Design tools
Peak runoff calculator
Rational Method (Q = C × I × A) for design peak discharge. Live BOM IFD intensity at your time of concentration, with PDF runoff coefficients and relevant GRAF system suggestions.
Peak runoff
Peak runoff calculator
Uses the Rational Method (Q = C × I × A) for design peak discharge. Intensity from live BOM 2016 IFD at your time of concentration, or enter I manually.
Fetches BOM IFD depths for short durations (including 10 min tc) and converts depth to intensity.
Enter I manually, or load a postcode to pull BOM IFD.
Using C = 0.9. Source: Argue / MRWA as cited in training notes.
Units: Q (m³/s) = C × I × A(ha) / 360, same as C × I × A(m²) / 3,600,000 from the PDF worked example.
Peak discharge Q
678 L/s
0.678 m³/s
- C
- 0.9
- I
- 83.5 mm/h (manual)
- A
- 3.2463 ha (32,463 m²)
- Check
- CIA/360 = 0.678 m³/s
Relevant systems for this order of peak runoff (guidance only, not certified sizing). Scale band: Major catchment (678 L/s).
Relevant systems for this runoff
GuidanceRECYFIX HICAP F
High-capacity slot drainage for very large catchments and logistics yards.
EcoBloc Inspect Smart Module
Scalable modular detention for major catchments where tank banks are impractical.
GRAF Treatment Mako Shark Sedimentation Plant
Catalogue hydraulic capacity 832 L/s (size 2500 / DN400). Match treatment flow separately; peak Q is not a certified plant size.
Channel and detention picks follow catchment scale from peak Q. Mako Shark uses published catalogue hydraulic L/s where available. No channel hydraulic capacity matrix is published in this catalogue, so surface drainage is category guidance only.
Indicative early-design estimate only. The Rational Method assumes uniform steady rainfall and ignores network storage, so peaks can be under- or overestimated. Confirm with a hydraulic consultant and council requirements before specifying treatment or conveyance plant.
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Need detention, treatment or pump packaging from this peak flow?
Results are indicative for early design only. The Rational Method does not replace certified stormwater design. Product suggestions are catalogue guidance by runoff scale, not certified hydraulic sizing. Confirm with a licensed engineer or GRAF Australia for site-specific conditions and council requirements.
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