ABSTRACT:This paper looks at the use of off‐line detention systems as a means of stormwater management. Conventional detention basins are typically designed and built as in‐line systems in which all runoff is directed to the basin. Off‐line systems are designed so that only a portion of the runoff is directed to the basin. Several simulation experiments were run to examine the behavior of in‐line and off‐line systems designed to reduce the peak flow from a developed area to the pre‐development level. The results demonstrate that off‐line systems require considerably less storage than in‐line systems to achieve the same management goal. The results also show that off‐line and in‐line systems have significantly different flow‐duration characteristics with the off‐line system generally producing lower flows over longer periods. Unfortunately, off‐line systems may exacerbate downstream flooding problems, especially when used in the upper portions of a watershed. Nevertheless, an off‐line system can be an alternative to in
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