The Influence of Dam Construction on the Catchment Hydrologic Behavior and its Effects on a Discharge Forecast in Hydrological Models

The hydrological properties of a river basin are extremely affected by the construction of a dam. The discharges and sediment flow distribution, in a modified river basin will not be the same as to a natural catchment. Hydrological models contextually focus on a natural river basin without any modification. Unfortunately, most of the river basins have been under such modification, which is not favorable for a model simulation at a normal condition. This research was done at the Awash River Basin, already modified because of dam construction. A systematic approach was applied to handle the modification in the basin, through an application of the Soil and Water Assessment Tool (SWAT) and Hydrologic Engineering center’s River Analysis System (HEC-RAS) consecutively. SWAT model was implemented to simulate the upstream part of the basin. At the downstream parts of the basin, a simulation process was difficult on a SWAT model, due to the modified hydrologic parameters. Hence, the HEC-RAS model was applied because of its applicability under such circumstances. The model outputs indicate that the SWAT model can simulate the upstream part of the basin, in a good performance range that can be used for practical implementation. The downstream i.e., the modified catchment was simulated relatively better in the HEC-RAS model with good accuracy. Also, this research pointed out that a combined hydrologic and hydraulic model system development can be the best solution for modified catchments.