The Experimental Study On Sediment Deposition In Front Of Power Generation Hole Of Mahl Reservoir

Mahl reservoir is a proposed large(Ⅱ)type water conservancy project on Jhelum River,one of the branches of Indus River located in the northeast of Pakistan.As a medium sand containing river,the annual mean sediment discharge of Jhelum River is 1.23kg/m3,but its sediment trap rate is only about 5 due to its small storage capacity,the sediment problem is far from optimistic.Aiming at the sediment deposition problem,a physical model of Mahl hydropower station,which belongs to the normal model,was built on the basis of geometry similarity,water motion similarity and sediment flush deformation similarity.The horizontal scale and vertical scale are both 80.In view of the some different operation regulation,We did the experiment of water level、the experiment of flow velocity-flow regime、the experiment of "the clean front" and the experiment of optimization programme.The results of model showed that:1.When the reservoir working under low water level,areas in front of the generation hole is situated in the primary recirculation zone,the coarse sediment deposit in front of power tunnel.When the flow is 3570m3/s,the maximum deposition thickness is about 2.5m～3m,the average deposition thickness is 2.04m.When the flow is 8120m3/s,the maximum deposition thickness is about 3.46m～6.12m,the average deposition thickness is 2.55m.2.To keep "the clear front",The optimization scheme of the experimental design can reduce the deposition of the power generation hole to a certain extent.The average sedimentation depth of the optimization scheme 1 is reduced by 0.13m compared to the basic scheme;and for the reduction of optimization scheme 2.The reduction is 0.2m.As the results show,the effect of the optimization programs are not ideal.3.Whatever measures are taken,it is difficult to avoid sedimentation before the power generation hole when operating at low water level according to the current layout of key water control projects.This paper suggests that the key water control projects be rearranged,to avoid backflow before the power generation hole when operating at low water level.So the sedimentation could be reduced effectively,achieving "the clear front" of the power generation hole.