Knowledge Centre
Free hydrology calculators
Screening-level tools built on standard published formulas — each with the notation, variable definitions, and a worked example, so you can see exactly what is being computed.
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Time of Concentration Calculator
Estimate Tc with the Kirpich and SANRAL Drainage Manual formulas from watercourse length and average slope.
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Return Period & Flood Risk Calculator
Convert a return period to annual exceedance probability and the chance of at least one exceedance over a design life.
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Rational Method Peak Flow Calculator
Compute peak discharge Q = C·i·A for small catchments, with hectare and square-kilometre inputs.
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Design Rainfall Lookup
Site-specific design rainfall depths by duration and return period. Planned — pending data licensing. Meanwhile, our design rainfall explainer covers where the numbers come from.
Planned
All calculators produce screening-level estimates — useful for orientation and sanity checks, not a substitute for a professional study. When the number has to stand up to a reviewer, talk to an engineer.