Determination of Sustainable Yield in Urban Groundwater Systems: Beijing, China

Abstract

The city of Beijing has long-term concerns over the sustainable yield from its groundwater aquifers. The aquifers provide half of the city’s water supply and have seen falling water tables over the past century. The sustainable yield of aquifers below urban Beijing is assessed based on changes to the groundwater budget equation from virgin conditions. Sources of anthropogenic recharge, including leakage from water mains and sewer pipes, seepage from septic tanks, irrigation, gardening, and artificial recharge, are together as large as changes to the groundwater flux as a result of groundwater withdrawals. Changes to natural recharge, and to a lesser extent natural discharge, also significantly impact the water budget. Uncertainty persists in several components of the budget equation, in particular changes to the groundwater flux. Estimates of the upper and lower bounds for sustainable yield are relatively unchanged for the years 2000, 2010, and 2015. However, the components of the budget will change as seepage from septic tanks is expected to decrease. Uncertainty in the likely range of sustainable yield is reduced by conducting Monte Carlo simulations. The simulations indicate there is a 96% chance that the lower pumping rate established in 1990 is sustainable. However, with between 30 and 60% of the water budget provided by treated or untreated wastewater, there must be long-term concerns over the quality of the groundwater supply.