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

Water exchange during the recharge-discharge process of groundwater meets the law of mass conservation, 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 476×106m3 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.