Recovery scheme of Yuquanshan spring in Beijing
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Abstract:
Yuquanshan spring,located in the foothills of Beijing Xishan,is an essential source of water supply for ecology and environment of Beijing.However,the famous karst spring had been dry since 1974.Since the South-to-North Water Transfer Project was implemented at the end of 2014,the mountainous areas in western Beijing have been planned as "ecological conservation belts". The resurrection of Yuquanshan spring has become a new topic to many researchers.Several hydrogeological surveys of water supply have been carried out in the Beijing Xishan.The hydrogeological conditions have been identified,the exploitation potential of karst groundwater resources has been evaluated,and some preliminary discussions have been made on Yuquanshan spring′s recovery. Based on the comprehensive analysis of the hydrogeological conditions in Yuquanshan areas,a heterogeneous and anisotropic unsteady threedimensional numerical model of groundwater flow is established,which includes the Yuquanshan-Tanzhesi karst water system and the quaternary groundwater system in the upper part of Yongding River alluvialproluvial fan.The study area is divided into 200 m×200 m grids,and the aquifer is generalized into five layers in the vertical direction.The simulation period is from September 2012 to September 2015,with one month as a stress period and a time step of 10 days. The numerical simulation results showed that the groundwater system was in a negative balance during the simulation period.The main factors that played significant roles in the karst water system′s equilibrium were the Yongding River′s seepage (54.72% of the total recharge) and the extraction of karst water (93.55% of entire drainage).Supposing the groundwater level in this area was to be restored,it is necessary to make up the groundwater artificially and adjust the groundwater exploitation layout to reduce the groundwater exploitation according to the background of the South-to-North Water Transfer Project′s operation. In order to evaluate the feasibility of Yuquanshan spring recovery,six recharge and exploitation schemes were designed based on the seepage of Yongding River,the recharge of wells,and groundwater extraction as variable factors.These schemes included the current exploiting plans,extreme reduction exploiting plans,plans for increasing infiltration and reducing extraction,a long-term recovery plan with the goal of spring recovery by 2050,the short-term plans (until 2030) and longterm plans (until 2050) for recharging wells with sandpits at western outskirt in Beijing. If the channel seepage is increased by 0.8×10.8 in the Yongding River gorge and the groundwater extraction is suppressed to 71% of the present situation,the Yuquanshan spring is expected to recover in 2050;if the groundwater extraction is reduced to 45% and the seepage of the river channel is increased by 0.8×10.8m3/a,it is possible to recover in 2030.Besides,to avoid new environmental problems caused by the excessive groundwater levels when Yuquanshan spring is recovered,the appropriate groundwater level for restoration should be considered in groundwater system restoration.The seepage rate can be increased by 0.3×108 m3/a in the Yongding River gorge.At the same time,the groundwater is suppressed to 24%.Although the Yuquanshan spring can not guarantee recovery in a short time,the loss of groundwater resources will be reduced year by year.The groundwater system′s ecological environment will be gradually restored,which is more in line with the actual conditions and conducive to sustainable water resource utilization in this region.
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