Flash Flood Hazard Prevention using Morphometric and Hydraulic models. An example implementation.

Abstract

Flash floods are the prominent type of flood hazard among the Black Sea and the Mediterranean countries. They occur within a few minutes or hours of excessive rainfall, a dam or levee failure, or a sudden release of water and pose a threat to public safety, human health, stream ecosystems, soil and stream bank erosion, people’s properties, public infrastructure and overall to sustainable development and integrated water management. A lot of research has been conducted in respect to this issue. Several early warning systems have been proposed and installed in a few cases but, even if they can provide the tool to protect human life, they can hardly be used to fully protect property and public infrastructure. Effective Flood Hazard Prevention based on scientifically proven methodologies and as accurate as possible data can provide the tools to decision makers in order to mitigate the problem. As flash floods mostly develop on ephemeral streams, little or no runoff data are available so, statistical, probabilistic or hydrologic models used elsewhere to assess the flood hazard cannot be efficiently applied in this case; on the contrary, morphology based models are usually used. In the present paper, a methodological approach combining the morphometric parameters and stream power methodology and the use of geologic, hydrogeologic, topographic, geographic and meteorological data, is used to assess the flash flood hazard on a regional scale and to pinpoint the exact location of flooding. The hydraulic model HEC-RAS is used at the next stage, to calculate on a local scale, all flood related parameters including the inundation area and depth so that Risk can be accurately assessed. Based on these calculations, problematic areas where spotted according to the hydraulic analysis performed. The procedure has been implemented in the area of Serres (Kentriki Makedonia) and the results were compared with the recorded results of previous flooding events. The use of these combined methodologies can provide reliable and accurate enough information in order to assess the Flash Flood Hazard and Risk, to design the appropriate preventive measures, to plan efficient post event actions and to help make decisions in order to effectively mitigate the Hazard. This methodology provides an essential tool for environmental protection, since it concerns river ecosystems and water bodies.