Calculation,Analysis And Simulation Of Water Quantity Based On Leakage Of Plain Reservoir

Water supply from the Yellow River plays an important role in the social and economic development of Shandong Province.In addition to long-term irrigation with the Yellow River water,the Yellow River water has become the main water supply source for some cities along the Yellow River in recent decades.A large number of plain reservoirs have been built along the lower reaches of the Yellow River as diversion works in local low-lying areas.Most of the plain reservoir dams are surrounded earth-rock dams with long dam and large water area,which are constructed by semi-excavation and semi-filling.Since the 1960s,770 plain reservoirs have been built in Shandong Province,with a total reservoir capacity of 1.654billion cubic meters,mainly distributed on both sides of the Yellow River.However,the geological conditions along the Yellow River are complicated,most of the dam foundations are soft soil foundation,permeable foundation,even infinitely deep permeable foundation,and the technology level during construction is limited,so the leakage problems are also common.Since some reservoirs still play an irreplaceable role in urban water supply up to now,it is difficult to reconstruct the reservoir itself.In this paper,combined with the surface water spreading method of MAR,the application of groundwater recharge in seepage plain reservoir is researched.Taking the leakage of a Yellow River Diversion reservoir in Jinan City as an example,the dam foundation is used as the filter medium to make the leakage water move through the aquifer and reach the pumping well to be pumped out for reuse,so as to achieve the purpose of saving water resources,reducing the groundwater level around the reservoir and providing high-quality drinking water.The ground seepage method can effectively replace the conventional water treatment process in water plant.Moreover,this method can also use the aquifer to regulate and store the Yellow River water,which is an effective water resource management measure.(1)This study mainly solves the water volume problem.The reservoir seepage model is generalized as a homogeneous isotropic stable seepage model in combination with engineering practice.Based on the foundation pit dewatering well method and seepage resistance coefficient method,the large diameter well model of reservoir seepage considering the action of cut-off curtain is proposed.The calculation shows that the reservoir head is the key factor affecting the leakage.Under the existing interception conditions(the insertion ratio of seepage curtain is 0.3),the leakage is 85,000 m~3/d at the reservoir head of 34.75 m and145,000 m~3/d at the reservoir head of 38.86 m.The higher the water level,the greater the immersion range.Reducing the reservoir operating level is the most direct and effective way to reduce the leakage and immersion hazards.However,the calculation also shows that the existing seepage-proofing works play a very limited role in reducing seepage flow.(2)In order to further study the roles of water head and cut-off curtain during reservoir seepage and their effects on groundwater quantity for seepage recharge,a two-dimensional sand box model is designed based on engineering example and calculation model of reservoir seepage large well method.The physical experiments show that the large diameter well model of reservoir seepage can better calculate the head loss around the seepage.The experimental results show that the leakage decreases with the increase of the insertion ratio,but it shows a stepped change trend with the increase of the insertion ratio.When lambda the insertion ratio of the cut-off curtain increases in the range of 0.15～0.3 and 0.5～0.7,the leakage decreases significantly,while the leakage decreases slowly when lambda increases in other ranges.Whenλis constant,the seepage interception rate increases with the increase of water head.Whenλ=0.7,the cut-off efficiency of the unit depth cut-off curtain is very high and the cut-off effect is good,which is the optimal insertion ratio of the suspended cut-off curtain.If the cut-off curtain ratio is increased to 0.7,the seepage flow will be reduced by about 50%.(3)On the basis of the above research,a groundwater numerical model is established to further study the impact of reservoir leakage on the surrounding groundwater environment,and the favorable groundwater exploitation scheme is verified by the numerical model.The numerical simulation shows that the average daily leakage of reservoir water level 34.76m and 3885 m corresponds to 40000 m~3/d and 78000 m~3/d respectively when the insertion ratio is 0.7.The leakage is reduced,with a ratio of 52%and 49%.These results are similar to those of the large diameter well model of reservoir seepage and sand box test.The area to the west of the reservoir is the area with high groundwater level and the most susceptible to immersion.The immersion range is also significantly smaller under the insertion ratio of 0.7.(4)In the study of exploitation scheme,seepage deformation in the study area is mainly of flowing soil and transitional type,and the allowable hydraulic gradient is 0.10.Under the condition that seepage failure does not occur and sufficient underground dwell tim e is reached,the exploitation well is at least 99.23m away from the dam toe.From the MAR point of view,exploiting groundwater near reservoir can effectively promote the seepage of reservoir water to transform into groundwater.Therefore,with the increase of single well exploitation,the seepage of reservoir will increase,but the net leakage loss will decrease.The exploitation volume can reach 32000 m~3/d,the daily leakage of reservoir is 109900 m~3/d and the net loss is699900 m~3/d.(5)From the point of view of reservoir benefit,seepage loss should be minimized as far as possible,so mining wells should be far away from reservoir.There are 10 mining areas in villages and towns around the reservoir,with a total exploitation volume of 33000 m~3/d.At this time,the reservoir leakage is 86000 m~3/d and the net loss is 53000 m~3/d.Groundwater table in the northwest of reservoir has been effectively controlled.The study on MAR utilization mode of reservoir leakage is a further exploration of MAR mode for saving water resources.It is hoped that this study can provide a new solution for seepage of plain reservoir in the lower reaches of the Yellow River,provide a systematic reference for the development and utilization of seepage water,and provide a reference for projects involving suspended anti-seepage curtain.