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2576 - SBSMP-01 (Feb 2026)
Attached to the e-mail Fw_ Email 2 of 3 - DA lodgement - 18 Taylor Ct Cooroy Lot 2SP197518 - Combined MCU_ OPW_ RAL under CTS (Pt 2).msg.
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Rational Method Calculations
Cooroy
Job Number 2576 IFD ANY LOCATION NEW IFD
Address mfr-cmp By CL
Pit 1/1 Pit 1/2
Ref 1 Catchment Details Catchment Details
Area 1.8403 ha Area 1.8403 ha
fi 0.00 fi 0.86
C10 0.7 C10 0.872
I10 84.24 mm/hr I10 84.24 mm/hr
Ref 2 Standard Inlet Time Standard Inlet Time
Time 0 mins Time 5 mins
Ref 3 Overland Sheet Flow (Friend's Eqn) Overland Sheet Flow (Friend's Eqn)
Length 240 m Length 20 m
Slope 1.32 % Slope 2 %
Surface 'n' av. grass 0.045 Surface 'n' paved 0.015
Time 28.31 mins Time 3.79 mins
Ref 4 Pipe Flow Travel Time Pipe Flow Travel Time
Flow Distance 0 m Flow Distance 200 m
Avg. Dia 0 mm Avg. Dia 450 mm
Fall of Channel 1 m Fall of Channel 1 m
Time 0 mins Time 1.52 mins
Kerb Flow Kerb Flow
Length 0 m Length 0 m
Slope 1 % Slope 1 %
Time 0.0 mins Time 0.0 mins
Ref 4 Channel Flow (Figure 4.8 QUDM, or Channel Flow (Figure 4.8 QUDM, or Manning's
Manning's Equation) Equation)
Flow Distance m Flow Distance m
Fall of Channel m Fall of Channel m
Time mins Time mins
Time of Time of
28.3 mins 10.3 mins
Concentration Concentration
Peak Discharge Calculations
Pit 1/1 Pit 1/2
Design
Frequency
Storm Area (ha) Cy Iy (mm/h) Qy (m3/s) Area (ha) Cy Iy (mm/h) Qy (m3/s)
Factor (Fy)
(AEP)
63% 1 1.84029982 0.80 0.56 73 0.209 1.84029982 0.6976 116 0.414
39% 2 1.84029982 0.85 0.595 91 0.277 1.84029982 0.7412 145 0.549
18% 5 1.84029982 0.95 0.665 113 0.384 1.84029982 0.8284 179 0.758
10% 10 1.84029982 1.00 0.7 130 0.465 1.84029982 0.872 205 0.914
5% 20 1.84029982 1.05 0.735 147 0.552 1.84029982 0.9156 233 1.091
2% 50 1.84029982 1.15 0.805 171 0.704 1.84029982 1 268 1.37
1% 100 1.84029982 1.20 0.84 188 0.807 1.84029982 1 294 1.503
Ref 5 Advice on Selection of AEP design events for various scenarios
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