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.

大坝的建设极大地影响了流域的水文特性。在改良的流域，其排放量和泥沙流量分布将与自然流域的排放量和沉积物流量分布不同。水文模型在上下文上侧重于天然流域，无需进行任何修改。不幸的是，大多数流域已经进行了这种修改，这不利于正常条件下的模型模拟。这项研究是在阿瓦什河流域进行的，由于大坝的建设已经对其进行了修改。通过依次应用土壤和水评估工具（SWAT）和水文工程中心的河流分析系统（HEC-RAS），采用了系统的方法来处理流域的改造。实施了SWAT模型来模拟流域的上游部分。在盆地的下游部分，由于修改了水文参数，在SWAT模型上很难进行模拟过程。因此，由于在这种情况下的适用性，因此使用了HEC-RAS模型。模型输出表明，SWAT模型可以在良好的性能范围内模拟盆地的上游部分，可用于实际实施。在HEC-RAS模型中，相对较好地模拟了下游，即改良集水区。此外，这项研究指出，水文和水力模型系统的联合开发可能是改进集水区的最佳解决方案。之所以使用HEC-RAS模型，是因为其在这种情况下的适用性。模型输出表明，SWAT模型可以在良好的性能范围内模拟盆地的上游部分，可用于实际实施。在HEC-RAS模型中，相对较好地模拟了下游，即改良集水区。此外，这项研究指出，水文和水力模型系统的联合开发可能是改进集水区的最佳解决方案。之所以使用HEC-RAS模型，是因为其在这种情况下的适用性。模型输出表明，SWAT模型可以在良好的性能范围内模拟盆地的上游部分，可用于实际实施。在HEC-RAS模型中，相对较好地模拟了下游，即改良集水区。此外，这项研究指出，水文和水力模型系统的联合开发可能是改进集水区的最佳解决方案。