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Stormwater Management: Structural BMPs
Many so-called Structural BMPs are actually based on natural systems and rely upon vegetation and soil mechanisms in order to perform as intended. Others are considered more conventional “brick and mortar” techniques. The use of these mitigative techniques is not meant to replace the use of non-structural BMPs, but rather to work in tandem with these planning and design-based approaches to minimize unavoidable impacts.
The decision about which structural BMPs are most appropriate comes not ass a post construction fix, but rather as a result of the Site Design Procedure For Comprehensive Stormwater Management. More information about the process is found in the Planning section of the site(to Planning/ SWM Planning Procedure)
The PA DEP Stormwater BMP Manual contains details on some 21 Structural BMPs, several of which offer variations on a central theme. Like the Non-Structural BMPs presented in the Manual, the list of Structural BMPs is expected to grow as stormwater management practices continue to evolve and mature.
A detailed discussion of Structural BMPs can be found in Chapter 6 of the Stormwater BMP Manual.
6.6.3 Dry extended detention basin
A dry extended detention basin is an earthen structure constructed either by impoundment of a natural depression or excavation of existing soil, that provides temporary storage of runoff and functions hydraulically to attenuate stormwater runoff peaks. The dry detention basin, as constructed in countless locations since the mid-1970’s and representing the primary BMP measure until now, has served to control the peak rate of runoff, although some water quality benefit accrued by settlement of the larger particulate fraction of suspended solids. This extended version is intended to enhance this mechanism in order to maximize water quality benefits.
