A GIS method for rapid flood hazard assessment in ungauded basins using the ArcHydro model and the Time-Area method

Abstract

Geomorphology plays an important role in hydrological processes, as it largely controls a catchment’s hydrologic response. Study of morphometric characteristics becomes even more significant in ungauged basins, especially when systematic hydrological data are scarce. A very well suited tool for accurate quantification of these characteristics is GIS software and especially ArcHydro model. In this work, four catchments in Greece, with rich flooding history are studied in terms of flood hazard spatial distribution. ArcHydro is used for rapid computation of catchment and sub-catchment characteristics. Based on these computations and with the aid of the time-area method, instantaneous unit hydrographs are developed in numerous locations across each catchment. Subsequently, peak discharge values extracted from these hydrographs, are interpolated across each catchment to visualize the runoff pattern, highlighting the areas where there is an inherent tendency for higher peak flow rates. In this way, the method allows the detection of locations where higher peak discharge creates a higher flood hazard potential. Results of the method are compared with historical floods damages for verification purposes, showing good correlation with the resulting flood hazard zonation.