reservoir sizing

8/13/2019 Reservoir Sizing

1/78

ENGlNEEXING FIELD MANUAL

CHAPTER11. PONDSAND RESERVOIRSCompiled by: George M. Renfro, Agricultural Engineer, SCS, Fort Worth, Tex.

Contents .PART I - GENERAL

Definition . . . . . . -. . . . . . . . . . . . , . . . . , . 11-1Uses for Water on the Farm ................ 11-lWater for Livestock .................. 11-lIrrigation Storage ................... ii-2Regulation of Irrigation Streams ............ 11-2Field and Orchard Spraying ............... 11-3Fish Production .................... 11-3

Fire Protection .................... 11-4Recreation ....................... 11-4Waterfowl and other Wildlife .............. 11-6Multiple Uses ..................... 11-6Legal Requireixnts ................... 11-6Types of Ponds and Reservoirs . . . . . . . . . . . . . . . 11-6Selecting the Pond Site ...................Preliminary Site Studies .................Adequacy of the Drainage Area ..............

Minimum Pond Depth ...................Drainage Area Protection ................Adequacy of Pond Capacity ...............Engineering Surveys . . . . . . . . . . . . . . . . . . .

P CT II - lBWWKMENT PONDSGeologic Investigations ..................Soils.in the Ponded Area ................Studies of Foundation Conditions ............Availability of Suitable Fill Material .........

Soils in the Spillway Area ...............Records of Soils Investigations ............Spillway Requirements . . . . . . . . . . . - . . . . - . ,Trickle Tubes . . . , . . . . . . . . . . . , . . . . . . . 11-13

Page

11-711-811-811-811-911-911-9

11-1211-1211-1211-1311-1311-1311-13


2/78

efinitionesign Capacttyrincipal Spillwaysefinitionrop.In1et Spillwaysesignood.Inlet Spillwaysmergency Spillwaysimitationsesign Spillway Capacityxcavated SpillwaysElements of Excavated SpillwaysSelecting Spillway DimensionsNatural SpillwaysDischarge through Na tu~al egetated SpillwaysDetermining Maximum Water Elevation in ReservoirProtection against ~roaionrains and Water Supply Pipesrain PipesWater Supply Pipesesign of Earthfill EmbanhntsoundationsoundationCutoffsmbankment Top Widthmbankmnt Side Slopesreeboardllowance for Settlementarthwork Computation

lans and Specificationstaking for Construction

Construction Methods and SpecificationsPond and Reservoir ProtectionProtection Against ErosionProtection from Wave Actionermsoomsiprap

Other Methodsencinghecking for Compliance with Standardsnspection During Constructioninal Inspection and measurement ^Records of the Completed Work

Page11-1311- 16

EFM Notice 9 4 80


3/78

Pond and Reservoir MaintenanceInspect ion and Repairsanitation

P RT XCAVATED PONDSypes of Excavated Ponds

Sp Lllway nd Inlet RequirementslanninganExcavatedPondShape and CapacitySelecting Pond Dimensions

Estimating the Volume of an Excavated PondDisposal of Waste MaterialExcavated Pond Construction

P RT IV E LING PONDS ND RESERVOIRSSealing Methods 11 47General 11 47SeallngbyCompaction lone 11 47Use of Clay Blankecs 11 47Sea l in gwi t hBe nton i te 11 48Treatment with Chemical dditives 11 49Use o Flexible Membranes 11 50

FiguresFigure 11 1Figure 1 2Figure 11 3Figure 11-4Figure 11 5Figure 11-6Figure 11 7Figure 11 8Figure 11 9

Deepening pond edges by cu t and f i l l methodDetails of dry hydrant ins ta l la t ionSample notes for a pond design surveySoil invest igat ion formProfi le and cross sect ion of exc v ted e a r t hpillwayProfile and cross sect ion of a natural vegetatedpillwayEmbankment pond equipped with a stock wateringf a c i l i t ySample plan of farm pondample profiles of embanlarent and spillway


4/78

Figure 11-10 Construction layout notes .Figure 11 11 Construction check nates . .Figu re 11-12 Excavated pond and - ty p ica l sections. Notefenced de si l t in g area bwe pond .Figure 11-13 Cross sectiona of excavated pond showingmethods of waste material disposal .Fig ur e 11-14 Excavated pond fed by ground water

Table 11 1 Daily cotrsumption of water by livestockTable 11-2 Capacity guide fo r small i rr ig at io n reser voir sTable 11-3 Recommended minimum depths of ponds dreservoi rsTable 11-4 Recommended top widths fo r e a r th e m b a n h n t sTable 11-5 Reconrmended si de slopes fo r ea rt h e m b a n h n t sTable 11-6 Sample v o l w computations using sum of endareas method

Exhibi tsExhibit 11 1 Guide for estimating approximate acres ofdrainage area required per acre-foot ofs to rage in farm pond .Exhibit 11 2 Design of excavated spillwaysExhibit 11-3 ReservedEkhibit 11-4 Estlmate of p rin ci pa l eplllway dischargeallowing for temporary storageExhibit 11-5 Discharge through natural vegetatede p i llwaya .Exhibit 11-6 End area ta ble for em ba nh nt se ct ions forvaxious s i d e s lo pes and c r m widths . .Exhibit 11 7 Diamzters of p ipe in l e t s r equi red t o d iacharge various r at es of inflow int oexcavated ponds .

EFM Notice 9 4 80


5/78

ENGINEERING FIELD MANUAL

CH PTER 11. PONDS AND RESERVOIRS

P RT GENER L

1. DEFINITIONPonds and reservoi rs are bodies of water create d by const ructin g adam o r embanlanent across a watercourse or by excavating a p i t or dugout.Ponds constructed by th e f i r s t of these methods ar e refer red t o herein-a f t e r as ''Embanlanent Ponds and those constructed by the l a t t e r methodas Excavated Ponda . Ponds resulting from both excavation and embankment are c l a s s i f i e d as Embanhnt Ponds where the depth of water impoundedagain at th e embankment a t emergency sp illway ele va tio n i s 3 fee t or more.

2 USES FOR W TER ON THE FARMW TER FOR LIVESTOCK

Water i s as important as forage i n the product ion of l ivestock. In-adequate sto ck water developmente i n pas tur e and range areas contr ibute toae unstable l iveetock industry and l ivestock losses, prevent us of neededgrazing areas, and encourage overgrazing i n the v ic in it y of exi st in g watersuppl ies .Prwiding adequate water for l ivesto ck on range and pasture consistsof developing enough water t o s a t ie f y st ac k needs and providing a properd i s t r i bu t ion in r e l a t i on t o t he ava i l ab le fo rage .

pond should be of a s i z e t h a t w i l l meet the needs of a l l l ives toc kt h a t w i l l use the surrounding grazing area. Table 11-1 showing the averageda il y consumption of water by various kinds of li fe st oc k, should be helpfuli n estimating water needs.Table 11-1. Daily consumption of water by l ives tock

.

Kind of LivestockBeef Cat t l e add HorsesDairy Cows (drinking only)Dairy Cowe (drinking and barn needs)HogsSheep

..

Gallons per Headper Day


6/78


7/78

FIELD AND ORCH RD SPRAYINGPonds may provide water fo r applying i ns ec ti ci de s and fungic ides t of i e l d and orchard crops. The amount of water needed fo r spraying i s re-l a t iv e ly smal l, but i t i s important tha t t be available when needed.About 100 gal lon s pe r acre .f o r each a pp lic at ion should be enough fo r most

f ie ld crops . Orchards, however, may require 1,000 gallons or more peracre for each spraying.Sui table means should be provided t o convey water from th e pond t othe spray tank. I f th e pond i s of the embankment type, a pipe placed i nthe dam and equipped with a valve a n d a f lex ible hose at the downstreamend w i l l permit the apray tank to be f i l l e d by grav i ty. I f the pond i sthe excavated type, a small pump w i l l be r eq ui re d t o f i l l t h e t an k.

FISH PRODUCTIONpond that i s conetructed and managed properly may yield from 100 to

300 pounds of f is h annual ly f or each acre of water surface. This i s aboutequal to the beef production realized from average improved grassland.Ponds with a surface of 114 acre to several acres can be mauaged f o rgood f i s h production. Those less than two acres have proven popular sincethey are not as di f f ic ul t t o manage as the larger ones.Shallow water a t the edges of a pond p ro mte e waterweed growth, whichmakes f i s h management d i f f i c u l t , and provides a breeding place for mosquitoes.These problems can be overcame t o a la rg e e x te n t by deepening th e shallowedges around th e pond. Thi s can be done by borrowing from the pool edgeduring construct ion, or by cut t ing and f i l l in g s shown i n Figure 11 1.

TOVOID WEED HOBLEYN S W uO W WbTERI

REMWE SOIL T EEPENFigure 11 1 eepening pon edges by cut and fill metho


8/78

FIX FXOTECTIONThe f i r e pro tec tion pond should be loc ated reasonably near th e build-ings t o be pro tec ted . A ce nt ri fu ga l pump wit h power u n it atta che d and al ength of hose suf f ic ien t t o reach a l l s ides of the fa r th es t bui ld ingshould be provided. t i s good prac t ice i n a reas subjec t t o f reez ing to

provide f o r one or more dry hydrants s im ila r t o th e one shoyn i n Figure11-2.A sa t i s fac tor y f i r e s tream should not be l es s than 250 gal lons perminute with a pressu re a t th e nozzle of no le ss than 50 pounds per squareinch. Fi re nozzles usua l ly range from 1 t o 1 nches i n diameter. Goodqua l i ty rubber-l ined f i r e hose, 2 t o 3 inches in d i ame t e r should be used.The length of the hose should preferably not exceed 600 feet.

typ ica l example of a f i r e hose l in e i s one con sist ing of 500 fe et of3-inch hose t o which a 1-l / inc h smooth nozz le i s attached. A cen t r i fuga lpump, ope rated a t 85 p . s . i . w i l l provide a stream of 265 g p m with anozzle pressure of 50 p.s.i . Such a stream running for 5 hours would re-quire 114 acre foot of water. Local de a le rs i n pumps, engin es, and s i m i l a requipment should be a bl e t o fu rn is h th e d at a required regar ding pump capa-c i t i e s and engine horsepower.

A f i r e protec t ion pond may al so serve as a source of supply for loc alf l r e departments when acc essib le t o larg e tank t rucks. These trucks areheavy with a maximum capacity of about 1 000 gal lons. They normally carryabout 20 f ee t of suc tio n hose and general ly must operate from all-weatherroads. These poi nts should be considered i n locat ion of dry hydrants.When used fo r th i s purpose, hydrant f i t t i n g s should be designed t o f i tl o c a l f i r e company equipment. To make bes t use of these i ns ta ll at io n s thef i r e department should be kept up t o date on the loc at ion of in st al la t i on saccessible to their equipment .

A pond or rese rv oi r can provide rec rea tio n, such as swinming, b o a t i qand f ishing for the owner h i s family, and fr iends . The area inrmediatelysurrou nding th e pond can be made i n t o an a t t r ac t i ve p lace f or p icn ic8 andgames

Where a pond i s used fo r public re cre atio n, th er e should be a supplyof water adequate t o wercome ev apora tion and seepage lo ss es and maintaina des i rab le water l eve l . h waters must be f re e of pol lu t ion , espec ia l lywhere they are used f o r swinrmlng and bathing. I f bathing I s one of th eintended a c ti v it ie s th ere should be an adequate depth of water i n thevi ci ni ty of a gent ly s loping shore. Minimum f a c i l i t i e s for publ ic use ndsafety such as access roads, parking areas , bo at ramps or docks, f ir e -places , picnic ta ble s , and dr inking and san i tar y fa c i l i t ie s , should beprwided

For protec t ion of the publ ic heal th, most s ta te s have laws and regula-ti o ns governing water s upp lies being used for such purposes as bathing andhuman consumption t o meet c e r t a i n pre scr ibe d s tan dar ds. Such su pp li es usual-l y must be teeted and approved before their use by the publ ic is permitted.


9/78


10/78

W TERFOWL ND OTHER WILDLIFE

Ponds and re se rvo irs a t t r a c t many kinds of w il dl if e. Migratory water-fowl often use them s r es t ing p l aces in th e i r f l i gh t t o and from the North.In some of th e northern s t a t e s ducks ofte n use them as breeding pla ces ,pa rt i cu lar ly where there s an ample supply of good food . Upland game andg me birds use ponds as watering places.MULTIPLE USES

Where po ss ib le , a pond should be con str uc ted to provide water for twoor more purposes. For example, t could be used t o provide water f or liv e-stock, fo r f is h production and for spraying one or more field crops. Storge requirements f o r each purpose should be considered t o be su re of anadequate supply for,,a l l in tended uses.

The s ev er al purposes f o r which water s t o be used should be.compat-ib le . Some combinations a r e no t. For example, a pond would not: normallybe used fo r both ir ri ga ti on and .recre ation. Unless the re servoir i s verylarge, ost of the water might be removed during the irrigation season,thereby lowering the water le ve l t o a .po in t where boa tin g and swimmingwould not be practical.LEGAL REQUIREMF NTS

any s t a t e s have laws that require permits to construct dams for waterstorage for any intended use. The technician should know the requirementsi n h i s s t a t e and comply with them i n the planning, design, and layout ofponds and reservo i rs .3. TYPES OF PONDS AND RESERVOIRS

Farm ponds and reservoirs may be divided into two general types;namely, embankment and excavated ponds. n embankment pond i s a body ofwater created by constructing a dam ac ross a stream or wa tercou rse . Theseponds usual ly a re bu i l t i n areas where land slope s range from ge ntl e t omoderately s teep and where stream vall eys ar e su ff ic ie nt ly depressed topermit the storage of water to a consid erable depth.n excavated pond i s a body o water cr ea te d by excavating a p i t o rdugout. These us ua l ly .a re constructed i n re lat ive ly lev el areas. Thefac t t ha t t he i r capac i ty s obtained almost en ti re ly by excavation lim its

t h e i r use t o lo cat ions where only a small supply of water s required.Ponds ar e a lso b u il t i n gen tle to moderately sloping areas where capac-i t y s obtained by both excavation and the con stru ctio n of a dam. For thepurpose of cl a ss if ic at io n, the se a re considered t o ' b e embankment-type pondsi f th e depth of water impounded a ga in st t he embankment exceeds th re e f e e t .


11/78

4 SELE TING THE PON SITEThe se le ct io n of a su i t ab le pond s i t e should begin with preliminary

s tud ies of poss ib le s i tes . Where more than one s i t e i s avai lable eachshould be s tudie d se par atel y with a view of s el ect ing the one th at provesmost p r a c t i c a l and economical.

From an economic viewpoint a pond should be l ocat ed where th e l ar ge sts tor age volume can be obtained with th e l ea st amount of e a r t h f i l l . Thiscondi t ion genera l ly w i l l occur a t a s i t e where th e val l ey is narrow sides lopes a r e r e l a t i ve ly s t eep and the slope of t he va l l ey f l oo r w i l l permita l a rg e deep bas in Such s i t e s tend t o minimize the area of shalluw water;however they should be examined ca re fu ll y for adverse geologic con diti ons .Except where the pond i s t o be used for wi ld l i f e la rg e a reas of shal lowwater ehould be avoided due t o exces siv e evapo rati on lo ss es and t h e grcrwthof aoxious aqua t ic p lan ts .

Ponds t o be used fo r water ing l ive sto ck should be spaced s o th at l ive -s tock w i l l no t have t o t r av e l more than one-quarter mile t o reach them i nrough broken co un try no r more tha n one m i l e i n smooth r e l a t i ve ly l eve la r ea s. Fo rc ing l i ve s tock t o t r av e l l ong d i s t ances fo r water i s det r imenta lt o bo th the l ive s toc k and the graz ing a rea . Overgrazing near water andunused feed fa r f rom water are cha ra ct er is t i c s f inadequa te water d i s t r i -bu t ion .

Where wa te r must be conveyed fo r use els ewhere such as f o r i r r i g a t i o nor f i r e p ro tec t i on ponds should be loca ted as c lose t o t he poin t o f u sea s i s p r a c t i c a l .Ponds t o be used for f ish ing boat ing swimming and other forms ofrec rea t io n ehould be rea di ly acc essi ble by automobile. This i e p a r t i c u l a r -l y t ru e where the genera l publ ic i s charged a fee f or use of th e pond Thesuccess of such an income-producing ent erp ris e- ma y we ll depend on th e acces-s i b i l i t y of t he pond.Po ll ut io n of farm pond water should be avoided by s el ec ti ng a s i t

where drainag e from farmsteads feeding l o t s co rr al s sewage l in e s minedumps and similar areas w i l l not reach the ponds. Where t h i s cannot bedone prac t ica l ly the drainage from such areas ehould be diverted fromthe pond.

The pond should not be lo cat ed where sudden re le as e of t h e water duet o f a i l u r e o f t he dam would r e s u l t i n l o s s of l i f e in ju ry t o pe rsons o rl ives tock damage t o res idences or ind us t r ia l bu i ld ing s ra i l road s or h igh-ways o r cause i n t e r rup t ion of u se o r s e rv i ce o f pub l ic u t i l i t i e s Wherethe on ly su i ta b le s i t e p resen ts one or more of these hazards a more detail-ed investigation should be made.

Low-hanging powerlines present a hazard t o fishermen and oth er s usingfarm ponds. They may be with in reach of a f is hin g rod held by a m o n ef i sh ing f rom the top of th e dam S i t e s under such li n e s should be avoided.


12/78

check should be made t o in su re th a t no buried pipel ines or cablese x is t i n th e const ruc tion area. These might be broken or punctured by theexcavating equipment re su lt in g not only In damage to the u t i l i t y but i ninj ur y to the operato r of the equipment as we ll. Where such a a i t e mustbe used the u t i l i t y owners should be contacted prio r t o foundation inves ti-gation or construction.

5. PRELIMIN RY SITE STUDIESI n add itio n t o the considerations mentioned fo r the se lec tio n of apond loc atio n th er e are other physical character i s t ics o f the drainagear ea and the pond s i t e which should be inve stigate d before the fi n a l selec-t i o n i s made

DEQU CY O THE DR IN GE AREAWhere surface runoff i s the main source of water supply the co nt ri-

buting drainage area should be la rge enough t o yie ld su ff ic ie nt runoff t omaintain the water supply i n the pond during a l l periods of intended use.The drairiage are a should not be so la rg e however as t o req uire l arg e andexpensive overflow st ru ct ure s t o bypass runoff saf ely .The amount of runoff that can be expected annually from a watershedof a given area depends on so many fac tor s th at no s e t rul e can be givenfor i t s determination. The physical cha ra ct er ist ics of the watershed thathave a dir ec t ef fe ct on the y ie ld of water are land s lopes s o i l in f i l t ra -ti on vege tal cover and surfac e storag e. Storm ch ar ac te ri st ic s such asthe amount in te ns it y and dur atio n of r a i n f a l l a l s o a f f ec t wa te r y i e l d

l l of the se ch ar ac te ri st ic s vary widely throughout the United St at es .Exhibit 11 1 c n be used as a general guide for est imating the sizeof a watershed required f or each acre-foot of capac ity i n a pond or reser-voi r t o maintain normal pool lev el i f more precise loc al data i s notavai lab le . The map does not apply when ponds are used for i r r iga t io n .

MINIMUM PON EPTHFor a permanent water supply t i s necessary t o provide s uf f ic ie ntwater depth t o meet the intended use and t o of fs e t seepage and evaporationlosses . These losses vary i n di ffe re nt sect ions of the country nd a l s ofrom year t o year i n ny section. Table 11-3 shows recommended minimum

dep ths of water f o r farm ponds assuming normal seepage and evaporationloss es. Greater depths ar e des ira ble where a year-round water supply i se s s en t ia l or where seepage l os se s may exceed t hr ee inches per month. SeeS ta te Standards and S pe ci fic at io ns fo r lo ca l miniaturn depths.


13/78

Table 11-3, Reconrmended minimum depths of ponds and reservoirs

IlRAINAGE AREA PROTECT ON

Climate

SuperhumidHumidSubhumid MoistSubhumid rySemiaridArid

To maintain the required depth and capacity of a f rm pond, i t i sneceesary that the inflow be reasonably free from sediment. The bestprotection i s adequate erosion control on the contributing drainage area.Land under a cover of permanent vegetation, such as trees or grasses,makes the most desirable drainage area. If such an area i s not available,cul tiv ate d areas t ha t ar e protected by necessary conservation practi ces,such s terrac ing, contour ti ll ag e, strip-cropping, conservation croppingsystems, vegetated d es il ti ng are as, and other soil-improvement p rac tic es,may be u t i l i z e d a s a l a s t r e s o r t . Allowance should be made for the expected sedimentation during the effe ct iv e li f e of th e stru ctu re.DEQU CY OF POND CAPACITY

AnnualRainf a1(inches)

Over 604 6030 4020 30I d 20Under 10

To insure th at t he water stored i n a farm pond w i l l be adequate tosa tie fy the intended uses, a reasonable estima te of th e pond capa cit yshould be made The following i s a simple method of estimating capacity.

Minimum Water DepthOver 25 percent ofthe Area( f ee t )69101214

The pond-full water elevation i s establ ished and the wate rline i sstaked a t t h i s e l e va ti on . The widths of the va lley a t th i s e leva t ion a r emeasured a t regular in te rv als and these measurements are used t o computethe pond-full surface area in acres. The surface area i s multiplied by0.40 t ms th e maximumwater depth a t t he dam. For example, a pond witha surface area of 3.2 acres and a depth of 12.5 f e e t a t the dam wouldhave an approximate capacity of 0.4 x 12.5 x 3.2 16.0 ac .f t . (1 acre-foot 325,857 ga l lom) . If a more accurate answer i s required, thesurface area a t successive interv als of elevation may be determined andthe average end-area method may be used t compute the volume.

6 . ENGINEERING SURVEYSOnce th e l oc at io n of t he pond or re ser vo ir has been determined, suffi-cient engineering surveys should be made so that th e dam, spil lway andother features of the pond can be planned.urveys for embanhnt-type ponds normally w i l l consist of a pr o f i l eof the cente r l ine of the dam a profile o the centerline of the earth


14/78

spillw ay and su ff ic ie nt measuremants fo r estim atin g the pond capacity .For the l ar ge r and more complex re se rv oir s pa rt ic ul ar ly those used t os to re wate r fo r I r r iga t io n a complete topographic survey of th e en t i r epond s i t e and cross -sectio n surveys of em ba nb ut and spillway locati onsmay be re qu ired .The profile along the centerline of the proposed dam should extend upboth sid es of th e valley above the expected ele vat ion of the top of thedam and beyond th e probable loc at ion of th e ea rt h spillway. The p ro f il eshould show ground surface elevations a t a l l s ign i f ica n t changes i n theground slope and a t in t e rva l s no g rea te r than 50 feet. The p ro f i l e ass i s t si n es tab l i sh ing c r i t ic a l e levat ions for the s t ructure including normal poolc r e s t of th e emergency spillw ay and top of th e embankment. t i s used a lsot o compute the volume of e ar th requ ired t o cons truc t the dam.

s lmi lar p rof i le should be run a long the cen ter lhe of t he ea r thspillway from a point on th e upstream end we ll below th e se le ct ed normalwater s ur face ele va tio n t o a po int on th e downstream end where water c ube s af el y discharged without damage t o the str uc tur e. This p rof i le servesas a ba si s f or determining the slo pe and dimensions of th e spillw ay.l l surveys made a t th e pond s i t e should be ti e d t o refere nce poi ntsand a bench mark These may be a lar ge spilce driven in to a tr ee an i ronrod driv en flu sh with the ground a point on the c oncre te headwall of acu lver t o r ny other ob ject so located that i t can be expected t o remainundisturbed unti l construct ion of t he dam has been completed. Fig ure 11-3shows a sample set of tlotes for a farm pond design survey.

Engineering surveys for excavated ponds a re r el at iv el y simple whereno water i s stored against an embanlauent. Usually the four corners of theproposed excavation are located on the ground and rod readings taken a tthese po in ts . These readings should be referenced t o a bench mark andrecorded. Engineering surveys fo r bo th embankment and excavated ponds maybe recorded on approved standard forma or d a ta s heet s.


15/78

igure11 3 Sample notes for pond design survey


16/78

PART I M NKMENT PONDS1 GEOLOGIC INVESTIGATIONS

SOILS I N THE PONDED REThe su it ab il i t y of a pond a i t e depends on the ab il i t y of the s oi ls i nthe rese rvoir area t o hold water . The s o i l pr of i l e should contain a layerof materia l that i s su ff ic ie nt ly impervious and th ic k to prevent high seep-

ge losses . Clays and s i l t y c lays ar e excellent materia ls fo r t hi s purpose.Sandy cla ys usuall y a r e sa ti sf ac to ry . Coarse text ure d sands and sand-gravelmixtures ar e highly pervious and th eref ore a re genera lly unsuitabl e. Theabsence of a layer of r e la t iv ely impervious materia l w e r a port ion or por-ti on s of th e ponded ar ea does not necessarily mean th at the s i t e must beabandoned. It usu ally means, however, th at the se por tion s of th e are a w i l lhave to be t rea ted by one of the several methods described l a t e r i n th i schap ter under the heading, Seal ing Farm Ponds. ny of these methods mayprove t o be expensive.

I n some areas , such as coa stal plains , lake plains , and r i ve r de l ta s ,i t i s of te n po ss ibl e t o impound a lim ite d depth of water over a re as whereno impervious layer ex is ts i n the s o i l pro fi le but where a permanentlyhigh water t a b l a e x i s t s a t o r n ear t he g r o ~ d urface.Some of the limestone areas are especially hazardous for use as ponds i t e s . There may be cre vi ces , s inks , caverns or channels i n the limestonebelow the s o i l mantle and not vi s ib le from the sur face . These may dra inthe pond i n a s ho rt time. In add it ion , the s o i l s i n these a reas are of tengranular . The granules do not bre ak down re ad il y i n water and th e s o i l s

remain highly permeable. Without extensive investigations and laboratoryt e s t s , i t i s d i f f i cu l t t o recognize a l l of the fac to rs tha t might make alimestone s i t e undesirable, One of the be st guides to the s u i ta b il it y ofa s i t e i n such a reas i s th e degree of success experienced with farm pondsi n the immediate vicinity.Borings or t e s t p i t s should be made a t i r i tem als i n the reservoir areat o determine the nature of the s o i l pro fi l e . The frequency of th es e bor ings

w i l l depend on the occurrence of si gn if ic an t changes i n the s o i l pro fi le .The bor ings should be made t o a depth suf fic ien t t o iden tify the underlyingmaterials th at may af fe ct th e design or saf ety of the s tructure . record,or log, of each boring or t e s t p i t should be made showing th e lo ca ti on , depthand classes of materials encountered. The location of each boring should bemarked on the ground so i t can be referenced to other or more detailed surveys.STUDIES OF FOUNDATION CONDITIONS

The term foundation, as used he re, incl ude s the val le y f lo or and i t sai de slopes , o r abutments.. The requirements of a foundation for an earth-f i l l dam a re tha t i t p r w id e s ta bl e support fo r the embankment under a l lconditio ns of sa tu ra ti on and loading, nd t h a t i t p r w i d e s u f f i c i e n t r e s i s t -ance t o seepage t o prevent e xcessiv e lo s s of water. Adverse foundation con-di ti on s can lead t o f ai lu re of a dam due t o cracking, piping, s l iding,s e tt l emen t, o r up l i f t .


17/78

The foundation conditions under the proposed damsite should be investi-gated thoroughly t o insure that the s i t e i s su i t ab le and that a safe s t ruc-t u re can be designed. The ex ten t of the foundation examination w i l l dependupon the complexity of th e con dit ion s encountered and on th e heig ht of th edam. Borings should be.tak en or t e s t pi t s excavated a t in te rva ls along thecen te rl in e of th e dam. The depth and spacing of the borings o r p i t s shouldbe su f f i c i e n t to dete rmine the su i t a b i l i t y of the foundation.AVAILABILITY OF SUTTAELE FILL MATERIAL

F i l l m a te ri al must be avai lab le in suff ic ie n t quant i t ie s for construc-t i o n of the dam and should be located close enough to the s i t e s that place-mexit cos ts w i l l not be excessive. S oi l borings should be made i n the se le ct -ed borrow areas i n order t o est imate the kinds and amounts of s ui t ab le f i l lmaterials avai lable.Materials selected for construct ion of a dam must have sufficientstre ngth for the dam to remain st ab le and a sufficiently low permeability,when compacted, t o prevent harmful seepage of water through th e dam

SOILS TN THE SPILLWAY AREAIn most cases t i s necessary t o bypass excess sto rm runoff around t heembankment of a f rm pond through n excavated earth spillway. For economicreasons, au ita ble materi al excavated from the spillway should be used i n t h ee a rt h fi l l . Thus, s o i l borings should e made along the approximate center-li n e of the proposed spillway to determine the type of ma terial th at w il l . bee n c o ~ t e r e d , t s erodibi l i ty , and i t s s u i t ab i l i t y f o r use i n the embanbent.

RECORDS OF SOILS INVESIIClfCIONSA permanent record of a l l s o i l borings and t s t p i t s made i n the reser-

v o ir ar ea, foundation, borrow ar ea , and spillway a re a should be maintainedn the work unit offick Form SCS 538, Figure 11-4 or a similar form,should be used t o record s o i l borings.

See Chapter 4 of t h i s manual f o r guidance i n t he c l a ss i f i ca t ion ofthe soils encountered, nd in determining the ir su i t ab i l i t y as foundationor construct ion materials .2. SPILLWAY REQUIREMENTS

A l l reservoirs formed by d nnning natural drainageways require theprotection of a ca re ful ly designed spillway or combination of spillways.The function of spillway s i s t o pass s t o m - unoff around or under the e mb a n b n t t o revent overtopping. The spil lway also must convey the waterfrom the pond sa fe ly t o a s ta b le o u t l e t below without damage t o th e down-stream slope of the embankment. Spi llways are usual ly c las s i f i ed as t r i ck letubes, principal spi l lways, and emergency spillways.

3 TRICKLE TUBESDEFINITION

A small pipe spillway i s provided i n many farm ponds nd r ese rvo i r st o prot ect the ve getative c w e r i n th e emergency spillway from prolongedsa tu ra ti on by continuous flow, spri ng flow, or l ow flows that may continuefor several days during snawmelt or following a storm. This type of s p i l l -way i s designed t o discharg e such a small percentage of the peak flow th a t


18/78

11 14F m CS 5 8

SOIL INVESTIGATION TO DETERMINE SUITABILITY OF PROWSED POND SITE

Figure 11 4 Soil investigation form. Sheet of 2 )

CROPLAND DACRES PASTURE CRESW O O D ~ / / A C R E S 35 CRES8KEIY;X-I OF PROWSED WN D SHOWING WH R BORINGSW R MADE Appmx. d e feet)

~ o c o r r rfemicc point on mtu Ilna of dam d a a t ~ yn +rt ~h.POND CUSS

H mithWORK UNITCONSERV TIONIST


19/78

TYP S OF M TERUL EN OUNTERED IN ORINGSWell graded gravels; gravel-sand mixturesPoorly graded gravelsSilty gravels; gravel-sand-silt mixturesClayey gravels; gravel-sand-clay mixturesWell graded sands; sand-gravel mixturesPoorly graded sandsSilty sandClayey sands; sand-clay mixturesSilts; silty v. fine sands; sandy or clayey siltsClays of low to medium plasticity; silty sandy or gravelly claysInorganic clays o f high plasticity; fat claysElastic silts; micaceous or diatomaceous siltsOrganic silts and organic silty clays of lo w plasticityOrganic clays of medium t o high plasticity

1 Suitable material for em L vailable Yen n O m r td on dh.sht m-

Figute 11-4 Soil investigation f a rm Sheet o


20/78

i t has no measurable effect on the emergency spillway design. This typeof spillway i s conrmonly cal le d a t r i c k l e tube.ES GN C P CITY

The design capa city of a t r i c k l e tube should belong-duration, continuous, o r frequent flows withoutspillway.

4 PRINCIPAL SPILLW YSDEFINITION

adequate t o dischargeflow through the earth

The principal spillway i s constructed of permaxlent material, and usu-a l l y i s designed t o provide flood pr ote cti on or t o reduce the frequency ofop er ati on of t he emergency spiliway . t s discharge capacity depends uponthe purpose of t he res er vo ir and the use fo r which the spillway i s designed.f the reservoi r i s t o be used fo r reta rdin g flood flow, i t discharges alow percentage of the peak flow. t locations where an emergency spillwayi s not fea sib le th e prin cip al spillway should be designed t o discharge therunoff for the design storm.

DROP INLET SPILLW YSOne type of pr in ci pa l spillway t ha t i s c o ~ n l ysed with farm pondsand reservoirs i s the drop inlet spi l lway. t consists of a pipe ba rre lloca ted under the embankment wit h a r i s e r connected t o th e upstream end.The elev atio n of t he cr es t of the r i s e r determines the normal pool l ev elin the re se rvo ir . This type of sp ill wa y may be used to d ra in t he pond o rt o supply water fo r i r r i ga t i on or other purposes by in st al l i ng a valve orgate i n the upstream end of the bar re l.

esignS m a l l diameter pipes are par t icu l a r ly suscept ib le t o c logging withtr as h and rodents. For th i s reason no ba rr el smaller than 6 inchea i ndiameter and no riser smaller than 8 inches i n diameter should be used.Where the riser i s t o be constructed of reinf orced concrete or concreteblock, the inside dimensions should not be smaller than 4 by 24 inches.The cr e s t elev ati on of t he emrgency spillway should be located a tan elevation above the crest of the drop in le t equal to the head requiredt o develop design flow through the p ri nc ip al spillway conduit.Drawings and design inform ation a r e given i n Chapter 6 of t h i s manual.Construction methods and materials re cwe red i n Chapter 17, Also seeExhibit 11-4 f or determining the cap acity of p rin cip al spillways consider-ing temporary s tora ge.

HOOD INLET SPILLWAYSAnother type of principal spillway commonly used with farm ponds andreservo irs i s the hood i n le t spi llway. t cons i s t s of a p ipe l a i d i n thee a r th e m b a n b u t i n a manner tha t t he ele vati on of the i nv ert of th e pipea t i t s upstream end esta bl is hes the normal pool leve l in the r eservoir . Theinle t end of the pipe i s c u t a t an angle t form the hood. An anti -vo rtexdev ice, us ua lly made of metal, i s attached t o the entrance of the pipe to


21/78


22/78

11-18

Note: Neither the location nor Note: Use care tothe alignment of the level por- ke ep all machineryhas to coincide with the and traffic out ofer line of dam.) the spillway dischargearea to protect aod.)

Excavated Earth Spillway Optional witheod or riprapon wing dikePLAN VIEW OF EARTH SPILLWAYS

Water Surface

PROFILE ALONG CENTERLINE

CROSS-SECTION OF LEVEL PORTIONDefinition of terms:

p Depth o water in reeervoir above creetL Length of level portion m l n 7 6 meter 25 ft.)Bottom width of spillwaySo Slope for exit channelSe Slope of inlet channel

Figure 11-5: Profile and cross-rection of excavated earth spillway


23/78


24/78

The level portion should be located near the intersection of theextended centerline of the dam with the centerline of the spillway andhave a length of at least 7.5 meters (25 feet).The exit channel must have a slope that is adequate to discharge thepeak flow within the channel. The slope, however, muat be no greaterthan that which will result in maximum permissible velocities for the

soil type or the planned grass cover. The exit channel should bestraight and should confine the outflow to a point where the water maybe released without damages to the fill.Selecting Spillway Dimensions

With the required discharge capacity, the degree of retardance,permissible velocity, and the natural slope of the exit channel known,the bottom width of the level and exit sections and the depth of theflow ~ p ) ay be computed from Exhibit 11-2. The natural slope of thechannel should be altered as.little as possible.The selection of the degree of retardance for a given spillway willdepend mostly upon the height and density of the cover chosen (Exhibit11-2, Table 2). Generally, after the cover is selected, the retardancewith a good uncut condition will. be the one to use for capacity deter-mination. Since a condition offering less protection and less retard-ance xists during the establishment peroid and after mowing, it may beadvisable to use a lower degree of retardance when designing for stability.When the anticipated average rise of a spillway is more frequent thanonce in 5 years, the maximum permissable velocities shall be in accord-ance with Exhibit 11-2, Table 1 for vegetated spillways and Exhibit 11-

2, Table 4 for earth spillways. For vegetated spillways only, themaximum permissible velocity may be increased 10 percent when theanticipated average use is not more frequent than once in 5 years or 25percent when the anticipated average use is not more frequent than oncein 10 years.Water surface profiles were cajlculated by computer for all theanticipated spillway conditions and based on the retardances describedin SCS TP-61. Critical slope and depth proved to be of minor importancein detting Hp, so Exhibit 11-2, Tables 3A through E were developed fromthe water surface profiles and will carry the design flow as shown.Tables 3A through E give minimum and maximum slope requirements for the

various discharges q, velocities V, and retardance given.Some velo~ities njExhibit 11-2 Tables 3A E show different dis-charges in m /s/m (ft /s/ft).for the same Hp values. The Hp values areset to insure design q at the mini~num slope, but velocitiea at minimumslope may not reach maximum velocity. The maximum velocity will only beachieved where the exit channel is at maximum slope. Rounding is.alsopart of the reason. Table 3A E are not appropriate for bottom widthsless than 2.4 meters 8 feet). Table 3E should be used for earth spillways .

EFM Notice 9, 4/80


25/78

Spil lway s id e s lopes should be no s teeper than 3 : l un less thesp i l lway s excavated in to rock i n which c se th e si de slo pe s mayb e v e r t i c a l .

Usually th e se le ct ed bottom width of th e channel should not exceed 35times th e design depth of f low. Where th i s r a t i o of bot tom width todepth s exceeded th e channel s l i k e l y t o be damaged by meanderingflow and accumulated debris. Whenever t he r equi red bottom width of th esp i l lway s excess ive conside rat ion should be given to t he use of asp i l lway a t each end of t h e dam. These two sp il lw ay s need no t be ofequal width so long s t he i r t o t a l capac i ty mee ts requ i rements . Incases where the req uire d disc harg e cap acit y exceeds t he ranges shown inth e above ex hib i ts o r topographic condi tons w i l l not permit the con-s t r uc t io n of th e e x i t channe l bot tom wi th a s l op e t h a t f a l l s w it hi n t h eranges shown i n t h e s e e x h ib i t s t h e d e s ign s beyond t he scope of t h i smanual.

See xhibit 11-4 f o r pr in ci pa l spi l lway disch arge requirements ad-jus ted f o r temporary s torag e provided i n th e reserv oir . Emergencyspi l lway desig n f low may be adjusted t o consider th e outf low through t hepr inc ipa l sp i l lway .N TUR L SPILLWAYS

Many t i m e s la rg e expanses of good sod a r e destroyed t o provide th eminimum sl op es f o r an excavated spil lwa y. This may i n c r e a s e t h e con-s t r u c t i o n c o s t a n d w i l l inc re ase maintenance cos ts. Wherever th er e s agood vegetative cover i n th e spi l lway area and t he topography su i t ab leconside rat ion should be given t o t he use of a na tura l sp i l lway . Thedischarge capaci ty can b e computed by th e follo win g procedu res.Discharge Through Natural Vegetated Spillways

I n a na t ura l sp i l lway t he ou t f low takes p lace a round the end of theembankment on n a t u r a l o r und istu rbe d ground. The number of p o s s ib l ec r o s s s e c t i o n s and p r o f i l e s ha pe s s s o g r e a t t h a t a n a n a ly s i s here ofth e r a t e of f lo w f o r e a c h c o n d i ti o n s imprac t ica l .

I n most c a s e s th e l e v e l p o r t i o n of t h e f l ow r o u t e w i l l be V-shapedone s i d e determined by t h e embankment end s lo p e and wing dike and theo th e r by the natural ground. The ground slope should be determinedalong a l i n e p er p en d ic u la r t o t h e c o n to ur d i r e c t i o n w i th in t h e f l owdepth range. See Figure 11 6.

The end of th e dam should be approx imately perpe ndi cula r t o t hecontours of th e abutment. A sh or t wing d ik e may be used t o pr ot ec tt h e t o e of t h e embankment. The e x i t sl op e away from th e con tr ol se ct io nshould be wit hin th e s lo pe ranges given i n Exhibi t 11-5.

EFM Notice 9 4/80


26/78

PRO LE

Figure 11 16sp llww

we t oprotectembankment.

PLAN VIEWPlan profi le and eross sect ion of a natural vegetated

Discharge Q), velocity V) and depth of water n the reservoir abovethe crest Hp) , were determined using water surface profiles calculatedby computer. The spillway was segemented into 0 6 meter 2 foot) segments,then using dat? from water surface profiles a discharge for each segementwas determined for a specific depth, length of flow, and retardance.Total Q is the sum of the discharges of each segement. ~xhibit 1-5 wasthen developed using the given parameters.Determining the Maximum Water Elevation in Reservoir

With the required discharge capacity Q), the end slope of theembankment Zl),and the slope of the natural ground 22 , known; themaximum depth of water above the level portion Hp), can be obtainedfrom Exhibit 11-5. The depth is added to the elevation of the spillwaycrest to determine the maximum elevation to which water will rise in thereservoir.

EFM Notice 9, 4/80


27/78

Exhibit 11-5 has been developed for an end slope of 3:l and naturalground slopes of 1 to 5 percent.An example showing the use of Exhibit 11-5 is as follows:

(SI Units) (English Units)Given Given

3Q 2.43 m /a (From Chapter 2) Q 86 ft3/s (From Chapter 2)Vegetation: Bermuda~rass ood Stand Vegetation: Bermudagrass Good StandHeight: -15 to 25 cm Height: 6 to 10 inchesSlope of Natural Ground 1.0 Slope of Natural Ground 1.0Solution:From Table 2 Exhibit 11-2:Determine a Retardance of CFrom Exhibit 11-5:Enter under Z2 slope 1Under Retardance C columnfind a Q 2.43 m /sat Hp 0.40 m andV 0.82 m s

Solution:From Table 2 Exhibit 11-2:Determine a Retardance of CFrom Exhibit 11-5:Enter under Z slope 1Under Retardance C column3find a Q 86 ft /sat Hp 1 3 Et andV 2.7 ft/s

Velocity is well below the maximum permissable velocity of 2.4 m/s(8 ft/s) given in Table 1 Exhibit 11-2. Hp can be determined by inter-polation when necessary. For a Q greater than listed in Exhibit 11-5,the spillway should be excavated according to Exhibit 11-2.PROTECTION AGAINST EROSION

Earth spillways should be protected against erosion by a good vegetalcover, if soil and climate permit. As soon after construction as ispractical, the entire spillway area should be thoroughly preparedfor seeding or sodding. Liberal amounts of fertilizer should be usedwhere moisture is available or can be applied. In cases where thesubsoil is low in fertility, it may be desirable to save the topsoiland spread it in the excavated spillway. Adapted perennial grasses orperennial grasses and legumes should be sown, protected, and treateduntil a good stand has been established. Mulching is usually necessaryto protect the seeding on the spillway slopes. Irrigation of the spill-way area is often needed to assure adequate germination and growth,particularly when seeding must be done during relatively dry periods.Where the added cost is justified, sprigging or sodding with suitablegrasses will afford quick protection.

EEM Notice 9, 4/80


28/78

6 DRAINS AND WATER SUPPLY PIPESD M I N PIPES

Some s t a t e agencies require that provis ion be made f o r draining farmponds, f luc tua t ing t he water sur face e lev a t io n t o e l iminate breeding p lacesfor mosquitos, or meeting o ther S t a t e r equ i rem nts . Provid ing for dra inageof farm ponds i s a d e s ir a b l e p r a c t i c e i n that t pe rm its good f i s h manage-ment and llows for maintenance and needed re pa ir s without c ut t i ng the f i l lor r e s o r t i n g t o o t h er d ev ic e s t o remove the water . The dra in pip e shouldbe extended beyond th e upstream to e of t h e d m and be equipped with a suit-able gate or valve.WATER SUPPLY PIPES

A water supply pipe should be ins ta l l ed under or through the damwhere water i s t o be used below th e dam, such as f or s tockwater , i r r i ga -t ion , io f3J %. .zsqwy~ z4~.k.his pipe us ua l l y i s i n add i t i on t o t h ep r i nc i p a l s p i l l way o r t r i c k l e t ube . The water supply pipe should havewater - t ight jo in t s and be equipped with a s u i t ab l e va l ve and s t r a i n e r ti t s upper end. For small ra te s of f low, such as are needed t o f i l l l i v e-s tock or spray t anks , inch d iameter s t e e l p ipe i s genera l ly used . Wherelarg er r a t es of flow. a r e r equi red , such as f o r i r r i g a t i o n p ur po se s, l a r g e rdiameter pipe are cormnonly used. Water su pply pipe s should be providedwi t h an t i -s eep co l l a r s t o r e t a r d s eepage . See Figure 11-7 f or a sketchof a s t o c k w a te ri ng f a c i l i t y . )

Figure 11 7 Embankment pond equipped with a s t o c k w a te ri ng f a c i l i t y


29/78

7 DESIGN OF E RTHFTLL EMB NKMENTS

t i s poss ib le t o cons t ruct a sa fe e a r t h f i l l dam on alnrost any Eounda-ti on i f the foundation has been thoroughly investig ated nd the design andconstruction procedures are adapted t o s i t e condi tions . Some foundationr d i t i o n s require cons t ruc t ion measures t ha t a re re la t i ve ly expens ive which,I n the case of small farm ponds, cannot be ju st if ie d. S it e s with such founda-tion conditions ordinarily should be abandoned.

The most sat isf ac tor y foundation i s one th at con sis ts of , or i s under-la in a t a shallow depth by a - t h i c k layer of re l a t i ve ly impervious consoli-dated ma te ri al . Such foundations cause no s t a b i l i t y problems. Where asuitable layer occurs at the surface, no speci al masur es are required.t i s su ff te ie nt t o renrove the top- soil nd sca r i fy o r d i sk the a rea toprovide a bond with the mater ia l i n the dam.

Where th e impervious la ye r i s o ve rl ai n by previou s ma ter ial a compact-ed cla y cut of f, extending from the sur face of t he ground in to t he imperviouslayer , i s required t o prevent possi ble fa il ur e by piping and t o preventexcessive seepage.Where the fouadation consists of highly pervious sand or sand-gravelmixture and any impexvioua cl ay la ye r i s beyond onomical reach wi thavailable equipment, a de ta il ed inv es ti ga ti on should be made. While sucha foundation might be sa t is fac tor y insofar as s ta b il i t y i s concerned,,co rr ect ive measures w i l l be requi red t o prevent exce ssi ve seepage andposs ib le fa i lu re .

foundation consisting of or under la in b y .a h igh ly p la s t i c cl y orunconsolidated m ateria l req uires a very car eful invest iga t ion nd designi n or de r t o o b ta i n s t a b i l i t y .Water impounded on bedrock foundations seldom gives cause for concernunless the rock contai ns seams, fi ss ur es o r crevi ces through which watermay escape a t an excessive rate . Where rock i s encountered i n the founda-t io n, a very carefu l invest i gat ion of the nature of the rock i s required.See Chapters 4 and 17 of t h i s manual fo r f ur th er guidance.

FOIRPD TION CUTOFFSWhere the foundation co ns ist 8 of pervious ma teria ls a t or near thesurface, with rock or impervious materials a t a gr ea te r depth, seepagethrough the pervious lay er should be reduced t o prevent piping and exces-s ive los ses . Usually a cutoff joining the impervious stratum in thefounda tion with th e base of th'e dam ie needed.The most orumon type of cutoff i s m e constructed of compacted clayeymateria l . t rench i s cu t pa ra l l e l t o the cen te r l ine o f the d m t o adepth th at extends well i nt o the impervious lay er. The trench i s extendedin to and carried up the abutments of the d b s far as pervious materia l


30/78

exists that might allow seepage under the embankment. The trench shouldhave a bottom width of not l e ss than 4 fe et but adequate t o allow use ofequipment necessary t o ob ta in proper compaction. I t s sides should be noe teeper than 1:1 The t rench should be f i l l ed wi th successive th i n l ay ersof r el at iv el y impervious ma teri al, each la yer being thoroughly compacteda t near optimum moisture conditions before the succeeding layer i s placed.Any water col lec ted i n the trench should be removed before b ac k fi l l opera-t ions are s t a r t e d . See Chapter 17 of t h i s manual).EMBANKMENT TOP WIDTH

A conservative top width f or dams under 10 fe et i n heigh t i s 8 f e e t .The top width should be increased as th e heigh t of th e dam inc rea ses .Table 11-4 contains recommended top widths for embankments of variousheights. See St at e Standards and Spec ificatio ns fo r local equirements.Where the top of th e embanbent i s t o be used f o r a roadway, the fopwidth should provide fo r a shoulder on each si de of t he trav ele d way t oprevent raveling. The top width i n such cases should not be less than14 feet .

Table 11-4. Recommended to p wid ths fo r e a r t h embankments

EMB NT SIDE SLOPES

Height of Damfee t )Under 1010 t o 1515 t o 2020 t o 25

The side slopes of a dam depend primar ily on the s t a b i l i t y of thema te r i a l i n the e m b a n b n t . The g rea t e r t he s t a b i l i t y of t he f i l l mate-r i a l , the stee per th e .side slopes may be. The =re unstable mater ialsr equ i r e f l a t t e r s i de s l opes . able 11-5 contains -reconmended maximumslopes for the upstream and downstream faces of dams constructed of vari-ous materials. See State Standards and Specifications for local require-ments.

Top Widthfee t )816

1 214

Table 11-5. Recmamded s ide s lopes fo r ear th em ban bnt a

F i l l M a t er ia lClay CHClayey sand SC Sandy c lay CLS i l t y c l ay s i l t y sand SMClayey gravel GC S i l t y g ra ve l M

S i l t ML o r MH Clayey s i l t ML

Side Slope8H o r i e w t a l t o V e r ti c alUpstream

t o 12 t o 13 t o 1

Dclwnstream2 t o 12 t o 1

t o0 r


31/78

FREEBO RDFreeboard i s the added height of the dam provided as a sa f e ty f ac to rt o prevent waves or runoff from storms gr ea te r than th e design frequencyfrom over topping the embanbnt . It i s the ver t ical dis tance between theele va tio n of the water su rface i n th e pond when th e spil lway i s discharg-

ing a t designed depth and th e e leva t ion of the top of the dam a f t e r a l ls e t t le m n t has taken place. Where the maximum length of a pond is l e s sthan 660 feet , a freeboard of not less than 1.0 foot should be provided.For ponds with lengths between 660 and 1,320 feet the minimum freeboardshould be 1.5 feet . For ponds up t o mile i n len gth , th e minimum fre e-board should be 2.0 f e e t , ee State Standards and Spec i f i ca ti ons fo rlocal requirements.LLOW NCE FOR SETIILEWNT

Sett lement inc ludes the consol ida t ion of the f i l l mater ia l s and thecon solid atio n of th e foundation materials due t o the weight of t he damand the increased moisture caused by the storage of water.

Sett lement o r conso lidat ion depends on th e chara cter of th e materi alsi n th e dam and fou ndation and o n ' t h e methods and speed of c on str uc tio n.The design hei gh t of e ar th dams should be inc reased by an mount equal tothe est imated set t lement . This increase should not be le ss than 5 percent .E RTHWORK COMPUT TION

The es ti ma te of th e volume of borrow re qu ir ed should inc lud e th e dam,a llowance for se t t lement , ba ck f i l l for the cu tof f t rench , bac kf i l l f orex is t i ng s t ream channels and holes i n the foundation area, and any otherembankment the contractor i s required t o perform.

Volume estimates for dams usu all y a re made on the ba si s of cu bicy ar ds of e a r t h f i l l i n place. The onrmon method of estimating the volumeo f e a r t h f i l l s i s the sum of end areastt method. With the f i l l heig hts,aide slope s and top width esta bli sh ed , the end area of t h e cross sec t iona t each s ta t io n a long the cen ter l in e may be obta ined from Ex hib it 11-6.For example, assume th a t a dam has s lo pes of 3 t o on both upstream

nd downstream sides and a top width of 12 fe et . For a point a long thecen t e r l i ne where t he f i l l height i s 15.0 fe et , the exh ibi t shows th at theend area a t tha t poin t i s 675 180 or 855 square f e e t . The number ofcubic yards of f i l l between two poin ts on the ce nte r l in e of the dam i sequal t o t he sum of th e end are as t t he two po in t s m l t i p l i ed by t hedistance between these points and divided by 2 27 o r 54. The to ta lvolume of e a r t h f i l l i n the dam i s the sum of a l l such segments. Asample volume est imate i l lust rat ing the use of the sum of end areasttmethod i s presented i n Table 11-6.


32/78

11-27

Table 1 1 - 6 Sample volume computations using sum of end areas method

Station

0 501 68

1375375

2 001932

I 364043

1; 6

4 593 4- 00

3560

3 96

GroundElevation3 5 03 2 . 725 92 1 520.019.81 9 . 520.320.31 8 . 81 8 . 218.51 9 . 61 9 . 82 0 . 82 7 . 73 1 . 635.0

F i l lHeight(feet)0 .02 . 39 .1

13.51 5 . 015.215.51 4 . 714.716.216.816.515.415,2l4,27.33.40 .0

EndArea L(sq.ft.)Sum o fEndAreas(sq.ft.) Distance(feet)

DoubleVolume(cu.ft.)

Total

3 7 9 5 4 8 = 7,029 cu. yds.5

1/ End

Allowance for settlement (5%) = 51 cu. yds.Total Volume = 7,380 cu. y d e .

areas based on 12-foot top width and 3 to 1 slopes on b o t h sides.2 Double volume in c u . f t . is d i v i d e d by 54 t obtain volume in cu.yds.


33/78

The sample voluple estim ate of 7,380 cubic yards in cludes o n l y t h a tvolume of e ar th required t o complete the dam i t s e l f . n estima te of thevolume of e ar th required t o ba ck fi ll th e core trench, old stream channelsand oth er re qu ire d ex cav atio n should be made and added t o th e es tim atemade forshown i nsions of

The

the -dam. For example, assume th a t i n ad dit ion t o t he volumeTable 11-6, th er e i s a cutoff trench to be bac kfil led . The dimenthe trench are as follows:Average depth 4.0 f e e tBottom width 8.0 f e e tSide slopes t oLength 77 f e e tvolume of b a c k f i l l i s computed as follows:End rea (8 4 4 4 )32 16 48 square fe e t.Volume 48 177 315 cubic yards.

7Adding t h i s t o the volume require d fo r th e dam i t s e l f , t h e t o t a lvolume becomes 7,380 315 7,695 cu bic yards.

PLANS AND SPECIFICATIONSA l l information developed during the design process should be recordedfn the form of an engineering plan for the pond. This plan should show a l lpertinent elevations and dimensions of the dam, the dimensions and extentof the cutoff trench and other areas requiring bac kf il l , the location anddimensions of the t r i c k l e tube and other planned appurtenances, and a l lothe r information pert ine nt Fo the co nstr uct ion of t he dam. The plan shouldalso include a b i l l of mater ia ls l i s t in g the quanti ty and type of a l l con-s t ru ct io n mater ia ls requi red . A sample plan of a farm pond embankment i sshown i n Fig ur es 11-8 and 11-9.Applicable engineering standards and construction specifications havebeen developed i n each s t a t e fo r ponds and re se rvo irs . To obta in a qua l i tyjob of co ns tr uc ti on -t he owner and cont ra ct or must understand a l l requir e-ments. Both the owner and the co ntra cto r should be furnished copies ofthe plans and spec if ic at io ns.

8. STAKING FOR CONSTRUCTIONStaking i s a means whereby the information on the farm pond plans i st ransmi t ted to the job site This information w i l l pxovide lines, grades,and elevati ons required fo r constructio n of the job i n accordance with theplans. Cmsl deration should be given t o the con trac tor s wishes i n stak-ing so that he can make the most eff ec ti ve use of t he sta kes. The qualityand appearance of the completed job w i l l reflect the care and thoroughnessexercised i n the staking procedure.


34/78

storm R a i n f a l l kjR u n o f f Depth 6Peak R u n o f f fgo fs

GEM ER lll N FORMAT ON

1311-SICS C O L l I R Spr :Core MetOj

YO reau l red : 2

+ 0' ---1Cross t on

C IP r I l C A r l O lI c e r l r tha t I have made, or cause4 to Oe W e , a f i na Is p e c t l on o f t h i s PO p r o j e c t AM t h a t a 1 1 art r e l at e a t h e r e SECT1O THROU H FILL ALONG C M D U Tt o bas been c a r o l e t e d ~n accordante w i th t h es e p l a n s a r m m i l h Bench M a r t Dr s e r i p t i o n~ I I . O ~ M ~p p ~c ab le s ~ e c ~ ~ i c a ~ n o n sm c e p l a s l i s l e * o the roof 30 o k 4e VWa ttached shee t o f N. ~ n d o f durn.(chech hc rc d i m e r c c p t i o n s ) n s . Mark o u t w i t h r e d p e n c i l t h o s e i t e m s not r e q u i r e d .

k t l r id8 b a te / 0 / 6 3 Figure 11-8 Sample plan o farm pon

PLAN OF FARM WNOCherokee C o u n t y


35/78


36/78

The areas t o be cleared usual ly w l l co ns ist of th e damsite thesp i l lway s i te th e borrow are a and the area over which water i s t o beimpounded. Each of thes e ar ea s should be c l ea r ly marked with stakes orf l ag s . I n th e ca se of the pond area the-proposed wa terl ine should belocated accurately with a l eve l and rod. Clearing stak es should be a tl e a s t 15 fee t ou ts ide t h i s waterl ine t o give a cleared area around theedge of the reservoi r .

The emb anb ut i s located by se t t ing s t akes along i t s cen te r l ine a tin te rv al s of 50 f e e t o r l e s s . Usually this w i l l have been done during thecourse of the in i t i a l planning survey. F i l l and slope stakes are then se tboth upstream and dawnstxeam from the centerline stakes marking the pointsof in te rs ec ti on of the si de elopes with the ground surf ace . See Chaptersand 17 fo r procedures on slope sta kin g.The earth spillway i s located by staking the centerl ine and then set t -ing cut and slope stakes along the l in es of int ers ec tio n of the spillway

sid e slopes with the na tur al ground su rface. The procedure for settingthese stakes i s the same as f or st ak in g the embankment except th a t theya r e cu t stakes r a t he r th an f i l l s takes . They should be offset so they w i l lremain i n place for ready reference during co nstruction.Where s ui ta bl e f i l l mat eria l must be obtained from a borrow are a i ti s e ssen t i a l t ha t t h i s a rea be c l ea r ly loca ted . Cut stakes should be setto control excavatton within the l im its of sui t able material and t o drainthe borrow area.A pri nc ipa l spillway or tr ic kl e rube should be located by stake s off -set from the ce nte rli ne of the conduit and placed a t i nt er va ls not exceeding

50 f ee t . The principal spillway should be located where i t w i l l res t on afir m foundation. Cuts from the tops of the stakes to the grade ele vati onof the tube should be plainly marked on the stakes. The locations of ther i ser d ra inage gate ant iseep co l l ars conduit ou t le t s t ructure andother appurtenances should be located by additi ona l stakes cl ea rl y marked.Figure 11-10 presents a sample set of construction layout notes foran embankrent and ea r th spil lwa y. Design lay out and check notes may berecorded on approved standard forms or data sheets

9 CONSTRUCTION METHODS ND SPECIFIC TIONSAttent ion t o de ta i l s of conetruct ion and adherence t o specif ic at ionsa r e as important as adequate investigations and safe design. saf e designcan be ruined by poor construction.Chapter 17 of t h i s manual pr w id es guidance on construction methodsfo r the various elements of a pond or re se rv oi r. Speci f icat ions for thework should conform to S ta te Standards and Sp ec ifi ca tio ns ap plic able t othe e i t e and t he purpose of the s t ruc tu re .


37/78

Figure 11 10 onstruction layout notesSheet of 2


38/78

igure11 10 Construction layout notes sheat 2 of 2

10. POND ND RESERVOIR PROTECTIONA farm pond should not be considered complete u n t i l proper pr otec tionfrom er os io n wave ac ti on li ve st ock and othe; sourc es of darnage-has beenprovided. Ponds that lack such protection may be ahort- l ived and thecost of maintenance i s usual ly high

PROTECTION AGAINST EROSIONI n most ar ea s the exposed su rfa ce s of th e dam spillwa y borrow are asand other dis turbed su rfaces can be protected again st erosion by esta blis h-ing a good cover of sod-forming grass i n accordance with the local Technical

Guide.PROTECTION FROM W VE CTION

Occasionally there s need for be tt er p rote ctio n against wave actio nthan w i l l be provided by a grass cover. Some methods used t provide thispr ote ct ion a re ear th berms log booms and rock r iprap.

A berm 8 t o 10 fe et in width located a t normal pond level oftenw i l l provide adequate protection from wave act ion. The fac e of th e dam


39/78

above the berm should be protected by vegetation.

A boom may cons is t of a sin gl e or double l in e of logs chained togethernd sec ure ly anchored t o each end of th e dam. The logs should be t i e d end

t o end as close together as i s pr ac ti ca l . There should be enough sla ck i nthe l in e to a l low the boom t o adjus t i t s e l f t o f luc tua t ing levels i n thereservoi r . Double rows of logs should be framed tog eth er t o act a s a u n i t .The boom should be placed so as t o f l o a t about 6 f ee t upstream from theface of th e dam f o r b e s t r e s u l t s . I n t he c se of a curved dam anchor pos tsmay be required on the face of the dam as w e l l as a t the ends i n order t oprevent the boom from riding on the slope. B o a afford a high degree ofprotec t ion and are re la t i ve ly inexpensive espec ial ly i n areas where t imberi s r e a d il y a v ai l ab l e. They should prove sa ti sf ac to ry f o r the smaller lessimportant s t ructures .

Where the water l eve l in the pond c n be expected t o fl uc tu at e widelyor where a high degree of p ro te cti on s required the use of rock r ip rap i sa most ef fe ct iv e method of co nt ro l. Riprap should extend from the top ofthe dam down th e upstream fa ce t o a l e ve l a t l e a s t 3 feet below the lowestexpected le ve l of the water i n the res erv oir . Riprap may be placed bymachine or by hand. Machine pla cin g re qu ir es more stone but l e s s lab or i nplacing. The layer of stone should be a t le as t 12 inches thick. Stonesshould be durab le and lar ge enough not t o be displaced by waves.Where ri pr ap i s not continuous t o t he upstream toe a berm should beprovided on the upstream face t o support the layer of riprap. See Chapter

7 for guidance on instal l ing r iprap.Other Methods

Other methods include increasing the top width of the dam f l a t t e n i n gthe f ron t sl ope of th e embankment and applying a layer of coarse sand andgravel on a 10:l slope. These methods a re a ppl ica ble t o a ri d a re as wherevegetat ion i s not dependable and rock and timber i s not readi ly avai lable .

The complete fencing of e mb an hn t- ty pe ponds i s recommended wherel ivesto ck are grazed or fed i n adjacent areas. The fencing pr wi de s t hepro tec tion needed t o develop and maintain veget ative c w e r . When combinedwit h a watering f a c i l i t y below the dam fencing provides good drinki ngwater and elimin ates the danger of po llu tio n by l ivesto ck. Fencing al soimproves wildlife environment.

11 CHECKING FOR COMPLIANCE W I T ST ND RDSWhile both the owner and th e cont ract or have re sp on si bi l i t i es f o r

compliance with standa rds insp ect ion i s als o required i f h igh s tandardsare t o be maintained.


40/78

INSPECTION DURING CONSTRUCTIONThere ar e numerous items i n th e c on str uct ion of a.f arr n pond th a t mustbe checked during construction. Since i t w i l l be impossible fo r work un itpersonnel t o spend as much t i m e as may be de si ra bl e o the job responsibi-l i t y nust be assumed y the owner. The owner or his representative should

be encouraged t o watch th e cons truc tion and rep or t h i s obser vations t o thework uni t s t a f f . I f cor rec t ive ac t ion i s necessary th e owner can be ad-vised of the course t o follow. The following ar e i t e a t hat might bechecked by the owner.1 l l clearing and grubbing operations should be completed accord-ing t o s pe cif ica tio ns before any work on the eabankment i ss t a r t e d .2 Before embankment construction begins the foundation should beproper ly prepared. The completed cu to ff t ren ch should be in-spected t o insure th a t t i s excavated t o impervious ma ter ial

and i s free of water before t i s b a ck f il l ed .3. The completed ins ta ll at io n of the drop i n l e t spillway drainpipeant iseep col la rs and oth er appurtenance should be inspecte d beforeembankment construction i s s ta rte d. Materia ls used and loca t ionalignment grades and dimensions should be checked.for compliancewith the plans.4. The earth excavation and the se le ct in g placing spreading andcompacting of the ma ter ial i n the emb nhnt should be inspectedfrequently t o insure th at the sp ecificat ion s are met.

FINAL INSPECTION AND MEASUREMENTSThe f i na l inspection by the technician should include su ffi c ie nt pro-f i l e and cross-sect ion readings to insure tha t the height top width s id eslopes and other dimensions shown on the plans have been me t Elevationsof the top of the t r i ck le tube or pr inc ipa l sp i llway wi th re la t io n to thecont ra1 se cti on of t he s pillway should be taken. Cross sections and profileof th e emergency spillway ehould be surveyed t o in su re th at i t i s constructedi n accordance with the plan dimensions and l e f t i n the spec ifie d condition.The f i n a l in sp ect ion should be made immediately a f t e r completion ofth e work and before the con trac tor mw s his equipment from the site.S ince th i s may not always be possible tra i ning of loc al contracto rs tounderstand and meet co ns tru cti on requirements can save time of both th econtractor and the technical s taff .

RXCORDS OF THE COMPLETED WORKl l obs erva tion s and measurements made i n connection with th e f i n a lins pect ion of farm pond con stru ctio n should be recorded i n engineeringloose-leaf or f ie ld notebooks and noted i n red on the constru ction plans.sample of the measurements required i s shown i n t he Con etru ction CheckNotes Figure 11-11 The note s ehould be f i l e d i n accordance with S ta te


41/78

igure11 11 onstruction check notes


42/78

memorandums. Some S t a t e l a w s r equ i r e a formal completion report and as-b u i l t p l a ns .

12 POND ND RESERVOIR M INTEN NCEfarm pond must be adequately maintained i f i t s purposes ar e t o be

real ized throughout i t s expec t ed l i f e . Severe d m ge t o o r t o t a l f a i l u r eof dams and sp ill wa ys have been caused by l ac k of maintenance. For th es ereasons i t i s important th at th e owner car ry out t he measures describe di n the following paragraphs.INSPECTION ND REP lRS

Farm ponds should be inspected pe r io dic al ly es pe cia l ly af t e r heavyra in s t o determine the need fo r minor re pa ir s . Tnrmediate re pa ir of te ne l imina tes t he need f or more cos t ly repa i r s l a te r - .

R i l l s on th e slop es of th e dam and washes i n the e ar th spi llw ay shouldb e f i l l e d w it h s u i t a b l e m at e ri a l. nd thorou ghly compacted. These ar ea sshould be reseeded or resoclded and f e r t i l i z ed as needed. Should the up-s t ream face of the e a r t hf f l l wash or s lough due to wave ac t ion pro tec t ivedevices such a s booms or r ipr ap should be in st a l le d. I f t h e r e i s seepagethrough o r under t he dam an engin eer should be co ns ul te d t o recormnendproper co rre ct i ve measures .

The vegetative cover on the dam and earth spillway should be maintainedby mowing and f e r t i l i z i n g when needed. Proper mowing prev ents th e forma-t i o n of woody growth and te nds t o develop a cover and r oo t system morere s i s t an t to runof f. Fences should be kept i n good rep a i r .Appur tenances such as t r ic k l e tubes t r as h racks ou t l e t s t ruc tu resva lves and water ing t roughs should be kept f r e e of t ra sh .Burrawing a nimal s may caus e se ve re damage t o farm pond dams o r s p i l l -

ways. I f such damage remains un repa ire d it may lead t o fa i l u r e . t h i c klaye r of sand o r grave l on th e f i l l d iscourages burrowing. P o u l tr y n e t t i n gcan be used e f fe c t iv e ly bu t it w i l l rust out and need replacement. I fthes e pe st s per s i s t aggressive t rapping and poisoning should be undertaken.

t i s d e s i ra b l e t o keep th e water i n a faxm pond as cle an and unpol luteds poss ib l e . Unnecessary trampling by l iv es to ck should not be permit ted.Where it i s no t p ra c t ic a l t o exclude l ive s toc k from a pond by fenc ing sm llrocks or gravel should be used t o pave t he approaches t o th e water . Drain-age from barn l o t s feed yards bedding grounds outhouses se pt ic tanksor oth er source s of contamination should be d iv ert ed from farm ponds. This

i s es pe ci al l y important where the water supply i s t o be used fo r harves t ingice f i sh and wi ld l i fe development or recrea t i on .In ar ea s where sur fa ce waters encourage t he breeding of mosquitoes

th e pond should be stocked wi th top-feeding fi sh . Gambusia minnows a r epa r t ic u l a r ly e f fe c t iv e . Where malar ia prev a i l s aqua t ic growth and


43/78

shorel ine vegetation should not be permitted, and sp ec ia l precautionsshould be observed in the planning, construction , and operation of th epond Most s t t e s i n malar ia l sec t ions have hea l th regula t ions cover ingthese prec utions whlch should be followed.In some are as th e development of alg ae and oth er forms of pla nt l i f e

in r e se rvo i r s m y become obje ctio nab le. Generally , the se a r e harmless,but they may cause disagreeable tastes or odors, encourage ba ct er ia ldevelopment, and make the pond unsi ghtl y. Treatment with blue ston ecopper sulfate w i l l check the development of algae. The usual dosagei s o r 3 pounds per mi ll io n gallon s of water, w e l l dist r ibuted through-out th e re se rv oi r. Overdosage m y be harmful t o both wi ld l i fe and l ive-stock.


44/78

P RT I EXC V TED PONDSAn excavated pond i s the s implest type t o construct and i s the onlytype that can b e co ns tr uc te d i n r e l a t i v e l y f l a t t e r r a i n . The fact that-the capacity of these ponds i s obtained almost solely from excavation

l i m i t s t h e i r p r a c t i c a l s i z e , Since excavated ponds can be constructed t oexpose a minlnnam water surface are a i n proport ion t o volume,. they a readvantageous where evaporation lo ss es ar e high and water i s scarce. SeeFigures 11-12 and 11-13.1 TYPES OF MC V TED PONDS

Excavated farm ponds may be div ide d i n to two types: tho se fe d bysurf ace runoff; and those fed by ground water aq uif ers , usu ally lay ers ofsand and gravel, In some instances a pond may be fed from both of the sesources.2 LOCATION OF EXCAVATED PONDS

The lo ca tio n of excavated p o d s depende on the purpose for which thewater i s t o be used and on othex fac tors d i scussed previous ly i n t h i schapter .Excavated ponds f ed by su rf ac e run off may be loca ted on almost anytype of topography. They a re , however, most s a t i s f a c to ry and most conrmoq-l y used i n areas wi th compara tive ly f l a t t e r ra i n . A pond may be locatedi n a broad na tu ra l drainageway or t o one sid e of a drainageway i f th e run-off can be dive rted in to t he pond. The l o w point of a natu ra l depress ioni s of t en a good location for an excavated pond. After the pond i s f i l l e d ,excess runoff eecapes through na tu ra l drainageways. Thus, loc ati on s withfavorable discharge cor~ di t io ns hould be selec ted.An excavated pond fed by ground water aquifers can be located onlywhere shallow underground flow exiata or where the permanent water t a b l eIs within a few feet of the sur face . See Figure 11-14.

3. SOILS INVESTIGATIONWhere the excavated pond i s t o be fed by su rface runoff, r e l a t i v e l yimperv. iws so i l a t the s i t e i s e s s e n t i a l t o avoid excess seepage losses.Clays and s i l t y cla ys extending below the planned r ese rvo ir depth a re

.most des i rable , and s i te 8 wi th sandy c lays usual ly pr we sa t i s f ac to ry .Si te s where so i l s ar e poroue or ar e underlain by sands or gravel shouldbe avoided unless th e owner i s prepared t o bear th e expense of an a r t i f i -c i a l l in ing, Soi le underla in by l imestone contain ing crevices , s inks orchannels should be avoided.The performance of nearby e xi st in g ponds i n a si mil ar s o i l i s a goodindica tor of the s ui ta bi l i ty of a proposed s i te . Such observations .ofex is ti ng ponds should be supplemented by subsurface in ve st ig at io ns . Someindica t ion of the permeabil i ty of the s o i l may b e o bt ain ed b y f i l l i n g t h etest holes with water and observing the seepage ch ara c te r i s t ics of themater ial


45/78

C R O S S SEC T t ON

LONGITUDIN L S E C T I O N( f o s ca l e

igure 11 12 Excavated pond and typic l sect ions Note fenced desi l t ing re abwe pond


46/78

WASTE M TERI L STACK E

NO+ o scale WASTE M TERI L REMOVEDFigure 11 13 ross sections of excavated pond showin methods of waste material disposal


47/78

Figure 11-14 Excavated pond fed by ground wa te r.

S it e s proposed fo r aqu ifer-fed excavated ponds re qu ir e a thorough sub-surface- invest igat ion. T e s t holes should be bored t o determine the e xi s t -ence and physical ch ar ac te r i s t ic s of the water-bear ing mat er ia l . The levelt o which water w i l l r i s e i n t he t e s t ho l e s u sua l ly i n d i ca t e s t he normalwater le ve l i n th e completed pond. The ve r t ic a l d i s tan ce between t h i sle ve l and th e ground sur fac e w i l l determine th e volume of ex cava tion re-qu i r ed tha t w i l l not co nt r ibu te t o th e usab le capac i ty of the pond. Froman economical s tandpoint t h i s ve r t ic a l dis ta nce between water lev el andground su rfac e or di na r i ly should not exceed s i x fee t . The r a t e a t whichthe water r i s e s i n t h e t s t hole s should a ls o be observed. A r a p i d r a t eof r ise i nd i ca t e s a high y ie ld ing aqui fe r . t a l s o i n d ic a t es t h a t t h ewater may be expect ed t o r e tu rn t o i t s normal le ve l with in a short t imea f t e r drawdown. A slow r a t e o f r i s e i n t he t e s t ho le s i nd i ca t e s a low-yielding aquifer and a slow rate of recovery i n th e pond. Observationsof the t s t holes should be made during dr ie r seasons t o avoid being m i sled by a temporary high water t able .

4 SPILLW Y ND INLET R QUIR M NTSWhere an excavated pond fed by surf ace runoff i s located on slopingt e r r a i n a po rt io n of t h e excavated ma te ri al may be used t o c r ea t e a lowdam around th e lower end and si de s of t h e pond t o in cr ea se i t s capac i ty .In such cases an ear th sp i l lway i s r e q u i r e d t o pass excess storm runoff


48/78

around th e dam. The procedures f o r planning t he sp illwa y and prov idingfor prote ct ion against erosion ar e the same as those previously discussedunder Embanlanent PondsSometimes surface runoff must enter an excavated pond through a chan-nel or ditch rather than through a broad shallow drainageway. In such

cases the w e r f a l l f rom the d i tch bottom t o the bottom of the pond maycrea t e a serious erosion problem. Scouring w i l l t ake p l ace i n . t h e s ideelope of th e pond and fo r a considerable dis tanc e upstream i n the di tc h.The resulting sediment w l l l reduce the depth and capacity of the pond.Protect ion can best be provided by th e use of one or more lengths of pipeof adequate s i ze p laced i n the d i tch backf i l l ed and extended over thesi de slope of the excavation. The extended po rt io n of th e pipe may becantilevered over timber supports. The required dianreter of the pipe foran on-channel pond w i l l depend on the peak rate of runoff that may beexpected t o occur once i n ten ye ars. The procedure for estimating peakr a t e s of runoff s presented i n Chapter 2 of t h i s manual. Exhibit 11-7shows the capa city of various si ze s of pipe in le ts . Where more than onepipe i n l e t i s required th e ir combined capacity should equal or exceedthe estimated peak rate of runoff.

For off-channel ponds th e pipe s iz e should be such th at t w i l l dive r tfrom the channel. su ff ic ie n t runoff from normal annual ra in fa l l or low flowsto supply the reservoir . ere du rati on of flow s of prime importance.Off-channel ponds also can b e f i l l e d by pumping from th e stre am dur ingstorm flows. The pump must be large enough to f i l l the pond before streamflow re turns t o normal.I n areas where a considerable amount of s i l t i s c ar rie d by the inflow-

ing water a grassed f i l t e r s t r i p should be provided in the drainagewayirmnediately above th e pond. The width of t h i s s t r i p should be equal to orsomewhat g re at e r tha n th e width of th e pond and i t s len gth should be 100feet or more. The pere nnial gra sses used should crea te a high n valueso that flows through the grass w i l l be reduced in ve loc i ty t o a pointwhere the s l t w i l l s e t t l e out and t he water e nterin g th e pond w i l l ber e l a t i v e l y s i l t - f r e e . See small in se rt Figu re 11-12.5. PL NNING N EXC V TED POND

SH PE AND C P CITY

Excavated ponds may be co nst ruc ted t o almost: ny shape desi re d how-ever a rectangular ahape usually i s the most convenient for excavatingequipment.The required capacity of an excavated pond fed by su rfa ce runoff i sdetermined by t h e purpose fo r which water is needed and the amount ofinf low that can be expected. These fa ct or s have been discu ssed underEdmnlanerrt Ponds.The required capacity of an excavated pond f e d by an underground


49/78

water-bearing layer i s di f f ic u l t t o de te rmine s ince the es timated r a t e ofinflow ih to the pond can ra re ly be estimated with reasonable accuracy.For t h i s reason the pond should be cons truc ted i n such manner t h a t i t canbe enlarged i f the o rigi na1 capaci ty proves inadequate.SELECTING POND DIMENSIONS

The selected dimensions of an excavated pond w i l l depend upon therequired capacity. Excavated ponds fed by s ur fa ce runoff should have adepth equal t o or gr ea te r t han th e minimum requ ired by S t at e Standardsand Specifications. Where an excavated pond i s fed from ground wa ter thedepth should extend we ll i n t o th e water-bearing ma te ri al . The maximumdepth w i l l depend on the clim atic conditions the nature of the materialt o be excavated and th e type of equipment t o be used i n excavatin g thepond.

The width of an excavated pond w i l l not ord ina ril y be limited exceptthat th e type and s i z e of th e excav ating equipment m y become a limitingfac to r . For example i f a dr ag li ne i s used t he le ngt h of th e boom w i l ldetermine the maximum width of excavation that can be made with properplacement of t he waste ma te ri al .

The minimum length of the pond should be t h a t needed t o obt ain t herequ ired pond cap aci ty. However t h i s leng th may need t o be increased t omeet the needs of t he excavating equipment such as a car ry al l.

The side elopes of an excavated pond should not be steeper than thenatu ral angle of re po se of the materia l being excavated. This angle w i l lvary wi th d i f f e ren t so i l s but n most cases t he side slopes should bef l a t t e r t ha n 1: 1Where the water i s t o be used f or watering l ive sto ck a ramp wit h aslope of 4:1 or f l a t t e r should be provided a t one or both ends fo r accessRegardless of the intended use of t he water these f l a t slopes a t the endsof th e pond a re necessary when tract or -pu lle d scr aper s or bulldoze rs ar eused or construction.

ESTIMATING THE VOLUME OF N EXCAVATED PONDAfter the dimensions and side slopes of the pond have been selected

i t i s usually necessary t o prepare an est im ate of th e volume of ex cavation .Such an estimate determines the cost of the pond and serves as a bas i s fo rpayment i f th e work i s done by contract.

The volume of excavation re qu ir ed ca n be estimated with s uf fi ci en taccuracy by use of the p rism oidal formula:A B C where:z

V Volume of excavation i n cubic yardsA Area of the excavation a t the ground surface i n square fee tB Area of t he excavatio n a t the mid-depth po int 112 D , i nsquare f e e t


50/78

C = Area of t he excavation a t th e bottom of t he pond, i n squarefee t .D = Average depth of th e pond, i n fe e t27 = Factor converting cubic fe et t o cubic yardsAs an example, assume a pond with a depth , D, of 12 f ee t ; a bottom

width, W of 40 fe e t , and a bottom len gth , L, of 100 f e e t a s shown i nFigure 11-12.The sid e slope a t the ramp end i s 4:l and the remaining slopes are2: l. The volume excavation, V, s computed as follows:Top length = 12 2) 12 4) 100 = 172 feetTop width = 12 2) 2) 4- 40 = 88 feet

A = 88 x 172 = 15,136 square feetMid-length = 6 2) 6 4) 100 = 136 feetMid-width = 6 2) 2) 40 = 64 feet

4B = 4 64 x 136) = 34,816 square feet= 40 x 100 4,000 square f e e t

A 4B C) = 53,952 square feetThen V = 5 y 95 x = 3,996 cubic yards or 4,000 cubic yards)6 27Assuming th a t the normal water le ve l i n th e pond i s a t t he groundsur fac e, the volume of water t hat can be st or ed i n the pond s 4,000 cu,

yds. x ,00062, or 2.48 acre fe et . To convert to gallon s mul tipl y 4,000cu. yds. by 202.0 t o ge t 808,000 ga llon s. The s me procedure s used tocompute the volume of water tha t can be st or ed i n th e pond when the normalwater level s below the ground surface. I n t h i s case, the value assignedt o the depth, D i s the a ctu al depth of water i n the pond ra th er than thedepth of excavation.DISPOSAL OF WASTE MATERIAL

The placement or disposal of the excavated material should be plannedi n advance of con stru ctio n. Proper disp osal w i l l prolong the useful l i f eof the pond, improve t s appearance and f a c i l i t a t e maintenance and estab-lishment of vegetat ion . The waste ma ter ial may be stacked, spread, orremoved from the s i t e as cond itions wa rrant.

The waste ma te ri al , when no t removed from th e s i t e , should be placedi n a manner tha t i t s weight: w i l l not endanger th e s t a b i l i t y of t he ponds ide s lopes and the ra infa l l w i l l not wash the material back into the pond.Stacked material should be placed i n a uniform bank with side slopes nosteeper than the natural angle of repose of t he s o i l . A berm with a widthequal to the depth of the pond, but not l es s than 12 fe et should be l e f tbetween th e toe of t he waste bank and th e edge of th e pond. I n the caseof l ar ge ponds, t i s o f t e n des i ra b le t o stack the waste material alongtwo side s of th e pond t o reduce the heig ht of the banks. I n the NorthernPlains the waste banks may be placed on the windward side of th e pond t oserve as a snow fence fo r coll ectin g d r i f t s i n the pond. ee Figure 11-12.


51/78

anks placed i n t h i s manner m y al so reduce evaporation los ses by break-ing th e fo rce of pr eva ilin g winds across the pond.Spreading th e waste mater ial along one or

reservoir sizing

Documents