Laboratory Sand Tank Experiment On Water Distribution And Sediment Transport During Yellow River Water Recharge Yufuhe River

Jinan City is famous for its "Spring City" in the world.The karst spring adds a beautiful landscape to Jinan City and provides high quality water for life and production.However,with the rapid development of economy,society and urbanization in Jinan City,the water demand is increasing day by day,and a large amount of groundwater has to be extracted,which leads to the continuous decline of groundwater level,the decrease of groundwater volume and the sharp contradiction between water supply and spring protection.For this reason,Jinan City has taken various measures to open up resources,reduce expenditure and protect springs,such as the construction of Yuqinghu reservoir,Queshan reservoir and other urban water diversion projects,and the replacement of groundwater with Yellow River water.At present,the water supply of the Yellow River accounts for about 80% of the urban water supply.On this basis,the water from the eastern route of the South-to-North Water has also been supplied.The water sources of the external water transfer in Jinan are diversified.These measures play an important role in protecting the spring water from gushing all the year round.However,the water quality of the Yellow River and the Yangtze River is not as good as that of the karst water.How to improve the water quality of the external water transfer and at the same time achieve the goal of maintaining the spring? The effective measure is to choose the appropriate way and region to establish the managed aquifer recharge(MAR).The Yufuhe River in the west of Jinan City is an important part of the artificial recharge project.The Yellow River water,the rain flood and the South-to-North Water accumulated in Wohushan reservoir are put into Yufuhe river for recharge,and then the water source of the lower reaches is used for water supply.The recharge water source in the lower Yellow River has the characteristics of high sediment content.After sedimentation in the grit chamber,there are still some suspended fine particles.Therefore,based on field investigation,laboratory experiment,model simulation,prevention and control of suspended matter blockage,this paper explores the water distribution and the mechanism of migration and blockage of suspended fine particles in the recharge area when artificial recharge is conducted in Yufuhe River by water spreading method.Furthermore,it can provide parameters and basis for the stable operation of the recharge area,slow down the clogging problem caused by the suspended fine particles,extend the operation life of the recharge project and ensure the effective infiltration of the riverbed.In this paper,two groups of single-layer and double-layer sand tank experiments are designed.After analyzing the data,the research results are as follow:(1)When other conditions are the same,the infiltration will increase with the increase of the total amount of recharge.However,when the infiltration amount reaches the critical value,the remaining water flows to the lower reaches of the river in the form of surface runoff,which belongs to the invalid recharge amount.Part of recharge water formed the lateral seepage into the sand gravel layer.In the actual recharge process,the drainage volume should be controlled to ensure the effective infiltration volume and reduce the invalid volume.And through the verification of the physical model by Hydrous-2D,the simulation results are good,and the rationality of the data is verified.(2)In the suspended solids experiment,the prepared montmorillonite suspension is used as the water source for recharge.With the increase of recharge time,the amount of infiltration decreases gradually,and the surface runoff increases gradually,and with the increase of turbidity of recharge water,the clogging degree of media surface is faster and more serious.The amount of infiltration under unblocked condition accounts for 60-70% of the total recharge amount.The permeability of porous media will decrease with the increase of suspended matter deposition,which will lead to physical clogging,and the amount of infiltration will be reduced to 10-20%.After the formation of the clogging,the surface clogging will be alleviated by scouring with high velocity water.After the laboratory experiment,we take out the surface part for sand washing,and then put it back into the sand tank,the infiltration amount can be restored to 60-70%.It is concluded that the suspended fine particles deposited in the pores of the surface layer of the porous media,and the suspended thin clay layer is the main cause of physical clogging.(3)According to the turbidity calculation of the suspended fine particles amount,to explore the distribution of suspended fine particles.With the increase of the turbidity of reinjection water,the remaining amount in the tank will increase gradually.The suspended fine particles are mainly the surface outflow amount and the remaining amount in the sand tank,and the remaining amount is mainly distributed in the surface and upper area of the sand tank.(4)In this paper,the feasibility of building rubber dam in the study area is verified by placing water retaining plate on the surface of sand layer.It is concluded that the construction of rubber dam can retain the surface water and improve the infiltration capacity,but the suspended fine particles and degree of clogging will increase.After the rubber dam is demolished,the high velocity scouring has the function of dredging the thin clay layer on the surface,but the capacity of recharge has not been obviously restored.After the experiment,we take out the surface part for sand washing,and then put it back into the sand tank,the infiltration amount can be restored.It shows that the periodic sand and gravel scraping can effectively maintain the sustainable utilization of the recharge project.(5)The prevention of physical blockage generally needs to control the reinjection water source.Infiltration and sedimentation can reduce the concentration of suspended fine particles in the recharge water.Yufuhe River,as a river in front of the mountain,has a large slope and a fast velocity.In the recharge process,the formation of clogging can be further slowed down by intermittently adjusting large flow to scour the river channel.