Rainfall-runoff modeling using HEC-HMS model for Meki river watershed, rift valley basin, Ethiopia

Detail understanding of rainfall-runoff processes is tremendously important for a watershed with variable streamflow generation. The streamflow of the Meki River fluctuates seasonally causing flooding on surrounding agricultural land. This study adopted Hydrologic Engineering Center Hydrologic Modeling System (HEC-HMS) to model the streamflow and predict flood in the Meki watershed, Rift valley basin. The model was calibrated with observed streamflow data from (1987-2004) whereas the consecutive year's data (2005-2010) was used for model validation. The evaluation criteria namely: Nash Sutcliff Efficiency and coefficient of determination were preferred to evaluate the model performance. The finding relieved that, the model can perform very well (NSE = 0.83, R2 = 0.91) during Calibration, and (NSE = 0.804, R2 = 0.89) at validation period. Moreover, the predicted floods at 2, 10, 25, 50, and 100 years were 133.2, 178.1, 239.7, 313.2, and 346.19 m3/s, respectively in the watershed. The novelty of this study lies in evaluating the model results using both statistical parameters (NSE and R2) and the Generalized Extreme Value method). The finding of this study is vital to developing flood mapping and designing flood mitigation measures in the study area. Further, the developed models can be applied to other hydrology with similar hydrological conditions.