Deciphering the floodplain inundation maps in Greece

Floodplain inundation is caused by heavy rainfall, while its evolution depends mainly on land cover and geomorphologic characteristics of the river basins. The aim of this work is to decipher the similarities and differences of flood inundation maps that have been produced for various areas in Greece in the framework of the European Floods Directive (2007/60/EC). The adopted mapping methodology was accomplished through the use of the HECHMS software, which simulates the hydrologic processes of river basins and determines the design flood hydrographs for given return periods, as well as the HEC-RAS software, which simulates the hydraulics of open channel flow (computation of energy gradients and piezometric heads). Both packages are compatible with ArcGIS, which can be used for further data processing and visualization for cartographical purposes. The outcome of floodplain inundation mapping is anticipated to help in planning and prioritizing environmental and flood protection actions in a pre-disaster stage. The mentioned multi-methodology has been implemented to a great number of flood prone river basins in Greece. Flood maps, which can depict a variety of parameters, such as flood extent, water depths and piezometric heads for various return periods, were deciphered taking into account the specific characteristics of each area. The values of the aforementioned parameters are dependent on the (a) intense rainfall regime of the area (IDF curves), (b) geometrical characteristics of the river channel (cross sections areas, roughness, slope) and (c) geomorphologic, geological and soil characteristics of the flood plain (land cover, land use, elevations, slopes, soil permeability, hydraulic conductivity etc).