Flood mappinga methodology based on mathematical modelling and satellite imaging

Resumo

A 2DH mathematical model assembled at CEHIDRO, IST, is employed to model 2000/2001 Tagus river floods over a 70 km reach, with the key objective to assess its performance envisaging its use as a forecasting tool. The model is suited for highly unsteady discontinuous flows over complex geometries, employing a finite-volume discretization scheme, based on a flux-splitting technique incorporating a reviewed version of the Roe Riemann solver. New boundary conditions were developed, based in the Riemann invariant, in order to cope with the provided hydrographs in a mathematically coherent manner. Detailed discharges and water levels are available for the inlet and outlet sections, as well as for the inlet at river Zêzere, a Tagus affluent. A high resolution Digital Elevation Model (DEM) is used. Spatially heterogeneous roughness characteristics are derived from land-use databases built from satellite data. Synthetic Aperture Radar (SAR) satellite imagery of the floods is available and is used to validate the simulation results. The delimited areas from the satellite and simulations are over imposed and show a very good agreement in all major flood extents, with small structures, with lengths at the order of the spatial discretization, clearly reproduced. Flow depths and registered discharges are recovered from the simulation and compared with data from a measuring station in the domain. The comparison shows remarkably high accuracy, both in terms of amplitudes and phase. Further calibration of the roughness parameters and inclusion of detailed terrain structures like small levees should improve the flood extents regarding the comparisons with satellite data