ROLE OF THE LONG-TERM WATER-BALANCE IN MANAGEMENT OF STORMWATER INFILTRATION

Artificial infiltration of urban stormwater can potentially recharge ground water and sustain stream base flows while improving stormwater quality and contributing to flood control. It involves capturing stormwater in basins where it is stored while infiltrating the surrounding soil. This paper suggests that management of these basins with design-storm approaches needs to be supplemented by the long-term water balance. The long-term water balance incorporates continuous low-level background flows, in contrast to the design storm, which is an isolated, rare and brief event. Background flows can accumulate in basins with no regular surface outlets, potentially reducing basin capacity and causing nuisances associated with standing water. A model is described for routing monthly average flows through infiltration basins. Using this model, 12 infiltration basins representing different construction methods and management objectives were designed for a hypothetical catchment in the Atlanta area. The effects of these basins in terms of cost, presence of standing water, capture of flood flows and average annual disposition of water were evaluated. The results show that background flows cannot be disregarded in infiltration management, since the performance of basins designed without considering background flows can be considerably hampered by their presence. The results also invite discussion of alternative basin geometries, materials and hydroperiods as ways of meeting site-specific objectives for water resources and urban amenities. © 1990.