4.0 Run-off Calculation For Overall Catchment Total Catchment Area Run-off Coefficient
A= C=
23.5 acres 0.75 for bare earth
Overland Flow Distance Overland Flow Velocity Overland Flow Time
do = vo = to = to =
135 2 221.45 3.69
m ft/sec sec min
Drain Flow Distance Drain Flow Velocity Drain Flow Time
dd = vd = td = td =
340 5 223.09 3.72
m ft/sec sec min
Time of Concentration
tc = tc =
to + td 7.41 min
Storage Coefficient
Cs = Cs =
2tc 2tc + td 0.799
Extracts from DID Guidelines Figure A-9 : Rainfall Intensity - Duration - Frequency Relationship for Kuala Lumpur (pg. 56) Adopt : Storm duration = 10 min, Rainfall Return Period = 2 years Rainfall Intensity i2 = 5.2 in/hr ='> Peak Discharge
Q2 = Cs. C. i2. A Q2 = 73.266 cusecs Cs = C= i2 = A=
0.799 0.75 for bare earth 5.2 in/hr 23.5 acres
='> Peak Discharge
Q2 = Cs. C. i2. A Q2 = 73.266 cusecs
SILT TRAP DESIGN CRITERIA Adopt : Storage Capacity =
0.50 watershed inches
Regular maintenance works on the temporary silt trap shall be carried out, involving the followings: a) Repair all damages cause by soil erosion or construction equipment at or before end of each working day b) Sediment shall be removed from the basin and deposited in a suitable area when it reaches the clean out level c) Keep trash track and anti-vortex device clear of debris (1) Required Storage Volume Site Acreage, A = Storage Volume, S1 = S1 = S1 = S1 = S1 = S1 = (2) Depth of Maximum Storage Adopt Storage Length, L = Adopt Storage Width, W = Storage Plan Area, A1 = Storage Volume, S1 = Required Depth, d1 = Adopt d1 =
23.5 0.50 23.500 11.750 1,579.72 42,652.50 1,207.83
acres watershed inches x catchment area * 0.50 acre - inches acre - inches yd3 ft3 m3
40 m 22 m 880 1207.828 1.373 1.400
m2 m3 m m
(3) Height Of Clean Out Level Silt trap to be cleaned out when the storage capacity is reduced by sedimentation to 0.20 watershed inches Site Acreage, A = Storage in Basin, S2 = S2 = S2 = S2 = S2 = S2 =
23.5 0.30 23.500 7.050 947.83 25,591.50 724.70
Storage Plan Area, A1 = Storage Volume, S2 = Required Depth, d2 = Adopt d2 =
880 724.697 0.824 0.850
acres watershed inches * 0.30 acre - inches acre - inches yd3 ft3 m3 m2 m3 m m
(4) Design Discharge for Principal Spillway, Qp Since an emergency spillway will be used, design discharge for the principal spillway, Qp is based on 0.34 cfs per acre. Principal Spillway Discharge, Qp = Qp = Qp =
0.34 * acres 0.34 * 23.500 cusecs 7.990 cusecs
(5) Design Discharge for Emergency Spillway, Qes Emergency Spillway Discharge, Qes = Q2 - Qp where Q2 is 2 year design discharge Q2 = Qp = Qes = Qes =
73.266 7.990 73.266 65.276
cusecs cusecs 7.990 cusecs
(6) Size Of Emergency Spillway Extracts from DID Guidelines Figure J - 4 : Earth Spillway (pg.252) Table J - 2 : Design Table for Vegetated Spillways (pg. 253) Emergency Spillway Discharge, Qes = Table J-2, Refer Discharge Value of Slope Range between = Bottom Width = Stage Hp =
65.276 70 2.5% 8.00 1.88
cusecs cusecs and 2.8% ft = 2.44 m ft = 0.57 m
(7) R.L Of Critical Level Adopt Design High Water Level = Existing Platform Level = 105.00 m Table J-2 : Stage Hp = Allow Freeboard =
1.88 ft = 1.00 ft =
0.57 m 0.30 m above Design High Water Level
Design High Water Level = Emergency Spillway Crest Level + Stage Hp R.L of Top of Dam = Design High Water Level + 0.30 m Freeboard Emergency Spillway Crest Level = Design High Water Level - Stage Hp = 105.00 0.57 = 104.43 m R.L. of Top of Dam = Design High Water Level + 0.30 m Freeboard = 105.00 + 0.30 = 105.30 m R.L. of Base of Dam = Emergency Spillway Crest Level - Depth D1 = 104.43 1.400 = 103.03 m
R.L. of Clean Out Level = R.L. of Base of Dam + Depth D2 = 103.03 + 0.850 = 103.88 m (8) Size Of Principal Spillway Extracts from DID Guidelines Figure J - 5 : Circular Risers with Splitter Wall (pg. 254) Allow Head at Crest of Riser, h = 1.50 ft = 0.46 m Riser Flow Capacity = Principal Spillway Discharge, Qp Principal Spillway Discharge, Qp = 7.990 cusecs Minimum Pipe Riser, d = Suggested Inlet Proportions, D =
18 inches f 15 inches f
To check - the available head, H for the pipe spillway does not control the size. Available Head, H = Emergency Spillway Crest Level - R.L. of Base of Dam = 104.43 103.03 = 1.40 m = 4.59 ft Extracts from DID Guidelines Table J - 3 : Pipe Flow Chart for Concrete Pipe Drop Inlet Spillway (pg. 255) H= Inlet pipe, D = Inlet pipe discharge capacity = Principal Spillway Discharge, Qp =
4.59 15 12.660 7.990
ft inches f cusecs cusecs
> Qp
='> Available head does not control the size (9) Top Of Riser In Principal Spillway Top of Riser is h feet (>1') below the crest level of emergency spillway. Allow Head at Crest of Riser, h =
1.50 ft =
0.46 m
Top Of Riser in Principal Spillway = Emergency Spillway Crest Level - Head = 104.43 0.46 = 103.97 m Design High Water Level Emergency Spillway Crest R.L. of Top of Dam R.L. of Base of Dam R.L. of Clean Out Level Top of Riser of Principal Spillway
= = = = = =
105.00 104.43 105.30 103.03 103.88 103.97
m m m m m m
='> Peak Discharge
Q2 = Cs. C. i2. A Q2 = 5.996 cusecs
SILT TRAP DESIGN CRITERIA Adopt : Storage Capacity =
0.20 watershed inches
The temporary earthdrain to be provided to channel the surface run-off into the excavated basement. The basement will act as a temporary silt trap. Water will be sumped into the temporary silt trap and finally discharged into the existing external roadside drain Regular maintenance works on the temporary silt trap shall be carried out, involving the followings: a) Repair all damages cause by soil erosion or construction equipment at or before end of each working day b) Sediment shall be removed from the basin and deposited in a suitable area when it reaches the clean out level c) Keep trash track and anti-vortex device clear of debris (1) Required Storage Volume Site Acreage, A = Storage Volume, S1 = S1 = S1 = S1 = S1 = S1 = (2) Depth of Maximum Storage Adopt Storage Length, L = Adopt Storage Width, W = Storage Plan Area, A1 = Storage Volume, S1 = Required Depth, d1 = Adopt d1 =
2.08 0.20 2.080 0.416 55.93 1,510.08 42.76
acres watershed inches x catchment area * 0.20 acre - inches acre - inches yd3 ft3 m3
5m 10 m 50 42.762 0.855 0.900
m2 m3 m m
(3) Height Of Clean Out Level Silt trap to be cleaned out when the storage capacity is reduced by sedimentation to 0.20 watershed inches Site Acreage, A = Storage in Basin, S2 = S2 = S2 = S2 = S2 = S2 =
2.08 0.12 2.080 0.250 33.56 906.05 25.66
acres watershed inches * 0.12 acre - inches acre - inches yd3 ft3 m3
Storage Plan Area, A1 = Storage Volume, S2 = Required Depth, d2 = Adopt d2 =
50 25.657 0.513 0.600
m2 m3 m m
(4) Design Discharge for Principal Spillway, Qp Since an emergency spillway will be used, design discharge for the principal spillway, Qp is based on 0.34 cfs per acre. Principal Spillway Discharge, Qp = Qp = Qp =
0.34 * acres 0.34 * 2.080 cusecs 0.707 cusecs
(5) Design Discharge for Emergency Spillway, Qes Emergency Spillway Discharge, Qes = Q2 - Qp where Q2 is 2 year design discharge Q2 = Qp = Qes = Qes =
5.996 0.707 5.996 5.289
cusecs cusecs 0.707 cusecs
(6) Size Of Emergency Spillway Extracts from DID Guidelines Figure J - 4 : Earth Spillway (pg.252) Table J - 2 : Design Table for Vegetated Spillways (pg. 253) Emergency Spillway Discharge, Qes = Table J-2, Refer Discharge Value of Slope Range between = Bottom Width = Stage Hp =
5.289 10 3.3% 8.00 0.83
cusecs cusecs and 12.2% ft = 2.44 m ft = 0.25 m
(7) R.L Of Critical Level Adopt Design High Water Level = Proposed Platform Level = 53.00 m Table J-2 : Stage Hp = Allow Freeboard =
0.83 ft = 1.00 ft =
0.25 m 0.30 m above Design High Water Level
Design High Water Level = Emergency Spillway Crest Level + Stage Hp R.L of Top of Dam = Design High Water Level + 0.30 m Freeboard Emergency Spillway Crest Level = Design High Water Level - Stage Hp = 53.00 0.25 = 52.75 m R.L. of Top of Dam = Design High Water Level + 0.30 m Freeboard = 53.00 + 0.30 = 53.30 m R.L. of Base of Dam = Emergency Spillway Crest Level - Depth D1 = 52.75 0.900
=
51.85 m
R.L. of Clean Out Level = R.L. of Base of Dam + Depth D2 = 51.85 + 0.600 = 52.45 m
(8) Size Of Principal Spillway Extracts from DID Guidelines Figure J - 5 : Circular Risers with Splitter Wall (pg. 254) Allow Head at Crest of Riser, h = 1.50 ft = 0.46 m Riser Flow Capacity = Principal Spillway Discharge, Qp Principal Spillway Discharge, Qp = 0.707 cusecs Minimum Pipe Riser, d = Suggested Inlet Proportions, D =
15 inches f 12 inches f
To check - the available head, H for the pipe spillway does not control the size. Available Head, H = Emergency Spillway Crest Level - R.L. of Base of Dam = 52.75 51.85 = 0.90 m = 2.95 ft Extracts from DID Guidelines Table J - 3 : Pipe Flow Chart for Concrete Pipe Drop Inlet Spillway (pg. 255) H= Inlet pipe, D = Inlet pipe discharge capacity = Principal Spillway Discharge, Qp =
2.95 12 6.420 0.707
ft inches f cusecs cusecs
> Qp
='> Available head does not control the size (9) Top Of Riser In Principal Spillway Top of Riser is h feet (>1') below the crest level of emergency spillway. Allow Head at Crest of Riser, h =
1.50 ft =
0.46 m
Top Of Riser in Principal Spillway = Emergency Spillway Crest Level - Head = 52.75 0.46 = 52.29 m
Design High Water Level Emergency Spillway Crest R.L. of Top of Dam R.L. of Base of Dam R.L. of Clean Out Level Top of Riser of Principal Spillway
= = = = = =
53.00 52.75 53.30 51.85 52.45 52.29
m m m m m m
