| In recent years,small rivers in the lower reaches of the Yellow River,and some wandering sections of rivers have abnormally developed river regimes,which are prone to small floods,often causing problems such as beach collapses and river-controlling structures.In addition,the risk location is in time and space.Due to the uncertainty of the above,the design and layout of traditional river improvement projects are faced with many problems,which poses a certain threat to the safety of dikes and the people's lives and economic development in beach areas.This paper takes a typical wandering section of the lower Yellow River as the research object and proposes a technology that can be dismantled and assembled with pipe pile inserting plate permeable spur dike.It uses MIKE 21 FM to construct a two-dimensional hydrodynamic model and studies the different water permeability and challenge conditions.The flow angle and flow rate of the local flow field of the pipe pile insert permeable spur dike in the natural river course of the lower Yellow River can provide some references for the management of the wandering river course in the lower Yellow River.The research content and results are as follows:(1)Collect basic data of the study area,including the geographic location,riverbed geology,and basic overview of the beach area.From 2015 to 2019,the water and sediment process of the river section in the past five years shows that in the flood season of 2019,the highest water level of the river section was 59.34m,and in the non-flood season of 2017,the lowest water level was 56.95m.From 2015 to 2019,the annual average water level of this section has a slight downward trend year by year,the water regime is relatively stable,and there is no excessively high water level or excessive flow;The maximum sand content appeared in August 2019 and was 22.1Kg/m~3,and the minimum sand content appeared in September 2016,which was 0.406Kg/m~3.The annual runoff of this section from 2018 to 2019 was 410.Billion cubic meters,an increase of nearly 20%over the past ten years;the annual sediment transport volume was 315 million tons and 330 million tons,respectively,compared with the largest sediment transport volume in the past ten years in 2003,an increase of 15%,20%;the annual sand content has increased by 3 to 4 times from 2015 to 2017.(2)Based on the existing problems of the existing permeable spur dike on the Yellow River,a new type of repeatable detachable pipe pile inserting plate permeable spur dike is proposed.It can arrange the opposite and staggered permeable spur dike groups in the dry season,and the water level of the high channel is blocked.Realize the concept of navigability;in the mid-water period,use the plug-in machine to first fix the pipe piles with grooves,and then according to the incoming water and sand conditions,flexibly adjust the angle of the jet stream and install the plug-in plate to restrict the swing of the main trough and promote the fall of the silt behind the dam.During the flood period,the board is removed to reduce the impact of the renovation of the building on the flood carrying capacity,in order to achieve rapid flood discharge.The hydrodynamic model of MIKE21 FM is constructed,and other parameters such as river roughness are calibrated based on the measured data,and the hydraulic characteristics of the pipe pile inserting plate permeable spur dike are studied.(3)The center of the vortex in the recirculation zone gradually moves downward as the water permeability increases.The maximum length l and the maximum width w of the recirculation zone will decrease as the water permeability increases,and as the water permeability increases,the maximum length of the recirculation zone is more susceptible to the influence of the water permeability.In addition,the maximum length l and the maximum width w of the recirculation zone are related to the length L of a single spur spur,and both l/L and w/L decrease with the increase of?.In the horizontal direction,with the increase of the jet angle,the center of the vortex in the return zone gradually moves closer to the dam.The maximum length of the recirculation zone increases with the increase in the angle of the jet stream,and the maximum width is not affected by the angle of the jet stream.As the flow rate increases,the vortex center of the recirculation zone shows signs of upward movement,and the maximum length of the recirculation zone also increases.At the same section,the change of flow rate does not change the local flow velocity distribution law of the permeable spur dike.When the flow rate increases from 4000m~3/s to 6000m~3/s,the maximum return flow length increases by 50%,and the maximum return flow width increases by 33.3%.When6000m~3/s increases to 8000m~3/s,it increases by nearly 20%;but when the flow exceeds6000m~3/s,the maximum return width will not increase anymore and gradually stabilizes.(4)Compared with the flow velocity before the spur dike is arranged,the flow velocity in the slow flow area before and after the spur dam is reduced by about 72%year-on-year;the flow velocity between the spur spur dikes increases by approximately 55%;the flow velocity near the dam head close to the mainstream increases by about 53%.The flow velocity near the front and back of the dam will decrease with the increase of the jet angle,and decreases by57.1%,68.6%,and 80%respectively as before the spur dike is not arranged;the flow velocity between the slab dams increases with the increase of the flip-flop angle.,it increased by48.6%,57.1%,and 68.9%.(5)The range of the area with high water level in front of the dam increases firstly,and then decreases with the increase of water permeability.Within 250 m in front of the dam,the water level increases with the increase in the angle of the jet stream.The water level in front of the dam will reach its maximum,and the change of the jet stream angle will not affect the water level in front of the dam.The maximum value.When the water flows into the range of 50 m behind the dam,the water surface line will drop and be lower than the normal water depth.The difference between the maximum water level and the minimum water level is about 0.1 m;the water level behind the dam decreases with the increase of the jet stream angle.small. |
PDF Full Text Request