

{ 2 0 - 6 0 ) x 1 0 *(140 - 240) x 10 {

320

410

3 5 - 5 5

20 -35

77

77

14

9.3

lfthe steel quality is uncertain it rs besr b ask for samples and have them independently tested at laboratories. Properties of PVC and HDPE vary

considerably: they should be confirmed from manufoctures' catalogues or by laboratory tests.

The requined doto for the design ofthe Golkot penstock ore os follows:

. Q = 421 l/s (colculoted in Exomple 4.2)

t hnror, = 22m

r two verticol bends, n : 200 & 420, both mitred.r Penstock moteriol: uncooted mild steel, 35 m long ond flonge connected.

r turbine type: crossflow

Refer to Drowing 42010413A01in Appendix C for the ground profile ond bend ongles.

Pipe dicmeter cqlculation

S e t V : 3 . 5 m / s

Colculote the internol pipe diometer:

96

d =- V n V { [ x 3 . 5

Calculote woll loss:

From Table 4.3 choose k = 0.06 mm for uncooted mild steel.

k 0.06

d =

391 =0.00015

1.2Q 1.2x0.421_ : _ = t - . 2 ,

d 0.391

f = 0.013 (Moody Chort, Chopter 4)

LVz 35 x 3.52h = t _ = O O l ?-'wolr ross dxag 0.391 x 29

h*o,, tor, = 0'73 m

Inlet loss:

K,n,*n.. = 0.5 for this case (Toble 4.4)

- V, 0.5 x 3.52h,nln lorr

= K.n,.n..X -;- = L-

= 0.31 mzg zg

Note thot Exit loss = 0 since the flow at the end ofthe penstock is converted into mechonicol power by rototing the turbinerunner.

For mitred bends. from Toble 4.4

0 = 220, \.no = 0.11

0 =420 , \ . no=0 .21

Bend losses = (0.11 + 0.21) * T'- = 0.20 mzg

Totol heod loss = 0.73 m + 0.31 m * 0.20 m= 1.24 m

1.24% heod loss =

;;- x 100 %= 5.60/o < l0% OK.

Although the colculoted pipe diometer wos 391 mm internol, Drowing 4}olo4l3cozin Appendix C shows the outside pipediometer to be 388 mm, i.e. internol diometer 388 - 2 x 3 = 382 mm. This wos chosen to correspond to o 1200 mm stondodplote size (1200/n = 382). In proctice, however, the monufocturer proposed 400 mm internol diometer pipes for the somecost, becouse this corresponded to the plote size thot he hod.

Pipe woll thickness cslculqtions

Colculote the pressure wove velocity 'o'

1440

E : 2.0 x 105 N/mm'zfor mild steel (Toble 6.2)

97

v

d : 4 0 0 m mt = 3mm

14400 r o :

-*(-rttno-,-ro_r,J6 - \ 2oro = 923 m/s 3

Now colculote the criticol time:

2L 2 x35T. :; =

Sr3 : 0.08 s. Note thot it would be

impossible to dose the volve in the powerhous€ in 0.08 secondsl

Choose closu€ time T = 10s > 2T. = 0.16s

-:[-'*-l t.**-lorK = 0.003. Since K is less thon0.01

h*r. : hn^,, x 6K = 22 no.oo3orh = 1.20 m

h . = h + h = 2 3 . 2 mq6 snr!.

The pipes were monufoctured by welding (1 .1) rolled llat ste€l

plotes (1.2). 1.5 mm hos been subtrocted to ollow for ot leost 15

yeqrs of lif€.

t.-". = 3/(1.1 x 1.2) - 1.5 - 0.Z/ mm

Now check the sofety foctor:

2 f f i x1 . xs

h . x d

S : 320 N/nunz for ungroded mild steel (Toble 6.2)

2@x0-nx32OS F =

23.2x 400

or SF : 5.3 > 3.5 OK.

Not€ thot the sof€ty foctor is higher thqn required but the

minimum recomm€nded thicleess for flot rolled mild steel pipe is

3 mm.

The Golkot p€nstock olignment before ond ofter pipe instollotion

con be se€n in Photogrophs 6.7 ond 6.8 r€spectively.

Photo 6.E Penstock olignment, colkor

Photo 6.7 Excovotion for penstock olignment, Colkot

98

The required dota for the design of the thonlcre penstock are os follows;r Q = 4 5 0 U st hn*r, = 180 m

. ten verticol bends, 0 = 690 , 230, 260,310,400, 20, 30, 120, g0 & 30, all mitred.r Penstock moteriol: mild steel, flot rolled ond site welded, 550 m long. High quolity steel plotes were bought ond tested for

tensile strength ot the loborotory. Minimum tensile strength, S = 400 N/mm':wos ensurcd through the tests.r furbinetype3PeltonturbineswithZnozzlesineochturbine,thereforen = 3x2 = 6.

Colculqte the required pipe dicmeter qnd woll thickness. Note thot since the penstock is long, it will be economic to decreosethe thickness ot lower heqds.

Pipe dicmeter cqlculation

Since the pipe is long set V = 2.5 m/s to minimise heodloss.

Colculote the internol pipe diometer:

. fT tux0-150-d : \ ' / n i =

J I I - 25 =o '479m

Colculote woll loss:

From Toble 4.3 choose k = 0.06 mm for uncooted mild steel.

k 0.06

d 479

1.2Q 0.450

o 0.479

f = 0.0014 (Moody Chort, Figure 4.7)

LV2 550 x 2.52h : f - = 0 0 1 4"worr ross d x 29 0.479 x2g

h . : 5 . 1 3 mwon loss

Inlet loss:

Kun,,on., : 0.2 for this cose (similor to fourth entronce profile in Toble 4.4)

vz 0.2x2.5'zh . . = ( x - - - : -

rnre( ross enrron(e zo 29h . . = 0 . 0 6 m

lnlel loss

Exit loss : 0.

For mitred bends, interpolote from Toble 4.4:

for0 = Of ,q"o = O.:e

f o r 0 = 2 3 0 , \ . n o = 0 . 1 1

f o r 0 : 2 € c , K o . n o : 0 . 1 3

for 0 = 37r, eno: 0.18

for0 = 4or , \ *no = o.2o

99

for0 = 20,\.*= 0.02

fo rO =30 , l f und=0 .02

for0 =120, l tnd=0.06

fo rO =80 , l q .nd=0 .04

fo r0 =30 ,Q"o=0 .02

Bendlosses = (0.34 + 0.11 + 0.13 + 0.18 + 0.20 + 0.02 + 0.02?-52

+0.06 +0.04 +0.02)* U

=0.36m

Total heqd loss = 5.13 m + 0.06 m * 0.36 m- \ A m

5.6% heod loss = -:-- x 10070 = 3.7oh <5c/0,

180

Therefore, the diometer can be mode smoller. The odopted diometer of theJhonlce penstock is 450 mm, which gives 4.10lo

heodloss, thmugh o repeot ofthe obove colculotions.

Pipe woll thickness cclculotions

First colculote the thickness required 0t the downstreom end of the penstock (i.e. h,,0,.. = \*, = 180 m) using d = 450 mm.

Tryt = 6mm

0ro =

oro=1071 m/s

40 4 x 0.450V = -i: --:------- = 2.83 mls.

ndz zx(0.450)'?o v 1

h - _ x _surge g n

1071 x 2.83 1i . - - - - = 5 2 m"rurg.- 9,8

^ 6

h . = h + h : 1 8 0 * 5 2 = 2 3 2 mrdot qrcss surle

6t _ = _ _ 1 . 0 = 3 . 5 5 m meilectrve

1.1 x 1.2

(1.1 for welding, 1.2 for flot rolled, qnd 1 mm for corrosion sllowonce: the corrosion allowance is less than previously recom-

mended for lorger schenres becouse Jhonkre wcs designed to provide construction power to o lorger project).

Colculqte the sofety foctor:

2 0 0 x t - x Seilcdtve

SF: -_-----.-n . x 0

rotol

200 x 3.55x 400

232x450

.(-**u1

100

SF = 2.72 > 2,5, olthough SF is less thon 3.5, it is occeptoble in this case since:

1. There were experienced stoff at site. The site staff hod instolled penstock pipes in vorious other micro-hydro projeas.

2. The volves ot the powerhouse ore of slow closing type.

3. The pipes were pressure tested os follows:

Tensile test of steel plotes wos performed ot o loborotory ond on ultimote tensile strcngth of 400 N/mm'z wos ensured os

mentioned eqrlier.

Rolled pipes were pressure tested ot the workshop ot h,o,or using o hydroulic pump'

Finolly, the pipes were olso pressure tested on site sfter installotion by simuloting h,u*. ot the entronce (foreboy) using o

hydroulic pump.

4. The olignment wos ossessed to be foirly stoble. In cose of pipe burst it wos not expected to instontoneously cause

Since the Jhonkre penstock is long, to optimise the design, it wos decided to decrcose the pipe thickness ot lower heods {i.e.,

upstreom) using the some sofety foctor (SF).

Colculotions of the stqtic heod ot which the penstock thickness con be decreased by t mm (i.e. thickness = 5 rnm) using the

some sofety foctor (SF = 2.721ore os follows:

t440n = : = i 0 2 7 m r S-

l,-l z-Eqrqg_\Jt ' t -ZTxlT'xT/

Note thot t = 5 mm in this case

V = 2.83 m/s, (some Q & d)

ov l 1027 x2.83 ih - - x - = - - := - X - - =49m- - 5 u r s e o n 9 . 8 6

)t - = - 1 . 0 = 2 . 7 9 m m€lrecrve 1.1 x 1.2

2 0 0 x t - x s€IecItve

\ t s = - -h . x d

I0 t0 l

or rewriting this equotion in terms 0f h,o,ori

2@ X t"o..,,""X SL _ -r r lo to l -

SFxd

200x2.79 x400^ - k = 1 8 2 mvr 'froror -

2.72x 450

h = h - h = 1 8 2 - 4 9 : 1 3 3 mqroJs to(01 surg€

Therefore the pipe thickness wos reduced to 5 mm ot o stotic heod of 133 m inJhonlcre, keeping the some foctor of sofety (i.e.

2.72\ osshown in Figure 6.4. The Jhonkre penstock olignment for the lost section con olso be seen in Photogroph 6'7. These

calculotions were repeoted for lower stotic heads ond o wall thickness down to 3 mm hos been used to reduce the cost.

101

Photo5.9 JhqnlsE mini.hydro pensl ock olgnment

qPe,

t tur b incp6ntlock

Figurp 6.4 JhoDkp mini-hydm penstock olig nment ot downstreom end

between the flonges for tightness ond to prevent leokoge. Th€

colkot penstock (Photogroph 6.8) is offlonge connected type.

A comporison ofthese two methods oJong with generol

rccommendotions ore Dr€s€nted in Toble 5.3.

5.7 Pipe jointing

6.7.1 GENEMI.

Individuol mild steel penstock pipes con bejoined ot site by two

conventionol methods, nomely site w€lding ond vio flonges.

Eoch ofthese methods hqs its own odvontoces ond disodvon-

toges os discussed in Toble 6.3.

6.?.2 Sm WEU)ING

This involves tronsporting q welding mochine ond diesel or

petml to site, then joining the pipes by welding together the

ends os shown in Photogroph 6.10.

6.73 FI.ANGE CONNECIION

This involves welding flonges (thot hov€ bolt holes) ot both ends

ofthe pipes in the workshop, thenjoining them 0t site by

bolting th€m together A rubb€r gosket should be ploced

Photo 6.10 site welding ofpenstock pipes, Jhonla€ minihydro

102

Toble 63 Comporison between site welding ond flonge connection

PIPEJOINING

METHOD

ADVANTAGE DISADVANTAGE GENEMI. RECOMMENDAIIONS

AND COMMENTSSite welding Eosy to fobricote ot

workshop since flonges

do not hqve to be welded

ot pipe ends.

A properly welded pipe

will not leqk ond requires

less mointenonce.

Higher degree ofprecision work requiredqt site to weld the pipe ends. Improper

welds con couse leoks cnd pipe burst othigh heods.

Need to trqnsport o welding mqchine

ond 0 generot0r ot site. Also requires

supply ofpetrol/diesel to site.

Diflicult logistics if the site is more

thon o doy's wolk from the rood heod.

Generolly not economic for smoll

schemes ond/or short penstock lengths.

Select this option only ifthe site stoff

ore experienced, site is less thon o doy'swolk from the roodheod ond penstock

length is more thon 50 m.Flonge

connection

Eosy to instqll qt site.

Site instollqtion work

involves plocing o gosket

between the flonges ond

hn l t inn thpm

Fqbricqtion cost is high since flonges

need to be welded ot ends. Also there issome wostoge since the flonge isprepored by removing the centrol disc of

o diometer equol to the externol pipe

dicmeter.

The pipe o\ignment ond the bends connot be odjusted qt site.

Con leok if the bolts qre not well

tightened or if gaskets ore of poor quolify.

Higher risk ofvondolism since the bolts

con be removed.

Flonge connection is oppropriqte for

schemes thqt ore locoted more thqn odoy's wolk from the roodheod ond/or

hove q relotively short penstock length.

Minimum flonge thickness should be

ot leost twice the penstock wo.ll

thickness or 8 mm whichever is lorger.

A minimum bolt diometer of t2 mm is

recommended.

A minimum gosket thickness of 5 mm

is recommended.

Should be obove ground.

6.7.4 HDPE AND PVC PIPES

For HDPE pipes the best method of joining them is by heot

welding os described in Chopter 4 (Box 4.7). Aithough speciol

flonges ore ovoiloble to connect HDPE pipes, they ore gener-

olly more expensive thon the cost incurred in heot welding

them. HPDE pipes ore ovoiloble in rolls for smoll diometer (up

to 50 mm) ond for lorger diometer they ore ovoilqble in

discrete lengths (3 m t0 6 m in Nepol)

PVC pipes with smoll diometer (up t0 200 mm) hove

socket ot one end such thot onother pipe con be inserted

inside ofter opplying the solution ot the ends. Lorger

diqmeter PVC pipes ore joined with o couplet which is o short

pipe section with inside diqmeter equol to the outside

diometer of the pipes to be joined. The solution is opplied on

the connecting surfoces ofboth the coupler ond the pipes ond

thenjoined together.

6.8 Pipe lengths

Mild steel pipes con be mqnufoctured ot the workshop in qlmost

onylength required. PVC ond HDPE pipes ore ovoiloble in fixed

lengths (3 m t0 6 m in Nepal). Although, shorter pipes cre eosy

t0 tronsport, odditionol costs will hove to be incurred in joining

them ot site (more flanges or welding work). it should be noted

thot, unlike cement bogs, onimols (mules ond yoks) do not

usuolly corry penstock pipes becouse of the shopes ond lengths

involved.

Sometimes, due to the weight involved the only option

for trcnsporting the generotor qnd turbine to remote site is by o

helicopter. In such cqses, it moy be possible t0 tronsport the

penstock pipes in the some trip becouse the current tronsport

helicopter ovoiloble in Nepol con corry up t0 three tons

(depending on oltitude). The combined weight of the generotor

snd turbine hordly ever exceeds one ton ond the helicopter

103

chorge is dependent on the flying hours ond not on loods.

When this is the cose longer pipes {up to 6 m l€ngths) con be

tronsport€d to site qnd hencejoints con be minimis€d.

Recommendotions for pipe lengths und€r vorious

conditions oIe discussed below:

MiId steel pipe

The following foctors should b€ consider€d while sizing mild

steel pipes.

1. In generol pipes long€r thon 6 m should not be morlufqc-

tured since they wjll b€ difficult to tronsport 0n trucks.

2. lfth€ pipes ne€d to be corried by porters from the

roodhe0d, the weight should be such thot on individuol

length con be c0rried by 1-2 porters. For exomple, ifthe

pipe weight is obout 50 kg, usuolly one port€r con co y

it. Similorly two poners moy b€ oble c0rry up to 90 kg.

Therefore, ir is optimum t0 size pip€s occordilgly,

esp€ciolly ifthe penstock length is long ond the site is

locoted more thon o doy's wolk from the ro0dheod.

3. For flot rolled pipes the monufocturing costs will be less

ifthe pipe length rs o multiple ofth€ 0voiloble steel plote

width. For exomple if pipes ore rolled from 1.2 m wide

plotes,lengths 0f1.2 m,2.4 m 0r3.6 m etc. wil l lower

monufocturing costs.

HDPE an.l PvC pipes

As mentioned eqrlier, these pipes ore monufoctured in the

loctory qt f ixed lengths. but they con be cut in holfor one third

ofthe length for eose oftronsportqtion. However, o PVC p'pe

with 0 socket ot one €nd should not b€ cut since IejOining wil l

not be possible without o specicl co)lor The following foctors

should be considered while determining the length ofHDPE 0nd

PVC pipes.

L in Nepol the moximum ovcilcble length of these pipes is

6 m Even if longer pipes become ovoiloble, such lengths

should nor be used for micro-hydro sch€mes. Gen€rolly

it is eosier to corry two 3 m pipes rother thon one 6 m

pipe ofthe sonre type.

2. lfthe prpes need to be c0rried by porters from the

roodheod, then the crit€rio outl ined in No 2 for mild

steelolso opply.

6.9 Exposed versus buried penstocl(

HDPE qnd PVC prpes should alwoys be buried. This minimises

lherm0l movemenr o r rd p ro tec ts the p ipe oqo ins t lmpoct ,

vondolism ond ultro-violet d€gr0dotion

Flonged steel pip€ should be obove ground. This is

b€cous€ the goskets moy need to be repioc€d durrng the life of

the scheme.

Mild sreel penstock with welded joints con be either

buried or obove ground. However, mointenonce ofburied pipe

is difncult. therefore the originol pointing ond bocktrlling must

be c0refully supervised to ensure thot corrosion does not reduce

the l ife ofth€ penstock.

Sometimes port ofth€ penstock olignment moy be oboveground ond pon buried. In such coses. it is best to moke the

tronsition ot on onchor block, otherwise coreful detoiling is

required. An exomple ofsuch detoiling ot the tronsition is the

use of o retoining mosonry woll with 0 l0rger diqmeter mild

steel pipe through which the p€nstock comes out ond con

occommodote thermol exp0nsion ond controction, see Figure

6.5. An exponsionjoint should normolly be used immediqtely

downstreom ofthe retaining woll. Not€ thot the design ofqnchor b,ocks is covercd in Chopter T.

Toble 6.4 compor€s the 0dvontoges ond disodvontoges of

buried penstock pipes.

Phoro 6ll P€nstock, Purong

r[

104

Tobl€ 5.4 Advontoges qnd disqdvqntqges ofburied penstock pipe

ADVANTAGES DISA"DVANTAGES

Protects the penstock ogqinst odverse €ffects 0f

temperoture vonoll0ns.

Protects the woler irom lieezing due to low 0lr

tempetotures.

Protects the pipe from folling d€bris ond trees.

Prorects the pipe from t0mpering 0nd vondollsm.F l i m i n n r o . c , , n n ^ d n i a r (

Smoll bends do not need onchor blocks.

Does not chqng€ the londscope.

Pip€s or€ less 0cc€ssible for rnspection, ond foult frnding

becomes dimcult.

Repoir ond mointenonce ofthe pipes is dif l icult.

Instollotion is exp€nsive in rock ond where soil cover is thin

Improcticobl€ on steep slopes (>30").

F.gule65 I ronsr ' .on f tomLuned topx|ovdppn,to, l ' ,Jhonkrtmrnr l "ydrc

5.10 Expansionjoints

Penstock pipes ore subjected to t€mp€roture vo qtions due to

chonges in the ombient temperoture. When the ombient

temperotur€ is high the pipes wiJl expond ond when it drops,

the pip€s will contr0ct. Such th€rm0l exponsion couses str€ss€sin th€ pipes ifthey ore not free to expond.

Photo 6 l2 An exponsionjoinr should b€ locoredjust below ononchor block ioprotect the block from fon€s whr(h it rnoy nor be designed to rpsNt (S*tis)

For buried pipes, o minimum cover of 1 m should be

provided in ollcoses (i.e. HDPE, PVC ond mild steel pipes) See

Iigure 4 8 Ibr trench detoils.

Buried pipes do not require support piers, ond he sovings

m0de 0n the pi€rs moy equol or even exceed the cost ofexcqvo-

tion ond bockll l l . Since this ts o site specific c0s€, q c0st

colculotion should be done ifbuned mrld steel pipe is being

considered.

Both €xposed 0nd buried p€nstock pipes Iequire onchor

blocks ot significont bends. However, for relotively low heod

ond flow, qs well os smollbend ongles, lhe I m depth of well

compocted sorlcover on buried pipe moy be odequote (see

Chopter ?, Anchor blocks ond support piers).

The norure ofthe terroin ond the sotldepth moy olso

govern whether to bury 0r expose the penstock pipe. Buried

penstock is not pr0cticoble on roures steeper thon 30o b€couse

the bocl1il l wil l be unstoble Where topsoil is thrn or rock is

exposed, the costs involved in excovoting the rock moy mqke

buriol ofthe pipe impossrble

105

rAn qbove grcund penstock is subjected to gr€oter

temperotuE vqriotions rcsulting in high€r thermol exponsion.

The thermol exponsion or controction is high€st when the

penstock is empty, such os during instollotion or repoir work.

The temperotur€ voriotion is relotively low when the pipe is full

since the flow ofwoter witl foirly constont temperoture

prcvents the pip€ ftom ropidly heoting up.

As long 0s pipes ore free to move ot one end, thermql

exponsion does not cous€ odditionol strcsses. However, o

penstock pipe section between two qnchor blocks is kept fixed

0t both ends. In such o cose thermol exponsion could couse

odditionol stresses ond the pipe con even buckl€. Ther€fore,

provision must be mode for the penstock pipe to expond ond

controct, by instolling on exponsion joint in o penstock pipe

s€ction betw€en two onchor blocks.

The most common type of exponsion joint used in Nepol

is ofsliding type. This is shown in Figure 6.6 ond Photogroph

6.13. Such on exponsionjoint is ploced between two cons€cu-

Figure 6.6 Sliding type expo$ionjoint

tive pipe lengths ond bolt€d to them. The stoy rings orc

tightened which compresses the pocking ond prevents leoking.

Jute or othff similor type of fible is used for pocking. When the

pipes expond or controct, the chonge in lengths is occommo-

doted insid€ th€ joint section since there is o gop between the

Prpes.An odvontog€ ofon exponsionjoint is thot it r€duces the

siz€ ofthe onchor blocks since they will not need to withstand

forces due to pipe exponsion. Another ddvontoge is thot they

con 0ccommodote slight ongulor pipe misolignment.

Exponsion joint rquirements for vqrious penstock

conditions ore discussed below.

Mild steel pipes

An exponsiorjoint should olwoys be incorporoted imm€diotely

downstrcom ofthe forebcy ond immediotely downstreom of

eoch onchor block, for both obove ground qnd buried steel pipe.

One is olso recommended immediotely downstrcom ofo

tronsition from buried to obove ground pipe.

HDPEPiPfs

Exponsionjoints orc not necessory for HDPE penstock pipes

pmvided thot they ore buried (which should qlwoys be the

cose). This is becouse HDPE pipes ole flexible ond con bend to

occommodote the expqnsion effects due to the differences in

temperqture b€tween instollotion ond operotionol phoses.

PVC pipes

PVc pipes with gluedjoints require provision for exponsion, ot

the some locotions 0s for steel pipes.

Sizing of expsnsion joints

The sliding surfoce of the exponsion joints should be mochine

fi shed (such os in o lqthe mochin€) to o toleronce of obout I

0.1 mm. The recommended thickness ofthe steel pofts (Etqiner

ond stoy ring)is qbout twice the thiclaless ofo well-designed

penstock pipe,

The gop in the exponsionjoint should be obout twice the

calculoted moximum pipe exponsion lergth.

The moximum exponsion length is co]culoted using the

following equodon:

A = cr{t -T ..)L

where:

A L = pipe exponsion length in m os shown in FiguR 6.7.

o = coefficient oflineor exponsion in m/m "c ofthe pipe.

which depends on the pipe moteriol. This coemcient r€lotes to

the length thot q moteriol will expond per 1oC increose of

temperoture. Different moteriols expqnd ot differcnt rotes. The

106

Photo 5.13 Slidng exponsion joint, Jhonlxe mini_hydro

volues of this coe{Iicient for mild steel, HDPE ond PVC ore shown

in Toble 6.2.

Tno, = highest temperoture in'C thot the pipe will experience.

Note thot this con even be during mid-summer qfternoon when

the pipe is empty (either during instollotion or repoir wor$.

T,o,o = lowest temperqture in'C thot the pipe will experience.

This cqn be during winter when the woter temperoture is just

obove the freezing point. Note thot iffreezing temperotures ore

expected, the pipe should either be emptied or provision should

be made for constont flow. If the woter in the penstock

stognqtes during freezing temperoture, ice will form inside the

pipe ond could burst it, becquse when wqter freezes, the volume

exponds.

L = pipe length in m.

Since it moy be difficult to determine when the expon-

sion joint wiil be instoiled ot site, the monufscturer should be

qsked ollow on exponsion gop of 2AL. Then, during instollo-

tion, the temperoture should be noted ond the gop left occord-

ingly.

Exomple 6.3 shows on opplicotion of this equotion.

figure 6.7 Thermdl exponsion ofo penstock pipe

5.11 Pointing

Since mild steel pipes ore subjected to corrosion, oppropriote

coots ofpoint should be opplied before dispotching them to site.

Proper pointing of mild steel pipes significontly increqses their

useful lives.

The pipes should be sond blqsted ifpossible, otherwise

they should be thoroughly cleoned using o wire brush qnd o

piece ofcloth. Prior to pointing, the pipe surfoce should be

cleqn from oil, dust ond other porticles. When opplying

subsequent coots ofpoint, the previous coot must be dry. .The following coots of point ore recommended:

Ou*ide swfsce of obove ground mild steel pipes

First two coots of primer should be opplied on the pipe surfoce.

Red Oxide Zinc Chromote primer is qppropriote for this purpose.

Then onother two coots of high quolity polyurethone enomel

point should be opplied on top of the primer.

Outside surfoce pipe of which will be buried 0r cost into

onchor blocks'lwo coots of primer similor to qbove ground pipe should

be opplied. Then, onother two coots othigh-build bituminous

point should be opplied over the primer. Provide on extro coot

of bituminous point ot tronsition qreos, which ore more prone

to corrosion (see Figure 7.1).

Inside surfsce ofpipes

For smoll diometer pipes it moy not be possible to point the

inside surfoce. However whenever possible, the inside surfoce

should be pointed with two coots of good quolity red leqd

primer.

A mild steel penstock pipe is 45 m long betrveen theforebay ond the first cnchor block. The steel temperotureduring instollotion wos 40"C, ond the expected lowesttemperotur€ during the operotional phose is 40C duringwinter. Whot exponsion gop should be recommended to

the monufocturer? AIso, if the temperoture duringinstollotion is 2ffC, whot gop should be provided?

a = 1 2 x 1 0 { m / m o CTno, = 40 oC

T . . : 4 o Cc0ld

L = 4 5 mAL = u(\",-\",u)Lo r A L = 1 2 x 1 0 { ( 4 0 - 4 ) x 4 5or AL = 0.019 morAL - 19mm

Therefore minimum recommended exponsion gop= 19.4 x 2 = 38.8 mm, soy 40 mm.lf the temperoture during instollotion is 2dc

AL = 12 x 10 -5(40 - 20) x 45or AL = 0.011 morAL = 11 mm

Therefore, during instollotion qn exponsion gop of 11

mm x 2 = 22mm should be provided.

107

If therc is o doubt obout the quolity ofpoint, the suppli-

er's speciflcotions should be checked prior to its use. Note thotpointwork is not requiEd for HDPE or PVC pipes.

Any pointwork domoged during tronsport ond instollo-

tion must be mod€ good, so thot the full number ofcoots ispRsent everywher€. This is especiolly importont for bu ed

DiDes.

6.12 Instqllqtion

The following procedure should be used.

o The centreline ofthe penstock should be s€t our using q

cord ond pegs olong the selected route os shown in

Figuft 6.8. For micro-hydro schemes obove 20 kW of

insto]led copociry o theodolite should olso be used to

ensuR thot the bend ongles comspond to the fqbricoted

oioe bends.

4i#

Figurp 68 Sstthg out the centrEline ofthe p€nstock olignment

A line should be morked by spEoding lime on the

surfoce ofthe gmund t0 pploce the cord. Then thepositions ofondror block ond support piers should bemorked t0 the r€quiftd spocing for exposed pipes ondexcovotion corried out olong this line os l?quil€d.

For buried pipes, the penstock is instoll€d in the

excovoted trench ond bocldrlled os shown in Fioure 4.8.

The bocldll should be rornmed in loyersond o slight hump obove the level of theground helps to keep the olignment dryAn improperly bocldlled penstockoligment con quickly become theroute for droinoge woter down thehillside. However, note thqt bocK lshould be completed or y ofter the pipehos be€n pressure tested.. For exposed pipes, the onchors ondsupports should be consuucted os willb€ discussed in Chopter T. The pipeshould be cost into the onchors ondploced on one support pier ot o time.No further supports or onchors shouldbe built until the pipe is secured to theprevious onchor block or suppon pier

For both site welded ond flong€ connected pipes, the

end should pmtrude from the lost support block with

odequote morgin (- 300 mm) so thqt either the flonge

or the weld line does not lie on the support pier during

thermol expqnsion or controction. If mor€ thon one

pipe section n€eds to be welded between the supportpiers, temporory supports should be used os shown in

Photogroph 6.15. Flonge connected pipes should bejoined ond the bolts tightened os the instollotion

Progresses.

l

Photo6.15 ltmporory support for sit€ v{elding worhJho_Dhe minihydro, Nepo.l

.108

Photo 6 14 Penstod ot Cbondruk with villqge in the bqckground

The instqllqtion of the penstock should stort

lrom the mochine foundqtion ond proceed upstreom.

This qvoids ony misolignment between the penstock

ond the turbine housing. Since the turbine needs to be

firmly fixed to the mochine foundotion, there is olmost

no toleronce at this end qfter the mqchine foundotion

hos been constructed. Furthermore, the pipe sections

below the exponsion joints con slide down if instollo-

tion proceeds downstreom from the foreboy. Minor pipe

deviotion ccn be odjusted ot the foreboy wqll, but such

odjustment is not feosible ot the mochine foundotion.

For micro-hydro schemes, loying of penstock in discrete

lengths is not recommended since this cqn leod to

misolignments of the pipes.

r Penstock pipes should be pressure tested 0t the foctory

before tronsport to site. For schemes where the heod is

more thon 15 m the completed penstock should olso be

pressure tested during the commissioning phose. lf

feosible such pressure test should include the surge

heod (i.e., pressure test ot hror..). This con be done by

simuloting the expected surge heod ot the foreboy

using o mqnuol pressure purnp. If ony leokoge is

noticed, the section should be repoired such os by

tightening the bolts, chonging foulty goskets or

welding. For buried pipe olignment, the bockfill should

only be completed ofter successful pressure testing;

however, if there ore ony minor bends without qnchor

blocks, these must be bockfilled before pressure testing.

once the pipe trench is bockfilled, it will be difficult ond

time consuming to re-excovote ond identify the leoking

sectlon.

6.13 Mointenonce

Above ground mild steel penstocks should be repointed every 3

to 4 yeors depending on the conditions. Nuts, bolts ond goskets

offlonge connected mild steel pipes should be checked qnnu-

olly, loose bolts should be tightened ond domoged goskets

should be reploced. A visuql check for flonge leoks should be

corried out monthly.

For buried penstock sections, signs ofleokoge such os

the sudden oppeoronce ofsprings olong the olignment

(especiolly during winter) ond moist ground where the qreq

wos previously dry should be checked. Ifony leokoge is

noticed, the penstock should be droined ond corefully exco-

voted for repoir ofthe leoking section.

6.14 Checklist for penstock work

Refer to Toble 6.i ond decide on the penstock moterial.

When in doubt compore the costs of qll ovoiloble

options.

Is the olignment on procticol ground slope? Is there

odequote spoce for the powerhouse oreo ot the end of

the penstock olignment? Hqve the bends been mini-

mised?

For mild steel pipes refer to Tqble 6.3 to decide on flonge

connection or site welding. Also be sure to specifo

oppropricte coots of point.

If o buried penstock olignment is being considered, refer

to Tobl€ 6.4 to compore the odvqntoges qnd disodvon-

toges, ond Figure 4.8 for the trench detoils.

Is the pipe diometer such thqt the heqdloss is between

5o/o snd 70o/o?

Hqs ollowqnce been mode for surge effects while sizing

the penstock woll thickness?

Is the sofety foctor sufficient os discussed in Section 6.6?

Are the pipe lengths ond weights such thqt they ore

tronsportoble ond porteroble?

Refer to Section 6.12 for pipe instollation ot site.

a

a

109

7. Anchor blocks andsupport piers

7.1 Overview

Ar qnchor block is on €ncosem€nt of0 penstock d€signed to

rcstr0in the plpe movem€nt ln oll drr€ctlons. Anchor blocks

sh0uld be ploced ot 0ll shorp horizontol ond venrcol b€nds,

since there ore forces ot such bends which will t€nd t0 move the

pipe out of oligrlm€nt. Anchor blocks ore qlso requir€d to resist

oxiol forces in long stroight sections ofp€nstock.

Support piers ore short colLlmns thot ore ploced between

onchor blocks qlong stroight sections ofexposed penslock pipe.

These strucrurcs prevent the pipe from sagging ond becoming

overstressed. However, the suppon piers need to ollow pipe

movement porqllel to the penstock olignment which occurs du€

t0 thermol expqnsion ond controction.

7.2 Anchor blocks

72.I GENERJqI

Locoti0ns ot which onchor blocks ore required ond their

construction orc described in this section.

7.2.2 LOCATION OF ANCHOR BLOCrc

Anchor blocks ore required ot the following locotions:

At verticol or horizontol bends ofthe penstock os shown

in Photogroph 7.2. A filled p€nstock exefts forces ot such

bends ond th€ pipe needs to be properly 'onchored'.

lmmediotely upstreom of th€ powerhouse. This

minimises forces on the turbine housing.

At sections ofthe penstock where the stroight pip€

lengrh exceeds 30 m. This is to limit the thermol

exponsion ofthe pipe since on exponsionjoint will be

ploced downstreom ofthe onchor block.

723 CONSTRUCIION OF ANCHOR BLOCXS

A[ch0r blocks should normolly be constructed of 1:3:6 concr€te

(1 poft cemenr, 3 pqrts sqnd. 6 ports oggregote)with 400/0

plums ond nomrnol reinforcernent. Plums ole boulders thot ole

distributed ever y oround the block such thot they occupyqbout 40% ofthe block volume. The boulders odd weight to the

block ond therefore incrcose stqbility while decr€osing the

PhotoT'l A stroight penstock with four suppons ond ononchor block befoR the powerhouse

Photo ? 2 Jhonhe mni'hydro onchor block for on upword venicol bend

1 1 1

. r m , n r r , ^ 1 " m , . e n " i r D l

Hoop reinforcement is required 0round the pipe lo resist

crocking ofthe concrete due t0 tensile forces from the pip€.

Three l0 mm bors ore generolly suincient, os shown in Figure

7.1. The hoop b0rs sh0uld be opproximotely 150 mm cleor of

the pipe, cnd should exrend to 100 mln from the b0se, so thot

rhe whol€ weight ofthe block cqn be nobil ised without

crocking Ifthe reinforcement is inodequote, the block con

crock. os shown in Photogroph 7 3. A collor 0r metol togs moy

be welded to th€ prpe to eusure thot rhe pipe does not slide

within the onchor biock

For downword bends, the onchor block is moinly in

compression, therefore o st0ne mosonry structure (1i4 cement

monor)con be considered ifcosts con b€ brought down.

Composite onchor blocks c0n ols0 b€ considered to sove

cost os shown in Figure 7.2. Foundotion ports ond centrol

portion ofth€ block con be mode of lr1.5r3 reinforced concrete

ond outer poftion ofthe block con be mad€ ofstone mqsonry rn1 . 4 l . p m o n r ' c . n d ) m n r l n r

Note: All dimensions

ore ln mmh d i n g ( 1 , 3 : 6

Figu.e 7 I Anchor block seclion

The cement requirements [or plum concrete 0nd cementm n c ^ n r u . r D . c f ^ l l ^ u , c .

. 1:316 concrele with 40% plums: 132 kg ofcement per ml

ofblock volume.

. 1t1.5:3 concretet400 kg 0fcement per ml

. Stone mos0nry in 1:4 cemenl moffor 159 kg ofcemenl

per m ' .

Although more cem€nt ls required for cement mosonry

blocks, sovings moy be mode by ov0iding the cost of formwork

Photo 73 Crocking otthe Dppcr sudoce o[on unrcinforc€d onchor block

(where wood is expensive) ond crushing ofstone to preporc

oggreg0tes. Th€r€fore, whether pluln concrete or cement

mosonry rs economicol is site sp€cil lc but this issue should be

investigoted ifthere ore o number ofdownword venicol bends.

Cost con qlso be reduced by using permonenr dry stone

wqlls os formwork for the bu ed portion 0fthe onchor block os

shown ln Photogroph 7 4 At sires where wood is expensiv€ this

opprooch is worth considering.

Both ploin concrete or stone mosonry in cement mortor

\(

f -

Stone mosonrY in l :4 c/m

_ _i-- * ___j___<*--|-z-F=i- |

------

t : t5 :3

Note: Alldlmensions

ole ln mm.

Ir{,1

t12

lholoT4 useof drynonerv(r1 l forkr fD$ork.J l r (Lnk|c

blocks shoLrld be cured os discuss€d in Ch0pt€r I by keeping

them noist for ot leost o week.

The design oionchor blocks is covered rn s€ction 7 4.

Toble 7.1 Suppon pier spocing lcentre to centrc horizontol length in metresl

7.3 Support piers

?.3.1 GENERAL

l.ocotions ot which suppoft piers or€ required ond their

construcrion ore described in this sectiol|

7.3.2 LOCATION OF SUPPORT PIERS

Suppon piers ore requrred 0lorg thc stroight sections ofexposed

penstock betrveen onchol blocks. The moximum spocing of

support piers to ovoid overstressing the pipe is given in Toble

7 l. Pleose reod the notes under rhe toble'lhin-lvolled ploin pipe con buckle ot the suppon piers

with relotively short spons. In this cose the permissible spon

con be increosed by welding o w€qr plot€ to the pipe at e0ch

supp0n, see figure 7.3. This nroy be economicol for pipes lorger

thon 300 mm diomeler Corners ofweor ploles should be cut

with o rodius, to ovoid stress concentrolions Not€ thot o weor

plote is olso requir€d where the pipe leoves on onchor block, if

the spon t0 the first suppon pier exceeds thot ollowed for ploin

prpe.

It is usuqlly n0t economicol ro increose the pipe woll

thickness in ord€r to increose the support prer spqcing, but this

should be considered where the cost ofsuppon piers rs signrll

c0 n t .

PLAIN PIPE PIPE WITH WEAR PLAIESIFFECTIVE PIPE WAIL

THICKNESS, t,r.., ".

(mm):

320 Nimrnr STLEL

410 Nimmr STIEL

1 3

1.0

1 9

1 5

2.6

2.0

3.9

3 0

1.3

1 . 0

1 .9

1 5

3 93.0

2 6

2.0

h,,. < 100 r1r

100 mm dio

200 mm dio

300 mm dio

400 mm dio

500 mm dio

4.0 4.7

?.3 8.38.6 10.59 1 11.?

9.3 12.0

2 A

4 l

2 5

I 4

3 2

6 0

5 7

2.6

2 1

4.0

7 3

8.6

5.8

3.7

4 .7

8 .1

10.5

11.7

8.7

2 0

4 t

4 .9

5 1

4.1

3.2

6.0

? 0

7.4

7 5

(b) 100 < h,",", < 150 m

100 nnl dio

200 mm dio

100 mm dio

400 mm dio

500 mm dio

1 9

3.9

2 .5

1 4

3.1

5 8

5.7

2 6

2 T

4.0

7.1

8 2

5.8

3 7

4.7

8 .3

1 0 5

1 1 2

8 7

1.9

3 .9

4.4

4.4

4.0

1 .1

5 .8

6 .7

6 9

6.8

4 . 0 4 7

7 . 7 8 3

8.2 10 5

8 .6 11 2

8 .7 11 .5

1 1 3

. Continued

...Continued

rc) 150 < h,dor < 200 m

100 mm dio

200 mm dio

300 mm diq

400 mm diq

500 mm dio

2.7

2.5

l . a

2.35.05.72.6z . r

3.5

6.5

7.6

5.8

3.7

A A

8.3

10.1

10.6

8.7

2.7

3.2

3.0

z-u

2.3

5.0

5.8

6.0

5.8

3.5 4.7

6.5 8.3

7.6 10.r

7.9 10.6

7.9 70.7

(d) 200 < h,otor < 250 m

100 mm dio

200 mm diq

300 mm dio

400 mm diq

500 mm dio

1 .8

2.7

1 .8

4.4

5.2

2.6

2.1

J . l

6.07.05.83.7

9 . t

8.3

9.7

10.1

8.7

1.8

2.1

1 .8

a . a

J .Z

5.1

, . t

J . t . t . t

6.0 8.3

7.0 9.7

7.2 10.1

7. t 10.1

i,

Notes:

1. Applies only to steel penstocks welded or flonged to British Stqndord (minimum flonge thickness : 16 mm). In other coses

use one support pier for eoch individuol pipe length, with the pier in the middle.

2. Weor plotes to be of some thickness os pipe woll, ond welded on oll edges, covering bottom 180" of pipe. The length should

be enough to extend ot leost 0.5 times the pipe diometer beyond eoch side of tire support pier. See Figure 7.3.

3. For the colculqtioD 0ft"u".,u. reler to Section 6.6.

4. Interpolote between the obove volues for intermediqte pipe diometers, wqll thicknesses or steel grodes.

SECTION A.A

Figure.7.3 Arrongement ofweor plote ot o support pier

114

733 CONSTRUCTION OF SIJPPORT P|ENS

Support piers ole generolly constructed out ofstone mosonry in

1:4 cem€nt moftor. Dressed stone should be used for the outsid€

surfoces ofthe pi€r A 140'beoring oreq from the centft ofthe

penstock di0meter should be provided to support the penstock

pipe os shown in Figurc 7.4. Plocing o steel soddle plote obove

the support pier wh€re the penstock pipe rests olong with o 3

mm thick tor poper os shown in Figure 7.4 minimises friclionol

effects ond increoses th€ useful life ofthe pipe. c-clomps mqy

olso be provided to protect th€ pipe from vqndolism ond c

sidewoys movement. but there must be o gop between the

surfoce ofthe pipe ond th€ C-clomp, so thqt oxiol forces ore not

tronsferred to the support pier. stone mosonry support piels

wilh c-clqmps con be seen in Photogroph 7.5.

Wooden support piers hove occosionolly been used in

micro-hydro schemes, os con be seen in Photogroph 7.7.

Howev€r, wood is generolly expensive ond olso requips

frequent mointenonce such os pointing.

Ste€l support piers con olso be used qs on oltemqtiv€ to

srone m0sonry especiolly ot sites where cement is expensive or

the soil is weok in beoring. An exqmple ofsteel support piels is

rncluded in Chopter 10 (lnnovotions).

3 mm thickpaper

with steelsaddleplateundemeath

frgurp 7.4 T'?icol secrion rhrough o support pier

Photo 7 5 Stone mosonry support piers, JhonkP mini hydm scheme

Photo 7.6 The use ofon extension toth€ concrEte suppon lifts the pipe cleoro[on block, qllowinq droinoge ond preventing cormsion between the block ond

the pipe (ftomche)

1 1 5

7.4 Design ofqnchor blocksond support piers

7.4.1 GENERAI

The design ofonchor blocks ond support piers requires resolving

some common forces, which are therefore discussed together in

this section. First the structurcs orc tentotively sized orld the

vorious forces thot oct on them ore resolved. The minimum

colculqted block size thot is sofe ogoinst beoring, sliding ond

overtuming is occepted. It should be not€d thot the designpr0cess involves o few iterotions.

Vorious forces thot con oct on onchor blocks qnd supportpiers ore summorised in Toble 7.2 ond discussed ther€ofter

Photo 7 7 Wooden support li€rs ot Komche micro.hydro scheme, Nepol

Tqble 7.2 Forces on onchor ond slide blocks

FORCE lkNl DIRECIION OF POIENTI,AI MOVEMENT OF

ANCHOR BLOCK OR SIJPPORT PIER

COMMENTS

SYMBOLS ARE DEFINED AT THE END OF

T1IIS TASLE

F,

Fr = combinotiol ofFr, ond F,d

F,,: (We+w*) 1," cos ct

Frd = (Wp+W*)Lrd cos 0I f n i n p i < c r r n i n h r

F, = {w"+ w,.,)(1,,,+ 1,,)cos G

Uphill portion Downhill portion Fr is the component ofweight ofpipeond woter perpendiculor to the pipe.

Applies to both support piers ondonchor blocks

F,

F?,

F,o

= f (We+ W*)1,. cos cr= f (wp+ w*)Ld cos cr

Fz Expqnsion: onchor

below ond exponsionjoint obove

controctionr onchorbelow

ond expqnsion joint obove

Direcfions for forces on support pier

{t

F, is the frictionol force due to the pipe

sliding on the support pi€rs.

Applies to support pien ond onchor

blocks. The force octing qt on onchor

block is the sum offoEes octing 0n the

support blocks betw€en the onchor

block ond exponsion joints, butnnn^ . i rp in d iF . t i ^n

F,,

r, = zy*",.,h,",",x l{'r (?

=15.4h,"dd'zsin(?)

F, is the hydrostotic forte on bends th0t

octs olong the bisector ofthe bend.

0r y opplies to onchor blocks thqt

hove horizont0l ond/or verticol bends

if $rr

1 1 6

F, = combinqtion of Fou ond Foo

F = W L s i n u .4 u p 4 u

F = W L . s i n B4 d p 4 0 l

Uphill portion

F..,

Downhill portion Fo is the component of pipe weight

octing porollel to pipe.

Applies to onchor blocks only.

Colculqte only ifthe cngles (a or p) ore

lorger thon 20".

' 5

F s = i 0 0 0 E o T n ( d + 0 tSee Toble 6.2 in Chopter 6 forvqlues of E ond o

Uphill portion Downhill portion

\ - -

F, is the thermolly induced force

restroined by the onchor block in the

obsence oI on exponsion joint.

Applies to onchor blocks only.

Colculote only if exponsion joints ore

not instolled between onchor blocks.

F6

Fu=1oodF, directions os F, Fu is the frictionol force in the

exponsionjoint. The F6 force is felt

becouse the joint will resist sliding.

Applies to qnchor blocks only.

F7

F - = y h t l ( d + t ) t/ ! wo le r lo to l

: 31 h,o,o, (d + 0 t

Usuolly insignificont

Uphillportion X Downhill portion- - - -

\-.......-- ---.-

Fru- \

F, is the hydrostotic force on exposed

ends of pipe within expcnsion joint

Applies to onchor blocks only.

F8

\=(ftsJ""(T)=,5(sJ,'"(?)Usuolly insignificont

F, dirrctions os F, F, is the dynomic force ot o bend due to

chonge in direction of moving woter.

Velocities ore usuolly low in penstocks

so this force is smoll.

Applies to onchor blocks only.

F, n . ,

Fn = Y*o,.,h,o,o,X i(do,o' - d'..r,')

= 7 . 7 h ( d ' z - d ' z )l o lo l \ Drq snro l l '

F, is the force due to reduction in pipe

diometer from { n to d,.orr.

Applies to onchor blocks only.

F,o

u , r= !Fcos i xKoxw

F,o is the force due to soil pressure

upstreom ofthe block.

Applies to both onchor blocks ond

support piers

Colculote Fro if (hl - hr) is more thon

1 m. The force octs ot 113 of the height

(h,) from the bose ofthe block.

L

lii

W.D

W . = V o l . . . . x Y . .D Dloak I Dtftt

DEFINITION OF SYMBOIS USED IN TABI}7.2

cr = Upstreom penstock ongle with respect t0 the

horizontol.

B = Downstreom penstock ongle with respect t0 the

horizontol.

y : Unit weight in kN/mr

v - 9.8 kN/mrI wotPr

v : 22 kN/mlr concEle

y = 20 kN/mlr mos0nry

y see Tqble 6.2' p rpc moleno l

Y,o,r see Toble 7.3

O = Soil ongle offriction, see Toble 7.3q = Coeflicient of lineor exponsion ofpipe (oC r), see

Toble 6.2 in Chopter 6 where o is the symbol

used.

ADlg

E

I

sh

h")h

t0l0t

I

K"

Ko

I" l d

= Pipe internol diometer (m).= Internol diometer of lorger pipe in cose of

reduction in pipe diometer: Internol diometer of smqller pipe in cose of

reduction in pipe diometer.= Young's modulus of elosticity, see Toble 6.2 in

Chopter 6.: Coeflicient offriction between pipe ond support

piers: occelerotion due to grovity : 9.8 m/s'z: Buried depth ofblock ot the upstreom foce.: Buried depth ofbiock ot the downstreom foce.: Totol heod including surge.: Uphill ground slope (Figure 7.5). Note thct i moy

not olwoys be equol to a.: Active soil pressure coefficient qs follows:

_ cosi - l to tz i - .o tz 0cos i +\6sri - cos, O

= Hqlfthe distonce from onchor block centreline to

the centreline ofthe first downstreom support pier

Loo

L ,u

r"2d

Lru

I4U

aJ

AT

Wp

W

Wo is the weight of block.

Applies to onchor blocks ond support

piers.

(Figure 7.5).

Holfthe distonce from onchor block centreline to

the centreline of the first upstreqm support pier

(Figure 7.5).

,istonce between two consecutive support piers

downstreom ofthe onchor block.

Distonce between two consecutive support piers

upstreom ofthe onchor block.

Distonce from the onchor block centreline to

the downstreom exponsion joint (Figure 7.5).

Distqnce from the onchor block centreline to the

upstreqm exponsion joint (Figure 7.5).

Flow in the penstock pipe (mr/s).

Wqll thickness of penstock (m).

Moximum temperoture chonge ("C) thqt the pipe

will experience ofter being fixed ot onchor blocks.

Width of the onchor block in m.

Weight of pipe in kN/m

t l ( d + t ) t vr prpe n0(efl01

Weight of woter in kN/m

(Pipe oreo in m2) x y*o,",

118

Figure 7.5 Distdnces qnd ongles used in onchor block ond support pier equotions

7.4.2 DESCRIPIION OF FORCES

F, - F, is the component of the weight of pipe ond enclosed

woter perpendiculor to the pipe olignment. If therr is a bend qt

the onchor, however, both the upstreom ond downstreqm

lengths ofpipe contribute sepqrotely, eoch force perpendiculor

to the centreline of the pipe segment which contributes t0 it.

Fr-F, is the frictionol force ofpipe 0n support piers. Ifthe

penstock moves longitudinolly over supp0rt piers, o friction

force on the pipe is creqted ot eqch pier. A force'Fr", equol to

the sum of oll these forces but opposite in direction, octs on theqnchor. This force exists only where one or more support piers

ore locoted between the onchor block qnd on exponsion joint.

For exomple, if on exponsion joint is locoted immediotely

downhill of the qnchor, friction forces on the downhill length of

pipe will not be tronsmitted to the qnchor block from thqt side.

The friction coeflicient, f, depends on the mqteriql

ogoinst which the penstock slides ond is os follows:

steel on concrete, f: 0.60

steel on steel, rusty plotes, f : 0.50

steel on steel, greosed plotes or tor poper in between,

f : 0.25

F, - F, is the force due to hydrostotic pressure within o bend.

The hydrostotic pressure ot o bend creotes o force which octs

outword for upword bends ond inword if the bend is down-

word. This is o mojor force which must be considered in

designing onchor blocks. However, the block size con be

significontly reduced if the bend ongle (B-a) con be minimised

while fixing the penstock olignment.

F. - Fo is the force due to the component of the weight of pipe

porollel to the pipe olignment. On o slope, the component of

the weight of the pipe which is porollel to the pipe tends to pull

it downhill ond exerts o force on on onchorblock. The sections

ofpipe both upstreom qnd downstreom ofon onchor block moy

hove to be considered. The lengths 'Lou'ond'Loo'in the equotion

for the force "F," qcting on qn onchor block ore the lengths of

the upstreom or downstreom section of the penstock which is

octuolly to be held by thot block. The upstreom section moy

begin ot the foreboy 0r, more usuolly, ot on exponsion joint. The

downstreqm section usuolly ends qt on exponsionjoint. Ifthe

exponsion joint downstreom of on onchor block is locqted neor

the onchor, os it usuolly is, the force crising from the weight of

the downhill section of pipe between the onchor ond the joint is

insignilicont ond is usuolly neglected. Also, the onchor block

will not experience this force if the penstock is buried since the

ground friction will resist this force.

F, - F, is the force thot is tronsmitted t0 the onchor block due to

thermolly induced stresses in the obsence of on exponsion joint.

Ifon exposed section ofo rigid pipe does not incorporote on

exponsion joint, thermolly induced stresses build up in the pipe

and oct on the onchor block. The ossocioted force "Fr'moy

push ogoinst the onchor block (with increosing temperoture) or

119

illl

pull the onchor block (with decreosing tenperoture).

F. - Fu is the force due to friction within the exponsion joint. To

prevent leoking, the pocking within qn exponsion joint must be

tightened sufliciently. However, this tightening olso mqkes it

more diflicult for the joint t0 occept ony longitudinol move-

ment of the pipe. Friction between the pocking ond the

concentric sleeves in the exponsion joint creotes o force "Fu"

which opposes ony exponsion or controction 0fthe pipe. This

force is dependent on pipe diqmeter, tightness ofthe pocking

glond ond smoothness ofsliding surfqces. lfthere is not o

chonge in the pipe direction (cr = F) upstreom ond downstrecm

ofthe onchor block, the forces (from upstreqm ond downstreom

exponsion joints) concel out.

F - F, is the hydrostotic force on exposed ends ofpipe in

exponsionjoints. The two sections ofpenstock pipe entering

on exponsion joint terminote inside the joint; therefore, their

ends ore exposed to hydrostotic pressure, resulting in o force

"F," which pushes ogoinst the onchors upstreom qnd down-

streom of the joint. This force usuolly contributes minimolly to

the totol forces on on anchor since the rotio 0fpipe thickness to

the diometer is low. However, this force con be significont ot

mild steel-HDPE joint sections (since HDPE pipes ore thicker).

Note thot h,o,o, is the totol heod ot the exponsionjoint.

F, - F, is the dynomic force ot the pipe bend. At the bend, the

woter chonges the direction ofits velocity ond therefore the

direction of its momentum. This requires thot the bend exert o

force on the woter. Consequently, on equol but opposite

reoction force "F." octs on the bendl it octs in the direction

which bisects the exterior ongle of the bend (some os F,). Since

velocities in penstocks ore relotively low (< 5 m/s), the mogni-

tude ofthis force is usuoliy insignificont.

F, - Fn is the force exerted due to the reduction of pipe diometer.

Ifthere is o chonge in the diometer ofthe penstock, the hydro-

stotic pressure qcting on the exposed oreo creotes o force "Fr"

which qcts in the direction of the smqller-diometer pipe. if the

penstock length is long (os in the cose of Jhonkre mini-hydro),

then the pipe thickness is increqsed with increqsing heod.

However, the effect of chonging the diometer by o few mm does

not c0ntribute significont forces ond can be ignored.

Fro - F,o is the force on the onchor blocks or support piers due t0

the soil pressure octing on the upstreom fqce. Ifthere is o

significont difference between the upstreqm ond downstreom

buried depth (h, - h, > I m) of the block then o force will be

exerted on the onchor block due to soil pressure. In such cqses,

this force should be considered since it hos o destqbilisino effect.

Note thqt the resultqnt ofthis force octs ot 1/3 h..

7.4.3 DESIGN PROCEDURE

Once oll of the obove relevont forces hove been cqlculoted the

design procedure for onchor blocks ond support piers requires

checking the three conditions 0f stobility os follows:

Safety against overturning

The forces octing on the structure should not overturn the block.

For structures thot hove rectongulor boses, this condition is met

if the resultqnt octs within the middle third of the bqse. This is

checked qs follows:

r First toke moments obout one point of the block olong the

loce porollel to the penstock olignment.

r Find the resultont distonce qt which the sum ofverticol

forces oct using the following equotion:

/ I M \, . 1 _ I _ I" - \ I v /

where:

d is the distqnce qt which the resultont octs.

Itr,t is the sum o[ moments obout the chosen point of

the block.

IV is the sum ofvertical forces on the block.

r Now colculqte the eccentricity ofthe block using the

following equotion:

l r Ie : I

o o t t - d lt 2 I

r For the resultont to be in the middle third of the block, the

eccentricity must be less thon 1/6 of the bose length os

follows:

Finolly check thot e < €orowobre

Safety on bearing

The lood trqnsmitted to the foundqtion must be within the sqfe

beoring copocity limit of the foundotion moteriol. If the trons-

mitted lood exceeds the beoring copociry limit of the foundotion,

the structure will sink. The beoring pressure ot the bose is

checked using the following equotions:

p . =

where:

P. : moximum Dressure tronsmitted to the foundotion.mta

L&s€-ollowot l. 6

* ( ' . * - )

flri

r20

the sum ofverticol forces octing on the block.

length ofthe bose.

the bose oreo ofthe block.

eccentricitv colculoted eorlier.

The colculoted Pbo,, must be less thon the ollowoble

beoring pressure (Po'o,our,) for the type ofsoil ot the foundotion

level. Allowoble beoring pressure for different types ofsoil is

shown in Toble 7.3.

Toble ?3 Unit weight |7f, ongle of friction lOl snd ollowoble beoring pressur€ for difierent soil types

S r r -/ r v -

T -mse

A =ms€

r -

SOIL TYPE UNIT WEIGHT, y (kN/m') FRICION ANGrc(Aol AttOwABLE BEARING PRESSURE (kN/m')

Soft cloys ond silts

Firm cloys ond firm sondy cioys

Stiffcloys ond stiffsondy cloys

Very stiffboulder cloys

Loose well groded sonds ond

scnd/grovel mixture

I b

t7

20

20

18

22

25

30

32

31

50100200350100

Safety against sliding

The structure should not slide over its foundotion. The follow-

ing equotion is used to check this condition:

uIv' - > 1 . 5 :Itl

where:

I H = sum ofhorizontol forces

u =Friction coeflicient between the block ond the foundotion.

A volue of p : 1on ,, but not exceeding 0.5, is recommended for

friction between mosonry or concrete on soil.

lV = Sum ofvertical forces octing on the block

Design for one of the Jhonkre mini-hydro onchor blocks. The following information is provided:

Pipe diometer = 450 mm,

Pipeth ickness:4mm.

hntr, = 6o m'

\o*. = 48 *,

6 1 = i = 1 3 o , p = 2 5 '

Distonce to upstreom support pier, = 4 m,

.'.L,u = 2 m

Distance to downstreom support pier, = 4 t

" 'L 'a = 2 m

Distonce to upstreom expcnsion joint = 30 m.

" 'L* = 30m

There ore 8 support piers ot 4 m centre to centre spccing (L^ = 4 m) up to the upstrcam onchor block. To reduce friction, oll

support piers ore provided with steel shaddle plotes ond tor poper on top ofthe plotes os in Figure 7.4.

An exponsion joint will be locoted just downstreom of the block.

The soil rype is stiffcloy.

72r

CALCULAnONSh . = h + h

rorot gffi srge

= 6 0 m + 4 8 m = 1 0 8 m

Consider the block shope shown in Figure 7.6.Block volume excluding volume of the pipe =

{(2.2s x r} *(+- :x i.os)} x 2- 1 x fIx0.4582

/4 cos 13o - 2 x fl x 0.458'? /4 cos 25o = 16.12 m3

Unit weight of concrete, (y.oo.*.)= 22 kN /m3Weight of block, Wr = 16.12 x 22= 354.64 kN

Weight of pipe,

Wo =il (d + t) t y,,*r= f[ x 0.454 x 0.004 x 77= 0.,14 kN/m

n (0.4sorW* = ----;- x9.8 = 1.56kN/m

Wp+W, = 2.00 kN/m

Colculote the relevont forces:

3.00 mWdth = 2.00 m

Figure 7.6 Pmposed onchor block shope

1. F,u = (Wo * W*) L,ucos cr= (2.00) x 2 x cos 13' = 3.9) kl,f

2. F,o = (Wo*W*) L,ocos P= (2.00) x 2 x cos 25o = 3.63 kN

3. Frictionol force per support pier:= + f (Wp* W,)L^ cos cr

f = 0.25 for steel on steel with tor poper in between,= "r 0.25(2.00) x 4 cos 13o= -r 1.95 kN per support pier

Since there ore 8 support piers

F^onAnchorblock = t 1.95x8 = t 15.6 ld,{

Note thot F, is zero since on exponsion joint is locoted immediotely downstream of the anchor block

4. F, = 15.4h,o,o,0'r* (?)

= 15.4 x 108 x (0.450), r* (tt;- tt"

)= 35.20 kN

5. F.u = Wolru sin u: 0.44x 30 x sin 13'= 2.97 kN

122

Note thot Fou is insignificont since a is less than zff and could have been ignored cs discussed in Toble ?.2. F* hos beencolculated here only t0 show how it is done. F* is negligible since on exponsion joint is ploced immediotely downstreom ofthe onchor block., i.e., L* - 0 and therefore

F .=0 .

6. Fu =100xd = 100x0.450 = 45kN

7 . F I = 3 1 h , o , r ( d + 0 t

F7u = 31 x (108 - 30 sin cr) x 0.454 x 0.004= 5.70 kN

Fro = 31 x 108 x 0.454 x 0.()04 = 6.08 kN

Note thot os disclssed eorlier the rrsultont ofthese forces is insionificant.

/ Q ' \ / p - c \8 . F8 : t . t I

a , / s i n [ , /

^ _ 1 0 . 4 5 0 ' z \ . / 2 s " - 1 3 " \: 2's I o3so'? /th t z /

: 0.26 kN

Note thot os discussed eorlier, this force is insiqnificont.

9. F, = 0 since the pipe diometer does not chonge.

10. Soil force, F,o.

From Toble 7.3, y,o' = 20 kN/m3 ond

0 = 3oo for stiffclay.

Reco l l t ho t i =13o

. _ cosi - . , /coszi -coFI

K" = cosi +mffi =o'371

v . h 2F ,o= eXLcos i xKoxw

zJ x r.a'= -T- cos 13o x 0.37txz

= 23.45 kN

This force octs ot U3 ofthe buried depth ot upstrcom fqce ofonchor block from point o asshown in Figure 7.7, which is (U3 x 1.8) = 0.6 m.

123

Resolution of forces

c r = 1 3 " , b = 2 5 "

Forces (kN) X - component (kN) ++ Y - component (kN) + +

l u

F- l d

* F[cos a= *3.80

F,o cos P= * 3.29+ Fzusin cr= + 3.51

Positive during exponsion O

Negotive during contrcction @

/B+0 \- f r cos \

, /= -33.29

* Fou sin cr= * 2.97 sin 13o= * 0.67+ Fu (sin p - sin ct)= t 45 (sin 25" - sin 13")= -r 8.90

Positive during exponsion O

Negotive during controction @

* F^ sin cr: 5.70 sin 13"= * 1.28- Fro sin P= * 6.08 sin 25o= - 2.57

/0+cr1- r ,cos \ 2 /

= - 0.25

f F,o sin i= 23.45 sin 13'= * 5.28

+ 354.@

= 3.90

= 3.63

= - + 15.6

' 4 u

= 35.20

= 2.97

Fru : 5'70

Fro: 6'08

F, : o'26

F,o : 23.45

Wr: 354'64

* F,u sin cr: - 0.88- F,o sin B= - r - l j

-f F2u cos 0.

= -r 15.20

Positive during exponsion O

Negotive during controction @

/ p+cr\* F , s i n \ , ,= f l l .4 t )

+ F4u cos ct= * 2.97 cos 13o= * 2.89+ F, (cos a - cos B): +45 (cos13 ' - cos25 ' )

: -{- 3.06

Positive during exponsion O

Negotive during controction @

* F^ cos cr= 5.70 cos 13"= *5.55- Fro cos B= - 6.08 cos 25o= - 5.51

/ F+41*F rs i n \ , I

/ 250+ 130\= 0.26 sin | -l

\ 2 |

: * 0.09

* F,o cos i= 23.45 cos 13o- * 22.85

0

' a r

F' 3

= 4 5

Iv:345.26OExponsionIV = 320.44 @ Controction

l H = + 5 3 . 1 8 O E x p o n s i o nIH = + 16.66@ Controction

SUM

Note thot forces ore positive in X-direction is towords the right ond Y-direction downwords.

Colculote the centre of grovity of the block from the upstreom foce of the block toking the moment of moss. The eflect of the

pipe possing through the block is negligible, so need not be colculoted.

{(3x2.25)3 12 + | 1 /2x3x 1.05) 1 /3x3 } x2

{ (3x2.25]t + (Uzx3x 1.05) } x2

124

= 1.41m

.'. the weight of the block WB octs 1.41 m from point 0.

Sum ofhorizontol forces thot oct ot the bendI s - n

O Exponsion case 53.18 -22.85: 30.33 kN -r

O Controction cose 16.66 -22.85 = - 6.19 kN +-

Sum ofverticql forces thqt sct qt the bend

Iv -F ,oy -wBO Exponsion cose

345.26-5.28-354.64 = - 14.66 kN t

@ Controction cose

320.44-5.28*354.9 = * 39.48 kN T

Now drow q force diqorom on the block os shown in Fioure 7.7.

Check ifstructure is sofe ogoinst overturning:

O -+ Exponsion cose

Tqke sum 0f moments obout point 0 with clockwise

moments os positive:

I u@r o = 30 .33x2 .15 * 22 .85x0 .6

+ 354.& x 1.41 - 14.66 x 1.0= 564.30 kN-m

, /:r,r\ 564.30o: \ - tu /= i f i : 163m

t 3 |e = l - - 1 . 6 3 l = 0 . 1 3 m

I'IL 3

P - = 0 . 5 m'o l lowohle

6 6

. ' . e < e . O Kon0woDte

@ + Controction cqse

Tqke sum of moments obout point O with clockwise moments os positive:

IM@ 0 = -6 .19x2 .15 * 22 .85x0 .6

+ 354.64 x 1.4i - 39.48 x 1.0: 460.96 kN-m

, /ru\ +oo.sod = l - l = - = 1 . 4 4 m

\ Iv I 320.44

l : Ie : l - - 1 .44 | : s .96 m

l ' l

39.48014.660 e

@Expansion

Contrac{on

Penstock

Figurc 7.7 Force diogrom on the onchor block

Recoll thot €ouo*obl. = 0.5

. " e < e . . . . 0 K .otowoDt€

Since e < eo,,*ob,. for both coses, the structure is sofe ogoinst overturning.

Check if the structurc is safe on beoring copocity:Note thot for stiffcloy ollowoble beoring pr€ssure is 200 kNlm'? (Toble 7.3).

O -r Exponsion cose:

= Iv / t *6 f )mre 4.," \ Lb""I

,*..= 44 (r + $r:) = 72.5 N/mzm 5 € 3 x 2 \ r l

@ + Controction cose:

p = l ' v ( r + !s - , )'bose

A*r, \- q",./

P. -320'44 /r + -6Iq'06) : 5e.8 kN/m2d * 3 x 2 \ r l

In both coses P*," ( Pouo*orr. = 200 kN/mz. .'. the structure is sofe ogoinst sinking.

Check ifthe block is scfe ogoinst sliding:

O -+ [xponsion cose

I H < p I V

p = 0.5 for concrete/mosonry on soil

53.18 kN < 0.5 x 345.26 kN

53.18 kN < 172.53 kN OK.

O + Controction cose

T H < p ' V

16.66 kN < 0.5 x 320.,14 kN

i5.66 kN < 160.22 kN 0K.

Since I H . p I V in both coses the structure is sofe agoinst sliding.

.'.The onchor block is stable. The colculotions could be repeoted to justiff using o smoller, more economicol block.

7.4.4 STZNG OF ANCHOR BLOCKS FOR SMAI.L SCHEMES

For micro-hydro schemes with o gross heqd less thon 60 m qnd

on instqlled power copocity less thon or equol to 20 kW the

following guidelines cqn be used to determine the size of on

onchor block:

o At o stroight section, locote one onchor block ofter every

30 m distonce (os discussed eorlier) by plccing 1 m3 of

plum concrete for eoch 300 mm of pipe diometer. For

exomple, if the pipe diometer is 200 mm, then:

/ 2 0 0 \t

" f1*, = 0.67 m3 of concrete volume is required.

r At o penstock bend, where the bend ongle is less thon 450

(i.e., 0 - a), double the concrete volume thon whot is

126

required for o stroight section. For exomple ifthe pipe

diometer is 200 mm ond the bend is 20'. then:

/ 2 0 0 \2 xl--:=- | = 1 .33 m3 of concrete is required for

\ 3 0 0 /the qnchor block.

r Similorly, if the bend ongle is lorger thon 45', then the

required concrete volume should be three times thot for

o stroight section. For exomple if the pipe diometer is

350 mm ond the bend is 500, then:

, - (-:+) = 3.5 mr of concrete is required for the\ 3 0 0 /

onchor block.

John Bywoter hos developed o more sophisticoted

method of sizing onchor blocks for smoll schemes. This is

ovqilqble through ITDG.

7.4.5 SIZNG OF SUPPORT PIERS FOR SMAII SCHEMES

For smoll schemes (gross heod less thon 60 m cnd power

copociry limited t0 20 kW) Figures 7.8 qnd 7.9 con be used osguidelines to size for support piers.

If the penstock olignment is less thqn 1 m qbove theground, Figure 7.8 cqn be used os o guide for the shope ofthe

support pier. The minimum length ond width ot the bose

should be 1 m x I m ond the top width porollel to the penstock

olignment should be 0.5 m. The width qt the top perpendiculor

t0 the penstock pipe route should be kept 1 m ond the uphill

woll surfoce should be perpendiculor to the penstock pipe. A

minimum foundotion depth of 300 mm should be provided.

Similorly, if the penstock pipe is 1-2 m obove the ground, Figure

7.9 con be use qs o guideline. Note thqt the structure is similor

t0 Figure 7.8 except thqt the bose length ond width ore 1.5 m x

1.5 m.

For lorger schemes qll relevont forces should be resolved

ond conditions ofstobility should be checked qs discussed

eorlier.

Note: All dimensions

qre in mm

Figure 7.8 Suppon pier for smoll schemes with ground height of less thon 1 m

Note: All dimensions

ore in mm

Figure 7.9 Support pier for smoll schemes with ground height of I m to 2 m

7.5 Checklist for onchor blockond support pier works

o Hove onchor blocks been locoted ot exposed penstock

length intervols exceeding 30 m even when there ore no

bends?

o For onchor blocks, hos o minimum cover of 300 mm

oround the pipe been provided? Is odequote reinforce-

ment included?

o If there ore o lot of downwords bends qnd wood is

expensive ot site consider using mosonry onchor blocks.

Also for the buried sections, dry stone wolls con be used

os permonent formwork.

r Hos odequote foundotion depth been provided for both

support piers ond onchor blocks? Be sure to include steelplctes ond tor poper on support piers to minimise

friction.

o Hove oll relevont forces on both support piers ond

onchor blocks been checked os discussed in Section 7.4?r Finolly reler to Chopter 9 for issues concerning stobiliry.

127

E.l Overview

the powerhoust occommodotes electr0 nlechonic0l equlpment

such 0s the turbine, generotor, ogro processlng units ond

controlponels. The morn luncti0n ofthls butlding is to protect

the electro-mecllonicol equipnrenr fronr odverse weother os

well0s possible rnisllondlin0 by un0uthonsed persons. The

powerhouse should hove cdequote spoce such thot oll equip-

menl con fit in 0nd be occrssed without dimculty. Costconb€

bmught d0wn if the c0nstrLrction is simil0r to other houses in

Itr€ Communrty.

The powerhouse ofthe Borpok rriclo'hydro scheme r..,r

h seen in Phot0gr0ph 8 1 This buildrng is similor to other locol

hous€s in the community. Note thot the tronsformer is f€nced

t0pr€vent occidents due to unouthorised occess.

Th€ g€nerot0rs, Iurbines 0nd rhe belt drives need ro be

$cuRly lixed on the mochine I0undotion in the powerhouse.

Il is Rquires 0 cqreful oesrqrsln.r lhe equiDment generores

8. Powerhouseond tailrace

129

Photo 8 I Powerhous€ oflhe Eorpok micro.hydm schem€

dynomic forc€s ond even q slight displocement con cous€

excessive strcsses on vorious ports ofthe €quipment ond leod to

equipmerIt molfunction.

The toilroce is 0 chonnel or o pipe thot conveys woter

from the turbine (ofter power generotion)bock into the str€qm;

generolly the sqme str€om from which the woter wos initiolly

withdrown.

The powerhouse ond toilroce ofthe S0ll€riChiolso mini-

hydro scheme con be seen in Photogroph 8.2

PhotoE2 Powerhoute ond toilroce ofthe SolleriChnlso minr-hydro scheme

E.2 Locotion ofpowerhouse

The locotion ofthe pow€rhouse is govemed by th€ penstock

olignment since this building must be locoted ot the end ofthe

penstock. Aport from this, the following crit€rio oIe recom-

mended for locoting the powerhouse:

o The powerhouse should be sofe from not only onnuol

floods but olso rore flood events. Discussi0ns should be

held with the locol community members to ensuE thot

floodwoters hove not rcoched the proposed pow€rhouse

site within ot leost the post 20 yeors. For micro.hydro

schemes of5G100 kW it is r€commended thot the

powerhouse be obove the 5Gyeor flood level.

. It should olso be possible to dischorge the toilwoter

sofely ftom the powerhouse bock to the streom.

. Ifpossible the powerhouse should be locoted on level

ground to minimise €xcovotion work.

o The proposed locotion should be occessible throughout

the yeor. At some ploces this moy r€quire constructing o

new foot troil.

o The powerhouse should be locoted close to the commu.

nity thot it serves, prcvided thot the penstock qlignment

ond other porometers or€ feosible ond economicol. This

will Rduce the tronsmission lin€ cost. ond ifo0ro.

pmc€ssing units ore olso instoll€d in the powerhous€,

the community will not hove to corry their groin for o

long distonce.

. Oth€r stobility issues discussed in Chopter 9 should olso

be oddr€ss€d.

E.3 Design of powerhouse

83.1 GENERAI

A powerhouse thqt is similor to other locol houses in the

community is generolly economicol ond oppropriot€. The

community m€mbers \a'ill be oble to construct such o building

with nominol supeffision.

Ifo decision is mode to construct tie powerhouse similor

to oth€r locol houses, then the civil design input requircd is to

size th€ plon oreo ofthe building ond design the mochin€

foundotion. The olto inside the powerhouse should be well lit

ond ventilqted with sufficient windows. Plocing o few trons-

porcnt fibrcgloss sheets (skyligh0 in the roof will pmvide

odditionol illuminotion os con be seen in Photoorooh 8.3.

832 SEE OF TIIE FOWENfiOUSE

The plon oreo ofthe powerhouse should be determined os

follows:

. The siz€ ofthe electm-mechonicol equipment should be

obtoined from the monufqcturer.

. All l€quil€d equipment should be drown to scole ond

ploced on the proposed powerhouse plon oreo. This moy

requir€ o few t ols to determifle the optimum loyout.

r30

Photo 8.1 Powerhouse of the Fonlcc minF hydlo

-\

833 POWERHOUSE WAII AND OTHER DETAII.S

Most houses in the hills of Nepol ore constructed of stone

mos0nry in mud mortor. Wooden truss with corrugoted iron

sheet (CGI), slotes or strow thatching ore used for the roofs. A

similor building is recommended for the powerhouse structure

with the following considerqtions:

o The minimum woll thickness of the stone mosonry

wolls (mud mortor) should be 450 mm. If funds ore

ovoiloble ot leost the externql surfoce of the wolls

should be plostered in cement-lime mortqr (12 mm

thick, 1:1:6 mix) to keep owoy moisture from roin.

r The penstock pipe should not normolly be built into the

powerhouse woll, otherwise the wqll could be domoged

by vibrotion from the turbine. The recommended

solution is to leove on oversized opening in the woll; on

olternotive is to ploce o bigger pipe outside the penstock

pipe where it posses through the wqll. At Jhonkre mini-

hydro the wqll wqs locolly thickened to act os o support

pier for the penstock pipes entering the powerhouse.

o The cleor height of the building should be 2.5 m t0 3 m.

r For lorger schemes, provision must be mode for liftingpnt r in rnpnt t \n t rnnnnt \2 l ; f tgd hy hnnd y ' r rnng i "

. 1 . . / . . . - . . . " J

, , " . , _ . 1 . r / u t l | t J

,' ,"r' slo(,c5

r3200

Figun 8.1 Powerhouse floor plon of the Jhonkre mini-hydm scheme

Adequote spoce should be provided such thot oll

equipment is eosily occessible. There should be q cleor

spocing of ot leost 1 m oround eoch item of equipment

thot hos moving ports (such os the generotor, turbine

ond the belt drive). Noted thot ifogro-processing

equipment is instolled, the community members will

regulorly visit the powerhouse (to process their groin).

Therefore odditionol spoce is required so thot the

powerhouse does not become overcrowded ond o

potentiol oreo for occidents. It is recommended thot

such qdditionol spoce is provided os o lobby ct the

entronce ond the equipment is ploced beyond it. A lobby

lorge enough for five people to woit with their groin

(obout 3 m x 3 m) moy be odequote in most coses.

Adequote windows should be provided for lighting ond

ventilotion. Note thot the door ond windows need to be

locoted such thot they do not obstruct occess to the

equipment. This requires co-ordinoting the locotions of

the equipment, windows qnd the door.

The powerhouse loyout of the Jhonkre minihydro

scieme i-s .rhou/.r,, in Fitrr 8 t

131

,7-

expensive; m0re oppr0pri0te is o block ond Iockle

supp0rted by o beom or lemporory A-fromc.

CGI sheets should be used Ibr the ro0llng, since th€y 0re

relotively fire resistont ond leok prooi

Th€ lloor ofthe powerhouse should be 300 mm to 500

mln obovc the 0ulside ground surlirce to prevent

dompness ond roinwoter entering Drqins should olso

be provjded outside the powerhouse

Doors ond windows should open outwords for scfety in. . .p ^ f f i rp ^ r f l ^^ . l in .

8.4 Design of mochine foundotion

The design ofthe mochine f0undotion is similor to thot ofon

onchor block, but simpler. The m0st significont Ibrces thot the

mochine foundqtion con experience ore os follows:

. The thrust due t0 hydrostohc force when the volve ot

the powerhouse is closed or Ihe totol heod Lncluding

surge due to sudden blockoge offlow lfthere is on

exponsionjoint upstreom ofthe volve, the entire h€od

will be tronsferred to the m0chine foundoti0n from the

turbine housing

r The venicol force due to the weight oflhe foundotion

block, thc turbine qnd lhe gener0lor

Soil forces do not need to be considered becouse rhey ore

bolonced on eqch side ofthe foundotiorr.

Since o homogeneous 0nd rigid srructure is required the

mochine found0tion shou]d be constructed ofreiuforced

concrete. Th€ design process is to t€nlotively size the mochine

Photo 84 Construct ion ofJhonkre mini 'hydro mochlne foundot ions

foundotion ond then ch€ck the structure 0g0rnst ov€fturning,

sliding ond sinking os in the cose ofonchor blocks.

The Jhonkre mini-hydro mochine foundotion pits cor be

seen under construction in Photogroph 8 4. Th€ mochine

fourld0tion ofthe colkot scheme cqn be seen in Drowing 420/C/

3C03 ofAppendix c. Plocing the turbine pit f loor 0.3 m below

toihoc€ invert level h€lps to r€duce obrosion by the woter

leoving the turbine.

Exomple 81 i l lustrotes th€ design principles ofo mochine

foundotion.

: \ :

Design o mochine foundqtion to support o directly coupled rurbine ond generotor. The following informotion hos been

provided:

Penstock pipe diometer - 300 mm, mild steel.

The pipe centreline is 300 mm obove th€ powerhouse floor

0 . = 150 Us

cross hecd (h0.,,) = 51 m

Expected moximum surge heod (h,"_.) - 50 m

Woter l€vel in the toilroce chonnei = 0.25 m

Weight ofturbine {Wr) = 300 k9

W€ight ofg€nerotor (W") = 350 k9

Site conditions reveol thol the f0undoti0n needs to be constructed on soil.

--l

Calculotions:Try a reinforced concrete structure with dimensions as shownin Figures 8.2 ond 8.3.h . = h + h = 5 1 m * 5 0 m = 1 0 1 m :

totd grcss surge

Force due to h,o,o,, F") = (Pipe oreo) x 101 m x unit weight of

w0ter

ilo.3,m2 x 101m x 9.8 kN/m3

4

orF, = 59,960N:70.0kN

Weight of turbine (Wr) : 300 kg = 300 x 9.8 = 2910 N = 2.94

KN

Weight of generotor (Wo) : 350 kg : 350 x 9.8 = 3430 N = 3.43

Ploce oll forces on the mqchine foundotion ond divide the

block in three sections W,, W, cnd W, cs follows:

Colculote the weight of three sections of the block using 22

kN/mr for unit weight of concrete.

W, = 0.4x 1.5m x 2.5mx 22kN/m3=33.00 kN

W, = [ ( 0 .45x 1 .5x2 .5 ) - (0 .45x 1 x0 .5 ) * (0 .a5x0 .5x 1 ) l x

22 = 27.23kN

W, = 2.35 x 1.5 x 2.5 x 22 = 193.88 kN

Check whether the block is sofe ogoinst overturning:

Toke sum of moments obout point B (counter clockwise

moments os positive):

tM@B

10 .4 \= *,* (i + o.4s + 2.35) + (w, + wr) x

1 0 . 4 5 1 / 2 . 3 s \[;

* 2.35) + (wc + w3) t;/

- FH x 1.8

= 33.00(3.0) + (27.23+2.94)(2.575) + (3.43+193.88)( 1 . i 7 5 ) - 7 0 x 1 . 8

or XM@B = 282.5 kNm

Note: All dimensions ore in mFigurc 8.2 Mochine foundotion section

Id,I

+IIII

l l

r I I O l l fOCO

l l

Note: All dimensions ore in m

Figurt 8.3 Mochine foundotion plon

Sum of verticol forces, IV : W, *Wr*W3+Wr+Wc Figure 8.4 Resolution of forces on the mochine foundotion

= 33.00 + 27.23 + 193.88 + 2.94 + 3.43

Note All dimensions ore in m

or IV = 260.5 kN

Equivolent distance ot which XV octs fmm point B:

d = & - ? . 8 ? . 5 = 1 . o B mry 260.5

[t^ Ieccentricity, e = l+-*d I" t, J

lz.z Ie = l__ 1.08

IL J

e = 0.52m

L 3.2€q'owobrc=

f= a =0.53m

Since e is less thon €orowobre, eccentricity is in the middle third.

.'. The structure is sofe ogoinst overturning.

Check bearing pnessure:

p**=* (,.tJ

=#('.s'n)

= &., n ,

< 180 uf

(mox. ollowed for soil)

.'. The structure is sofe ogoinst sinking.

Check sliding:

Assume thot the friction coeflicient between block ond soil, p = 0.5

X H = F r = 7 0 k N

F !V = 0.5 x 260.5 = 130.2 kNFoctor of sofety 0goinst sliding:

= pIv = -P9.2* = 1.g6 > 1.5 oKIH 70

.'. The structure is sofe agoinst sliding.

Hence, t}te structure os designed is odequote. The finol design including the reinforcement bors con be seen in Figure 8.5. A1:1.5:3 mix concrete with reinforcement pottern os shown in the figure is recommended for the mochine foundotion since thestructure must be rigid cnd strong enough to lvithstond the forces. A 50 mm cover (cleor spocing between the bors ond theedge of the concrete surfoce) should be provided for the reinforement bors. Such cover provides pmtection for the rcinfonement bcrs ogainst corrosion ond other odverse effects.

IjI

\,"

Note thot os con be seen in Figure 8.5, a 100 mm width of sand ond gravel hos been ploced ot the periphery of the mochinefoundation down to the depth of the powerhouse floor. This will structurolly isolote the mochine foundotion from thepowerhouse floor so thot the dyncmic forces (such os vibrotions) ore not tronsfened to the floor ond wclls. Crocla olong thepowerhouse floor ond walls have been observed where the mochine foundations hove not been structurolly isoloted. The 50mm thick bituminous surfoce prevents the grovel ond sond from being compocted (ond hence the possibility of tronsfeningforces to the powerhouse floor). This is done by pouring hot bitumen (os used in block topped roods). The 50 mm thickconcrete blinding provides on even surfoce for reinforced concrete work ofthe mochine foundotion.

AIso note thqt, if o belt drive system is required, the mochine foundotion should be extended to cover it. However, the depth offoundotion for the belt drive con be lowercd to 300 mm but with similqr reinforcement pottern.

Bose f rome (dimensims ore to be

- l tl l

' l l

l lt lI tl lr l'r==J

2 .. l

t . , .- t

. t

5Omm thick biluminous srrfoce

5Omm thickb l i nd ing ( l : 5 : 6 ) Anch bol ts

450

Notes

1. All dimensions ore in mm.

2. A minimum of six 20 mm diometer, 700 mm long onchor bors ore to be used to fix the bose frome

foundotion.

3. 10 mm diometer Tor steel bors ore to be used for reinforcement. Moximum spocing to be 150 mm

mm on other foces. Lop length sholl be 400 mm minimum.

4. Minimum reinforcement cover sholl be 50 mm.

5. Structurql concrete shqll be 1:1.5:3 mix.

to the mqchrne

in turbine pit ond 200

Figure 8.5 Proposed mochine foundotion section for Exomple 8.1

135

E.5 Tqilrqce

E.5.1 GENEn TTh€ toilroce is the finol civil structuft thot conveys the designflow. Similor to the heodroce, op€n chonrel or pipes con beused for the toilroce section. Toihoce chonnels of the ftonlcemhi-hydro ond Solleri Chiolso schemes ore shown in Photo-grophs 8.5 ond 8.6 Rspectively.

often, inodequote ottention is given to tie design ond

construction ofthe toilroce since the flow ot this stoge does not

contribute towods power production. However, such o

proctice con result in inodequote depth ofthe tqilroce pit or

erosior ofslopes, which could threoten the powerhouse

structul€,

8.52 I'ESIGN OF THE TAIIRACE CIIANNEL

Design of the toilroce chqnnel is similor to thot of the heodloce

csnol discussed in chopter 4. However, since heodloss does not

need to be minimised o higher veiuciw con usuolly be ollowed,

within the limits giv€n in'lbble 4.1. Not€ thot ot higher

velocities o strong€r grode ofmortor or concrete is r€quired to

resist erosion. Reinfored concrcte moy be economic for o steep

dnnnel os shown in Figure 8.6.

Note thot the downstr€om end of the toihoc€ must be

orronged so thot thel€ is no donger oferosior either by the river

or by the flow from the toilr0ce. Id€olly the dischorge point

should be orto mck or large boulde$. In erudible moteriol o

sti.lling bosin moy be required to dissipote the energy ftom o

steeD toilroce chonn€I.

E.53 DESIGN OF IAIIIACE PIPElfdue to site conditions, o pipe is rEquired for the toilroc€, thedesign procedur€ discussed in Section 4.5 (Heodrocr pipe,chopter 4) should be used t0 size the pipe. similor to o toihocechonnel. o higher heodloss con be ollowed for the pipe.

f HDPE pipe is used, the velocity should be limited to3 m/s ond the pipe should be loid t0 o uniform grodient. Higher

Phoro 8.5 Toilmc. dlonnel ofthe Jhonlae mini.hydm sdeme Photo 8.6 Toilroce dnruIel of the soleri chiolso mini-hydm scheme

mincorer:5Omm

Fioull E.6 R4info@d concrrte roillo(e chonftl

136

velocities 0r non-uniform grodient con result in oir entenoln_ment ond surge problems.

Ifpossible, the toilrqce should empty onto lorge rocks qtthe riverbonk so thqt there is no erosion qt the confluence.

E.6 Checldist forpowerhouse ond toilroce

ls the powerhouse locoted obove the oppropriote flood level?(Refer to Section 8.2)

Is the powerhouse oreo stoble? Refer to Chopter 9 forfurther detoils on stobility.

Hos odequote spoce been ollowed inside the power-house such thot oll equipment con fit in ond permit occesswithout difliculty?

Hos the mochine foundqtion been sized such thot it issofe ogoinst overturning, beoring cnd sliding? Also, be sure tostructurclly isolote the mochine foundotion.

o Is o chonnel or o pipe odequote for the toilroce? Hovethe velocity limits been checked?

r Is the toilwoter likely to couse erosion ot theriverbonk?

737

9. Slope stabilisqtion

9.1 Overview

Nepol's mountoin slop€s, porticulorly the slopes ofthe Middle

Mountoins, ore undergoing ropid chonges due to riv€r cutting,

weothering, ond soil erosion. The rote ofsoil erosion is very

iltense in the Middle Mountoins becouse ofthe subtropicol

clim0te ond intense rqirfqll (2000 to 2500 mm per yeor folling',,dthh 3 to 4 months). This oreq is qlso widely cultivoted using

i[igoted terroces ond heovily deforested due to populotion

pressuRs. Poor woter monogement ond forest mismonogement

h this oreo hov€ l€d to further d€cline of the hill slopes. The

n0turcl processes coupled with mon s influence hove led to

Iordslid€s, ond degrqdotion ofhill slopes offecting the

sustoinobility ond durobility of irrigotion chonnels, wqter

supply systems, micro-hydro schemes ond other development

work.

It is not possible to completely ch€ck these nqturol

processes, however it is possible to conuol them by oppropriote

choice ofmonogement, design ond construction pructices. The

underlying principle behind slope stobilisotion meosures is to

stQbilise hill slopes 0nd river bonks so os t0 protect th€ micrc-

hydm schemes.

Most slope stqbilisotion prcblems con be €ffectively

t0cki€d by moking sure thqt th€ hill slopes ore dry 0y diverting

th€ surfoc€ w0ter from the slopes), constructing retoining wolls

0s well os und€rtoking bio-engine€ring m€osur€s such os

plonting oppropriote vegetotion. Note thot dry slop€s on more

stobl€ thon soturoted ones ond londslid€s oenerolly occur on

wet slopes.

Photo 9 I Unsrobl€ dop€s orc o thrEot lo schemes.This powerbouse wosdestmyed by o londdide.

Retoining structures such os dry stone mosonry wolls,

gobions 0nd teffocing ore the most common method used to

stobilise slopes in mico-hydro schemes. In most micm-hydro

schemes constructing r€inforced concRte r€toining wolls is not

feosible due to their cost.

In the long term, prcventive bio-engineering meqsurcs

would be more effectiv€, sustoinqble ond cheoper thon I€mediol

works. These m€0surcs will often need the continued mointe-

nonce commitment ofthe community

9.2 Implicotions of noturolgeologicol processes

Soil erosion, river cutting, weothering, ond slope foilur€s hove

implicotions for d€sign, construction, operotion ond mqinte-

nonce of micro-hydro schemes.

fuv€r cutting cqn qllect intokes in severol woys, besides

triggering slope foilures, thot moy domoge o portion of

heodroce conol, foundotions ofsettling bosin, crcssings ond

powerhouse. For exomple, meqndering vers con leove intokes

high ond dry Similorly, degrading rivers con r€nder intokes

useless.

When heodroce cqnols ore built on hill slopes where

surfoce erosion hos qdvonced to o stoge where gullies hov€

olr€ody formed, there ore greqter sks ofconol foilure due to

d€ep€ning ond €nlorgement ofthe gullies.

The moin couse ofgully formotion is excessive run-off

due to deforestotiorl, overgrozing cnd burning ofthe vegetotion.

Excovotion work con olso trigger soil emsion. The

following is recommended to reduce the risk ofslope foilum due

to €xcovotion work:

cotch droins c0n be constructed obove the top ofon

excovotion, diverting surfoce woter to o sofe oreo.

When excovoting for conol construction, to prevent

surfoce erosion fresh hill cuts ond exposed slopes of

chonnel bonks must be quickly cover€d with topsoil so

thot vegetotion cqn be re-estoblished.

Spoil from excovotions should be corefully disposed ofso

thot soil erosion is not initioted.

Wherever possible conols should hove b0l0rced cut ond

fill sections to ovoid too much excovotion ond exposurc

offrogile loyers.

ii l: t' ! l

139

. Provide odequote berm width on the hillside ofheodroce

c0nols, to stop sh0llow londslips blocking the flow ond

cousing overtopping, which leods to erosion ofdownhill

slop€s.

9.3 Bio-engine€ringworks

All engineeriDg meosurcs such 0s ptoining wqlls ond check

doms should be well suppl€mented with bio-€ngineering

meosures os for os procticoble.

Plqnting gross or shrubs on the freshly cut hill or the

londslide oreo qre exomples ofbio-€ngine€ring meosul€s. Fost

growing, d€ep rooted orld dense cover type ofvegetotion thot is

oppropriote to the locol environment should be used for such

Purposes.only deep-rooted trces should be used for bio-engineering

purposes, ond they should not be plonted so close to conols or

structurcs thot their roots could cous€ piping or structurol

domoge. At leost 3 metres cleororlce is recommended. Fost

growing trees thot do not h0ve intens€ root systems should be

ovoided since they moy foll due to their own weight during

stoIIns.

once the slopes hove been stobilised, cole should be tol€n

to ensure thqt thele is no funher overgrozing.

9.4 Retoiningstructures

Retoining wolls ore stmctur€s thot support the bockfi.ll ond

surchorge lood fmm the odditionol conol width or plotform

over the wolls in hill sections. Though the per metre cost of

conol construction rrquiring retoining wolls is mon thon

constructing the some length by cutting inside th€ hill, the use

of retoining wolls sometimes becomes essentiol.

The most common types ofrctoining wqll used in micro-

hydro schemes ore grovity wolls ofgobions or cement mosonry

These depend on the moss of the structure to r€sist overturning.

Their design dep€nds on the woll densiry soil pqrometen,

droinoge ond looding conditions, typicolly Esulting in o bose

width of0.40 to 0.65 times the h€ight. The designs shown in

Figurps 9.1 ond 9.2 0re therefor€ sofe, but conservotive in mony

conditions.

For high or long wolls it will b€ economicol to design for

the sp€cifrc site conditions. site specific designs should olso be

mode wherc the bockfill is inclined rother thon horizontol.

The wolls should be checked for overturning, sliding ond

beoring pressure, os described for onchor blocks in Chopter T.

Altemotively rtfer to stondord cMl engineering texts such os

Photo 9.2 Mosonry stepr for energy dissipotion ond contml of spillwoy woterAlthough costly. eloborote contlol is essentiol wheR slop6 ore vuinemble toemsion {Siklis)

Ref. 7. (The unit weight offilled gobions is 1+18 l(N/nr,

dep€nding on the unit weight ofthe rock fill ond ossuming 3G

35% voids).

Woll foundotions must be deep enough to be sofe ogoinst

ercsion: normqlly qt leost 0.5 m below ground lev€I, but see

Section 3.8 for river worla. Lined toe droirs moy be used in

erodible oreos to corry seepoge woter sofely cwoy from the woll

foundotion.

C,obion l?toining wolls should be constructed with on

inclinotion 0f 1096, seeFiguE 9.1. Where gobions or€ to be built

on sond or flne soils, o loyer of filter cloth should be ploced

between the foundotion ond the gabions. The gobion boxes

should be loced together olong oll edg€s ond stptched beforc

filling with roclc The rock should be pocked with the minimum

ofvoids.

Stone mosonry wolls con be constructed in l:4 c€ment/

sond mortor os shown in Figur€ 9.2. Such wolls or€ suitoble for

retoined heights ofup to 2 to 3 m. The slop€ ofthe front foce

moy be steepened ifnecessory prcvided thot the bose width is

mqintoined. Tte reqr foce of the woll should be left rouoh to

140

ho9.SGrbion ot the ioe of on unstoble slope

hcrcqse friction with the bockfiil. Weepholes must be provided

to rclieve woter pressure behlnd the w0ll, ond their mouths

should be protected with ccrefully ploced stones. Bockfill

behind the woll should be free'droinrng grovel or stones; ifthe

Rtoined soil is fine, o filt€r cloth should be ploced os shown to

pEvent the soil ponicl€s blocking the drqinoge.

, O a . 6 .

9.5 Terrocing ond dry stone woll

Lock ofeffort in looking for oltemote woll types. such os

teffocrng 0nd dry stone wolls often rules out the dev€lopment

ofoth€r techniques thot ore mor€ economicol and duroble.

Minor londslid€ oreos con be stobilised by constructing

dry ston€ t€rroces as con be seen in Figure 9.3. The overoll slope

ofsuch terroces should be l imited to 30'(i.e. terroce widrh

should be twice its height). 500 mm thick dry stone wolls

should b€ used for the verticol foce of the rerroces. Such dry

stone wolls retoin the soil behind ond ollow the su oce woter

to droin out.

Constructiog smollcotch droins on the terroc€s helps to

reduc€ soil erosion by droining the surfoce woter

An olternotrve method used to stobilise the steeper

Jhonkre mini-hydro powerhouse slope is discussed in Box 9.1.

Pioto9.4 Stone mosonry con provid€slope

rlobilisotion olong th€ mute oflhe penstock (Borpok)

ri5

IIil

":i

h , f f i 8 , f f i

1.0 1.02.0 1.53 .0 2.04.0 2.55.0 3.5

Figure 9.1 Gobion retoining woll

,300 ,F+;+l

lmrn.l

75 dia.weep holes@2mdc

Figurc 9.2 Stone m0sonry retoining woll

Note:

1 . Cqtch drqins often lined with imperme'

oble lining mqteriols (i.e. stone

mosonry) to ovoid infiltroti0n. Woter

collected from cqtch droins needs to be

droined to neorest nqturol droin.

Londslide

Figure 9.3 Terrocing ond dry stone wolls to retoin slopes

tqz

In order to increqse the gross heod ofthe Jhonkre minihydro scheme, it wos decided to excqvote o 20 m depth ot the power-

house oreq. This required stobilising the hill slope behind the powerhouse oreq. This qreq qlso hod to droin ground woter due toseepoge from the cultivqted terrqces (paddy fields) obove. When irrigotion woter wos provided for the poddy frelds significontseepoge wos observed ot the powerhouse oreo. After considering vorious olternotives, it wos decided to use o grid of mosonrybeqms ond columns infllled with dry stone ponels.

Photogrophs 9.5 ond 9.6 show the hillside during excovotion

ond ofter the construction ofthe mqsonrv orid.

The hill slopes were frrst excqvqted qt 2:1 to 3:1 slopes (V:H) with two intermediote berms olong the hillslope qnd one ot the

sides. Then the grid of stone mosonry (in 1:4 cement: sand mortor) beoms ond columns with dry stone mosonry infill ponels

wos constructed olong the excovqted slopes. The beoms ond columns ore 500 mm wide ond 300 mm deep. The distqnce

between the columns is 2 m ond the verticol distonce between the beoms is 1.5 m (moximum). The dry stone infill soved the

cost of cement qnd focilitqtes drqinoqe. Cqtch droins hove been nrovided ot the berm levels.

To dote this 16 - 20 m high structure is stoble. During the monsoon ground woter thot hos seeped from the poddy fields obove

con be seen droining out from the weep holes qnd the dry stone ponels.

Photo 9 6 Mosonry grid ot powerhouse slope

9.6 Check doms ond gully control

Gullies thot ore octive or smoll streoms where scouring of the

riverbed is prominent con be controiled by constructing check

doms. Check dqms ore smoll wqlls thqt prevent further erosion

on the wqtercourse ond qlso qllow deposition ofbed loqd

upstreom ofit qt o stoble grodient.

For smoll gullies thot ore oniy octive during the m0ns00n,

the check dom could consist of o simple dry stone woll. For

smoll streoms, bed erosion cqn be controiled by using gobion

check doms.

Gobion check doms hove been used to control riverbed

scouring ot theJhorkot micro-hydro scheme. The riverbed ot the

Jhorkot intoke oreo hod been scoured by more thqn 3 m ot

143

some plqces ond the scour depth wos g€tting deeper. It was felt

thot further scouring olong the riverbed would cquse totql

foilure of the existing gobion woll olong the left bqnk of the

river. A series of gobion check dcms wos constructed ot the

intoke oreo to prevent further scouring and to fccilitote the

deposition of bed lood. The first check dom is shown in Figure

9.4. Note thot to prevent the gobion wires from being broken by

rolling boulders, 100 mm thick ploin concrete wos provided ot

the top surfoce of the gcbion woll. A minimum foundqtion

depth of 1 m from the lowest streombed level hos been provided

for oll check doms.

These check doms were constructed by the end ofJune

1998. They hove survived the first monsoon floods ond

culrently their conditions ore being monitored.

9.7 Maintenqnce

Retoining woils, check doms ond other slope stqbilisotion

structures should be inspected regulorly; specificolly before qnd

ofter every monsoon. Remediol works should be done os soon

os ony problems ore noticed. For exomple, the gobion crotes, if

broken, should be repoired soon. Similorly, if stones ore missing

from the dry stone mosonry retoining wolls or check doms,

they should be replcced.

The droinoge system ofthe stobilised slope should be well

mqintoined. Deposition of boulders, grovel or soil in the droin

should be removed. If the ploster or mosonry is broken, it

should be repcired. Note that stcbility problems con occur in

even o well stobilised slope ifthe droinoge system stops

functioning.

It is importont to note thot some structures such qs

gobion wclls ore not mecnt to be permanent on their own.

They moy deteriorote ond collopse. However, once oppropriote

vegetotion over these structures hos token root ond hos

mqtured repoir of these structures moy not be necessory since

the roots o[the vegetation will stcbilise the soil moss.

In the cose ofbio-engineering meosures, ony plonts thot

ore missing should be reploced. If possible, newly plqnted oreos

should be fenced to prevent grozing of qnimols.

l O O m m t h i c k P C C ( 1 . t . s r J )

lnloke cdnol 5000

Dry woll

G o b i o n s Note: All dimensions ore in mm.

Figure 9.4 A gobion check don ot the intoke ofJhorkot micro-hydro scheme

144

10 Innovctions

10.1 Generol

A ru.mb€I of innovotive ideos, I€seolth, opplicotions ond pilotpmjects Rlevort to micm-hydro technology thot hove not yetbem fully field tested, especiolly in the Nepolese context, orEdiscussed in this chopt€r. some opplicotiors orc in the reseolthood development stoge, others hove beetr successfully impleE€nted in other countries or corded out os "pilot pmjects' inNep0l.

102 Cosndqintoke

A Coondo intok€ hos o speciol screen thot utilises the tendencyoffluids to follow o surfoce. This is krown os the "coondo

d€ct'. As shown in Figup 10.1, th€ Coondo scR€n is instoll€dolong the crest of the diversion weir ond is shoped in the ogeecrlrv€ configurotion. A curve occelerotion plote qt the top of thessrm stobilises ond occelerotes the flow. As the flow posses

ovs tfu srE€n surfoce, th€ sheoring oction of t}Ie bors com-Din€d with the Coondo effect seporotes the flow. Cleon woterp6ses down thmugh the screen wh€r€os sediment ond d€bris

Fss ov€r the screen to rejoin the woter couBe below the weir.0n dvers corrying cobbles snd boulders dudng flood, the

Cmfllo int0le must be cor€firlly locoted s0 thot heovy bedloodnot p0ss over the scRen ond domoge it.

The potmtiol odvontoges of th€ Coondo intoke or€ onportio or sites which sufrer ftom exposure to high silt lood orwhich offer scope for cost sovings in the heodroce. In the n$tcose, the intola con Educe the need for lorge or multiplesettling bosins. In the second cose, wher€ o site loyout issuitoble, it moy b€ possible to commmce the penstocl rundinctly ftom the Coondo, goining heod ond ovoiding the needfor o heodroce conol. 0f course, this might imply thot thepenstocl is longer thon other potentiol loyouts or thot it runsclose to t]rc river. A thorough frnonciol ond technicol onolysisof the options is l€quil€d beforE msking o decision on thesuitobility of the C0ondo for o porticulor site.

The Coondo scEens ort fobricoted to o high tol€ronc€from stoinless steel. The supplier ofthe Coondo scr€ens (olso

colled "Aquo Sh€or ScEens") in Europe, Du.los Limited, Woles lX,doims t}lot scEens con be pmduced with 0.5 mm to even 0.2mm deor spccings, whidl diminote 90% of 0.25 mm ond 0.1mm portides Espectively. Both types of screen diminote oll1 mm pqrticles. In most micm-hydro systems this would olsoeliminote the need for o settling bosirl

The flow copocity of these ss?ens is 1,10!/s per metre ofweir length. A scRen with o flow copocity of40 Us (0.3 mwidth) costs obout Us$ 1380 (197 price).

A Coondo intola hos been test€d ot 0 mioo-hydro site inWoles by Dulos Ltd., in conjunction with nDG, UK The designflow of this micm-hydrc scheme is ,10 l/s ond the intoke isshown in Photogroph 10.1.Wcir

werf lorv

Rou topowerptonl

l0l A Coondo intol(e scrEen Photo 10.1 Coondo intole ofo micrchydlo scheme in Woles, uX

Over o six.month period, the performonce ofthe screenhos shown the following chorocteristics:

r Around 90% of sediment between 0.5 mm ond i mm

diometer wos excluded.

o Some build up ofdlgoe wos noted, but this did not

inhibit flow during th€ triol p€riod.

. The effect on performonce due to ice wos not noticeoble.

even ot temperotuEs 12'C below freezing point.

Tests ore rtquircd over o longer period to check for

corrosion ofthe screens ond effect ofcontinued olgoe growth,

porticulorly in wormer temperotures.

More informotion on Coondo screens con be obtoined

from:

DUI"qS Limited,

Mochyr l€th, Powys sY20 8sX, Woles, UK

Fox: +44 (0)1654 781390

e.moil: dulos@gn.opc.org

10.3 De-beqder for HDPE pipes

As discussed in Chopter 4 (Box 4.7), HDPE pipes or€joined by

h€ot wdding which melts ond fuses the ends together. This

Ieods to rois€d "beods" on the inside 0nd outsid€ ofth€ pipe os

shown in Photogroph 10.2. The extemol beod is not o problem

but the internql beod promotes blockqges ond significont heod

loss. An effective de-beqder would reduce the rcughn€ss volue

for HDPE from 0.06 mm (Toble 4.3) t0 0.03 mm.

A "de-beoder" tool hos beer designed (for IT Nepol)torcmove the intemol beods ftom HDPE pipes while the joints qre

still hot [i.€., hot de-beoding). This equipment hos been de.

signed to rcmove beods for pipe diometers up to 250 mm. lt is

still in the experimentol phsse ond l€quiles some developrnent

for use in the field.

As shown in Photogroph 10.3, the de-beoder consists ofo

mild steel shoft with o sleeve on which o bush spring looded to

o locking collor (vio on ,tllen key) is ploced. There ore three

horden€d steel blodes (cutter orms) thot oI€ pin connected by

Rctongulor steel bors to the bush. By unlocking the bush the

connecting pin con be slid up the sleeve to incl€ose the cutting

diometer

Photo I0.3 De-beoder tool

De-beoding with this tool is done by first unlocking the

bush so thot th€ tool con fit inside the pipe. A mild steel md

with 0 hondle is connected to the de.beoder such thot the

hondle sticks out ofthe pipe. The rod is supported byo number

of mild steel discs inside the pipe (smoller thon the HDPE pipe

diometer) for loterol stobility. The de-beoder is then ploced

inside ofthe pipe such thot it is obout 100 mm in front ofthe

prcposedjoint. Th€ rodius 0fthe cutting orms orc then

onong€d by sliding the bush such thot the blodes ole in contoct

with th€ inside pipe surfoce. once the blodes snugly fit on the

pipe surfoce, thel€ is o clicking sound indicoting thot the

cutting orms hove been locked. As soon qs the two pipe ends

orejoined by heot welding os discussed in Chopter 4, the de-

beoder is push€d forword till the blodes come in contoct with

the beods. The hondle is then tumed ond the de-beoder is

pushed forword which rcmoves th€ b€od.

Photo 10.2 weld beods on llDP! joint surfoce

146

This de-beoder wos tested ot Nepol Yontro sholo Energ]1Kothmondu, on o 200 rnm pipe os shown in Photogroph 10.4.De-beoding wos tried on o joint obout 2 m from one end 0f thepipe. the test wos portiolly successfi:1. It wos not possible toItmove the entir€ strip of the beod. Port of the beod ond somethin stronds were left on thejoint, qs con be seen in Phorogroph10.4.

Photo 10.4 HDPI pip€joint debeoded using the de-b€oder

The following observotions w€I€ mode in the workshop:

The mojor constroint wos thot the rodius ofthe cutter

blodes is nxed ond the blod€s do not work eouollv well

on oll pipe diomders within the ronge.

f d€-beqding is not stqrted immediotely ofter the pipes

oI€ joined (i.e. within 30 seconds), the beods connot be

Rmoved,

The tuming ofthe hondle ond pushing ofthe de-beoder

hos to be contmlled. A suddenjerk pushes the de-beoder

beyond thejoint.

The de-beoding process is olso homp€rcd ifthe pipe ends

ore not totolly circulor.

Hence, design improvements ore rcquird befoE tNs de-

beodercon be used in the field.

Commeftiol de-beoders ore olso ovoiloble but they ore

expensive. Some such commemiol de-beqders con olso remove

beods oft€r thejoints hove cooled (i.e. cold de-beoding). Photo-

gmph 10.5 shows q section ofon HDPE pipe which wos cold de-

beoded usino q commerciol de-beoder.

Photo 10.5 HDPE pip*joint deb€oded using o conmeniol deb€od4 fte smollring in fiont ofthe piF scction is rhe b€od.

turth€r informotion on commerciol de-beoden con beobtoined from:

Fxsion Gmup PLCChesterfield Troding Estote,chesterfield S41 9Pz,Englond, (JK

Faxt + aApl7246 4fi472

10.4 Bursting disc

As discussed in Chopter 6, p€nstock pipes for micm-hydroschemes ore designed to occommodote the surge heod whensetting the pipe thicloess. An incftose in th€ pipe thicknessolso increoses the cost 0f the pipe. Funhermore, depending onthe locotion of the site, drc tronsportotion cost olso incposes.In o high heod scheme with o long penstock olignment, theincl€ose in cost to cccommodote the sume heod con be sionifi-cont.

TheR or€ mony wdys to guord ogoinst surge domoge butmost involve significont cost (whm, for sofety I€osons the llowhos t0 b€ constroined) or involve greot colt in instollotion ondmointenonce.

The "bursti4 disc' technology moy pmvide o plioble

m€ons of sofely r€leosing the excess heod in cose ofsurgepressure. A "bursting disc" is q commerciolly ovoiloble over.pnssurc sofety device mqde fiom o bdttle moteriol such osgrophite or 0n oppropriote metol, or o suitoble metol which isd€signed to ruptuE extEm€ly quickly once o criticol pl€ssul€ isexceeded, such os the surge heqd induced inside the penstockpipe in the event of o j€t blockoge. Such discs or€ connmiollyused in the chemicol industry to protect pipdines ond pressure

147

Y

vessels (thqt conveygqs ond petroleum fluids) from high surge

pressure. Pipes thot hove bursting discs do not n€ed to be

designed to occommodote surge plessules. Photogrqph 10.6

shows o commerciolly ovoiloble bursting disc (including the

bu$t plote). Note thot scrotch lines qre mode in th€ plote

during monufocture to introduce weql:nesses in th€ plote such

thot it bursts occording to the pottern shown in Photogroph

10.6 once the Dresc bed pressure is reoched.

Photo 10 6 A commerdolly ovoiloble bursting disc

Most grophite discs ore flot, deform very slightly under o

pressurc differcntiol ond becouse oftheir physicol pmperties, ot

the set plessule sh€or instontoneously oround the periphery of

the disc octive orco giving imm€diotely full bore venting. Such

discs orc suitoble for verting ofboth liquids ond goses. The disc

is monufoctured to burst within its toleronce onJy when

instolled in o suitobly designed ond monufocturcd holder

some ofthe moin odvontoges ofgrophite bursting discs

ore thot they ore not odversely offected by misoligned pipe

work or ov€rtorquing ofpipe flonge bolts. Due to the sum-

ciently high burst pressure, this type ofdisc does not requirc

bockpressure support to withstond full vocuum pressure. The

discs hove 0n operoting rotio of90% qnd ore guoronteed to

rupture within o moximum of30 milliseconds.

The discs ore qlso inexpensive ond in cose ofrupture due

to surge pressure, oll thqt is pquired to recommission the pipe is

to Rploce the grophite plot€. Henc€, this technology could be

highly suitoble for micro-hydro schemes including those locoted

ln remote oleos.

Theoreticol res€orch on the opplicobility ofbursting discs

for micro-hydro schemes hos been undertoken by Dulos in

conjunction with worwick Universiry The bursting disc

orrongement proposed by th€ study is shown below in Figure

10.2.

FigurE 10.2 Proposed orrongement for buNting disc instollotion in micrc-hydmschemes

Note thot in cose ofthe rupture ofthe disc, the flow

would dischorge inside the turbine cssing. such on orronge-

ment is well suited in micro-hydro schemes since o seporote

flow control structur€ is not required.

The comlusions ofth€ obove study werc os foUows:

. The disc could reduce surge pressure by 60% - 70% ifthe

subsequ€nt flow rote through the bronching orronge-

ment is only moderotely reduced. The rroson why the

entirc surge heod connot be eliminoted is becouse the

diometer ofthe disc is usuolly smoller thon the penstock

diometer ond hence the flow is reduced.

r The penstock sofety fqctor could be Educed from 3.5 to

2.5.

These theoreticol findings need to be thoroughly verified

by octuolly instolling the discs in existing micro-hydro schemes

ond monitoring the rcsults. ITDG Nepol hos plons to field test

the bursting discs in some existing micro-hydro schemes.

More informotion on the opplicobility ofbursting discs

for micm-hydm schemes cqn be obtoined from Dulos Limited

(some oddrcss os obove).

Informotion on commerciol bursting discs con olso be

obtoined from the following manufocturer:

IMI Moffton Limit€d

Woboston Rood, Fodhouses,

Wolverhompton WV10 6QJ

Englond,lx

Fox: + 44 l0) 7902 397?92

10.5 Flexible steel supportpier for Jhorkot micro-hydro

The 36 kWJhorkot micro-hydro scheme is locqted in Mustong

District, Nepol. This is o community owned scheme ond is

monoged by the Jhorkot Elect ncotion committee. ITDC Nepol

hos been involved in providing technicol support for refurbish-

ment work of this scheme for some time.

148

Similor to other oreos of Mustqng, the topogrophy of theproject oreo consists of frogile ond unstqble slopes ond is prone

to londslides. The intoke ond the initiql heqdrqce conol have

been domoged frequently by Iondslides ond floods.

Although the slope olong the penstock olignment is

relotively stoble compored to the intoke oreo, it is weok ond

0ls0 prone to lqndslides. The existing mosonry support piers

storted sinking due to their own weight os well os the weight of

the penstock pipe ond the woter inside it. Hence, the penstock

(flonge connected) storted to sqg qt vorious ploces.

As port ofthe preporotion ofthis text, o pilot project wos

corried out to design qnd instoll steel support piers for the

Jhorkot scheme with ossistonce from Mr. Shyom Roj Prodhon of

NYSE. The design criterio were os follows:

r The support pier hod to be light, to minimise self-weight.

r It hod to be fobricqted using ports thot could be corried

by porters or mules. Jhorkot is obout holf o doy's wolk

from the district qirport ond 5 dovs'wqlk from the

neorest roodheod.

r The design hod to sllow for the

sinhng of the foundotion. ln

cose ofsinking ofthe ground

below the foundotions, the piers

should not pull the penstock pipe

down olong with it.

The design ofthe support pier ond

the foundotion ore shown in Figures 10.3

ond 10.4 respectively. The totcl weight

ofq 2 m support pier is 60 kg (excluding

the foundotion work) whereos o

mosonry pier of simiior height would

weigh 4000 kg.

Note thot such support piers

should be instolled perpendiculor to the

penstock clignment (not verticolly) since

they ore only resisting force F, (see

Chopter 7).

Figup 10.3 Flexible steel support pier for

Jhorkot micro-hyd ro scheme

The top section of the pier consists of o chonnel which is

pin connected to two legs thot hove turnbuckles. The penstock

pipe rests on the chonnel qnd the pin connection ollows the

chonnel some rototion such thqt it is perpendiculor to thepenstock olignment. Two holes hove been provided on the

chonnel to clomp the penstock with o 12 mm diometer bor. The

turnbuckles con be odjusted to fine tune the height ofthe

support piers (up to 300 mm) during instollotion ond in cose the

foundction sinks in the future.

The bottom of the turnbuckles (40 mm rods) Iit inside o

hollow pipe os shown in Figure 10.3. In cose the ground

beneoth the foundotion sinks, the suppofi pier structurr below

the turnbuckles drops down olong with the foundotion ond

only the top port (up to the turnbuckle legs) hongs with the

penstock. Hence the penstock pipe is not drogged down with

the pier in cose ofsinking.

The bottom port of the pier consists of ongles which orr

bolted bock to bock (Figure 10.3). Bolt holes ot o distonce 0f150

mm ore provided for coqrse adjustment of the pier. The bottom

eaO arF

ffiE_

alcrDx A. a

. l O O E A l ! . O n

K

149

stclo|l t-A

t's€qnoN 8- B

Figure 10.4 Foundotion forthe Jhorkot fl exible supportpler

ongles orc pin connected to the foundotion so thot the moments

due to thermol exponsion 0fthe penstock pipe oI€ not token by

the support pier or the foundotion. During instollotion os well

os loter in cose the foundotion sinks, coo$e odjustment con be

mode using the bolt holes ofthe bottom ongles ond then fine

tuned using the turnbuckles ot the top.

The top ond bottom ports ofthe pier hove fixed heights.

The length ofth€ middle portion (ongles bolted to chonnels)is

voried such thot the totol pi€r height is €quol to th€ required

height. Note thor this support pier con be dismontl€d such thot

therE ore 12 individuol pieces (including the 12 mm stinup bor

to connect to the penstock).

18 support piers ronging fmm 1.0 m to 2.6 m height hove

been fobdcoted bosed 0n this design. To ensup thot the support

pier would function well. one (2.5 m totol height) wos tested ot

the mqnufqctuEr's workshop (iIYSE) os shown in Photogrophs

10.7 ond 10.8. About 500 kg ofoxiol lood (moximum

compressive lood expected on the pier) wos opplied on the pier

There wos no observqble effect on the pier (d€formotion or

deflection of ongles) during the test of obout 2 hours. lt wos

even possible to roise the height ofthe pier by rctoting the

turnbuckles with the full test lood 0f500 ka.

As ofJu.ly 1998, oll 18 support piers hove be€n instolled otthe Jhorkot scheme. Th€ir p€rformonce is currently beingmonitored.

Photo 10.7 Lood test ofsteel support pier (side el€votion)

150

$I

10.6 PVC pipes

PVC pipes ore fr€quently us€d by Intermediote Technology forp€nstocks in its micro-hydro progromme in the northem Andes.one ofthe first schemes to benefit wos Choldn. This projecthoso copocity of25 kW ond o heod of96 metr€s. The p€nstockdiometer is 200 mm. Connection of pipe lengths wos throughglued spigot ond socketjoinrs. On commissioning, it wos foundthot pinhole leoks oppeored in thejoints. o prcblem thot wos0ddressed through the qpplicotion ofodditiorql resin. Thewhole length ofthe penstock wos buried for protection fromsunlight, onim0ls ond oth€r potentiol sources ofdomoge.

10.7 Anchor block design

'lhe stobility colculorions for onchor block design ore rime

consuming. A spr€odsheet progrom for the stobility onolyseshos b€en written byJohn Bywoter to spe€d up rhe pmcess.

To dqte there is no monuol to occompony the progrom,nor evid€nce thot it hos been verified. However, the progromwos used to veriry th€ guidelines given in S€ction 7.4.4. forsizing 0nchor blocks for smoll schemes.

Photo l0E toqd test ofsreelsuppon pief (front elevotion)

151

11. References

1. Adom Horvey et.cl. (1993), Micro-Hydro Design Manual, A 5. Design Manuals for lrrigation Projects in Nepal (1990),

guide to small-scale water power schemes, Intermediote Plonning ond Design Strengthening Project (PDSP), His

Technology Publicotions, ISBN 1 85339 103 4. Mojesry's Government of Nepol, Ministry of Woter Re-

2. Allen R. Inversin (19861, Micro-Hydropower Sourcebook, A sources, Deportment of lrrigotion. Unit€d Notions Develop-

Practical Guide to Design and Imflementation in Develcp- ment Progromme (NEP/85/013)/World Bonk.

ing Countries, NRECA Internotionol Foundotion, 1800 6. Salleri Chialsa Small Hydel Project (1983), Technicol Report,

Mossochusetts Avenue N. W., Woshington, DC 20036. DEH/SATA, rmco.

3. Helmut Louterjung/Gongolf Schmidt (1989), Planning of 7 . PN. Khonnq (lffil, Indian Practical Civil Engineer's

Intoke Structures, GATEIGTZ, Vieweg. Handbook, l5'h Edition, Engineer's Publishers, Post Box 725,

4. Itethodologies for estimoting hydrologic charscteistics of New Delhi - 110001.

ungouged locations in Nepol (1990), HMG ofNepol,

Ministry of Woter Resources, Woter ond Energy Commis-

sion Secretqriot, Deportment ofHydrology ond

Meteorology.

153

Appendix A - Flow estimation

A.1 WECslDeportment of Hydrology andMeteorology (DHMI method

41.1 PROCEDURE FOR ESTIMATING INSTANTANEOUS

FLOOD PEAK

i. From ovoilqble topogrophic mops, find out the cotch-

ment oreo (km'z)below 3000 m elevotion.

2. In the following equotion, input coefficients from Toble

A1.

Q = o (Areo below 3oo0m * 1) m3/s

where subscript o is either 2 veor or 100 veor return

period.

Toble A1 Prediction coefficients for instqntsneous flood

flows

RETURN PERIOD (YEARS) CONSTANT

COEFFICIENT (a)

POWER (B)

I

1

100

3. Flood peok dischorge, Q", for ony other return period con

A.I.2 PROCEDURE FOR ESTITUATING FLOW DUMTION

CURVE

1. From ovoiloble topogrophic mops, find out the cotch-

ment oreo below 5000 m elevotion.

2. Use the following equotions to colculote the flows. The

volues of monsoon wetness index cqn be reod from

Figure A3. Q* is the dischorge (m'/s) for the specified

probobility of exceedence.

hq* - -3.5346+0.9398.In (Areo below 5000 m*1) +0.3739.

In (Monsoon wetness index)

lnQro. = -3.4978+0.9814. In (Areo below 5000 m* 1) +0.2670.

In (Monsoon wetness index)

lnQ,* : -5.4357 *0.9824.In (Areo of bosin) *0.4408. In

(Monsoon wetness index)

lnQ* : -5.9543+1.0070. In (Areo of bosin) *0.3231.In

(Monsoon wetness index)

lnQ** : -6.4846*1.0004.In (Areo of bosin) *0.3015.In

(Monsoon wetness index)

lnQ** = -4.8508f 1.0375.In (Areo below 5000 m+1)

ln%rru = -5.4776*1.0776.1n (Areo below 5000 m+1)

.61 = -o.oe8e2 +0.0814e. @'xtcrnr

AI3 PROCEDURE FOR ESTIMATING IONG TERM

AVEMGE MONTHTY FTOWS

1. From ovqiloble topogrophic mops, find out the cotch-

ment oreo below 5000 m elevotion.

2. In the following equotion, input coeflicients from Toble

A3 ond the volues of monsoon wetness index from

Figure A3.

Q,.on,on,h: C. (Areo of bcsin)Ar. (Areo below 5000 m*1)Az.

. (Monsoon wetness index)t

where subscript month denotes one of the months from

jonuory to December. A power of 0 indicotes thot porticulor

porometer does not enter into the equotion for thot month.

7.8767

14.630

0.8783

0.7342

i':'fiI'll"ii'"n'.(Ln &2T s'c..qr)where S is the stondord normol voriqte for the chosen

return period, from Toble A2, ond

, / Q , * \r n r - I\ Q , t

-rnqF - 2.326

Toble A2 Volues of stondqrd normal voriate for vsrious

return periods

RETURN PERIOD (T) (Yrs) STANDARD NORMAL VARTATE (S)

2

5

10

z050

100

200

500

1000

5000

i0000

0

0.842

1.282

1.645

2.054

2.326

2.576

2.878

3.090

3.540

3.779

155

Table Al Ptediction coefficients for long t€rm qvercge monthly flows

MONTl{ CONSTANT

COEFFICIENT

POWER, AREA OF

BASIN (km1

Ar A2

POWER, AREA OF BASIN

BELOW 50fi) m +1 (km1

POWEROFMONSOON

WEINESS INDEX

4JonuoryFebruoryMorchAprilMoy

JuneJulyAugustSeptember0ctoberNovemberDecember

0.01423

0.01219

0.009988

0.007974

0.008434

0.006943

0.02123

0.02548

0.01677

0.009724

0.001760

0.001485

0

0

0

0

0

0.9968

0

0

0

0

0.%05

0.9s36

0.9777

0s7ffi

0.99r8

1.0435

1.0898

0

1.0093

0.9963

0.9894

0.9880

0

0

000000.26100.25230.26200.28780.25080.39100.3607

Note: units of flow ore m3/s

A.2 Medium lrrigation Projectmethod IMIPI

Procedure for estimoting meon monthly flows of o selected

cqtchment.

1. ln the low flow period from November to April, visit the

cqtchment in question ond moke one flow meosure-

ment. Ensure thot there hos been no heovy roinfoll

during the preceding few doys ond thot the woter level

is not fluctuoting ropidly.

2. Ascertoin ifthere ore significont upstreqm obstrqctions,

ottempt t0 quonriry them ond odd this omount t0 the

meosured flow

3. Estqblish in which hydrologicol region the cotchment

lies, from Figure A2. Divide the mecsured flow by the

non-dimensionol hydrogroph ordinote (Toble A4) for the

oppropriote month ond region. If the flow mecsurement

wos conducted ot the beginning or the end of the month,

it moy be necessory to interpolote between the two

relevqnt ordinotes from Toble A4. The result represents

the meon April flow to be expected in thot cotchment.

Tqke the April flow colculoted in step 3 ond multiply it

by eoch non-dimensionol ordinote from Toble 44. The

result is the hydrogrcph of meon monthly flows.

It is usefirl to compore the hydrogroph colculoted in step

4 with the oppropriote regionol hydrogroph depicted

omong Figures A4 to A10. To do this, divide eoch

ordinqte ofthe cotchment hydrogroph by the cotchment

oreo. Normolly, the colculoted hydrogroph will corre-

spond to the regionol hydrogroph within the limits

indicqted. The limits mcy be used os c rough guide to

the reliobility of flow in the cotchment. If the

hydrogroph lies outside the limits then it is not typicol,

due perhops to unusuol lond use or o typicol detoil of

topogrophy ond geology.

156

Tqble A4 Non.dimensioncl regionol hydrogrophs

MONTH RECION

JonuoryFebruory

Morch

April

Moy

June

JulyAugust

September

0ctober

November

December

2.40

1.80

1.30

1.00

z.ov

6.00

14.50

25.00

16.50

8.00

4.10

3.10

2.24

L . ( V

1.33

1.001 ) 1

7.27

18.18

27.27

20.91

9.09

3.%

3.03

2.77

1.88

1.38

1.00

1.88

3.13

13.54

25.00

20.83

70.42

5.00

3.75

2.59

1.88

1.38

1.00

2.19

3.75

6.89

27.27

20.97

6.89

5.00

3.M

2.42

t.82

1.36

1.00

0.91

2.73

77.27

13.94

10.00

6.52

4.55

3.33

2.03r.627.271.002.576.0824.3233.7827.035.083.382.57

3.30

2.20

1.40

1.00

3.50

6.00

14.00

3s.0024.N

t2.N

7.50

5.00

ttI

tfi

A3 Design exomple

Cotchment nome

Cotchment locotion

Hydrologicol region

Bqsin qreo

Areq below 5000 m

Areo below 3000 m

Monsoon wetness index

Month ofgouging

Flow meosured

Q,o = e (nroo+z.oN W)=362 mr/s

bl FIow dumtion anrveSolu Kholq

Solukhumbu

3

330 km'z

308.5 km'z

97.7 lglrr'z

1500

April

2.8 mr/s

052040608095100

PROBABILITY oF EXCEEDENCE (%) DISCMRGE (m3/s)

98.4559.3332.629.474.583.002.031.78

exomple:

lnQ*: -3.4978 + 0.98141n(308.5+1) + 0.26701n1500 =

4.083+Q=gr 'oer=59.33lnQo* = - 5.9543 + 1.00701n(330) + 0.3231 1n1500 = 2.248 ->

Qn= e22a - 9'47

ln%r*= -5.4716 * 1.0776 ln(308.5+1) :0.708+Qrr= eo",= 2.03

Q,* = [-0.09892+ 0.08149x r/1:ot.s+t112 = l.z8

Figure A1 shows the cqtchment mqp.

A3.l WECSIDHMPROCEDURE

alFTod flows

RETURN PEUOD (Yrs) INSTANTANEOUS FTOOD

DTSCHARGE (mr/s)

2

5

10

20

50

100

106

175

228

283

362

426

exomple:

q= L8767.(97.7+l;o.rar : 106 m3/s

Q,* = 14.63'(9?.7 * 7)oB2 : 426

t t l

cl Long term sverage discharges

MONTH LONG TERM AVEMGE DISCMRGE (m3/s)

JonuoryFebruory

Morch

April

Moy

Junejuly

August

September

October

November

December

Annuol

3.88

3.30

3.00

3 .17

4.37

I ) . t /

43.86

52.45.tu.v I

77.59

8.06

5.24

16.68

exomple:

Qn,"on j,ry = 0.02123.(330)0.(308. 5 + 1)' 0nq1{ I 500)0 ,5,r = 43.86 m3/s

4.3.2 MIP PROCEDURE

Estimcting the hydrogroph of meon monthly flows

tt!

I

I

II

I

NON.DIMENSIONAI

HYDROCRAPH

MEASURED FIOW

(m'/s)

PREDICTED APRIL FLOW

(m'/s)PREDICTED HYDROGMPH

(m'is)

JonucryFebruory

Morch

April

Moy

June

JulvAugust

September

October

November

December

2.71

1.88

1.38

1.00

1.88

3 .13

13.54

25.00

20.83

10.42

5.00

3.75

2.71 x23 : 7.59

5.26

3.86

2.80

5.26.

8.76

37.97

70.00

58.32

29.18

14.00

10.50

i,2.8 2.8/1.00 = 2.8

A33 RESUTTS

1. The dry seqson m€qn monthly flows colculoted by the

WECS ond MIP methods ore presented in the toble ond

figure below. WECS shows c slightly higher figure thon

MIP for the month of April. By definition MIP shows the

meosured flow. Experience shows thot results obtoined

by WECS ond MIP methods vory for different cqtchments

ond it moy not be olwoys true thot MIP yields lower

vqlue thon WECS. It is worth mentioning thot Solleri

Chialso mini-hydro scheme uses o design flow of 2.5 m3is(Ref.6).

iiL

158

WECS MEASURED FLOW

October

November

December

JonuoryFebruory

MorchAnril

Mqy

I I . )v

8.06

5.24

3.88

3.30

3.00

3.17

1 . ) I

29.18

14.00

10.50

7.59

5.26

3.86

2.80

5.26

2.80

HYDROGRAPH OFMEAN MONTHLY FLOWS

2. The design flow of 2.5 mr/s is exceeded 857o of the time,

occording t0 the WECS flow durotion curve.

FLOW DURAIION CURVE

Flow (m3/s

35 f -

,|\-*f\2 0 -

"f-I1 0 r -

sLs l -

0d

[ , w a - w ]

159

|{I,:

FiguTe A1 CATCHMEI,TT OF SOLU KHOLA ABOVE Tl{E SALLERI CHTALSA INTAKE

160

B.E6 >: r r ih 7

ts

a

Key:

1. Mountoin cotchments

2. Hills to north of Mohobhorots

3. Pokhoro, Nuwokot, Kothmondu, Sun Koshi tributories

4. Lower Tomur Volley

5. River droining Mohobhqrots

6. KqnkoiMoibosin

7. Rivers droining from Churio ronge to th€ Teroi

BItt

II

II

iII

IE\III

J gr { io - El r t iZ o "

o

5

IIIIII

IiIItt , - ._ - . . -_ -_- - - -

I

'i --l

Figure 43 Monsoon wetness index isolines

(Source Ref. 4)

,6

5

i ,I

Il .1, ,I

t )t \t )i : 'l J

l l. l i{ ;t ;; i. a

i lu a. l ;

l ri . l

_9

- i

H }{ *Z A ?

9 3 8

t

s tT !? !t - E

r62

AprMarFebJanDecNov0ctsepAugJulJUnMay

1000

N

=YDJo(l'(r= 100o

lJ-

->co=

10

MOUNTAIN

Mean

Flow

Mean

\ [ f

A

\o

Figure A4 Meon Monthly Hydrogroph - Regi0n l

(Source Ref.5)

TAIN CATCHMENTS

alHills to North otOlBivers

Inner I

r 000

q

=YaJ(D

(qE { ^ ^= t u votr

c,o=

10

th of Siv

I

I

\

Max

I

I

I

I

I

I

I

I

I

J-

) -

\ \)

l \

MrMrFI

-\J

an1SO0n

ivl

Mean ,I

Min

)

l

) :l \ f

a -

May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr

Figure A5 Meon Monthly Hydrogroph - Regi0n 2

(Source Ref.5)

164

1000

N

=VaJ<1,(g

CE= 100Ilt

=co=

r0

May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Aor

80%

Figure 46 Meon Month.iy Hydr€gfoph - Region 3

(Source Ref.5)

+- -

165

1 000

N

=YaJ(l,

(q(r=ou-=co=

100

10

May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr

(

Figur€ A7 Meon Monthly Hydrogroph - Region 4

(Source Ref.5)

166

1 000

N

=YU)Jo(g

CE= 100o

lJ-

=co=

10

May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Aor

alRivers

20% /

Mean

Figure A8 Meon Monthly Hydrogroph - Region 5

(Source Ref. 5)

{ - -

167

KANKAIIMAIBA$IN

1 000

N

=:<aJ(D

oE=otrtEo=

100

10

May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr

- r \/ l \

\\

Mean

Flow

I 1l 1

I t

I

II

I

\ 1l 1l \

\\\ \20To

Mean

Figure A9 Meon Monthly Hydrogroph - Region 6

(Source Ref.5)

,t

L

_tbd

=--4--

)!

E

l/:\

Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr

TAIN

FarWestEast

A

i

lI

,-J'

May Jun

,/1

III

I

100

1 0 I

N

=Y(nJ<t,(q

E=ot L

-cco=

I - i.l 'l

- i . Ji /v

a,'l

I

I4/l ,t,'

TCHMENTS

Mean

Flow

\ r l

A

\o

Figur€ A10 Mecn Monthly Hydrogroph Region 7

(Source Ref.5)

i

169

Appendix B - Stqndqrd pipe sizesmsnufqcturers ond

suppliers

List of Tables los of March 19991

Nepothene HDPE pipe price l ist ond weight chort

Ponchokonyo HDPE pipes

Ponchokonyo PVC pipes

Hll 'CO/Hulos steel woter PiPesHll)COiHulos structurol steel pipes

B1

B3

B4

B5

B6

t71

-I

F A C T O R Y ; .

Ba la j u l ndus t r i a l D i5 t r i c t :

Ba la j u , Ka thn raodu , Nepa l .

Phone ; 350091

I

t

!

;I

IP'r. l LtJ.NtpdDEZruo

zuTPAt |JOLYITIIINE tI I)TASTII IruOtjSTftITSM a n u f a c t u r e o f H D P E P i p e s

TIF.AD OFFICE .

P o s t B o x N o . l 0 l 5

I ' r ipureswor . Kathmandu

P t r o n e : 2 6 1 > 0 1 , 2 6 1 1 4 9F a x N o . 0 0 9 7 ? - l - 2 6 1 8 2 8Te lax n 'o . 2365 KHANAL NP

Nepothene l- I igh Density Polyetbene Pipe Manufactured as per NS 40/010Price for H. D. P. E Pipes Manulactured as per NS 40/040

PR. ICE L IST

Outs ideDiamcter

( m m )

l 5 m m

S E R I E S

Working Prc2.5 Kgf/cm

W"ll Th',- Ikness I

M i n . M a x . I

I I

ssure. s q .

Price/Mt r .

Rs:. Ps.

SERIES I I t

Working Pressure4 Kgf.;cnr. sq.

_.-._--.-_.--.-Wall Thic- | Pricc

kness I /Mtr,Min . Max. I Rs . Ps .

SERIES IV

Working Pressure6 Kgficn. sq.

Wal l Th ic - | Pr icckoess | /Mt r .

M i n . M a x . I R s . P s .l -

S E R I E R

S'orking Prtl0 Kgf/cm

--.-Wal l Th ic - I

kness IM i n . M a x . I

- t .

2.0

v

rssu rc. s q .

Prl. ./Mt r .

Rs . Ps .

l t . l J

l0 inm i " 2 .3 2 .8 l o 2 l

2 5 m m i 2 . 8 3 . i 2 4 . 4 4

i 2 m m l " 2 . 3 2 . 8 27.35 3 .6 4 .3 40.4 I'

{c.;; l ,J' 2 .0 2 .4 30.37 2.9 3.4 42.35 4 . 5 5 . 2 6 7 . t 9

5Ornni l ) " 2 9 45.74 3 .6 4 .2 6s.5.8 5 . 6 6 . 4 96.32

b J M M Z

'2.0 2 .4 4 8 .76 3 0 3 . 5 70.7 ) 4 . 5 5 . 2 r02.85 7 l 8 . 1 I 5 3.55

/ f m m l (1 1 t Q 67.40 3 . 6 4 , 1 I 0 2 l 7 { 1 6 . 1 144. t I 8 . 4 o s 2r5.62

SOmm 3" l R 1 ' t 96.6S 4 . 4 ( ) 147.62 6.4 ' t .3 207.16 l 0 . l I t . 4 3 r 0 .71

l lOrnm 4" 3 .4 4 0 I 4 1 . 3 9 5 . 0 5 .8 206 06 7 . 8 8 8 30?-95 tz.41 3 . 9 459.9

l25rnrn 4|" 3 . 9 4 . 5 t s5I 3 6 . 0 6 . 8 276.97 E.9 l0 .E 398.45 l 4 . l 1 5 . 7 600.40

l4Onrnt 5" 4 . J 5 . 0 2.29.)4 6 8 351 .02 9.9 l l s02. I 5 15. E t7.6 7t5.29

l60mm 6" 4 .9 5 .6 296.8 r 7 8 8 . 8 4 5 6.53 1 l . l 1 2 . 7 64?.96 r8,020.0 917.56

J80mnr 7" 5 .6 6 .4 Jdu.y I 8.7 9 8 57 6.20 1 2 . El 4 . l 822.80 20.J 22,6 I 240.98

200mm 8" 6 .2 7 .1 q o d . 6 6 9 . 7 1 0 . 9 7t2.69 i r 1 I 5 . e l 0 l 22 5 25.0 I 527.02

225mm 9" 6 .9 7 .8 1 0 . 9 1 2 . 2 900.85 r 5.9 I t . t r 27 5.32 25.4 2S.2 937.69

250mm 10" 1 ; l 3 .8' t7 '1 .45 t ' ) I I 1 . 6 1 l 1 1 . 6 3 t7.'l 1 9 . 7 r 5 i7.96 28 .2 3 r . 3 2390.60

280mm l l 8 . 6 9 . 1 903.99 l l . 5 1 , 5 . 1 1386.06 19.8 22.0 l 975 .57 3 1 . 5 3 4 . 5 2989.6 7

3 l 5 n r m 1 2 " o ? r0.8 I I 39 .46 t 5 . 2 1 7 . 0 1 7 5 5 . 4 7 22.t 24.8 2501,97 36.4 J9.2. 3770.36

l 55mm t 4 t :

r00mm l6l;

10 .9 !2 .2--rL3

ll.s

I 446.80

l84rJ4

I 7 . t 1 9 . I

1 9 J ' l - s -

?224.22-?s24

J0

25.1 21 .9

283 3t .4

3 I 75.40

4010 39

39.9 44 . I

45 .0 40 .7

4'195.84

609 r .62

Ternrs & Cond_t t ig" t j -

l . l0% Tax rv i l l bc charge extra.

2. Thc pr ice are ex-factory pr ice excluding salcs tax & contract tax '

3 . Sub jec t t o Usua l ' Fo rce Ma jo r cond i t i on '

+. pr ice arc Subject to changc qi th out not icc, 25ld aclvrncc should bc peid at lhe t inte of order ing of goods and

balaoce should be paid before del ivery.

* Thase sizas arc not heina manttfacjttrad at nreqcnt

173

SERIES SERIES SERIES SERIESOutsideDiameter

Working Preszure2.5 Kdlcm sq.

Working Pressure4 Kef/cm so.

Working Pressure6 Ksf,/cm sq.

Working Preszuro10 Kef/cm sq.

rtm Wall ThicknessMin. Max. Weieht

Wall ThicknessMin. Max. Weieht

Wall ThicknessMin. Max. Weieht

Wall ThicknessMin. m&x. Weieht

16 rnm 2.0 2 .4 0.09220 mm 2.8 0 .13425 mm 7 .8 J . _ 1 0.20232 nnn 2 .3 2 .8 0.226 3 .6 4 .3 0 .33440 rnm 2.0 2 .4 0 .251 2 .9 3 .4 0 .350 4 .5 5 .2 0 .51450 rnm 2.4 2 .9 0.378 3 .6 4 .2 0 .542 5 .6 6 .4 0.79663 mm 2.0 2 .4 0.403 3 .0 3 .5 0.585 4.5 5 .2 0.850 7 .1 8 .1 r .26975 nun 2.3 2 .8 0 .557 3 .6 4 .3 0.846 5 .3 6 .1 i . t91 8 .4 9 .5 1.78290 mm 2.8 J . J 0.799 4.4 5 .2 I J 1 n 6.4 7.3 r .717 10.1 I 1 .4 2.568

110 mm 3.4 4.0 l . 185 5 .0 5 .8 1.703 1.8 8 .8 2.545 12.4 13 .9 3.801125 mm 3.9 A < 1.530 6.0 6 .8 2.289 8.9 10 .8 3.293 L4 I 15 .7 4.962140 nun 4 .3 5 .0 1 .897 6 .8 7.7 2.901 9.9 I t . r 4,1 50 I5.8 L ' t .6 6.209160 nrn 4 .9 5 .6 2.453 7 .8 8 .8 3.773 11 .3 12 .7 5 .355 18 .0 20 .0 8.079I80 mm 5.6 6 .4 3 . I 4 8 8 .7 9 .8 4.762 12 .8 14 .3 6.800 20.3 72.6 10.256200 mm 6.2 ' I ,T 3 .87 5 9 .7 10 .9 5.890 r4 .2 15.9 8 .391 22.5 25.0 12.620225 mm 6.9 7.8 4.822 10.9 12.2 7.445 l s .9 L7 .7 I 0 .544 25.4 28.2 r6 .014250 mm 7.7 8 .8 6.012 12.L 13 .6 9 .187 t7 .7 19 .7 13 .04 i 28 .2 31 .3 19.757

PANCHAKANYA PI-ASTIC IND. [P] LTD.I Manufaoturer of HDPE Pipes & Accessories ]

Pipes Manufacturored as per NS 40/040

IIEAD OFFICE: J3/12 Krishna Gallt, Lalitpu, P.O. Box. No. 2743I(othmandu, Nepal.Phone 52635'7,52511L Fax No. Slj.529.E-mail : sted@nchknya-mos.c om.np

FACTORY: I-nmini Zane, Kotihawq Bhairahawa, NepalPhone (071) 60368. I 'ax: 605?d

I

174

I

PANCr{AKANYA ROTOMOULDS [PJ LTD.[ \4anufactr-u'er of uPVC Pipes & Aooessories ]

Pipes Manufactruered as per NS 206/046

IflAD OITICE: J3l12l(rishna Galli, Lalitpur, P,O. Box. No. 2743l(athmandu, N"pal.Phone 526351,52571L Fax No. 52.6529.E-mail: steel@pnchknya.rnos.com.np

FACTORY: I-uminl Zone, Kotihawq Bhatrahawa, Nepal.Phone (0?1) 60368, Far: 6057{.

Class - I Class - 2 Class - 3 Class - 4OuGideDiameter

Working Pressure2.5 Keflcm so.

Working Pressure4 Kef/cm sq.

Worlcing Pressure6 Kpflsm sq.

Working Pressurei0 Kef/cm sq.

ln rnrn Wall Thickness\,Iirt. Max. Weielil

Wall ThicknessMin. Max. Weieht

Wall ThicknessMin. Max. Weieht

Wall ThicknessMin. max. Weielrt

20 rnm 1.1 1 .5 0.11 i25 mm t.4 1.8 0 .1 7032 mm 1 .8 2 .2 0.27040 rnm r .4 L8 0.28 i 1 ) , ) ' 1 0.41650 nu-n L - l 2.1 0 .418 28 J . J 0.64763 rnm 1.5 I .9 0.474 2.2 2 .7 0.668 3 .5 4 . t I .01075 rnm 1.8 2 .2 0.660 2.6 3. r 0.931 4 .2 4 .9 1.44390 rtun t a

L J t .7 0 .606 2..r 2.60.944 3 . i 3 .7 r .334 5.0 5 .7 2.&18110 mm 1.6 2 .0 0.894 2.5 3 .0 1 .369 3.7 4 .3 1 .938 6 .1 7 .0 3.077140 rnm 2.0 2.4 1 .413 3.2 3 .8 2.2?3 4.8 5 .5 3 .1 78 7.7 8 .7 4.955160 mm 2.3 2 .8 l.884 3.7 4 .3 7.94'l 5.4 6:2 4 .139 8 .8 9 .9 6.456180 mm 2,6 3 . r t . 5 5 3 4.2 4 .9 3.474 6. t 7 .0 4 .961 9.9 t 1 . r 7.830200 mm 2.9 3 .4 2.945 4 .6 5.3 4.563 6 .8 7 .7 6.464 11.0 t2 .3 1 0 .1 85

175

CtuGAs Steel Industries P. Ltd.G.P0.Box:4129, Kantipath, damal,Kathmardu, Nepal. Tel:977.1-253047, 228389,24U52,252475,252850, Far 9I/-1.22061 2Fac1ory: Simra, Bara, Tel: 977-53-20075, 20078,20170, Fax 977-53-20160

GATVANISED AND BLACKSl'El jL PIPES I 'OR ORDINARYUSES TN VATER, CAS AtR&STEAM LINtsS

TYPE NOTVIINALBORE

WALLTHICKNESS

APPOXOD

WEIGFT OFBLACK PIPEPLAIN EI{D

WEIGET OFGALVAMSI,D PTPE

THREADED &s(}rxx'.Tr'.D

CLASS M M TNCB M M MM KG/M MTR/T{.' KGIM MTR/II{.7

L IGHT' A '

1 5 1n 2.00 21.30 0.9? t050 1 .01 990

20 3t4 2.35 z o . w 1 _ 4 1 709 1 .48 o / D

z o J 33.70 2 .01 498 ? . 1 1 a74

32 l v , 2.65 4?.40 2.58 388 2.72 355

40 1 t a 48.30 3.25 308 3 . , 1 1 2812 9 0 60 30 4 1 1 213 4 3 3 222

65 2 t a 325 76 20 5 8 0 172 6 1 1 5 5

80 3 3.2s 88.90 6 . 8 1 117 7 .21 133100 4 3.65 1 1 4 . 3 0 9.89 1 0 1 10.49 9 1

I } lEDIUM' B '

1 5 21 .30 t . ?? E20 1 .28 7813t4 z o f , 26.90 t . 58 533 1 .65 o@

t < 3.25 33.70 2.41 4 1 0 2 5 4 394

32 - t 2 l 12 10 3 t 3 1 8 3.27 29240 1 , 4 3.25 48.30 ? A I 277 3.77 25150 3.65 60.30 5 .10 196 532 1 7 S

65 3.65 76.?O 6.51 154 6.82 110

80 3 rl 05 88.90 8.47 118 8.87 107100 4.50 1 14.30 12 .10 E3 12.69 75

4.85 139.70 16.20 62 16.95 55r50 6 I 4 8 s 16s 10 | 1s.20 | s2 l 20.00

IIEAVY'c '

20 3t4 J Z J 26.90 't.90 1 .97 508

25 4.05 33.70 2 .97 336 3 .07 3263Z 4.05 42.40 3.84 2& 3.97 23940 1 , 4 4.05 r18.30 .1.43 226 .1.59 201

)U 4.50 60.30 6 .17 t6? 6.39 1 4 E

65 2 ' a 4.50 76.20 7.90 127 8 .21 1 1 5

80 3 /t 85 88.90 10 .1 0 99 10.52 90

r00 1 5..10 1 1 430 14. /10 69 15 aa 63

125 5 5 4 0 139 70 17.80 56 t8 s2 5 1rso 5 r o 165 10 1 ) O A7 2 ) ? 2 12

200 mm (;Al,v^}'|lsl.:t) ^}{I) IILA(;K ST[tiL PIPTS (Detalled speclflc.tlon on requesl)

200 8 5.20 219 .10 27.71 36 29.20 3?2rn 8 5 0 0 2 1 9 1 0 31 82 31 aa2r] 28

Notee:1) Tenslle Strength: Tenslle slrength for water lubes when tested frorn etrlps, cut out from selected

tubes shall be more than 320 rVmm'.2) Tolerances: a) Thickness: Ught lubes: (+) not limited, C) 8% max.

Medium & Heavy prpes: (+) not limited, (-) 10% max.b) Weight: Single tubes: (+) 10%, G) 8%.c) Lengfh: Unless othenrlse specified 4 to 7 meters.

3) Pipes of hlgher tensile strengh and bigger diameter can also be manufac;tured as per requesl.

JorNr vFNruRE BFTwEEN---@mCeftr-

I

I

I

I

r { o

HiqGAS Steel Industries P, Ltd.G P O Eox l 1 29, Kantipath, Jamal.Ka ihmandu N epal Tel. 977.1 .253047. 228389, 243452, 25247: 2528n. F ax 9/7 '1'220612

F;: lory Srmra. Bara, Telr 977.53.20075, 20078, ?011A. F ax. 977'53'201 60

,--------..r f n nrr

/ t i l l t f l l t u t n Nu u " . u r r L t L _ ). - a d F B r € t i H F -

reSTRUCTURALSTEEL PIPES

f-nl fucturat steel pipes are manufactured in the same| \ | process as water pipes. However, the steel used is ofI U lhigher tensile/yield shength. We normally use highI grade steel with tensile sbengh of 42/55 kgs/cm as per

I

I

t

I

customers requirements. We normally use he steel as perJIS: G-3132, SPHT 2,3 or 4, or lS: 11513/1985 for he pur-poses. Structural pipes are basically used for manufactur-ing ples and welded sbuctures. Use of high grade stuc-fural steel reduces steel consumpton drastically Pipes ofstructuralgrade normally conform to lS: 1161/1979, JIS: G-3444/1993, BS: 1387/1985.

I I IPCO ST[TUCTIJFIAL' I - f ] ETESN q n i n

--;-l 5

al Bore

lu:rt--| /'),

9l*11"th q

2 l l 0

C l a s s

- t -T h i c k n e s a

g-m

2.00

vEr9nrB l a c k p i p e s

Area olCr. scllon

Mment o flnertl i

S e c t l o nM o d u l u s Gyra i ion

. x q m

0 9 6- AEl--

I a tc m .

0 5 7c m .

0 . 5 4C n r

0 6 9M 2 6 5 | 2 2 55 0.69 0.65 0 6'lil ) 5 l 4 i 84 0 . 1 1 0 . 7 1 0 .65

20 76 90 t L J l 4 l 8 l l 8 1 .02 0 8 7N,l 2 6 5 | 5 8 02 r 5 0 0 8 6H \ . 2 5 1 . 9 0 4 l | 7 2 1 2 8 0 8,1

t 7 0 2 6 5 2 0.1 5 8 t 4 1 8 6 l 0M f . 2 5 46 r 6 5 7 l t 0 8H 4 0 5 2.99 2 . 5 1 I 0 6

) / lv4 42.40 L 2.65 2 . 6 1 J I 6 5 7 I l 0 I l l

fvl 1 2 5 l 1 5 00 7 7 1 3 .64 l 9n ;1.05 1 . 8 6 4 8 8 9 0 7 4 . l 8 1 3 6

40 l 1 /2 4 8 l 0 L 2 9 0 J . ) I 1 . t 4 1 0 7 0 4 . 4 3 l 6 llvl 3 . 2 5 l 6 l 4 6 0 I t . 7 l 4 8 6 I 6 0

H 4.05 4 .43 5 6 1 l l 9 0 5 . 7 55 0 ) 60 l0 I I 2 9 0 4 . t 4 5 2 3 2 1 5 9 7 t 6 2 0 3

L2 j 2 5 4 5 7 5 8 2 23 7 . 8 9 2 0 2M 3 . 6 5 5 . l 0 6 5 0 2 6 t 7 8 .68 2 0 1H 4.50 6 . t 7 7 8 9 10 90 l 0 2 0 r 9 8

65 7 6 t 0 J .25 5 . E 4 7 .14 49 4.1 I 1 . 0 0 2 5 8M 1 6 5 6 5 1 E l I 54 65 t4.40 7 5 6H 4 5 0 7 9 2 l 0 l 0 6 5 t 2 7 t 0 2 5 4

80 88 90 L t 2 5 6 E O 8 7 4 8 0 l l 1 8 0 7 t 0 lM 4 0 5 8 4 8 t 0 8 0 9 7 ) 8 2 t .91 t 0 0H 4 8 5 1 0 . 0 1 l ? 8 0 I l l 4 6 25.53 2 9 8

t 00 l 4 . t 0 J . O ) 70 I Y q J ! 1 4 . 0 1 l 9 l2 . l 0 5 5 0 tJ4. t 4 1 .00 1 8 9

H 5 4 0 t 4 5 0 50 214 54 4E.O4 J E 6

t25 I 19 .70 L 4 .50 14.90 t 9 . 1 0 437.20 62.59 4 . 7 8M 4 8 5 16.20 20.50 467.64 66.95 4 . 7 7H 5 4 0 I ?.90 22.80 5 14 .49 7J .66 4 . 7 5

1 5 0 6 t 6 5 l 0 I 4.50 I 7 .80 22.70 7325 7 88.74 5 6 8M 4.85 t9. tu 14.40 1E4.49 95.0 5 .67H 5.40 2t.20 l 0 864.69 o1.7 ) . b )

175 7 t93.70 L 4 .85 22.60 28.70 284 00 31.00 6.68M 5.40 z) .w 90 416 .96 46 30 6.66H )_vu 21 .J0 34.80 516. I I 59.00 6.(A

200 E I t v . l v L 4 .U ) 2). tu 32.60 874.06 7 l . o 7 / . ) uM 5.60 t9.4U J I.OV z t4L.) , . 9) .4y / . ) )H 5 9 0 l t 00 2247 00 205. I t . >4

a n c e s :.) Thlctn.s: (+) nct l imled, C) 10% max b) lirrshr: (f) 1096, C) 8%

Q.8 mm., owr €.3 mm, (+) 1%c) outCda oimctcr : Up(o €.3 mm (+)0.4 trun.,

177

list of drowings

Appendix C Gqlkot drawings

Scheme lcyout

Itonsrnission l ine, route olignment

Heodworks ond heodroce generol orrongeluent, sheet 1 of2Heodworl<s ond heodroce generol orrongetnent, sheet 2 of2Fleodworks ond heodroce, intoke

Heo d'"vorks o nd heod roce, g rcrvel trop/overfl o',vHecdworks ond hccdroce, crossing nos. 1 ond 2Heodworks ond heodroce, crossing nos. 3 ond 4Penstock oreo, generol 0rrongement

Penstock oreo, settl ing bosinlforeboy

Penstock oreo, onchor block & support detoilsPenstock oreo, mochine lbundotion 0nd t0ilroce detoils

u r ( r v Y r r l q r

Drowing 2f i r r r r r r i n n I

Drowing 4

Drowing 5

Drowing 6

Drowing 7

Drowing 8

Drolvinq 9

Drowing 10

Drowlng l1

Drowing 12

179

I I jI Fi !

l ri t Il J l

i-lt lI ' I 'l l l !r ! [

l :!,iirf : : i i. l t "3 t r - . !

II

i(x

o

Drowing i Scheme Loyout

z4,---t-

3r i

I i3 g

:t,i l t

8 l i- l J

II

/III

!t

Ie

\IIt'+\ . \

\ \

tt

t!t

\ "1 \\ \\ \\ \

\ \\ \\ r\ \\\

tt

!t.rt

i iii

II

IIt r \ -

/\ \ l

\ \ /\ \

\ \\

I

II,

i . .tlrlfr,!ts

I

:o

a)

Et

o!

d

181

Drowing 2 Tronsmission line, route olignment

! tI! li!

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Index

AAir-releose volve, 55

Altimeter,65

Anchor blocks 2, 1 1 1

checklist, 127a n n c t r r l a f i n n 1 1 1

design, 116-127

exomple, 121

Iocot ion,1 l1 '

sizing,727

Anchor rod, 29

BBench cut,65

Bio-engineering works, 144

Bottom intqke

description, 31

design, 32

exomple, 34

troshrocks for, 32

Bursting disc,93, 147

Breok pressure tonk, 55

cConols

copocity, 46

concrete,40

construction, 67-69

crossrngs, 53

design,46-51

eorth, 39

economics,46

exomple, 50

excovotion,68

ferrocement,42

heodloss,46

lining,43, M,45,68

mosonry 46

oil drum,40

roughness,48

sediment tronsport,4T

seepoge,46

semi-circulor concrete, 41

setting out,67

side slopes, 46

stobiliry,49

stone mosonry in mud mortor,39

stone mosonry in cement,40

timber,40

types,39

velocity,46,48

Check doms, 147

Coondo intoke, 149

Components of micro-hydro, 2

Crossings, 2, 55

Cross droinoge, 13

Culvert, 33

Curing, 69

DDe-beoder, 150

Design flow

procedure to estoblish 11

Diversion weirs (see weirs)

Diversion works

checklist, 36

Droft tube, 3

Dry stone woll, 145

EEfficiency in power equotion, 3

Excovotion,68, 143

Exponsion joints, 109

Escopes, 2

exomple, 111

in HDPE pipes, 110

in mild steel pipes, 110

in in PVC pipes, 110

siz ing,110

Spil lweirs,2

Spil lweirs,2

Overflow 2

tt

*193

FFoll velocity of sediment, 74

Flood risk, 12

Flow

design colculotions, 51

estimotion, 10-11, Appendix A

FIow Durotion Curve, 1 1

Flume

ferrocement,42

Flushing

frequency, 81

verticql pipe method, 77

Foreboy 2,71,84

checklist, 88

design,84

pipe level, 84

size, 84

Forces

frictionol, 120

on onchor blocks, 120-124

Freeboord,50

Friction, 39,61-66

GGqbions,35

Gqbion weir, 126

Gobion retoining woll, 144

check dqms, 147

Cotes

penstock,86

sluice,79

Generotor efficiency, 3

Geology,8

Geotechnicol considerotions, 8

Grovel trop, 2,71,72

checklist,88

exomple,80

Ground woter, 8

HHeqd

gross, 3

net, 3

HDPE pipes

joining, 59

Heodroce (see conols ond pipes) 2,39-68

Heqdworks,2

Hydroulic rodius,47

Hydrology, 10, Appendix A

Hydropower, 1

IIntokes, 2

bottom (see bottom intoke)

Coandq (see Coondo intoke)

generol principles for selecting, 1Z

rypes, 21

side (see side intoke)

exomple,20

selection criterio, 21

Inverted siphons, 55-56

Irrigotion, 13, 39, 40, 42, 4

JJoints, rock,9

LLond ownership ond use, 13

Levels,3, 12,84

Limestones, 10

Lining

formers method,45

HDPE,43

soil cement,44

Locotion oIcomponents, 6

MMochine foundqtion

design, 135

exomple, 136

Monning's equotion,46

Mosonry, 10,26,40,42,48,49,50, 53, 56, 87, 116, 119, 135Micro-hydro, 1

comporison with hydropowe4 1

definition, 1

Moody chort, 62

oOrifice

design,23

exomple,24

I

I

194

PPeohng reservoir, 87

Penstocks (olso see pipes)

bosic loyout, 15

checklist, 113

description, 2

exomples,99-103

exposed versus buried, 108i n c t n l l n t i n n 1 1 ?

mointenonce, 113

moteriols,94

overview 91

point ing,111

selection of olignment, 9l-93

Pipes (olso see penstock)

buriol detoils,57,60

bends 58,61,63,92

design criterio, 56

design procedure, 61-66

diometer, 61,95

generol, 56

HDPE ond PVC, 58-59, 155jointing, 59,95, 106

lengths, 107

roughness, 62

stqndqrd size, Appendix B

submergence heod, 61

turbulence losses, 63

wqll thickness,99

Plonning,5, 13

Ploster,48,69,88, 135

Power,3

Power equotion, 3

Powerhouse

checklist, 141

definition,3

locqtion, 134

overview, 133

size, 134

Site investigotion, 6

Pressure

hydrostotic, 120-122

RReservoir pechng, 87

Retoining structures, 144

River troining works, 35

Rock types, 10

Roughness coefficient

conols,4748

pipes,62

Run-of-river schemes, 1

sScfety

ogoinst overturning, 124on beoring, 124

Sediment problem, 47, 71

Seepoge, 12,46

design colculotion, 12

Settl ing bosins,71,73

checklist,88

components, 75

design criteriq, 73

description, 2

exomple,80

flushing orrongements, 77-79

flushing copocity, T3

ideol,73

inlet zone,76

outlet zone, 77

settling copocity, 73

settling design,75

settling zone,77

storoge copocify, 73

storoge design,75

Shield's formulo,4T

side intqke,22

Sinkholes, 10

Site selection,5, 15

Slope stobility, 8, 143-747

Spillwoys, 79,86

definition, 2

exomple,53

locotion,52

Stobility of schemes, 16

Storoge schemes, 1

Support piers, 115

checklist, 131

construction, 1 1 9

description,2

design, 120

flexible steel, 152

locotion,117

Submergence heqd, 61, 84

Surge colculotion, 97-100

195

TTqilroce

checklist, 141

definition, 3, 140

design ofchonnel, 140

design ofpipe, 140

Tension crocks,9

krrocing, 145

Thermol exponsion, 115

Tlqnsmission l ines, 6, 15

Troshrocks, 22,32,57 , 85

wWoter ovoilobility, 10

Woter rights, 13

Woter retqining structures, 88

Weokness zones, 8

Werrs

diversion, 2, 25

gobion, 26, 28

heod over, 31

permonent, 29

temporory, 25

Wetted perimeter,4T

vVent plpe,61

Volves, 57,61

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t196

P R A C T I C A L A N S W E R S

T O P O V E R T Y\ /

BPC Hydroconsu l t