Abstract
Understanding the complex relationships between rainfall and runoff processes is necessary for the proper estimation of the quantity of runoff generated in a watershed. The surface runoff was simulated using the Hydrologic Modelling System (HEC-HMS) for the Gilgel Abay Catchment (1609 km2), Upper Blue Nile Basin, Ethiopia. The catchment was delineated and its properties were extracted from a 30 m × 30 m Digital Elevation Model (DEM) of the Lake Tana Basin. The meteorological model was developed within HEC-HMS from rainfall data and the control specifications defined the period and time step of the simulation run. To account for the loss, runoff estimation, and flow routing, Soil Conservation Service Curve Number (SCS-CN), Soil Conservation Service Unit Hydrograph (SCS-UH) and Muskingum methods were used respectively. The rainfall-runoff simulation was conducted using six extreme daily time series events. Initial results showed that there is a clear difference between the observed and simulated peak flows and the total volume. Thereafter, a model calibration with an optimization method and sensitivity analysis was carried out. The result of the sensitivity analysis showed that the curve number is the sensitive parameter. In addition, the model validation results showed a reasonable difference in peak flow (Relative Error in peak, REP = 1.49%) and total volume (Relative Error in volume, REV = 2.38%). The comparison of the observed and simulated hydrographs and the model performance (NSE = 0.884) and their correlation (R2 = 0.925) showed that the model is appropriate for hydrological simulations in the Gilgel Abay Catchment.
Highlights
Adequate knowledge of rainfall-runoff processes is vital to estimate the amount of runoff produced within a given catchment
The Hydrologic Modelling System HEC-HMS, which is a hydrologic modelling software developed by the US Army Corps of Engineers Hydrologic Engineering Center (HEC) is an integrated modelling tool for all hydrologic processes of dendritic watershed systems
Background map files, basin model files, meteorological model files, and a grid cell parameter are created by HEC-GeoHMS which are input to a hydrological model HEC-HMS
Summary
Adequate knowledge of rainfall-runoff processes is vital to estimate the amount of runoff produced within a given catchment. The Hydrologic Modelling System HEC-HMS, which is a hydrologic modelling software developed by the US Army Corps of Engineers Hydrologic Engineering Center (HEC) is an integrated modelling tool for all hydrologic processes of dendritic watershed systems It consists of different component processes for rainfall loss, direct runoff, and routing. Previous studies on HEC-HMS proved its ability to simulate and forecast streamflow based on different datasets and catchment types [9] Most of these studies clearly indicated that the results of the model simulation were location specific, in that different combinations of a model set containing the loss methods, runoff transform methods, and baseflow separation techniques were found to respond variably [10]. Despite the different modelling activities that are practiced in the basin, the HEC-HMS model was not tested, calibrated, and validated in the Gilgel Abay Catchment. Hydrological investigations in similar catchments within the basin and the nearby basins
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