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Original Application Part 8 - Stormwater Details [As Published] · 132008.1787
Calculation of Stormwater Runoff and Detention Requirements for: PO Box 1176 Buddina 4575
Project: SEAHAVEN HASTINGS STREET
Ref 1997 Date: 19/09/2008 whole site
Calculate increase in peak flow due to extra impervious area
Predevelopment Case
Maximum event = Q100
time of Concentration = 5 mins
Intensity ( I ) = 326 mm/hr
Existing site area (A) = 4722 sq.m
Calc coeff of runoff
From QUDM Table 5.04.2
for Q10 intensity = 200.00 mm/hr
With fraction impervious = 0.00
Interpolating C10 = 0.70
From table 5.04.3
frequency factor Q100 = 1.20
Therefore Coefficient of runoff for grassed site Q100 = 0.84
Peak runoff for predeveloped catchm = Coeff of R * Intensity * Area / 3600 L/sec
= 359 L/s
Post Development Case
a) New Impervious Catchment Area = 3606 sq.m
Coeff of Runoff = 1
Intensity as before = 326 mm/hr
Therefore peak Runoff = Coeff of R * Intensity * Area / 3600
= 327 L/s
b) New Pervious area = Total site Area - new impervious area
= 1116 sq.m
Coeff of runoff as before = 0.84
Intensity as before = 326.00 mm/hr
Therefore peak Runoff = Coeff of R * Intensity * Area / 3600
= 85 L/s
Total Peak runoff post development case = runoff pervious + runoff impervious
= 411 L/s
Difference in peak flow Runoff due to development
= Peak runoff post dev - Peak runoff pre dev.
= 52 L/s
Therefore Required reduction in peak flow for Maximum event
difference in peak flow between developed and undeveloped areas = 52 L/s
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Page 2
Detention tank design
From Urban Road design Manual Vol (10-7080)
For small catchments hydrograph may be approximated as folls:-
Use triangular shape with duration = 2.67 x Time of Concentration
Actual catchment area entering tank from proposed site 2124 sq.m. roof+terraces
Pipe rainfall design intensity entering tank Q20 = 252 mm/hr
Weighted Coeff of runoff = 0.95
Peak Flow entering tank = C * I * A / 3600
Therefore Peak Flow entering tank = 141.2 Litres/sec
(Note: Pipes entering the tank are designed for the above intensity. All flows in excess of this will be bypassed to O'Land Flow
or other pipework)
(However it is still necessary to produce the required reduction in peak flow for the maximum event shown above)
Outflow Hydrograph (from storage device)
Soil Permeability = 0 m/day
= 0.000 mm/sec
Absorption Area = 0 sq.m
Therefore absorption = 0.000 L/sec
Outlet Device
O'Flow device weir/pipe (W/P) = p
Outlet Pipe dia = 175 mm for calcs only
Outlet Pipe length = 10 m
Outlet Pipe grade 1:? = 200
Try Storage Length = 3 m. equivalent
Storage width = 6000 mm tank size
Available storage depth below Pipe outlet IL = 0.0 mm
Therefore Storage Vol below o'flow device = 0 Litres
(includes vol stored in absorption trench)
Storage Area above O'Flow = 18 Sq.m.
Void Ratio = 1
RESULTS
Max Inflow = 141.2 (L/sec) Max depth over weir/oflow IL 1310 (mm)
Max Outflow = 72.6 (L/sec) Area of storage above weir/Oflow IL 18 sq.m
Reduction = 68.7 (L/sec) Therefore Vol aboveOFlow IL 23.58 cu.m
Required Reduction= 52.2 (L/sec) Vol below oflow IL (from above) 0.0 cu.m
Therefore OK Therefore Total storage vol. 23.58 cu.m
therefore Total Storage depth 1310 mm
Page 3
Stormwater Hydrograph for OSD whole site
160
140
No Detention
Flow (Litres/sec)
120
With Detention
100
80
60
40
20
0
0 2 4 6 8 10 12 14 16 18 20
Time (mins)
Method:
Total inflow in litres = total outflow + storage (over any given time period)
Total outflow = Amount over weir + amount absorbed
Total storage = Static storage below the overflow + dynamic storage above the overflow
(Any storage utilised in a gravel bed is adjusted for the void ratio.)
Storage above the weir, and flow over the weir, are dependant on the depth above the weir, or outlet pipe IL.
All variables in the above equation are known except the depth above the weir or o'flow device.
To avoid intergration of the above formulas, time increments are used to solve for depth.
The time increment used is 0.1mins. These increments are hidden on the spreadsheet below to save space.
Flow increments are progressively added to produce the result.
Any difference between the final output volume and the input vol is approximately the amount still held in storage.
This storage is gradually absorbed, or used for irrigation between rainfall events or run out, or slow leaked out.
If the tank outlet is a weir, the weir formula is used to calculate the depth of water in the tank
If the tank outlet is a pipe, a pipe 'part flow' formula is used for all tank depths up to the pipe obvert level.
As the water depth in the tank rises, the pipe is then checked for both an orifice and pipe flow (manning) formula.
The formula that gives the most restriction to the flow, is the one selected.
This is then used to calculate the depth of water in the tank, or other storage device.
Sometimes a slight wobble can be seen in the curve where the transitions between formulas occur.
The tank water level is also adjusted for exit losses equating to 1.5V^2/(2g)
Depth of water in tank above outlet IL
1400.0
1200.0
1000.0
Depth mm
800.0
depth
600.0
400.0
200.0
0.0
0 5 10 15 20 25
Time mins
Page 4
Inflow in previous Cumulative Depth over Outflow thru Cumulative
Time 0.1min inc. Inflow weir/orifice Over flow Outflow
mins L/s Litres mm L/sec Litres
0 0 0 0.0 0.0 0
0.5 14.12 212 10.0 0.7 10
1 28.25 847 40.0 2.8 59
1.5 42.37 1907 90.0 7.9 230
2 56.50 3390 169.3 17.2 607
2.5 70.62 5297 237.2 22.6 1204
3 84.75 7627 331.1 30.3 2020
3.5 98.87 10382 428.1 36.7 3027
4 113.00 13560 525.1 42.2 4221
4.5 127.12 17161 646.4 48.2 5595
5 141.25 21187 791.9 54.5 7147
5.5 132.79 25297 913.1 59.2 8867
6 124.33 29154 1034.4 63.6 10723
6.5 115.87 32757 1110.0 66.4 12683
7 107.41 36107 1180.0 68.6 14719
7.5 98.96 39202 1240.0 70.5 16816
8 90.50 42044 1280.0 71.7 18952
8.5 82.04 44632 1300.0 72.3 21114
9 73.58 46966 1310.0 72.6 23290
9.5 65.13 49047 1310.0 72.6 25467
10 56.67 50874 1290.0 72.0 27632
10.5 48.21 52447 1250.0 70.8 29772
11 39.75 53767 1210.0 69.6 31878
11.5 31.29 54832 1160.0 68.0 33937
12 22.84 55644 1090.0 65.8 35936
12.5 14.38 56202 1034.4 63.6 37869
13 5.92 56507 937.4 60.1 39714
13.5 0.00 56570 840.4 56.4 41462
14 0.00 56570 767.6 53.5 43101
14.5 0.00 56570 670.6 49.3 44630
15 0.00 56570 597.9 45.9 46054
15.5 0.00 56570 525.1 42.2 47364
16 0.00 56570 452.4 38.2 48559
16.5 0.00 56570 403.9 35.2 49651
17 0.00 56570 331.1 30.3 50620
17.5 0.00 56570 282.6 26.5 51484
18 0.00 56570 258.4 24.4 52240
18.5 0.00 56570 219.6 21.2 52892
19 0.00 56570 185.6 18.6 53466
19.5 0.00 56570 140.0 14.5 53959
20 0.00 56570 120.0 11.7 54342
Note 0.1min. time increments are used but hidden to save space
Reinhold Koenning
Msc PhD MIEAust RPEQ.
[OCR of page images]
Inflow in previous Cumulative Depth over Outflow thru Cumulative
Time 0.1min inc. Inflow weir/orifice Over flow Outflow
mins Lis Litres mm L/sec Litres
0 0 0 0.0 0.0 0
0.5 14.12 212 10.0 0.7 10
1 28.25 847 40.0 2.8 59
1.5 42.37 1907 90.0 7.9 230
2 56.50 3390 169.3 17.2 607
2.5 70.62 5297 237.2 22.6 1204
3 84.75 7627 331.1 30.3 2020
3.5 98.87 10382 428.1 36.7 3027
4 113.00 13560 525.1 42.2 4221
45 127.12 17161 646.4 48.2 5595,
5 141.25 21187 791.9 54.5 7147
5.5 132.79 25297 913.1 59.2 8867
6 124.33 29154 1034.4 63.6 10723
6.5 115.87 32757 1110.0 66.4 12683
7 107.41 36107 1180.0 68.6 14719
75 98.96 39202 1240.0 70.5 16816
8 90.50 42044 1280.0 71.7 18952
8.5 82.04 44632 1300.0 72.3 21114
9 73.58 46966 1310.0 72.6 23290
9.5 65.13 49047 1310.0 72.6 25467
10 56.67 50874 1290.0 72.0 27632
10.5 48.21 52447 1250.0 70.8 29772
11 39.75 53767 1210.0 69.6 31878
11.5 31.29 54832 1160.0 68.0 33937
12 22.84 55644 1090.0 65.8 35936
12.5 14.38 56202 1034.4 63.6 37869
13 5.92 56507 937.4 60.1 39714
13.5 0.00 56570 840.4 56.4 41462
14 0.00 56570 767.6 53.5 43101
14.5 0.00 56570 670.6 49.3 44630
15 0.00 56570 597.9 45.9 46054
15.5 0.00 56570 525.1 42.2 47364
16 0.00 56570 452.4 38.2 48559
16.5 0.00 56570 403.9 35.2 49651
17 0.00 56570 331.1 30.3 50620
17.5 0.00 56570 282.6 26.5 51484
18 0.00 56570 258.4 24.4 52240
18.5 0.00 56570 219.6 21.2 52892
19 0.00 56570 185.6 18.6 53466
19.5 0.00 56570 140.0 14.5 53959
20 0.00 56570 120.0 11.7 54342
I
Note 0.1min. time increments are used but hidden to save space
Reinhold Koenning
Msc PhD MIEAust RPEQ.
Used in these records
Original Application Part 8 - Stormwater Details [As Published]Related documentApplication case desk ↗
001919A5.001.pdfRelated documentPublic source context ↗
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