Experimental Study On Slit Deposit Flushing Of Mahl Rservoir In Pakistan

Sediment deposition is a widespread problem in the hydropower stations and reservoirs.After the completion of a reservoir,the gradient of water level in the reservoir decreases and flow velocity significantly reduces,leading to sediment deposition within the reservoir.Therefore,prevention and drainage of sediment are key technical issues in the design of the hydropower stations.Mahl hydropower station,95 km away from Islamabad,is located in the tributary of Indus,Jhelum River,in the northeast of Pakistan.It is the Level 2 of Jhelum River cascade development.Catchment are above the dam is about 25300 km~2.The normal water level of the hydropower station is 585 m,total head is 59 m,and the total installed capacity is 590 MW.The physical model test of Mahl reservoir is conducted.It is a normal model with a scale of 1:80based on the principles of geometric similarity,water flow movement similarity and sediment movement similarity.Two problems are mainly researched.(1)the distribution of sediment deposited to analyze the possibility of desilting tunnels to be clogged when the water flow is 796m~3/s and 1350m~3/s respectively.The results show that the water stored is used for 35.6 days and 8.9 days,the average deposition depth in the front of the dam is 1.2 m and 0.9 m respectively corresponding to the flow of 796 m~3/sand 1350m~3/s.So it is possible for desilting tunnels to be clogged with high water level in a long period.(2)The precipitation erosion effects in the reservoir and the sediment deposition in the front of power holes when the water flow is 2000m~3/s,3570m~3/s and 8120m~3/s respectively.when the water flow is 2000m~3/s,and the problem of sediment deposition in the front of power holes is serious with precipitation erosion,it is recommended to take effective measures to prevent sediment avoiding affecting the normal operation of the hydropower station.