Flood Forecasting and Its Reliability

Abstract

Methodologies for forecasting flood hydrographs are discussed for (a) catchment floods from rainfall and (b) river floods with flow from upstream. Catchment flood forecasting methods include the unit hydrograph techniques, conceptual models, computer-based physical process models, and stochastic simulation models. River flood forecasting methods include physically-based routing models, deterministic lumped system models, station correlation methods, and stochastic process methods. Flood forecasting is inevitably under uncertainties from various sources. Therefore, it is desirable to have not only the forecast of a flood but also some measure of the reliability of the forecast. Techniques to evaluate the reliabili ty for flood forecasting of a catchment and of· a river are suggested.