Study On The Influence Of Sand Mining Activities On Sediment Erosion Changes In The Weihe Section Of The Three Gorges Reservoir

With the rapid development of national economic construction,the demand for construction sand and gravel has increased year by year,the scale of river sand mining has been expanding,and excessive mining has affected the structural stability of the riverbed.At present,the influence of human sand mining activities on the evolution of river courses mainly focuses on its influence on hydrodynamic conditions and sediment transport characteristics in river sections.The study of the distribution of sand mining in the Three Gorges Reservoir area and the evolution of sand mining activities on the river section is still relatively lacking,and it has a relatively important impact on the operation and channel conditions of the Three Gorges Reservoir,so systematic research is needed.Based on the measured topographic data of the Jiangjin-Fuling River section from2007 to 2019,this thesis statistically analyzes the distribution of sand mining pits in the changed backwater area of the Three Gorges Reservoir,and obtains the actual sand mining distribution characteristics of this section.Combined with the two-dimensional water and sand numerical model,the effect of sand mining pit on the hydrodynamic force and sand transport process of sand mining section was analyzed,and the influence of sand mining activities on the change of sediment erosion in the reservoir section was clarified,so as to provide theoretical and data support for the optimization of the calculation method of river channel erosion in the reservoir area.The main findings are as follows:(1)The total amount of sand mining in the Three Gorges change backwater area in2007～2019 was about 164 million m~3,and the intense sand mining activities were mainly concentrated from 2007 to 2016,the main sand mining section was the Jiangjin to Changshou River section,and the sand mining location was mainly distributed in the river beach.(2)There are about 105 sand mining pits in total,of which 61 with a volume of<1million m~3 are mostly located in the side beach,and most of them do not belong to the planned sand mining section,accounting for 19.51%of the total sand mining;1～2 million m~3 is 23,located in the side beach and side beach to river trough,etc.,the corresponding volume proportion is 19.51%;2～5 million m~3 is 13,located in the beach to the river trough,the corresponding volume proportion is 25%;The volume>5 million m~3 is 8,located in the beach to the river trough,corresponding to 36%of the volume.(3)Affected by sand mining,the water level of the sand mining section along the Three Gorges reservoir has been reduced to a certain extent.,the decrease was within0.1m,and the decrease of the water level gradually decreased with the increase of the incoming flow into the reservoir,and the decrease of the water level after sand mining in the Three Gorges variable backwater area gradually weakened with the decrease of the mileage of the waterway due to the influence of the backwater before the dam.(4)Due to the location of the sand mining pit in the typical sand mining section of the Three Gorges variable backwater,the flow velocity of the main river channel is small,so the shifting sand transport belt is basically the same as before sand mining.Since the distribution of sand pits is not on the main sand walking belt,the dredging rate of each type of sand pit is slow,and the maximum dredging in 10 years is within 6%.