| In 2018,after the collapse of Baige weir Lake on the Jinsha River,the process of water and sediment in the downstream channel was rapidly changed in a short time.A large number of weir bodies and landslide and collapse bodies along the bank slope entered the river channel,causing serious siltation and steep rise of water level in the downstream Changbo Reach.After the end of the outburst flood,the river bed was continuously adjusted and the water level fell back under the action of water erosion after the upstream cascade reservoir blocked sand.However,at present,the water level of Changbo tailwater reach still cannot meet the design requirements,and it is urgent to take dredging measures to reduce the water level.It is of great engineering application value to study and analyze the evolution characteristics of scour and siltation of Changbo Reach after the collapse of weir lake,predict the future evolution trend of the channel,and explore effective measures to reduce the water level of the tailwater reach.This thesis takes the Changbo Reach as the research object,and through the combination of prototype measurement data analysis and river engineering model test,analyzes the characteristics of water and sediment and the evolution of scour and silt in the study reach after the barrier lake outburst.The extreme water and sediment conditions of the weir lake,the overall response adjustment of the riverbed and the evolution process of the key beach trough under the annual water and sediment conditions from 2020 to 2021 were simulated and repeated.The evolution trend of the river channel under the flood process from 2022 to 2027 was predicted,and the treatment plan was proposed based on the evolution law of the river channel and the change of water level.The main research results are as follows:(1)Based on the measured hydrological sediment and river topographic data,the evolution characteristics of scour and siltation of the study reach at different periods before and after the weir lake burst were analyzed and compared.The results showed that:before the weir lake burst,there was no obvious trend scour and siltation change in the study channel from 2007 to 2018,and it was basically in a state of scour and siltation equilibrium;After the collapse of the barrier lake,the balance of erosion and sedimentation of the river was broken,and the study reach was seriously silted before the flood season in 2018～2019.After the flood season in 2019 to the flood season in2020,the study reach was unidirectional scour.Compared with the study reach before the barrier lake,the river was still in an unstable state of silting.(2)The repeated scouring and silting test of the study reach showed that,under the extreme flood process of the weir lake outburst in 2018,the riverbed of the study reach was unidirectional siltation,the original deep"V"shaped channel became a wide"U"shaped channel after siltation,and the river partially collapsed along the bank slope.In the process of water and sediment from 2020 to 2021,the whole riverbed of the study reach presents the evolution characteristics of up-washing and down-silting.The left bank of the CS63～CS69 reach has significant silting,and gradually develops into a narrow beach channel.(3)Based on the reconstructed pre-flood channel topography in 2022,a series of water and sediment years from 2022 to 2027 were selected to predict the evolution trend of channel erosion and sedimentation in the study reach in 5 years.The results show that:the study reach presents an upward erosion and downward erosion trend,and the water level in the tail-water outlet section of Changbo hydropower station continues to fall,but it still cannot meet the design requirements until 2027;The new shoal on the left bank of the CS63～CS69 reach hindered the downward transport of sediment in the upper reaches.(4)The original design treatment scheme of Changbo tailwater reach could not meet the requirements of the design tailwater level.The optimization test of the treatment scheme was carried out.The optimization idea was to first eliminate the left bank shoal of CS63～CS69 reach on the basis of the current topography,and rely on the natural water and sediment action before the operation of the power station in 2027 to intensify the channel erosion and downcutting.Then the treatment scheme is designed based on the river topography in 2027 after beach elimination.After the optimization of the treatment scheme,the water level of the tailwater outlet section is about2304.6m when the full discharge of the power station is 1380m~3/s,which can meet the requirements of the original design plant’s target water level of 2304.65m. |
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