北京市西山地区地下水数值模拟及预测

Numerical simulation of groundwater flow for Xishan area in Beijing

北京西山地区地下水资源丰富,水质优良,是北京市重要的地下水供水水源地之一。长期过量开采地下水已经引起了区域地下水水位下降等环境问题。南水北调客水进京后,将会改变区域用水结构,逐步实现对含水层系统的涵养目的。采用有限差分方法进行区域含水层系统数值模拟,分析不同开采条件下含水层系统响应特征。取得如下认识:西山地区地下水开采总量达到3.546 2×108m3/a,为达到可持续开采目的,需要将开采量压至2.798 8×108m3/a,实现采补平衡;维持现状开采至2030年,岩溶水水位下降22m,第四系承压水水位下降约28m,部分地区第四系潜水含水层出现疏干现象;南水北调进京后,按照规划压采方案实施,2030年末岩溶水水位平均恢复约5m,第四系承压水水位下降约6m。区域岩溶含水层恢复贮水0.185 4×108m3,第四系含水层系统贮水损失2.782 8×108m3。

The Xishan area,located in western Beijing,is one of the most important well fields supply the water for the city. The long-term groundwater overdraft has caused the regional groundwater depletion and other environmental issues. The South-to-North Water Diversion Project（ SNWTP） may partly change the water-use scenario and increase the aquifer system storage. A numerical groundwater-flow model of Xishan area was developed to synthesize estimates of water-balance components and hydrologic properties,and to analyze the response of aquifer system to the predictive scenarios. The following results were obtained：（ 1）Sustainable yield may be accomplished by reducing current abstraction of aquifer system from 3. 546 2 ×10^8m^3/ a to 2. 798 8 × 10^8m^3/ a;（ 2） The average drawdown of karst and quaternary confined aquifer are 22 and 28m to the end of 2030 with current pumping rates（ hypothetical scenario 1）. Localized cells near the pumping centers will go dry by the year 2028;（ 3） Under the hypothetical scenario 3,a projected decrease in abstraction rates from the entire system during 2019—2030 cause the water level of karst aquifer to rises about5 m. However,the water level of quaternary confined aquifer will continue to decrease with the maximum 6m at the end of 2030. The estimated storages of karst aquifer was increased by 0. 185 4 × 10^8m^3. And quaternary aquifer system will loss 2. 782 8 × 10^8m^3.