Toward Flood Routing in Natural Rivers

Floods in rivers can be modeled with one dimensional flood routing methods, which include an approximate solution of the one-dimensional (1D) Saint-Venant momentum equation and a solution of the corresponding mass conservation equation for a storage element representing the river reach. The accuracy of a method applied to a natural river can be improved by introducing an averaged compound section along the reach. But it is shown analytically and numerically that the irregular geometry and hydraulic roughness contribute to the section dimensions. These contributions can be introduced either by the concept of storage areas in the model section or by routing flows along a randomly irregular model of the reach. By compartmentalizing the model section and adopting analytical, parameterized functions for the terrain in each compartment, an optimal section can be obtained by comparing the predicted with the observed hydrographs downstream. The accuracy of the routing method normally increases as the number of parameters is increased for a sequence of standard cross sections. This new method is applied to the River Wye, United Kingdom. (C) 2017 American Society of Civil Engineers.