Hydrology and flood modelling, explained for South Africa

What Is a 100-Year Flood? Return Periods and AEP Explained

Last reviewed 2026-07-10

What a 1-in-100-year flood actually means, how return periods convert to annual probabilities, and your real flood risk over a 50-year design life.

The Rational Method in South Africa: Q = C·i·A, Properly Applied

Last reviewed 2026-07-10

How the Rational Method estimates peak flow in South African practice — the formula, runoff coefficients, rainfall intensity, units, and its limits.

The SCS-SA Method Explained: Curve Numbers for South African Catchments

Last reviewed 2026-07-10

How the SCS-SA method estimates design floods in South Africa — curve numbers, soil groups, storm distributions, and when to use it over the Rational Method.

Time of Concentration: Formulas, Methods, and Common Pitfalls

Last reviewed 2026-07-10

How to estimate time of concentration with the Kirpich and SANRAL Drainage Manual formulas, what the variables mean, and the mistakes that skew results.

Design Rainfall in South Africa: TR102, RLMA&SI, and How Estimates Are Made

Last reviewed 2026-07-10

Where South African design rainfall numbers come from — TR102, the regionalised RLMA&SI approach, IDF relationships, and how estimates enter flood methods.

DEM and LiDAR Accuracy: Why Terrain Data Makes or Breaks a Flood Model

Last reviewed 2026-07-10

How DEM resolution and vertical accuracy drive floodline reliability — LiDAR vs drone survey vs SRTM, and what survey quality a flood study really needs.