Hydrological modeling using HEC-HMS model, case of Tikur Wuha River Basin, Rift Valley River Basin, Ethiopia

Modeling rainfall-runoff is widely recognized as one of the most complex types of hydrological modeling, primarily because it involves the integration of a diverse array of watershed characteristics. Due to its ability to emulate the hydrological behavior of a watershed, the modeling of rainfall-runoff plays a crucial role in predicting the runoff generated at the watershed's outlet. The present study aimed to simulate runoff by utilizing HECHMS in the Tikur Wuha River watershed situated in the Rift Valley Basin of Ethiopia. To achieve this goal, tools such as HEC-GeoHMS and ArcGIS were employed to establish the necessary input parameters for HECHMS. Various methods were implemented at different stages of the modeling process, including SCS-CN for estimating precipitation loss, SCS-UH for transforming excess rainfall, Muskingum for flood routing, and the monthly constant method for modeling base flow. The process of calibration and validation entailed the use of daily observed flow data from the periods (1990 to 2009) and (2010 to 2015) correspondingly. Nash Sutcliff Efficiency (NSE) and coefficient of determination (R²) were employed as metrics to evaluate the model's performance. The findings showed that the model exhibited high performance in both calibration and validation stages, producing values of (NSE = 0.83, R² = 0.91) and (NSE = 0.84, R² = 0.86) respectively. Furthermore, the Percent Bias (PBIAS) values in calibration and validation remained within acceptable ranges, registering at 2.69 % and 4.67 % respectively. After the calibration and validation of the model, the estimated peak flood discharge simulated by the model (206.3m³/s) was compared with the observed stream flow (197.1m³/s), indicating a significant similarity between the model's output and the observed data. Consequently, it can be inferred that the model exhibits a high capability in replicating hydrological parameters effectively for the Tikur Wuha watershed and other watersheds sharing similar hydrological characteristics.