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Commission briefed on Fairview/Grand bioswale: 18-inch bio-retention soil, pipes and staged planting
Summary
Staff explained the Fairview/Grand green-infrastructure project uses an 18-inch bio-retention soil profile with perforated subdrain pipes tied into existing storm drains; contractor delays affected schedule but paving was scheduled next week and planting will follow.
Park staff and public-works representatives updated the commission on the Fairview/Grand Avenue green-infrastructure project, describing the design, subsurface work and schedule. Nancy, a park staff member, said the bioswale requires a specific soil profile and subdrainage while Daniel, a public-works staff member, described the system as an engineered marsh that percolates runoff more slowly into the storm drain network.
"You have to have 18 inches of soil," Nancy said, describing the required bio-retention soil depth and the perforated pipes that collect percolated water and route it to the storm system. Daniel added that the feature functions much like a marsh: "This is essentially an engineered marsh, if you think about it." Staff acknowledged contractor delays but said paving on Grand Avenue was scheduled to start next week and that planting would follow the completion of subsurface work.
Why it matters: the bioswale is intended to filter pollutants, reduce peak runoff rates and provide visual improvements on a corridor draining to Lake Merritt; staff noted limits on site selection (flat, low areas that flood) and that the system has finite holding capacity during very large storms.
