Hydrology & Drainage

Hydrology and drainage cover the path water takes from rainfall to the channel: how much runoff a catchment generates, how it moves through pipes and channels, and what happens when the system is not enough.

The central tools in this category come from US federal agencies and are distributed free with source code. They are not cut-down versions — they are the engine underneath most commercial software in the field, so the calculation itself is identical.

Local adaptation is your responsibility: intensity-duration-frequency curves, runoff coefficients and return periods are set by national guidance. The model is valid anywhere; the data you feed it is local.