A simple raster-based model for flood inundation simulation

In this paper the development of a new model for simulating flood inundatio n is outlined. The model is designed to operate with high-resolution raster Digital Elevation Models, which are becoming increasingly available for ma ny lowland floodplain rivers and is based on what we hypothesise to he the simplest possible process representation capable of simulating dynamic floo d inundation. This consists of a one-dimensional kinematic wave approximati on for channel flow solved using an explicit finite difference scheme and a two-dimensional diffusion wave representation of floodplain flow. The mode l is applied to a 35 km reach of the River Meuse in The Netherlands using o nly published data sources and used to simulate a large flood event that oc curred in January 1995. This event was chosen as air photo and Synthetic Ap erture Radar (SAR) data for flood inundation extent are available to enable rigorous validation of the developed model. 100, 50 and 25 m resolution mo dels were constructed and compared to two other inundation prediction techn iques: a planar approximation to the free surface and a relatively coarse r esolution two-dimensional finite element scheme. The model developed in thi s paper outperforms both the simpler and more complex process representatio ns, with the best fit simulation correctly predicting 81.9% of inundated an d non-inundated areas. This compares with 69.5% for the best fit planar sur face and 63.8% for the best fit finite element code. However, when applied solely to the 7 km of river below the upstream gauging station at Borgharen the planar model performs almost as well (83.7% correct) as the raster mod el (85.5% correct). This is due to the proximity of the gauge, which acts a s a control point for construction of the planar surface and the fact that here low-lying areas of the floodplain an hydraulically connected to the ch annel. Importantly though it is impossible to generalise such application r ules and thus we cannot specify a priori when the planar approximation will work. Simulations also indicate that, for this event at least, dynamic eff ects are relatively unimportant for prediction of peak inundation. Lastly, consideration of errors in typically available gauging station and inundati on extent data shows the raster-based model to be close to the current pred iction limit for this class of problem. (C) 2000 Elsevier Science B.V. All rights reserved.