Assessment of discharge and sediment flows in a river through a combined hydraulic and hydrologic routing techniques

Abstract An advancement of flood routing methods is important for the design and management of the water resources systems. Hydraulic and hydrologic routing approach are widely applied in most simulation models, separately. The combined hydrologic and hydraulic routing method where recent approach to improve the modeling effort in hydrological studies. The main drawback of hydrologic routing methods was inaccuracy on downstream areas of the river basin, where the effect of hydraulic structures and the river dynamics processes are dominant. The hydraulic routing approaches are relatively good on a downstream reaches of a river. This research was done on the Awash River basin at the upstream areas of a Koka dam. A combined hydrologic and hydraulic approach was used to assess the discharge and sediment flow in the river basin. The hydrologic routing method was applied at an upstream part of a river basin through a SWAT model. HEC-RAS model was applied at the middle and downstream areas of the basin based on hydraulic routing principle. The combined routing method can improve the result from the simulation and increases the accuracy in the prediction of the peak flow. It can simulate all the discharges for both short and long-term duration with good model performance indicators. Besides, sediment modeling was done by comparing the regression model, SWAT model, and combination of HEC-RAS and SWAT model. The result from the sediment modeling indicates that the regression model and the combined models show good agreement in predicting the suspended sediment in the Awash River basin.