Study On The Influence Of The Cross Dam And Guide Wall In The Front Of The Shoal On Diversion Ratio Of Flow Discharge And Sediment Transport Of Dongxikou Channel

Dong Xikou waterway of the upper reaches of the Yangtze River is a typically curved and braided channel,whose navigation conditions are complex,the law of pebble movement is hard to grasp,and the waterway regulation is difficult.The distance between the shoals of the waterway are short and the mutual restriction of them leads to pebble beach group.The waterway is very difficult to regulate for the impact of the regulation of one shoal will transfer to another,thus deteriorate the waterway conditions.Therefore,the main regulation structure must be integrated planning and completing at once.This paper uses Flow 3D water and sediment numerical simulation software to carry out three-dimensional hydrodynamic calculation and analysis of different types of the cross dam and guide wall in the front of the shoal,and obtain the influence of the different parameters of the dam on the flow and its flow-diversion characteristics.Based on the results of three-dimensional hydrodynamic research,the reasonable parameters and structural types of the dam are put forward according to the actual conditions of the Dong Xikou waterway.Through the physical model test of the natural sand bed of the Dong Xikou waterway,the effects of the cross dam and guide wall in the front of the shoal on the flow structure and the diversion of water and sediment of the main and auxiliary branches of the Dong Xikou were studied,and the local scour rule of the dam was obtained.Based on the present experimental research,the main results are as followed:(1)When the occupation ratio of fish mouth dam(relative to the width of the channel)remains unchanged and the angle of the jetty head changes,the change law of longitudinal water surface line is similar,and the upstream backwater height changes little.When the occupation ratio is increasing,the upstream backwater is more and more obvious.The vertical distribution of longitudinal velocity is different from that of homogeneous flow,and the maximum of longitudinal velocity appears in the 0.55 times the depth of the water.The change amplitude of upper flow rate is small,and the lower flow rate is larger.(2)According to the results of numerical simulation,the empirical formula of the left-branch diversion ratio of fish mouth dam is obtained,and the main factorsaffecting the water diversion of Fish-mouth are gained.This paper also use the equation to calculate the rule of the water diversion of fish mouth dam in Dong Xikou,the calculation error is small and the result is reliable.(3)After the construction of the Fish-mouth of Dong Xikou,the flow rate of the left-branch reaches higher than 60% in low flow period,and the diversion ratio and water depth meet the design requirements.After the regulation,the diversion ratio of flow discharge and sediment transport of the Fish-mouth is obviously increased.If there is no sand upstream,in the process of water withdrawal,the sediment deposited in the inlet of dredged channel will gradually scour to downstream,which is conducive to the stability of the channel.(4)The head of the fish mouth Dam starts to scour at the small flow,the scour ability is strongest under the middle flow,and the scour ability of the main flood season is weakened gradually.