Urbanization and Water Quantity: Impacts and Mitigation

Urban and suburban development adversely impacts both surface and ground water resources by profoundly altering the hydrologic cycle. Conventional storm water management practices rely on storage to reduce runoff peaks and trap pollutants, but do not address impacts due to changes in the partitioning of water. The introduction of impervious surfaces increases the amount of storm runoff and decreases the amount of ground water recharge. Ground water pumping reduces the amount of ground water. Increased storm runoff causes channel enlargement and increased flood peaks, even when mitigation storage is employed. Reduced ground water results in decreased ground water discharges to aquatic systems. Enhancing the infiltration of storm runoff appears to be a feasible way to address the hydrologic alterations that usually accompany urban and suburban development. Practices that focus infiltration, such as rain gardens and bioretention facilities, appear to be particularly effective. Modeling indicates that a properly designed bioretention facility can preserve natural runoff amounts and increase ground water recharge amounts well above natural levels, perhaps even compensating for ground water pumping. Remaining research issues involve subsoil characterization, vegetation selection, ground water contamination, regulatory strategies, and long-term performance.