RAINFALL-RUNOFF SIMULATION OF A SUB-CATCHMENT USING HEC-HMS

Hydrological data in the form of stream flow is very scarce in most developing countries. This affects the planning and management of urban watersheds. Therefore, it is necessary to estimate peak discharge from rainfall using hydrologic models based on some measurable watershed characteristics. This study aims to model the rainfall-runoff process from a typical urban watershed using Hydrologic Engineering Center Hydrological Modeling System (HEC-HMS) software. The catchment basin has a total area of 21.91 km2, and a dendritic stream system. Soil Conservative Services (SCS) Curve number was used for getting excess rainfall from total rainfall, SCS dimensionless unit hydrograph for converting the excess rainfall to direct runoff and Muskingum for the channel routing. The rainfall-runoff simulation was conducted using six (6) rainfall events. Model calibration and validation were done using optimized parameters and the result shows a reasonable fit between the observed and simulated hydrograph. The model result has an RMS error of 1.5 m3/s, and a Nash-Sutcliff of 0.585. It is concluded that the model can be used to predict runoff from rainfall with reasonable accuracy. The result can be used for watershed planning and management.Keywords: HEC HMS, rainfall, runoff