Flood propagation models for real-time forecasting

It has been recognised that a flood propagation routine that operates within the framework of a real-time flood forecasting service should use hydraulic numerical models-simplified for steep reaches but based on the complete de Saint Venant equations when the free surface slope is small. Using as state variable the steady-state discharge, instead of the water level corresponding to it, the authors identify a 'homogeneous set' of five flood routing models, going from complete to kinematic. To choose the most accurate and economic model, the suggested criterion, based on the analysis of sinusoidal solutions of the linearised wave propagation, is the ratio between the desired time resolution and a channel response time, which is correlated with the slope. Congruence of spatial steps with the temporal ones is discussed; some numerical examples, illustrating accuracy and economy of the proposed numerical models, are presented.