Study On The Test Of Local Scour Hole Depth On The Dangka Downstream

Local scour downstream of discharge structure is an important factor which will affectthe safety of hydro-junction, and it is more and more attended by engineers with thespeeding up of the water conservancy construction. Based on the model of Dangkahydropower station and the existing data of water conservancy project, some groups ofexperiment at different discharges and bed material gradations were conducted, and themain influencing factors and formation mechanism of local scour pit downstream of floodsluice were studied and the main conclusions of this thesis are as follows:(1) Through observing the process of flowing water in the hydraulic model test, it isfound that local scour pit is formed by the flow scour of longitudinal and lateral flow, andthere divided three stages in the process of scour pit: strong scouring stage, continuousdeveloping stage, scour stability stage. And it is rapid in the early scour period and slow inthe later scour period.(2) Discharged flow and bed material gradation are the main affect factors to the depthof local scour pit downstream of flood sluice. With the increase of flow discharge, the depthand range of scouring pit increased; with the increase of the sediment diameter of river bed,the depth and range of scouring pit become smaller.(3) Based on the binary stream, the formula to calculate local scour depth was derivedthrough continuity equation. It is found that there is a quite difference between the values ofthe existing calculation formula and the values of measured data of local scour depth,however there is a small difference between the values by the author formula andmeasurement data of local scour depth. Moreover, the author formula has been correctedbased on the study of the difference between the calculated value and measured data oflocal scour depth, and finally, the calculation formula of scour pit downstream of Dangkahydropower station is proposed.(4) Based on the continuity equation and considered the influence factors on the depthof local scour, such as water diffusion in the pane, reflux, and so on, the calculation formulaof local scour depth was derived, and its range of application was given according to therange of water diffusion and the strength of reflux.