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You can use rain gardens to manage runoff from sidewalks to meet the "On-Site List Approach" if your project:
Find information about street types in the Right-of-Way Improvement Manual.
You can’t use rain gardens to meet:
Find detailed requirements in the Seattle Stormwater Code and Manual.
Are rain gardens feasible for your project? Use the Seattle Stormwater Manual On-Site List Infeasibility Criteria (Volume III, Appendix C).
When a rain garden is installed within a planting strip, runoff from the sidewalk flows to the planting strip. It is then collected and conveyed to the rain garden. Runoff slowly filters through the compost amended soil or bioretention soil, supplying water to the rain garden vegetation and recharges ground water. Ultimately, the rain garden reduces the quantity of runoff that would otherwise flow into the public drainage system.
During larger storm events, sidewalk runoff may exceed the rain garden’s infiltration capacity. In these instances, excess runoff overflows to the gutter over the curb or a depressed curb.
Your project must meet the following criteria to cover typical rain garden installations used for sidewalk runoff:
For a full description of requirements including alternate rain garden configurations, see the Seattle Stormwater Code and Manual.
CAM 1190 – Rain gardens for on-site stormwater management of sidewalk runoff (pdf) contains more information about: