Problems of fracture-karst aquifer recharge with urban roof rainwater

Many cities in northern China utilize fracture-karst groundwater as the drinking water supply source. On the one hand, the urban water shortage is serious, and on the other hand, rapid urban development results in increasing impervious areas which changes the natural hydrological cycle and necessitates discharge of rainwater runoff through the drainage system for flood control, thus resulting in water resource waste. Roof area accounts for 67%~70% of the city area, and roof patterns provide a natural catchment for collecting rainwater. The fracture-karst aquifer with high permeability coefficient provides large storage space for rapid rainwater infiltration in flood season. However the quality of roof runoff is variable and has been reported to exceed water quality guidelines. Thus effective pre-treatment measure are being assessed for the source water in the proposed reuse application, which will augment existing drinking water supplies and provide protection to the groundwater environment. During recharge the recharge water will change the groundwater level, temperature, water quality and recharge, runoff and discharge conditions in adjacent aquifer, and the water-rock-gas interaction between recharge water and carbonate rocks happens in aquifer tends to change groundwater physical, chemical condition and aquifer structure.