Evaluating the performance of Sistan and Zahak diversion dams in Sistan River using HEC-RAS hydraulic model

Rivers are the main arteries of human life, thus control and proper exploitation of these surface resources require a proper understanding of their behavior and investment in the river improvement. By reviewing and evaluating the projects carried out in this area, their positive and negative aspects can be checked and the obtained results can be used to overcome the projects shortcomings, improve their efficiency and make the future projects more fruitful. Sistan River is the major border river between Iran and Afghanistan and Sistan life depends on it. The length of this river in Iran is about 70 Km. This study attempts to evaluate the performance of Sistan and Zahak diversion dam structures and the structures alongside the river using HEC-RAS hydraulic model. The results show that these structures increase the maximum Sistan flood power transmission in the absence of these structures from 500 m3/s to 810 m3/s. Considering the importance of estimating Manning roughness coefficient with high precision for hydraulic calculation in the river engineering projects, the main river bed roughness coefficient for the main river and the flood plains of Sistan were estimated as 0.02 and 0.035, respectively. It was also found that Discharge-Return period relation can be expressed as. Existence of diversion dam structures on the unpredictable rivers such as Sistan River may double the flood power transmission in some cases. In this study, the effect of 310 m3 per power transmission increse through Sistan River was observed. The reasons for the relatively low impact (the xpectation was more) are slight slope of Sistan plain, and water expansion on flood plain and back water in the direction of Sistan River flow.