Study On Groundwater Recharge Scheme Of Baifu Spring Based On Numerical Simulation

According to Beijing urban plan to promote the protection and utilization of the Grand Canal Cultural Belt,the reflow of Baifu Spring is not only an important symbol of the successful reconstruction of the Grand Canal Cultural Belt,but also of great significance to the underground storage of water resources,the inheritance of the Grand Canal culture and the construction of regional ecological civilization.To provide technical support for the restoring scheme of Baifu spring,on the basis of fully collecting and analyzing the existing data,the recharge,runoff and discharge of Baifu spring is figured out through regional groundwater chemical and isotopic investigation,FEFLOW numerical model is established and several sets of restoring scheme of Baifu spring are simulated and predicted.The main conclusions of this paper are as follows:(1)Combined with the investigation and analysis of geophysical exploration,hydrochemistry and isotopes,the recharge,runoff and discharge of Baifu spring were determined.the northeast of study area is exposed of Wumishan limestone.After directly receiving meteoric water supply,groundwater flows from east to southwest along karst fissures in the contact area of Jurassic and Wumishan limestone,and discharge in the form of Qincheng Spring and Baoyu Spring along the mountain edge.The westward runoff is blocked by the magmatic rock in Huazhuang area,and discharge to form the Baifu Spring in the Longshan mountainside.The Wumishan limestone in the northern Ming Tombs receives the meteoric water supply,and flows southward along the Jixian strata.Most of which flows southward,and part of the water flows eastward to Baifu spring along the Nankou-Sunhe fault.The main source of groundwater in the study area is meteoric precipitation,and the age of groundwater is generally young and the water cycle is fast.(2)The water balance calculation results show that the main discharge in the study area are groundwater exploitation and lateral outflow,of which groundwater exploitation accounts for more than 90%,and the overall equilibrium difference is-61.8374 million m~3/a.The numerical model of groundwater in Changping District is established by FEFLOW.After model identification and verification,most of the water level lines simulated by the model are parallel to or coincide with the measured ones,and fit good in the verification period.The numerical model of groundwater was applied to the simulation and prediction of the present condition.The results show that the groundwater level in this area will decrease significantly in ten years.If the reflow of Baifu spring is to be realized,some measures must be taken.(3)The calculation results of groundwater adjustable storage capacity in Baifu spring area show that the adjustable storage space of Quaternary underground reservoir is 1.00 billion m~3,and the adjustable storage space of karst water for restoration is 300 million m~3.In view of the three schemes of Baifu Spring re-upwelling,the numerical model is used to simulate and predict the change of groundwater flow field and the water level of the observation wells and to optimize the scheme.The results show that the optimal scheme is to replace the surrounding Dengzhuang Water Works,Huazhuang Water Works and Zhenshun Water Works with the Changping Surface Water Works to be built soon,and to reduce the total amount of underground water extraction to 68%of the current amount,so that Baifu Spring can be re-upwelling in 2033.