| Changes in river sediment transport are the result of a combination of natural factors and human activities.In recent years,with the continuous construction of dry and tributary reservoirs in the upper reaches of the Yangtze River,coupled with rainfall distribution,water and soil conservation and other natural conditions and strong human activities,both the sand production in the upper reaches of the Yangtze River and the incoming sand from the Three Gorges Reservoir have undergone major changes.This has led directly to changes in sediment transport and deposition characteristics in the Three Gorges Reservoir area.To find out the source of the erosion and sediment of the Three Gorges Reservoir and to clearly reproduce the erosion and sediment yield and sediment transport process of each branch of the reservoir,which is of great practical significance to controlling soil erosion in the Three Gorges reservoir,reducing the amount of sediment in the reservoir,prolonging the service life of the reservoir and the scheduling scheme for sediment reduction in the Three Gorges reservoir.This paper,taking the Three Gorges Reservoir Area as the research object,uses field investigation,sample collection and analysis and model construction to determine the fingerprint characteristics of geochemical elements which distinguish the source of suspended sediment,and analyses the relationship between the three types of sediment,sediment and sediment deposition in the typical tributaries of the Three Gorges reservoir area,combined with the particle size gradation analysis and sediment The transport and deposition characteristics of suspended sediment in the Three Gorges Reservoir area are estimated by the budget method.The main conclusions are as follows:(1)By selecting 7 typical basins of the Three Gorges reservoir(Wu Bu River,Yu Lin River,Long river,Peng Xi River,Mo Daoxi River,Da Ning River and Xiang Xi River),and analyzing the characteristics of the geochemical elements(Cr,Cu,Pb,Zn,Ba,Ti,Mn,Al,Fe,Ca,Mg)of suspended sediment,the fingerprint factor library to distinguish the source of mud and sand is established by using the compound fingerprint identification method.Pb,Ca,Cr and Mg are the best combination fingerprinting factors between the Wu Bu River,Yu Lin River and Long River,and Fe,Mg,Ca,Pb and Cr are the best combination fingerprinting factors between the Peng Xi River,Mo Daoxi River,Da Ning River and Xiang Xi River.(2)Using the multivariate mixing model,the sediment contribution rates of the seven typical tributary areas were quantitatively calculated.The sediment contribution rate of the Yangtze River reach in the upper reaches of the Wu Bu River into the estuary is 61.19%,the sediment contribution rate in the Wu Bu River Area is 2.38%,the sediment contribution rate in the Yu Lin River Area is 5.29%,and the sediment contribution rate in the Long River Area is 3.86% The contribution rate of sediment in the Peng Xi River area is 8.55%,the sediment contribution rate in the Mo Daoxi River area is 3.50%,the sediment contribution rate in the Da Ning River area is 14.09%,and the sediment contribution rate in the Xiang Xi River area is 1.14%.(3)Based on the particle size distribution analysis method and the sediment estimation algorithm,it was analyzed that the long-term sediment discharge in the Da Ning River Basin was approximately 1.95 million t/a,and the erosion amount was approximately 8.4 million t/a.The average sediment transport ratio over many years was SDR.It is 0.23.Most of the coarser grain sediments above 0.05 mm are deposited on the river banks and slopes,and more than half of the finer grain sediments between 0.002 mm and 0.05 mm are transported down through the drainage section of the drainage basin,and 0.002 mm.Most of the following clays are still deposited on river banks and slopes.Compared with general natural rivers,the Da Ning River Basin is affected by the canalization of river courses and the operation of various types of reservoirs,and the average flow rate is slowed down,and the proportion of finer sediments is higher.In addition,due to the large-scale and long-term changes in the water level throughout the year,the fine-grained sediments tend to form flocculation and adhesion,and it is not easy to be moved by the water flow after sedimentation,resulting in serious sludge deposition below 0.002 mm.The long-term sediment discharge in the Xiang Xi River Basin is about 370,000 t/a,the erosion amount is about 5.43 million t/a,and the average annual sediment transport ratio SDR is 0.07.Among them,556,000 tons of erosion sediments with particle sizes between 0.5mm~2mm are all deposited on the river bank or slope foot;2.484 million tons of erosion sediment with sediment sizes of 0.05mm~0.5mm have sedimentation of 2.364 million tons.,accounting for 95.17% of the sediment erosion of the particle size group;1.364 million tons of sediment with a particle size of 0.002mm~0.05 mm had 1.127 million tons of sedimentation,accounting for 82.63% of the particle size of the erosion sediment;Less than 0.002 mm of 1.026 million tons of eroded sediment had sediments of 1.003 million tons,accounting for 97.76% of the eroded sediment in this particle size group.In general,the Xiang Xi River is seriously affected by channel canalization and reservoir interception.Most of the sediments that have been eroded are deposited on the river banks and slopes. |
