The Local Scour Depth Formula And Its Application Of Low-Head Dams In Mountain Rivers

With an increasing number of DAMS and sluice gate structure engineering in China,the safety problems caused by construction of hydropower project also get more attention.According to statistics,waterlogging is a main reason for threatening the safety of hydraulic structure,while the local scour under the dam is an important factor that causes waterlogging.In low head hydropower junction,there is a certain water level difference between upstream and downstream,which tend drainage flow often has a great velocity and carrying a large energy.If this huge energy were not dissipate,it will scour the riverbed and banks of downstream,and the cover of lower reaches are mostly formatting by alluvial,which has poor impact resistance and the riverbed will be flushed into the pit.When the position of the scour pit distance too close to the hydraulic structures and the pit depth is larger,it will produce damage to dams engineering and seriously affect the service life of the hydropower project.Therefore,when the hydropower projects are designed by units,accurately predicting the depth of part erosion of dam downstream.Reasonable layout the structures and buried depth of hydraulic.Will greatly reduce the risk of waterlogging after hub operation.Now local scour depth formula is often derived for a particular hub project,or considering only one or two main factors.The formulas that can effectively predict the scour depth are less.Especially in view of the underflow energy dissipation of low water head under the dam of scour study are more less.Therefore,in order to guarantee the safety of hydraulic structures,it is necessary to carry out local scour research of low-head dam of mountains rivers.This article mainly aimed at the local scour under the dam,adopting the method of theory analysis combined with physical model.The following results were obtained:(1)By reference to previous research on local scour problem under the dam,determine the main factors that influence local scour depth of low water head under dam.The method of dimensional analysis is adopted to establish the new formula for the local scour depth under the dam.A large number of models measured scour data were collected at the same time.Fitting the measured scour data by multiple linear regression analysis combined with least square method,determining the various physical quantity influencing factors of the new derived formula.(2)Verify the new formula through multiple model measured datas,comparing the formula with Sata Kerry formula,sluices design specification formula,Mao Changxi formula,and Gangqialuofu-Rossing Chomsky formula.Validation showed that the reliability of new derived formula is higher than some existed formula.(3)According to postoptimality scheme of Tongnan hub and Lize hub,carring out experiment of dam under local moving bed and then detailly analysing the test results.(4)The derived formula and conventional scouring depth formula are both used in calculating local scour depth under the dam of Tongnan hub and Lize hub.And verified by model test results.The results show that the new formula is derived relatively higher precision,and the structure is more simple,which can provide some references for estimating the local scour depth under the dam in actual projects.