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DRY SEDIMENTATION POND

A. Determine overland flow time of concentrationCHECK Catchment Area = 5.5 ha

CHECK Overland slope = 0.8 %

CHECK Overland length = 190 m

CHECK Manning "n" = 0.015

COMPUTE Overland time, to = 9.63 min

COMPUTE Adopted time of concentration, tc = 10 min

B Sizing sendimentation

Table 39.4CHECK Soils type = C

Table 39.5 for a 3 month ARICHECK Required surface area = 333

CHECK Total Volume = 400

COMPUTE Site surface area required = 1,831.50

COMPUTE Site total vomue required = 2,200.00

i) Settling zone

COMPUTE 0.6 m

COMPUTE Required settling zone = 1,100.00

CHECK 17 m

COMPUTE 107.84 m

COMPUTE Average surface area = 1,833.33

Check settling zone dimensions

COMPUTE 179.74 < 200 OK

COMPUTE 6.34 > 2 OK

m²/ha

m³/ha

m²

m³

Settling zone depth, y1 =

m³

Assume average width, W1 =

Required settling zone a. length, L1 =

m²

L1 / y1 =

L1 / W1 =

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C Sediment Storage Zone

COMPUTE Required sediment storage volume = 1100

CHECK For a side slope Z = 2(H):1(V) 2

COMPUTE 15.8 m

COMPUTE 106.64 m

Required depth for the sediment storage

CHECK 0.6 923.682CHECK 1100 0.7 1060.85CHECK 0.73 1101.08 > 0.3 OK

D Overall Basin Dimensions

At top water level

COMPUTE 18.2 m say 18 m


Base



Depth:

COMPUTE 0.6 m

COMPUTE 0.73 m

m³

.·. W2 = W1 - 2 d1/2 x Z

.·. L2 = L1 - 2 d1/2 x Z

V2 = Z²(y2)³ - Z (y2)² (W2 + L2) + y2 ( W2 x L2 )

Trial and error to find y2 y2 V2

V2

WTWL = W1 + 2 x Z x y1/2

LTWL = L1 - 2 x Z x y1/2

WB = W1 - 2 x Z x (y1/2 + y2)

LB = L1 - 2 x Z x (y1/2 + y2)

Settling Zone, y1 =

Sediment storage zone, y2 =

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E Sizing of outlet pipe

COMPUTE Total depth, y 1.33 m Cd = 0.6

COMPUTE Average surface area, Aav = 1,638.43

Draining time, 24 hr after filling

COMPUTE 0.0165 Equation 19.5, Volume 7

CHECK Using orifice size of 50 mm

COMPUTE Area of each orifice is, Ao = 0.00196

Total number of orifice required,

COMPUTE 8 nos

At height of increments of 300mm,starting at the bottom of the pipes, put 2 ro 4 nos of 50 mmorifices evenly around the pipe

F Sizing of emergency spillway

The emergency spillway must be designed for a 10 year ARI flood (see MSMA, Volume 15,Section 39.7.6c) The sill level must be set a minimum 300mm above the basin top water level.

Parametertc = 10 min

For Penang, 10 year ARI Area, A = 5.5 haA 3.7277B 1.4393 Fd from Table 13.3C -0.4023 Interpolate for 140mmD 0.0241 Fd = ###

From Equation 13,2136.648 mm/hr

68.32 mm

m²

Orifice area, ATOTAL

(2Aav x √y) /(tCd√2g)

m²

ATOTAL / Ao =

t=30 min, I30 =

P30 =

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92.833 mm/hr92.83 mm

255.83 mm/hr

From Chart 14.3, Runoff Coefficient, C = 0.843.28

IF Equation 20.2 for Orifice flowAn orifice discharge coefficient of = 0.64

Outlet riser, perforated MS pipe = 0.9 m0.3 m

0.99

2.29

D.Chart 20.2Trial Dimension, B

5 0.5 1.65

2.92 > 2.29 OK

Therefore, the total basin depth including the spillway is = 2.13 m

t=60 min, I60 =

P60 =

Rainfall Intensity, I10 = [P30 - Fd(P60 - P30)] / (10/60)

Equation 14.7, Q10 = m³/s

Ho =

Qriser = Cd Ao √ 2 g Ho = m³/s

Therefore Qspillway = Q10 - Qriser = m³/s

From Equation 20.9, Qspillway = Csp B Hp^1.5

Hp Csp

Qspillway =

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The emergency spillway must be designed for a 10 year ARI flood (see MSMA, Volume 15,Section 39.7.6c) The sill level must be set a minimum 300mm above the basin top water

Interpolate for 140mm

document.xls

WET SEDIMENTATION POND

ACHECK Catchment Area = 5.2 ha

75th % 5-day storm event 40 mm


Table 39.4CHECK Soils type = F clay

Table 39.6 for a 3 month ARICHECK Settling Zone Volume 200

CHECK Total Volume = 300

COMPUTE Settling Zone Volume = 1,040.00

COMPUTE Total Volume 1560

i) Settling zone

CHECK 0.6 m

COMPUTE Required settling zone = 1560

CHECK 30 m

COMPUTE 87 m

COMPUTE Average surface area = 2,600.00 m²


COMPUTE 144.44 < 200 OK

COMPUTE 2.89 > 2 OK

m²/ha

m³/ha

m²

m³


m³

Try settling zone average width, W1 =

The settling zone average length, L1 =

L1 / y1 =

L1 / W1 =

document.xls


COMPUTE Required sediment storage volume = 520

CHECK For a side slope Z = 2(H):1(V) 2Dimensions at the top of the sediment storage zone are,

COMPUTE 28.8 m

COMPUTE 85.47 m


CHECK 0.3 717.972 NOT OKCHECK 520 0.4 948.267 OKCHECK 0.35 833.68 > 0.3 OK

0.35 mD Overall Basin Dimensions

At top water level



Base



Depth:

COMPUTE 0.6 m

COMPUTE 0.35 m

m³

.·. W2 = W1 - 2 d1/2 x Z

.·. L2 = L1 - 2 d1/2 x Z

V2 = Z³(y2)³ - Z (y2)² (W2 + L2) + y2 ( W2 x L2 )


V2

Taken, y2 =

WTWL = W1 + 2 x Z x y1/2

LTWL = L1 + 2 x Z x y1/2

WB = W1 - 2 x Z x (y1/2 + y2)

LB = L1 - 2 x Z x (y1/2 + y2)

Settling Zone, y1 =


document.xls

E Determine overland flow time of concentrationCHECK Catchment Area, A = 5.2 ha

n = 0.02

CHECK Overland slope, S = 0.03 %

CHECK Overland length, L = 870 m

COMPUTE tc = (107*n*L^1/3) / s^1/2 117.95 min

Assume velocity, v = 1 m/s

Drain length = 1275 m

td = velocity/drain length = 1.3072E-05 min



The emergency spillway must be designed for a 10 year ARI flood (see MSMA, Volume 15,Section 39.7.6c) The sill level is set at the basin top water level.


For Penang, 10 year ARI Area, A = 5.2 haCHECK A 3.7277 Fd = 0.884CHECK B 1.4393CHECK C -0.4023CHECK D 0.0241

COMPUTE From Equation 13,2136.648 mm/hr

68.32 mm

CHECK 92.833 mm/hrCOMPUTE 92.83 mm

Therefore, Qspillway = Q10

t=30 min, I30 =

P30 =

t=60 min, I60 =

P60 =

Rainfall Intensity, I12 = [P30 - Fd(P60 - P30)] / (13/60)

document.xls

23.73 mm/hr

From Chart 14.3, Runoff Coefficient, C = 0.86 Category 4

0.29D.Chart 20.2

Trial Dimension, B3 0.35 1.55

COMPUTE 0.96 > 0.29 OK

Therefore, the total basin depth including COMPUTE the spillway is = 1.6 m

Equation 14.7, Q10 = m³/s

Hp Csp

Qspillway =

document.xls






Table 39.6 for a 3 month ARICHECK Settling Zone Volume 200 m²/ha

CHECK Total Volume = 300 m³/ha

COMPUTE Settling Zone Volume = 4,748.58 m²

COMPUTE Total Volume 7122.87 m³

i) Settling zone

CHECK 1.65 m

COMPUTE Required settling zone = 7122.87 m³

CHECK 30 m

COMPUTE 144 m



COMPUTE 87.21 < 200 OK

COMPUTE 4.80 > 2 OK




L1 / y1 =

L1 / W1 =


COMPUTE Required sediment storage volume = 2374.29 m³


COMPUTE 26.7 m

COMPUTE 140.60 m


CHECK 1.2 4029.81 OKCHECK 2374.29 0.6 2132.76 NOT OKCHECK 0.7 2465.17 > 0.3 OK


At top water level



Base



Depth:

COMPUTE 1.65 m

COMPUTE 0.7 m

Sedimentation storage required is (top)33mx(top)291m.

Sedimentation storage provided is (top)40mx(top)415m.

Provided storage is more than required storage

.·. W2 = W1 - 2 d1/2 x Z

.·. L2 = L1 - 2 d1/2 x Z

V2 = Z³(y2)³ - Z (y2)² (W2 + L2) + y2 ( W2 x L2 )


V2

Taken, y2 =

WTWL = W1 + 2 x Z x y1/2

LTWL = L1 + 2 x Z x y1/2

WB = W1 - 2 x Z x (y1/2 + y2)

LB = L1 - 2 x Z x (y1/2 + y2)

Settling Zone, y1 =


E Determine overland flow time of concentrationCHECK Catchment Area, A = 52 ha

n = 0.02











For Penang, 10 year ARI Area, A = 52 haCHECK A 3.7277 Fd = 0.884CHECK B 1.4393CHECK C -0.4023CHECK D 0.0241



5.23 m³/sD.Chart 20.2




t=118 min, I118 =

Equation 14.7, Q10 =

Hp Csp

Qspillway =


Size of the spillway is 3m x 1.2m










i) Settling zone

CHECK 1.65 m


CHECK 30 m

COMPUTE 144 m




COMPUTE 4.80 > 2 OK




L1 / y1 =

L1 / W1 =




COMPUTE 26.7 m

COMPUTE 140.60 m




At top water level

COMPUTE 33.3 m say 33


Base



Depth:

COMPUTE 1.65 m

COMPUTE 0.7 m





.·. W2 = W1 - 2 d1/2 x Z

.·. L2 = L1 - 2 d1/2 x Z

V2 = Z³(y2)³ - Z (y2)² (W2 + L2) + y2 ( W2 x L2 )


V2

Taken, y2 =

WTWL = W1 + 2 x Z x y1/2

LTWL = L1 + 2 x Z x y1/2

WB = W1 - 2 x Z x (y1/2 + y2)

LB = L1 - 2 x Z x (y1/2 + y2)

Settling Zone, y1 =


n = 0.02














2.39 m³/sD.Chart 20.2






t=91 min, I91 =


Hp Csp

Qspillway =

NOT OK

m

m

m

m

The emergency spillway must be designed for a 10 year ARI flood (see MSMA, Volume 15,










i) Settling zone

CHECK 1.65 m


CHECK 30 m

COMPUTE 72 m




COMPUTE 2.40 > 2 OK




L1 / y1 =

L1 / W1 =




COMPUTE 26.7 m

COMPUTE 68.66 m




At top water level



Base



Depth:

COMPUTE 1.65 m

COMPUTE 0.7 m





.·. W2 = W1 - 2 d1/2 x Z

.·. L2 = L1 - 2 d1/2 x Z

V2 = Z³(y2)³ - Z (y2)² (W2 + L2) + y2 ( W2 x L2 )


V2

Taken, y2 =

WTWL = W1 + 2 x Z x y1/2

LTWL = L1 + 2 x Z x y1/2

WB = W1 - 2 x Z x (y1/2 + y2)

LB = L1 - 2 x Z x (y1/2 + y2)

Settling Zone, y1 =


n = 0.02














1.19 m³/sD.Chart 20.2






t=118 min, I118 =


Hp Csp

Qspillway =

NOT OK

m

m

m

m

The emergency spillway must be designed for a 10 year ARI flood (see MSMA, Volume 15,

Download - Detention Pond CalculationPhaseII

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