Rainfall Accumulation and Flood Risk Estimator
Estimates total rainfall volume, runoff volume, and flood risk level based on rainfall intensity, duration, catchment area, and surface runoff coefficient.
Formulas Used
1. Total Rainfall Depth (mm):
D = I × t
where I = intensity (mm/hr), t = duration (hr)
2. Rainfall Volume (m³):
Vrain = D × A × 1000
where A = catchment area (km²)
3. Effective Runoff Coefficient:
Ceff = min(C × AMF, 1.0)
where C = Rational Method surface coefficient, AMF = antecedent moisture factor
4. Runoff Volume (m³):
Vrunoff = Ceff × Vrain
5. Peak Discharge — Rational Method (m³/s):
Q = Ceff × i × A
where i = intensity (m/s), A = area (m²)
6. Flood Risk Score (0–100):
Score = 25·Sintensity + 15·Sduration + 25·Srunoff + 20·Sdepth + 15·Sdischarge
Each sub-score is normalised to [0, 1] against reference extreme values.
Assumptions & References
- The Rational Method (Q = CiA) is used for peak discharge estimation, suitable for catchments up to ~25 km² (AS/NZS 3500, AR&R 2019).
- Rainfall is assumed spatially uniform over the catchment for the full storm duration.
- Runoff coefficients (C) are based on Australian Rainfall & Runoff (AR&R) 2019 and ASCE standard tables.
- Antecedent moisture factors (1.0 / 1.2 / 1.5) follow SCS/NRCS Curve Number AMC class adjustments (AMC I, II, III).
- The flood risk score is a composite index for comparative/educational purposes and does not replace formal hydrological modelling or official flood mapping.
- For large catchments (>25 km²) or critical infrastructure, use full hydrograph methods (e.g., RORB, URBS, HEC-HMS).
- References: AR&R 2019 (Geoscience Australia); ASCE Manual of Engineering Practice No. 36; NRCS TR-55.