| With the diversion of water from the south to the north into Beijing,the overdrawing of groundwater has eased.In the past two years,Beijing has carried out ecological water replenishment projects for Yongding River and Chaobai River respectively from the perspective of ecological environmental benefits and underground water conservation.Ecological water replenishment not solely contributes to the ecological restoration of the watershed,however conjointly plays a vital role within the recovery of groundwater reserves round the water replenishment and therefore the rise of underground water level.At the same time,with the enlargement of the center route of the South-to-North Water Diversion Project and also the jap route into national capital,the surface water resources can still increase.So it is necessary to store the increased surface water source in the underground storage area,on one hand,to supply the deficiency caused by the exploitation of groundwater over the years,on the other hand,to store it underground for the emergency protection of urban water resources.In this paper,the Beijing Plain is the research area,numerical simulation is the main research method,and the Feflow numerical simulation software based on finite element is used to establish a three-dimensional groundwater flow numerical model in the Beijing Plain,and the model is applied to the main water supply projects in Beijing.The main conclusions of the study are as follows:(1)Based on the analysis of water table,water resources development,utilization and alternative relevant data,a numerical model of groundwater flow in Beijing Plain area from 2005to 2018 was established,and the equilibrium analysis was carried out.The results showed that the average annual total groundwater recharge in Beijing Plain area during the simulation period was 18.97×10~8m~3,and the average annual total excrement was 21.56×10~8m~3.The average annual discharge is 2.6×10~8m~3,which is generally under negative equilibrium state.In recent years,the groundwater is under positive equilibrium,and the groundwater has been conserved.(2)Combined with the scheduling plan,the impact range and water level change of the ecological replenishment of the Yongding River in 2020 and the Chaobai River in 2021 are predicted and analyzed.The upper,middle and lower reaches of the Yongding River have an impact area of about 250 km~2,200 km~2 and 100 km~2.Respectively.the maximum groundwater level rebound is about 10m,7m and 3m.The groundwater level reaches its maximum in July and August,and then the water level gradually decreases.It is predicted that after replenishing the Chaobai River,the affected area will be about 400 km~2 by the end of July.The average rise of water level is about 13m within 1km of the main stream of Chaobai River,10m within 2km,7m within 3km.The affected area of groundwater below Niulanshan Xiaojiao Dam is about 100 km~2,but the average rise of water level is not large.By the end of 2021,the affected area of groundwater around Chaobai River will be expanded to about 600 km~2..(3)Combined with different objectives,the following suggestions are given for different replenishment schemes in the groundwater storage area of Mihuaishun area.In order to achieve the conventional water storage target of 1.26×10~8m~3 per year,it is recommended to adopt the water supplement method of 1×10~8m~3 for the Xiaozhong River and 0.5×10~8m~3 for each of the Huaihe River and Yanqi River;In order to achieve the emergency water storage target of1.5×10~8m~3 in the underground water source area,it is recommended to adopt the water supplement method of 1×10~8m~3 for the Xiaozhong River and 0.5×10~8m~3 for the Huaihe River;In order to require under consideration the development of Huairou Science town and therefore the joint regulation and storage of surface water and groundwater,it is recommended that the Xiaozhong River 1.2×10~8m~3,the Huai River 0.6×10~8m~3 and the Yanqi River 0.7×10~8m~3 be used for water replenishment. |
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