Shabelle nehrinde hidrolojik modelleme ve taşkın haritalaması: Somali Beletweyne şehri örneği

Hydrological and hydraulic modeling plays a vital role in water development, planning, flood inundation, early warning, and flood mitigation works. Shabelle Basin, a transboundary basin with an approximate area of 297,000 km2 originating from Ethiopian highlands, is a region with limited research and paucity of hydro-meteorological data. This study aims to fill the existing knowledge gap on hydrological modeling and flood inundation mapping of Shabelle Basin, targeting Beletweyne, a flood-prone city and amongst the worst flood-hit areas in the region. Beletweyne city has been experiencing unusual floods with a high frequency for the last two decades, paving way for increasing interest in the area. In this study, firstly, basin characteristics of the selected area are delineated using HEC-GeoHMS. Then, hydrological modeling is undertaken with the help of HEC-HMS utilizing a continuous processing method. Five years of calibration (2013-2017) and ten years of validation (2003-2012) resulted in a model Nash-Sutcliffe Efficiency of 0.776 and 0.611 respectively. A statistical flood frequency analysis is then applied to determine runoff values for certain return periods (2, 5, 10, 25, 50, 100, and 500). Finally, hydraulic modeling is carried out using HEC-RAS in order to achieve 2-dimensional flood inundation mapping for the city of Beletweyne for different flood levels. The results show that Beletweyne city is at high risk of flooding even for short return period floods. In a conclusion, a protection plan (construction of flood control structures and setting up an early flood warning system) is recommended to reduce flood damages and protect people's lives and property in the region.