A simple floodplain inundation model to assist in floodplain management

A simple floodplain inundation model has been developed to simulate flood extent and water depths on floodplains. Necessary inputs consist of a high resolution digital elevation model, cross section information, land use and roughness information and an inflow hydrograph. The inflow hydrograph can either be the measured hydrograph at the inflow point, or a simulated one using LISFLOOD or any other model. The LISFLOOD-FP model is designed to operate with high resolution raster Digital Elevation Models which are becoming increasingly available for many lowland floodplain rivers and is based on what we hypothesise to be the simplest possible process representation capable of simulating dynamic flood inundation. This consists of a kinematic wave approximation for channel flow solved using an explicit finite difference scheme with the flood-plain treated as a series of storage cells where the head difference between cells drives a flux calculated using uniform flow formulae. The model is applied to a 35 km reach River Meuse in the Netherlands using only published data sources and used to simulate a large flood event which occurred in January 1995. This event was chosen as air photo and Synthetic Aperture Radar (SAR) data for flood inundation extent are available to enable rigorous validation of the developed model. 100, 50 and 25 m resolution models were constructed and compared to two other inundation prediction techniques: a planar approximation to the free surface and a relatively coarse resolution two dimensional finite element scheme. The model out-performs both the simpler and more complex process representations. Simulations also indicate that, for this event at least, dynamic effects are relatively unimportant for prediction of peak inundation. Lastly, consideration of errors in typically available gauging station and inundation extent data shows the raster based model to be close to the current prediction limit for this class of problem.