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Key Design and Plan Review Considerations (view source)
Revision as of 15:18, 21 June 2022
, 2 years agono edit summary
==Provide Runoff Pretreatment==
==Provide Runoff Pretreatment==
[[Pretreatment]] refers to techniques or devices used to retain coarse materials suspended in stormwater runoff, either through filtration or settling, before it enters the BMP rendering it inefficient over time. Proper pretreatment extends the operating phase of the BMP’s life cycle by reducing the rate of accumulation of coarse sediment, thus delaying the need for at times expensive structural repairs like unclogging filter beds, pipes and orifices. Common pretreatment devices include [[vegetated filter strips]], [[grass swales]], [[geotextile]]-lined inlet filters/liners, [[check dams]], [[forebays]], eavestrough screens or filters, [[Oil and grit separators]] (i.e., hydrodynamic separators) and manholes containing baffles, filters and sumps. One important consideration for pretreatment is that these devices require frequent (i.e., at minimal, annual) sediment and trash removal maintenance and should be easy to access by inspection personnel.
[[Pretreatment]] refers to techniques or devices used to retain coarse materials suspended in stormwater runoff, either through filtration or settling, before it enters the BMP rendering it inefficient over time. Proper pretreatment extends the operating phase of the BMP’s life cycle by reducing the rate of accumulation of coarse sediment, thus delaying the need for at times expensive structural repairs like unclogging filter beds, pipes and orifices. Common pretreatment devices include [[vegetated filter strips]], [[grass swales]], [[geotextile]]-lined inlet filters/liners, [[check dams]], [[forebays]], eavestrough screens or filters, [[Oil and grit separators]] (i.e., hydrodynamic separators) and manholes containing baffles, filters and sumps. One important consideration for pretreatment is that these devices require frequent (i.e., at minimal, annual) sediment and trash removal maintenance and should be easy to access by inspection personnel.
==Design Low Maintenance Conveyance Systems==
The design of conveyance systems that carry stormwater into the BMP should anticipate potential maintenance issues and include features to minimize or avoid them.
For example, during large storm events, rapidly flowing water into or out of the BMP often causes [[erosion]] in vegetated practices. Inlet and outlet designs should consider protective features that prevent erosion. The size of inlets to BMPs and their slope also needs careful consideration as small, gently sloping openings are easily clogged with coarse debris and sediment which could cause stormwater flows to by-pass or not enter the BMP, increasing maintenance needs.
*[[Curb cuts]] should curve into the BMP so that flowing stormwater does not have to turn sharply to enter and inlets should be sloped at between 5 and 10%.
*[[Inlets]] should also be easily accessible and unobstructed by permanent covers to make trash, sediment and debris removal maintenance easy to perform.
**When designing stormwater infiltration BMPs, consideration should be given to where the majority of trash, sediment and debris will accumulate in the BMP and where snow storage will occur (a significant source area for sediment and debris).
*Infiltration BMPs should include [[pretreatment]] devices, inlet designs or forebays that allow accumulation to occur without blocking inflow (e.g., 5 cm change in grade between pavement surface and BMP surface) and
that isolate sedimentation areas from the main portions of the filter bed so that the area disturbed through routine sediment removal maintenance is minimized.