Determination of sand and gravel mine locations using HEC-RAS model (case study: Qurchay River in Golestan Province)

Rivers and streams was eroded by flood flows and destroy bridges, farmland, and in some cases homes every year. Study of rivers hydraulic pattern is necessary to control and manage rivers to make better decisions in critical situations. Irregular gravel mining is one of the most important factors to unbalance river hydraulic. The aim of this study is to evaluate the sand and gravel minig in river Qurchay that gravel mining operation was conducted in the range of 6 km. Therefore, collected of data contain sediment, discharge and map 1:1000. After entering data into the HEC-RAS model, hydraulic and sediment was simulate in period of 2005-2015. Yang relationship was predicted sediment transport very well. Bed slope changes in 6 km river in sections show that fluctuations of bed slope decreases in 2015 compared to 2005. It also shows the average speed is also reduced in 2015. The results of the simulation show that the rate of erosion and sedimentation at first 5 km is almost in equilibrium and does not cover gravel mining. The best area for gravel mining is final 720 meters of the river because flow velocity decreased due to slope and shape of cross section and sediment deposited with an average depth of 90 cm. Calculations show that the amount of gravel was mined almost 0.4 million tons per year.