Study On Groundwater Recharge Scheme In Mihuaishun Plain Based On Numerical Model

The Mihuaishun(Miyun District,Huairou District and Shunyi District)Plain is a rich groundwater resources and an important water supply source area in Beijing.Due to the overexploitation,the groundwater level continues to decline,forming a large funnel cone.After the water source of the South-to-North Water Diversion Project entered Beijing,the supply-water pressure was mitigated by replenishing,which also provided an opportunity for groundwater conservation.Base on the replenishments of the South-to-North Water Transfer Project,the Mihuaishun Plain area model was built for modeling the dynamics of groundwater level in this dissertation.The sensitivity analysis method was used to analyze the key factors that affect the groundwater dynamic in the study area.Five recharging schemes were proposed,and the evolution characteristics of groundwater were analyzed.The conclusion as follow:(1)In different sub-regions,the factors that affect the change of groundwater level are different.In the alluvial fan area,the key factor which control groundwater dynamics is lateral runoff;in the groundwater exploring area,the main factors is pumping.The riverbed recharging also control on the groundwater level change,and the closer it is to the replenishing riverbed,the greater the impact;in the perennial water-receiving area of the Shunyi River channel,the variation of the groundwater level is significant,mainly affected by the mining;in areas less affected by human activities,the main factor is rainfall.The groundwater is various significant with time.In the case of replenishing 100 million m~3 of water from the South-to-North Water Diversion in the plain water year,the total exploitation should not more than 150 million m~3 in order to avoid the continuous decline of the groundwater level.At the same time,the water supply period can be appropriately increased or decreased according to the amount of surface water resources during the wet and dry years;in wet year,multiple replenishment sites can be used to replenish at the same time to achieve the best effect.(2)The groundwater variation prediction was carried out under different replenishment schemes.The results showed that: In the normal year,the first replenishment option is selected,after 10 years of replenishment,the water level at the funnel was-1.6 m,the thickness of the aeration zone around the No.8 water source plant is reduced by 2.4 ～ 5.6 m,the scope of the funnel is reduced by 13 km~2,and the surplus of the safe water level is 30-35 m.In the dry year,the second scheme is used for storage,after 10 years,the minimum water level at the funnel is-9.3 m,and the thickness of the aeration zone is increased by 0.5 ～ 10.3 m around the No.8 water source plant,the scope of the funnel is expanded by 64 km~2,and the surplus of the safe water level is 35-42 m.In the wet year,considering the impact of the water replenishment risk,the fifth replenishment option is selected,after 10 years of replenishment,the funnel does not exist.The water level at the original funnel cone is10.4 m,the thickness of the aeration zone around the No.8 water source plant is reduced by 9.3 ～ 17.7 m,and the surplus of the safe water level is 15 ～ 25 m.Therefore,the use of the "supplementing the deficit" underground water reservoir regulation and storage scheme can effectively solve the problem of sustainable development and utilization of underground water.