The sources and processes of aquifer recharge in urban areas, however, can be greatly modified and the resulting extra infiltration can help to offset the effects of increased abstraction. In an extreme case in the Arabian Gulf region, recharge from imported water is so much greater than the negligible natural replenishment that it exceeds the capacity of the aquifer. As a result, water levels have risen to the surface, causing flooding of basements. Aquifers that had been de-watered over decades are now fully recharged. In fact, such cities as Birmingham, London, and Tokyo are starting to encounter problems of rising water tables affecting road tunnels, foundations, car parks and metro systems constructed before the ground became saturated.
Urban development has a significant impact on groundwater, affecting quantity, flow and quality.
Changes in groundwater levels, both reductions and increases, can also pose engineering problems for infrastructure and facilities. In fast-growing cities urban groundwater can be managed sustainably, but only if the sometimes conflicting needs and priorities of water supply, waste disposal and underground engineering can be reconciled. This goal seems within human capabilities. John Chilton, Hydrogeology Group, British Geological Society, London, United Kingdom. All rights reserved.