Transient Two-Dimensional Simulation of Real Flood Events in a Mediterranean Floodplain

Abstract

The application of a two-dimensional (2D) finite volume numerical model to real flood events in the Ebro River is presented. The hydraulic model used is based on the 2D transient shallow-water equations on the irregular bed that are able to compute flow advance over a dry bed. This study involves the reliable simulation of not only the flood wave advance but also the drying process in a series of events of different magnitude. The importance of the correct characterization of the roughness coefficient and the topography is emphasized in the study. The former is estimated from a previous classification of structurally homogeneous habitats, and the latter is defined by merging the digital terrain model data with a hydraulic river bed elevation reconstruction algorithm. The calibration of the full model resulting from the roughness, bed river, and flow simulation models is based on field measurements of the flooded area for two steady discharges. The validation is performed by comparing the numerical results with the water levels measured during five flood events at certain times, with the flooded area and time series of continuous point measurements of water depth during different situations throughout the year. Because the model provides correct predictions of the surface processes both for low and high flow discharges, the simulation results are used to analyze the present floodplain hydrodynamics. In the same way, different topographic scenarios, on the basis of changes in the hydraulic river-floodplain connectivity, are generated to analyze their potentially beneficial effect in the floodplain geomorphic dynamics.