A biofiltration swale adjacent to a paved surface. The pavement slopes at 2.0% toward the swale, with a 1-inch drop to a 2.0-foot wide aggregate shoulder composed of 4-inch streambed cobbles per Washington State Department of Transportation standard specification 9-03.11(2). The swale features 3:1 side slopes leading to a 2.0-foot wide base. Design parameters include a 1.0-foot freeboard, a 4-inch 100-year storm ponding depth, and a 2-inch water quality ponding depth. The opposite side transitions to grass land cover with vegetation specified per landscape plans and a 2.0% grade.
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