北京市平原区地下水动态要素的时间变化及其启示

Temporal variations of elements of groundwater regime in Beijing Plain and its implications

地下水补径排过程中的水量交换满足质量守恒定律，具体为地下水量的输人输出最终要满足水均衡方程。对反映地下水量交换规律的地下水动态要素及其时空变化规律的掌握，是进行地下水资源评价和未来供水能力预测的基础。采用水均衡理论和水位动态均衡法，对北京市平原区地下水动态与均衡要素（水位、补给量、排泄量）的时间变化规律及相互关系进行了分析，并得到以下主要结论：（1）地下水总输出量连续多年大于总输入量，使含水层长年“人不敷出”，储量亏损越积越多；（2）平均水位每下降（上升）1m，含水层可释放（储存）约4．76亿m^3的水量；（3）近些年地下水的开采量有相当一部分来自袭夺的天然排泄量，且两者呈良好的负线性相关关系；（4）地下水位变动带内（埋深在7．50，22．92m之间）含水层的给水度总体上随埋深的增加而减小，等效给水度为0．077。

Water exchange during the recharge-discharge process of groundwater meets the law of mass con- servation, which can be described that the input and output of groundwater should meet the water budget equation in detail. The comprehension of elements of groundwater regime and their temporal and spatial variations reflecting the mechanism of groundwater exchange process is vital for the groundwater evaluation and the prospective prediction of water supply capacity. The temporal variations and relationships of elements of the groundwater regime （including groundwater level, recharge, and discharge） in Beijing Plain were analyzed in this paper based on water budget theory and using water-table fluctuation method. The results show that, （1） the annual total output of groundwater is generally more than the annual input during the past decades, which leads to the yearly decreasing of groundwater reserve; （2） the aquifer can yield （store） about 476～106m^3 of water when the mean groundwater level drops （raise） per meter; （3） large part of the extraction quantity of groundwater during the past decades are from the natural discharge of groundwater captured and there exists a well negative linear correlation between these two water budget items; and （4） the specific yield of aquifer within the disturbed belt of groundwater level （buried 7.50- 22.92m below ground） is generally decreasing with depth with the equivalent specific yield of 0.077.