Study On The Influence Of Weir Bank Combination On River Flow Effect And Fish Passing Effect

Rivers in the north are generally seasonal rivers.During the dry season,a series of problems such as poor water surface landscape and cut-off are prone to occur.Cascade weirs are often used to solve the problem of high water level,but it may also cause reduced river connectivity and obstructed fish passage.Negative Effects.In addition,studies have shown that the meandering degree of rivers has a great impact on fish traffic and river biodiversity.Therefore,this paper puts forward the idea of arranging the discharge outlets on the stepped weirs and combining them with different forms of channel banks to repair the water-poor rivers,that is:on the basis of setting the same height and spacing of the stepped weirs,the linear channel For the combination of banks and cascade weirs,three outlet layout plans are set up,namely openings on the same side of the weir(Plan 1),openings on different sides(Plan 2),and openings in the middle(Plan 3).By using the hydraulic model The method of combining experiment and numerical simulation analyzes the results of flow field structure,turbulent energy,test fish passing success rate and average passing time of different plans,and obtains the optimal layout plan;in order to study the effect of different channel bank forms on water flow The influence of distribution and fish passing effect,two cases of submerged and non-submerged are set up,and the water flow characteristics and fish passing effects of the two forms of straight-line groove-bank combined stepped weir and curved groove-bank combined stepped weir are studied.The results show that:(1)The proportion of the mainstream area in Plan 1 is 15%,that of Plan 2 is 50%,and that of Plan 3 is 44%.Among them,the flow velocity partition phenomenon of Plan 2 and Plan 3 is more obvious;there is no obvious backflow in the flow fields of Plan 1 and Plan 2 In Plan 3,there are backflow areas of different sizes in the flow field.According to the degree of dispersion of water flow distribution,Plan 3 has the largest degree of dispersion and Plan 1 the smallest.(2)The success rate of test fish passing in Plan 1 was 62.2%,81.1%in Plan 2,and 55.6%in Plan 3,and the average passing times were 140s,133s,and 135s,respectively,among which Plan 2 had the highest passing success rate.From the perspective of passing success rate and passing time,the water flow distribution of Plan 2 is more suitable for fish passing.Through the analysis of numerical simulation results and fish passing test results,the water flow distribution of Plan 2(discharging outlets on different sides)is more reasonable.(3)Under the optimal layout plan of the discharge outlet,the numerical simulation results of the combination of different banks by the cascade weir show that:under the same conditions,the proportion of the mainstream area of the combined curved channel bank is up to 70%,which is higher than that of the combined linear channel The bank can be increased by about 15%,and the suitable area for passing through the combined curved trough bank is basically located in the middle of the longitudinal channel,with a more reasonable distribution;and the combined curved trough bank can effectively reduce the scope of the backflow zone.(4)The pass success rate of test fish on the combined curve trough bank is above 80%,the highest is 86%,and the pass success rate on the combined straight trough bank is 70%80%.Through the comparison of the same situation,the combined curve The success rate of passing through the slot bank can be increased by up to 10%.The shortest average transit time of combined curved banks is 85.4s,and that of combined straight banks is 111.8s.After comparison,in the same case,the average travel time of the combination curve channel bank can be shortened by 31.2%.(5)The passage of test fish in the combined curved trough bank almost does not involve the concave bank of the curved trough bank,and mainly passes along the suitable area for passage,and basically does not enter the non-mainstream area.Even if the experimental fish strays into the non-mainstream area,it can quickly find the direction of passage.It shows that the water flow distribution on the bank of the combined curve is helpful for the passage of the test fish,and reduces the situation that the test fish enter the non-mainstream area by mistake;when the form of the channel bank is the same,the test results show that the passage track of the test fish is more concentrated in the submerged situation.