The project was constructed in two phases

October 2005

KAHAMA-SHINYANGA

WATER SUPPLY PROJECT

HYDRAULIC CALCULATIONS

OF

INTAKE, PUMPING STATIONS, RISING MAINS,

TREATMENT STRUCTURES AT THE IHELELE WTP

AND

MABALE RESERVOIR

SHANGHAI MUNICIPAL ENGINEERING

DESIGN INSTITUTE

OCTOBER 2005October 2005TABLE OF CONTENT

Design Basis

2

1. Intake, Raw Water Pump Station and Rising Main.

Design Basis

Intake Structure and suction Well

Intake Grid arrangement

Intake Channel

Head loss from IntakeGrid head loss

Intake Grid head loss

Intake Channel head loss

Suction Well Screens

Total head loss from Intake to Suction Well

Total pump heads

Head loss in Suction Pipes

Head loss in Raw Water Pump Station

Head loss in Raw Water Rising Main

Static HeadTotal pump head

NPSH

Required NPSH (NPSHr)

Available NPSH(NPSHr)

Bottom level of Suction Well

Installation level of Pumps

Pump ChoiceHeight of Pump Station

2.0 Hydraulic Mixing Tank, Mechanical Flocculation Tanks and Sedimentation Tanks.

2.1Hydraulic Mixing Tank

2.1.1Design Criteria

2.1.2Design Layout

2.1.3Hydraulic detention time

2.1.4G-Value

2.2.0 Flocculation Tanks

2.2.1 Design Criteria

2.2.2 Design Layout

2.2.3 Hydraulic detention times

2.2.4 Flocculation Mixer

2.3.0 Sedimentation Tanks

2.3.1 Design Criteria

2.3.2 Calculations

2.3.3 Design layout

3.0 Rapid Sand Filters and Clear Water Tank

3.1

Design Criteria

3.2

Design layout

3.3

Inlet channels and Inlet valves

3.4

Clear Water Tank

4.0

Back wash Pumps and Browsers4.1

Design Basis4.2

Backwash Pumps

4.2.1

Backwash flow

4.2.2

Static pump lifts

4.2.3

Head loss in Filters Laterals

4.2.4

Head Loss of Supporting Layers and Filters media

4.2.5

Head Loss in Water Gullet

4.2.6

Head Loss in Backwash Main

4.2.7

Head loss in Fittings

4.2.8

Total head Headlosses

4.2.9

Choice of Pumps

4.3 Air Blowers

4.3.1 Air-scour flow

4.3.2 Air pressure requirements

4.3.3 Head loss in Air pipe fittings

4.3.4 Required Air Pressure of Air Blowers

4.3.5 Choice of Air Blower

5.0 Head Loss between Structures

5.1 Head Loss in Flocculation Tanks

5.2

Head Loss in Sedimentation Tanks

5.2.1 Perforated wall5.2.2

Outlet troughs

5.3

Head loss through Sand Filters

5.4

Head loss from Sedimentation Tanks to Filters

5.5

Head loss from Sand Filters to Clear Water Tank

6.0 Balancing Tank

6.1

Design Basis

6.2

Balancing Tank design

6.2.1

Balancing Tank Volume

6.2.2

Supernatant Pumps

6.2.3

Sludge & Storage

7.0 Chemical Dosing & Storage

7.1

Design Basis

7.2

Alum and Polyelectrolyte Storage

7.2.1

Design Basis

7.2.2

Required Alum metering pumps and solution Tanks

7.2.3

Required Alum and Polyelectrolyte storage

7.3

Lime storage requirements

7.3.1

Design basis

7.3.2

Required Lime storage areas

7.3.3

Required Screw Pumps for Lime Dosage

8.0 Chlorine Dosing & Storage

8.1

Design Basis

8.2

Storage requirements8.2.1 Chlorine Cylinders in operation

8.2.2 Choice of Chlorinators

8.2.3

Chlorine Cylinders

8.2.4

Ventilation of Chlorine Cylinder room and Chlorinator room

8.2.5

Chlorine neutralization apparatus

9.0 Clear Water Pump station and Rising Main

9.1

Design basis

9.2

Review the parameter of the pumps

DESIGN BASIS

The project was constructed in two phases. The phase I design demand for 2016 was 80,000m3/d, excluding 5% losses. The second phase design demand for year 2024 is 107,700m3/d, excluding 5%losses.

Most structures were designed for phase II, except the Mechanical Flocculation Tanks,

Sedimentation Tanks and Rapid Sand Filters which were designed for phase I only.The installation of pumps was phased with extra set of pump to be installed in Phase II, both in the raw Water Pump Station and Clear Water Pump Station.1 Intake, Raw Water Pump Station and Rising Main.

Design Basis

The design flows are:-

Phase I:80,000m3 x 1.05 = 84,000m3/d=3,500m3/h=0.972m3/sPhase II107,700x1.05

=113,085m3/d

=1.309m3/s

Intake Structure and Suction Well.

The intake structure was designed for phase II. There are steel grids on the intake mouth to keep the debris from entering the Intake. On the upstream, it is possible to close the Intake by inserting stop-logs designed in U-Shaped steel profiles embedded in the concrete sidewalls and middle column at the Intake mouth.The lowest water depth in the Intake Channel (without any clogging of the Intake grid) was 1.15m =1132.70-1131.55 where the former level was the estimated Lowest Water Level (LWL) in the Lake (by assuming a safety margin of 48cm below the historic low level in the lake of +1133.18 as per 29th August 2005) and the latter is the bottom slab level in the Intake Channel.

The chosen length of the weir was 2x2.7=5.4mFlow sections A =5.4x1.45=7.83m2 ( the water depth at the weir mouth is 30cm higher than in the Intake Channel as bottom is sloping in the opposite direction of the flow direction.)

The highest flow rate for phase II is therefore 1.309/7.29=0.17m/s at the Intake mouth.

As stated above, the bottom of the Intake mouth slopes are in the opposite direction with a slope of 2% with abrupt change of the bottom slab level of 20cm where the Intake Channel starts. This creates a sludge-pocket to avoid entering the Intake Channel. This part should occasionally be flushed clean by applying high pressure hose water.Intake Grid Arrangement

The grid is made of 20mm steel bars at 100mm center, say the free openings between the bars is 80mm.

Intake ChannelThe width of the Intake Channel is 1.8m and the length is 90m. The Channel slopes towards the suction well by a slope of 0.2%.

There are four (4) flat screens at the inlet to Suction Well. The flow rate passing the screen shall not exceed 0.4m/s.

The formula of area of screen:

F1= Q/( x x K1 x K2)

Where:

Q=1.309 (m3/s)

:flow rate passing the screen K1:Coefficient of reduced area due to grids

K1=b2/(b2 + d2)

Where: b

b: size of sceen opening10mm in diameter

d: diameter of screen grids2mm

K1 = 102/(102 +22)=0.6

K2: Possible clogging coefficient0.5: contraction coefficient

0.7

F1=1.309/(0.4x 0.7 x 0.96x 0.5)=9.74m2

1.4Head loss from Intake to suction Well

The following is calculated with the flow in phase II

1.4.1 Intake Grid Head Loss

The grids head loss in is taken as 0.1m assuming debris can be clogged on the grids.

1.4.2 Intake Channel head loss

From the LWL of 1+1132.70 in the lake the level may drop 10cm to 1132.60 if the grids are partly clogged. The bottom slab level at the intake mouth is +1131.25 and 0.02x5m= 0.10m higher at the start of the Channel, where a 20cm increment in the slab level occurs. The bottom level at the Channel inlet is therefore +1131.25 +0.30=+1131.55 and the water depth at this point minimum +1132.60-1131.55=1.05m if the grids are partly clogged and a head loss of 10cm is created.

The following formula applies for the gradient i (or water surface level in an open channel):

I 0.5 =Vn/R0.67 where;

flow velocity

v= Q/A= 1.309/1.8x 1.05=0.69m/s

friction factor

n=0.02 from Mannings Number M=1/n=k0.1666/25,8, where k=roughness.With a k =0.3mm, n=0.02

hydraulic radiusR= A/L 1.05x 1.8/1.8 x1.05x2=0.5

i= 0.027312=0.0000439

The drop in water level is therefore h= 0.0000439 x 90m=0.00395m or approximately 0.4cm.

When the water flows into the Suction Well the velocity goes from approximately 0.69 m/s to nil and a velocity head of approximately 2cm is lost.

The total loss is therefore estimated to be 2.4cm, say 3cm.

1.4.3 Suction Well Screens

The head loss caused by screen is taken as 0.10m

1.4.3.1 Total head loss from Intake to Suction Well

H1 = 0.10 +0.03+0.10=0.23m

1.5 Total Pumps Heads

1.5.1 Head loss in suction Pipes.

DN700 is adopted as suction pipe for each pump, with three (3) pumps in operation in Phase II, therefore the flow velocity is 1.309/3/(3.14/4x0.72)=1.13m/s

The length of each suction pipe is 3m.

There are fittings of one (1) bell-mounted pipe DN 1000x DN700, one (1) butterfly, one(1) flexible joint and one (1) taper DN 700x DN 400.

Local head loss efficiency

2/2g

Bell-mounted pipe

0.21.13m/s0.065

Butterfly valve

0.31.13m/s0.065

Flexible joint

0.211.13m/s0.065

Taper

0.181.13m/s0.72

Local head loss hL=(0.2 +0.3 +0.21)x 0.065+0.18 x 0.72=0.18m

Friction head loss hf is about 0.01m

Total head loss in the suction pipes:H2:=0.18 + 0.01 0.2m

In Phase I, the head loss in the suction pipe is almost the same.

1.5.2 Head loss in Raw Water Pump Station

The head loss within the Raw Water Pump Station, H3 is taken as 1.0m (Phase II).

1.5.3 Head loss in Raw Water Rising Main.

The total length of Raw Water Rising Main from the Raw Water Pump Station to the Inlet mixing tanks is about 3150m. The first 350m is laid with DN 1200mm pipes (originally from first proposed intake location ) and remaining 2800m with DN 900 mm pipes.

In phase I, friction head loss is 0.41m/km in the DN1200 mm and 1.7m/km in the DN900mm at Q=0.972m3/s (84,000m3/d). And local head loss is taken as 5% of friction head loss.

Total head loss in the Rising Main: Hf =((0.41x 0.35) + ( 1.7 x 2.8)) x 1.05 =5.3m

In phase II, friction head loss is 0.75m/km in the DN 1200mm and 3.4m/km in the DN90mm at Q= 1.309m3/s (113,085m3/d). The local head losses are taken as5% of the friction head loss

Total head loss in rising main: Hf = ((0.75x0.35) +( 3.4x 2.8)) x 1.05=10.3m

1.5.4 Static Head

The lowest measured lake level at Mwanza South Port was in August 2005 at +1132.15. This was 47cm lower than the lowest recorded level from February 1994 of +1132.62.

In August 2004, the level on site was recorded at +1133.18. It can be assumed that this level would also be the lowest recorded at the site as it will follow the relative recordings at Mwanza South Port. Further more, we would like to add a safety depth of 0.48m below this recorded low. We therefore assume the Lowest Water Level of +1133.18-0.48 = +1132.70m.

In phase II, the lowest water level in the raw water suction well:

+1132.70-H1=1132.70-0.23 =1132.47m

The Water Level in the Mixing Tanks is 1149.73m

Static Head is;

Hstatic=+1149.73-1132.47=17.26m or approximately 17.3m (Phase II)

1.5.5. Total Pump Head

Head loss in pump house:Phase II, Hp = H2 +H3 =0.2 +1.0 1.2m

In Phase II, the pump Head:

Ht =Hstatic + Hp +Hf = 17.3 +1.2 +10.3 = 28.8mWith high water level in the lake (approximately +1135.0) the static lift Hstatic =+1149.73-1153.0=14.7m pr 2.3m lower. The total pump head would then be 26.5mIn phase I the friction losses is 5m less when 2 pumps are running (compared with maximum 3 pumps running in Phase II) Also the internal losses in the ppumps station is less, say 60cm instead of 1.2m losses in the Intake Channel can be assumed to almost the same as most of the losses are taken as clogging on the Intake grid and on the screens (20cm out of a total of 30cm) The pump head for 2 pumps running in phase I can then be calculated as follows.

H= 17.3 + 0.6 + 5.0 =22.9M at LWL in the lake, and 20.6m at HWL in the lake.1.6 NPSH

1.6.1 Required NPSH (NPSHr)

NPSHr is depending on type of pump and the duty point. It shall always be lower than the available NPSH, indexed NPSHa.1.6.2 Available NPSH (NPSHr)

It is chosen to locate the suction line always to be submerged in water , i.e the suction height Hsu is negative.It is chosen to have the suction pipe centerline 0.80m below the lowest level in suction well,i.e Hsu. =-(0.80m-losses in the DN1000 mm suction pipe and the DN700 mm 90o bend ) =-(0.80-3.0v1 2/2g-0.5v22/2g)=-(0.80-3.0 0.562/2g-0.5 1.132/2g)=-0.72m.NPSHa=Hg-Hz-v12/2g-HsuWhere:

Hg:approximately 9.0m Atmosphere pressure on located pump elevation of about +1140m

Hz:=Saturated vapor pressure at 30Oc0.43m

Hsu:suction height of pump

v1: velocity in suction opening of pump, suction opening diameter of 400mm v1 =1.309/(3.14 x 0.42/4)/3 =3.47m/sSo:

NPSHa= 9.0 -0.43-(3.472/2g)- (-0.72) =8.68m or approximately 8.7m

1.7 Bottom Level of Suction Well

The Lowest Lake Level is 1132.70m (LWL). Total Head Loss from the suction Well is calculated as maximum 0.23m.Therefore Lowest Suction Level (LSL) in the suction well is;

LSL= +1132.70-0.23=+1132.47m

(The highest water level is approximately +1135.0m)

The centerline of the suction inlet to the pump is chosen to be 80cm below the LSL. The suction pipe has an eccentric DN1000 x 700mm 90o bend with a 1000mm suction inlet and a DN 700x 500mm eccentric taper. The level of the suction inlet is therefore:+1132.47-0.80-0.15-0.75=+1130.77. To avoid creation of a vortex, the suction inlet shall be located dmin.= 1.7D0 lower than the LSL, where D0 is the diameter of the suction inlet.

With D0 = 1.0m, dmin=1.7m or +1132.47-1130.77=1.70 meter, therefore OK.The space between the suction inlet and the well bottom shall be Hmin. =0.8 D0.

The bottom level of the suction well should therefore be at;

+1130.77-0.80=+1129.97 say +1129.90m

1.8 Installation Level of Pumps

The level difference between the bell-mounted inlet and the centerline of the suction pipe to the pump is 750mm.

Therefore the centerline of the suction pipe is +1130.77 +0.75=+1131.52m

The level difference between the suction nozzle and suction pipe is 150mm. Therefore the level of suction nozzle is +1131.52 +0.15=+1131.67

Height difference between pump shaft and pump suction nozzle is 350mm.

Pump shaft level is +1131.67 +0.35m

1.9 Pump Choice

Chosen pumps: Omega 350-360A from KSB

Three (3) pumps are chosen to meet the requirements for phase I, with two (2) duty and one (1) standby. In Phase II, four (4) pumps are chosen, with three (3) duty one (1) standby.

1.10 Height of Pump StationThe bigger part of pump and mortar is less than two (2) tones. Therefore the Model Lx electrical single girder overhead crane is adopted and its loading capacity is 2 tones.

The height of mortar is 1315mm, and the width is 1290mm.

The required height between the bottom of crane and the bottom of beam is 1014mm The minimum distance from hoist hook to the bottom of crane is 837mm.

Assuming pumps and motors will be carried into pump house by a car, which is 1.30m above the platform in height. The length of hoist rope is about 1.2times of pump width.

Therefore:

The length of hoist rope: = 1.2 x 1290 = 1548mm. The pump house height from indoor floor is:-

1315+1548+1014+837+1300+500 (spare height)=6514mm. The height is adopted as 6.6m.2.0 Hydraulic Mixing Tank, Mechanical Flocculation Tanks and Sedimentation Tanks.As shown in the drawings, the mechanical flocculation tanks and the sedimentation tanks are combined in one structure. There is only one mixing tank, where also the water is split in to four (4) equal flows, one for each of sedimentation tanks, two (2) lines with two (2) units each. There are three (3) compartments for flocculation, where the first two (2) have mechanical mixers.2.1 Hydraulic Mixing Tank.

2.1.1 Design Criteria

The adopted mixing method is waterfall. The main parameters are as follows.

G:400s-1T:Hydraulic detention time:60s

2.1.2Design Layout

As shown in the drawings, the raw water enters into a mixing tank by a DN900 pipeline. The single mixing tank has three (3) compartments. The middle one is for distribution. The water causes turbulence, with two weirs on each side. Water falls in to the side compartments. The height of the waterfall is controlled by the elevation of weirs and slide gates can shut the weirs individually. The dimension of the middle compartment is 1.20x 4.60m, with water depth of 5.23m. The dimension of the side compartment is 0.65 x 4.60m, with water depth of 4.28m.

There are two dosing points on the inlet pipe DN900 for lime, chlorine respectively. The aluminum sulphate and polyelectrolyte dosing point is set before waterfall, just being parallel with weirs.

2.1.3Hydraulic detention time.

Volume:

Middle compartment:

1.20x4.60x5.23= 28.87m3

Each side compartment:0.65x4.60x4.28=12.79m3

Total volume:

28.87+12.79x2=54.45m3

Hydraulic detention time:T=54.45/0.972=56.0S

2.1.4 G-values

Calculation of the value of G:

G=p/(V= gQh/(V=gh/Vt

The difference of water level between the middle compartment and the first flocculation tank is 1.00m.

P:Diffused energy P=gQh

[kW]

h: total head loss

1.0m

[m]

(: Kinetic viscosity(=v

[Pa s]

When temperature is 20 0C, v = 1.0105 x 10-6[m2/s]

V: volume V=QT

[m3]

g: gravitation acceleration 9.81

[m/s2]T: Hydraulic detention time 56.0

[s]

: density of water

1,000

[kg/m3]

So:G= (9.81 *1.0)/(1.0105*56.0*10-6)=416s-1 There are four (4) waterfalls weirs, each of which is 1.5m in width. q = 1.84x H1.5(for rectangular, sharp edged overflow), where:

q: quantity of water per meter width [m3/m/s]

H:water depth above weir

[m]

Trying 0.20mq = 1.84 x0.20 1.5 =0.1646m3/m/s

when the width is 1.5m,

The quantity of water: Q= 1.5 x 0.165= 0.247m3/s

Each weir: Q= 0.972/4 =0.243m3/s

So the water depth above weir is 0.20m.

The sum of waterfall and the friction caused by water flow opening between mixing tank and flocculation tank is taken as 0.80m.

The total head consumed in mixing tank is 0.20 +0.80=1.00m

2.2 Flocculation Tanks.

2.2.1 Design criteria

There are 2 lines of flocculation tanks, each of which comprises 3 tanks.

The main parameters:

The first tank: mechanical flocculation, the value og G of 40s-1, with a detention time of 180s

The second tank: mechanical flocculation, the value of G of 40s-1, with a detention time of 360sThe third tank: no mixer, with detention time 360s

2.2.2 Design layout

The main parameters:

The first tank:

the dimension: 4.60m x 4.60m, 4.23m deep;

The second tank:the dimension: 6.50m x 6.50m, 4.22m deep;

The third tank: two parts, the dimension of each of 6.75m x 3.10m, 4.21m deep

Water flows upwards and downwards in sequence through the three tanks.

2.2.3 Hydraulic detention times.

Hydraulic detention is calculated as follows:-

Water flow of each line 0.972/2 =0.486m3/s

Detention time in the first tank:= T1=V/Q=4.60x 4.60x4.23/0.486=184s

Detention time in the second tank=T2=V/Q=6.50x6.50x4.22/0.486=367s

Detention time in the third tank: = T3=V/Q=6.75x3.10x 4.21x2/0.486=363s2.2.4 Flocculation Mixer

The mixing equipment is vertical axial mixer. The first two tanks are furnished with mixers but the last one. Water flows upwards and downwards in sequence through the three tanks.Design Criteria for Mixer

The material of the paddle is 8mm steel board. The paddle should be 0.4m below the water surface and 0.3~0.5m above the bottom of the tank. The distance between the edge of the paddle and the wall of the tank should be no more than 0.25m.

The total area of paddles in any one tank should be 10%~20% (at most 25%) of the section area of flow. The width of the paddle is 0.1~0.3m and the ratio of the width to the length of the paddle should be 1/15~1/10.

To avoid short circuit, fixed baffles should be installed on the tank wall. Employed Formula

(1)Rotation Speed of mixer:

n0=60/D0(r/min.)Where:

:Linear velocity of the centre point of the paddle (m/s)

D0:Rotary diameter of the centre point of the paddle (m)

(2) Consumed power by each paddle

N'0 = yklw3/408(r24-r14)(kW)

w =0.1n0(rad/s)

k=/2g

Where

ynumber of paddle in a mixer (piece)

l length of paddle (m)

r2outer radius of paddle (m)

r1 inner radius of paddle (m)

wangular velocity (rad/s)

kfactor

Density of water (1000kg/m3)

Resistance coefficient (1.10)

(3) Mixer PowerN0=N0'

N=No/(kW)

N0Impeller Power

efficiency coefficient

(4) G-value

G=(102N0/(W)

(102x10-6 Kg.s/m2

Wsingle tank volume (m3)

The first Flocculation Tank

(1) Paddle Size

The distance between the edge of the outer paddle and the tank wall is adopted as 0.25m. Therefore, the diameter of the mixer is 4.6-2x0.25=4.10m.The length of the paddle is 2m and the width is 0.14m. The paddle is classified by three grades, totally 12 paddles.

The ratio of the total area of paddles to the sectional flow area:

12x0.14x2.0/ 4.6x 4.23= 17.3%

(2) Motor Power for Mixer.

The rotary diameter of the centre point of the paddle D0 is 2.64m.

Linear velocity of the centre point of the impeller is 0.62m/s.

Rotational Speed:

n1=601/Do=4.49r/min.

w1=0.449rad/s

(b/l=0.14/2.0=0.07