Prediction of Input Sediment to the Shirin-Darreh Dam Reservoir Using HEC-RAS Numerical Model

Sedimentationin reduced the capacity and useable life of reserivors. Estimation of reservoir sedimentation rate can help us to proper management of designed useful capacity. In the present study, the sedimentation process of Shirin-Dare dam, which is located 65 km form the northeast of Bojnord city, was investigated. It is an earth dam with clay core and the initial volume of the reservoir at normal water level is 91.5 million cubic meters (MCM). The numerical model HEC-RAS4.1 was used to simulate flow and sediment transport. The hydrographic data of the Shirin-Dare reservoir at 2012 and 2017 was used for calibration of the model. The results of simulation with different sediment transport equations such as Laursen, Engelund and Hansen , Ackers and White, Toffaleti , Yang, Meyer-Peter and Muller, and Wilcock showed that using Larsen equation (1958) as a sediment transport equation, Ruby equation as fall velocity equation, substrate sorting method with Exner 5 and also using the Manning coefficient of roughness 0.0035, there is a good match between the measured data and the results of the implementation of the HEC-RAS model. Also, simulation results for the next 100 years showed approximately 73.2 million cubic meters of sediment will enter the reservoir, which will be about 80 percent of the initial volume of the reservoir. On average, about 0.8% of the volume of the reservoir is lost annually due to sedimentation.