Hydrological modelling for determining flood zones in a mountain catchment under absence of observations

Abstract The floods occur up to 10 times a year, and periodically they are extreme in the Tisza river basin (Ukrainian part). The extreme floods with hazardous consequences have occurred several times over the last twenty years. The situation is threatening on the mountain tributaries of the Tisza River, where floods form with rapid levels rising in the cold period of the year. In the mountainous part of the basin, the floodplain is quite narrow and is the only place for settlement and economic activity, so flood risk determination is an important element of urban development planning within the concept of a sustainable city. The flood zone calculation is complicated by the lack of hydrological, hydraulic data and a reliable high-resolution topographic basis in mountainous areas. The aim of the work is to assess the flood risk and the possibility of using a free DEM for flood zone calculation on the example of a small mountain catchment and its application at the stage of feasibility study and environmental assessment. The work performed the results of 1% probability flood calculations along part of the river and flood zones simulation using HEC-RAS soft wear based on the field survey geometry and on cross sections taken from DEM free. The absence of the riverbed bathymetry on DEM free and the mismatch of elevations significantly affect the accuracy of the water level calculations. The evaluation of the results shows that the use of DEM free for the territory of Ukraine does not give accurate results, but can be used for preliminary works and the environmental impact assessment.