Rainfall-runoff Modeling using HEC-HMS Hydrologic Model for Guder River Watershed, Blue Nile Basin, Ethiopia

Abstract

Rainfall-runoff modeling is important for a number of hydrologic applications including flood forecasting, water resource planning and management. This study presents the result of a watershed rainfall-runoff modeling for Guder river watershed having area of 6597 km 2 using Hydrologic Engineering Center-Hydrologic Modeling Systems (HEC-HMS). The watershed runoff is varying spatially and temporally due to manmade factors and natural factors on the watershed. These issue needs efficient water resource planning and management which is based on the accurate information on runoff generated from the watershed. Therefore, the objective of this study was to model rainfallrunoff process of the Guder watershed using HEC-HMS Hydrologic model. The input data used for this study were spatial data and hydro-meteorological data collected from different sources. The use of Hydrologic Engineering Center-Geospatial Hydrologic Modeling System (HEC-GeoHMS) can easily and efficiently create hydrologic inputs that can be used directly for Hydrologic Engineering Center-Hydrologic Modeling Systems (HEC-HMS). To account for the loss, runoff estimation, base flow and flow routing, the Soil Conservation Service Curve Number (SCS-CN), Soil Conservation Service Unit Hydrograph (SCS-UH),Constant monthly varying and Muskingum methods were used respectively. The rainfall-runoff simulation was conducted using initial parameter. The initial results showed that there is clear difference between observed and simulated peak flow and total volume. Thereafter, a model calibration with an optimization method and sensitivity analysis was carried out. The sensitivity analysis was conducted to determine the most sensitive parameters that affect the model. The results show that the model was more sensitive to Muskingum (K) and (X). To check the performance of the model, Nash-Sutcliffe Efficiency (NSE), coefficient of determination (R2 ) and Root Mean Square Error (RMSE) statistical tools were used. The calibration and validation of the model was found good NSE, R2 and RMSE were found to be 0.788, 0.900 and 13.7 m 3 /s for calibration and 0.786, 0.873 and 15.5 m 3 /s for validation respectively. Therefore, HEC-HMS has performed well in simulating rainfall-runoff for Guder watershed. The daily runoff potential was generated after validation of the model. The daily maximum and minimum runoff potential of Guder watershed was 245.1 m 3 /s and 0 m 3 /s respectively. The hydrologic frequency model was used for determining the peak flow discharge for return periods of 2, 10, 25, 50 and 100 years and the result was found to be 174.7 m 3 /s, 351.9 m 3 /s, 525.3 m 3 /s, 685.3 m 3 /s and 879.8 m 3 /s respectively. This information will be useful as the input for flood mapping of the study area