Hydrologic Mitigation Using On-Site Residential Storm-Water Detention

Abstract
On-site storm-water detention systems can be used to mitigate the hydrologic effects of residential development and to provide a supplemental water supply at the scale of single residences. A three-year rainfall record from a site in the Puget lowland, Washington state, is used in a simple mass-balance model to simulate outflow from single- and multiple-purpose detention systems. Simulations are compared to time series of measured runoff from Evans Creek, a 37 km2, rural basis, and a 0.37 km2, zero-order forested subbasin. Discharge from a small on-site reservoir is sensitive to both the storage capacity and maximum controlled release rate of the system for extreme high flows (those exceeded 1% of the time) and low flows (those exceeded 80% of the time). An intermediate range of discharges (those exceeded 10–30% of the time) is primarily sensitive to release rate, rather than its storage capacity, suggesting that single-purpose systems with small reservoirs can be effective for hydrologic mitigation over a range of intermediate flows.