Study On The Relationship Between Sediment Delivery Ratio To Water And Sediment Response Of The Three Gorges Reservoir

Sediment deposition affects the comprehensive benefits of the reservoir and is not conducive to the long-term use of the reservoir.As a key project of the national inland river,the Three Gorges reservoir has been concerned about its deposition problem.The sediment delivery ratio is an important indicator of the effect of the reservoir's sediment discharge,which is of great significance in the study of the reservoir's deposition problem.With the operation stage of the Three Gorges Reservoir moving forward,the characteristics of water and sediment movement in the reservoir area change,which leads to the changes of reservoir sedimentation and sediment delivery ratio.There are few studies on the sediment delivery ratio in the reservoir area after the changes.Therefore,based on the measured data of water and sediment,topography and other data since the operation of the Three Gorges reservoir,this paper analyzes the characteristics of water and sediment from the reservoir area under the condition of new water and sediment,and the characteristics of erosion and deposition through the actual measurement of the Hydrological control station.Based on the water and sediment data,the sediment delivery ratio in different stages and periods is calculated,the characteristics and changes of the sand delivery ratio are analyzed,the main influencing factors of the sediment delivery ratio in the Three Gorges reservoir are summarized,the response relationship between the sediment delivery ratio and its main influencing factors is discussed,and the response relationship expression between the sediment delivery ratio and its main influencing factors is constructed,which can further alleviate the Three Gorges reservoir The reservoir sedimentation provides reference.The main research contents and achievements are as follows:(1)Through collecting and sorting out the basic data of the Three Gorges reservoir,the daily water and sediment volume of the Three Gorges reservoir is calculated from the measured daily average flow and sediment concentration of the selected control station,and the sedimentation volume and sediment delivery ratio in different stages and periods are obtained.The analysis shows that the water and sediment volume of the Three Gorges reservoir is concentrated in the flood season,the water volume of different stages of the reservoir changes little,and the sediment volume of the upstream cascade reservoir decreases greatly after it is put into operation The grain size of sand is refined,and the proportion of incoming sand in tributaries is relatively increased,but the distribution of inflow water and sediment does not change much in the year,the accumulated deposition amount increases year by year,and the sedimentation rate slows down.(2)Based on the measured topography and water and sediment data,this paper analyzes the overall scour and deposition characteristics,scour and deposition characteristics,longitudinal and cross-section scour and deposition characteristics of the reservoir area.It is found that since the operation of the Three Gorges reservoir,the siltation has gradually decreased,and the amount of siltation is positively correlated with the amount of sediment.92% of the siltation occurs in the perennial backwater area,mainly in the wide valley and the curved reach.The shape of river reach and flow velocity are the key factors affecting the deposition.The erosion and deposition in the fluctuating backwater area are also affected by sand mining.On the whole the thalweg line in the reservoir area does not change much,some of which are silted up or scoured deep,and the deposition patterns in the section are various.(3)Comparing the characteristics of sediment delivery ratio in different stages,it is found that the sediment delivery ratio in cofferdam impoundment period is the largest,followed by the experimental impoundment period,and the initial impoundment period is the smallest.The amount of water and sediment in storage and the water level in front of the dam are the important factors affecting the sediment delivery ratio.In comparison with different periods in the year,it is found that the sediment delivery ratio in main flood season and non-flood season is relatively large,the sediment delivery ratio in non-flood season and post flood impoundment period is relatively small,and the water in the Three Gorges is relatively small The sediment discharge in the reservoir mainly depends on the flood season.The sediment discharge is mainly fine sand,and the deposition degree of coarse sand is relatively heavier.The movement of fine sand in the reservoir may have flocculation.(4)through the above analysis,it summarizes the four factors that affect the siltation of the Three Gorges reservoir,which are the incoming and outgoing silt,the operation before the dam,the river course form and the human factor.From the perspective of engineering application,the sediment delivery ratio of the two aspects,such as flow Q,sediment concentration S(or sediment deposition),sediment grain size D and dam front water level Z,are taken into account.It is found that the sediment delivery ratio is positively correlated with the inflow discharge in flood season,negatively correlated with the water level in front of the dam and the flood detention time V/Q,and positively correlated with the sediment concentration under the effect of the discharge,but negatively correlated when regarded as an independent variable.(5)The main influencing factors in different periods of the reservoir area are different.The main influencing factors of the long-term sediment delivery ratio in the flood season are the flood detention time,the main influencing factors in the short-term are the flood detention time,the next is the inflow and outflow flow coefficient,and the last is the sediment concentration.In addition,it is also affected by the sediment particle size and other factors.The main influencing factor of sediment delivery ratio in the main flood season is flood detention time,and the main influencing factor of sediment delivery ratio in the non-flood season is sediment concentration.The comprehensive influence of various factors is stronger in the flood season and the flood season.As the operation stage of the reservoir moves forward,the response relationship between sediment delivery ratio and single influencing factor becomes worse,and the comprehensive effect of various factors is enhanced,so as to avoid flood detention as much as possible in the subsequent operation of the reservoir the time is about 16 days.(6)Through the analysis of the response relationship between the sand sediment delivery ratio and the main influencing factors,this paper constructs the response relationship between the annual and monthly sediment delivery ratio in flood season and the main influencing factors.By comparing with the existing sediment delivery ratio formula,it is concluded that the sediment delivery ratio response relationship can better reflect the relationship between the sediment delivery ratio and the main influencing factors of the Three Gorges reservoir,which is more effective for the follow-up research Sand measures provide reference.