Engineering Analysis and Design for a Vegetated Swale
San Francisco, California
Most storm water in San Francisco is collected in the combined storm water and sewage system and conveyed to the City's Southeast wastewater treatment facility in the Bayview-Hunters Point neighborhood. Reducing storm water discharge to the southeast treatment facility by managing it on site reduces contribution to the treatment plant during wet weather, when there is peak demand on the treatment facility's capacity. In order to reduce the storm water discharge, Weiss Associates designed a vegetated swale to drain the area served by Amador Street in the Pier 92-94 area of the Port of San Francisco's southern waterfront area.
Vegetated swales are open, shallow channels with vegetation covering the side slopes and bottom that collect and slowly convey runoff flow to downstream discharge points. They are designed to treat runoff via filtering by the vegetation in the channel, filtering through a subsoil matrix, and/or infiltration into the underlying soil. Vegetated swales trap particulate pollutants (suspended solids and trace metals), promote infiltration, and reduce the flow velocity of stormwater runoff.
Weiss Associates assisted the Port in developing a topographic land survey and performed engineering tasks, including hydrologic and hydraulic analysis for a 25-year storm event and designing the necessary size, cross-sections, and slope for storm drainage features. Weiss Associates prepared plans, specifications, and probable construction cost to implement the project. The project included a limited biological resource evaluation of the site and an adjacent emerging wetland. Our biology consultants developed a planting palette consisting exclusively of native plants, which our engineers then incorporated into the landscaping plan.
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