Large Wood Transport Influence on Flash Flood Risk in a Mountain Village in Central Spain

Abstract

The European Water Framework and Floods Directives have brought a legal framework favouring the good ecologic and geomorphological condition of water courses. This may conflicts concerning the current management of large wood in rivers in Spain, which has been traditionally focused on removal of this material from the rivers. In addition, identifying stream reaches where large wood is a potential hazard and where therefore its careful management is necessary is also needed for flood hazard and risk assessment. In this study, we have developed a numerical model to simulate wood transport coupled to a 2D hydrodynamic model. We applied this model in a mountain river reach crossing a village in Central Spain. This river is flash flood prone and large amounts of wood have been observed after flood events, but there is not detailed information about its influence on hydrodynamics so far. The aim was to analyse how the transport and deposition of wood influences flood risk estimation in this mountain village by means of a probabilistic approach to the numerical modeling. As a result, the most sensitive infrastructures to the passage of large wood have been identified, as well as the potential consequences of their blockage. When wood clogs these bridges, the main effect is the backwater effect upstream from these critical sections, where wood is trapped and deposited. High hazard areas (based on water depth and flow velocity) increases significantly and the potential economic damages may increase up to 50 % for the worst case scenario.