INVESTIGATING 2-DIMENSIONAL, FINITE-ELEMENT PREDICTIONS OF FLOODPLAININUNDATION USING FRACTAL GENERATED TOPOGRAPHY

Two-dimensional, finite element hydraulic models have been developed t o simulate river flood flows at high spatial and temporal resolutions over river reach lengths of 1-60 km. Such models have been shown to be capable of simulating bulk flow; however, model redesign to predict s patially distributed hydraulic variables has been constrained by lack of suitable topographic and hydraulic data. Here we begin this develop ment process using a hypothetical river channel/floodplain domain wher e the topographic surface is parameterized using scaling information d erived from a fractal analysis of a real floodplain DTM. This is used to test the relative effect of the boundary friction calibration, nume rical model grid resolution, topography sampling error and floodplain relative height on model predictions of outflow discharge, inundation extent and local hydraulic variables. Simulations indicate that model calibration is the dominant factor affecting the above three quantitie s. Moreover, model sensitivity to spatially uniform change is shown to be simple for bulk flow and inundation extent but spatially complex f or local hydraulics. The study has a number of implications for model calibration and set-up procedures, as well as indicating the need to d evelop a new suite of analysis techniques for this class of model. (C) 1998 John Wiley & Sons, Ltd.