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Planning commission hears engineers on stormwater for new developments in Clawson
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Summary
Clawson planning staff and engineering consultants briefed the commission on how recent redevelopment will add roughly 16–17 acres of on-site stormwater controls, explained limits of the city's combined sewer system, and outlined next steps: engineering standards and incentive options for detention and green infrastructure.
Clawson’s Planning Commission held an informational session April 14 on stormwater management that staff said is intended to align commissioners on what the commission can influence through the master plan and zoning, and what requires council-led capital projects. Planning staff said nine redevelopment sites approved or under construction will add roughly 16–17 acres of on-site stormwater controls that did not exist previously, which will help hold and slowly release stormwater rather than sending runoff directly into the combined sewer.
Planning staff explained that Clawson has a combined storm and sanitary sewer system, meaning stormwater and sewage flow in the same pipes in much of the city. That configuration raises the stakes during large storms because sanitary flows mix with storm flows. Mike Smith, the city engineering consultant, described how local flow enters the county drainage system and is conveyed downstream toward the regional treatment plant, and he clarified that “WRC is the water resources commissioner” for the county.
Why this matters: commissioners heard that adding on-site detention on redevelopment parcels reduces peak flows into a constrained downstream system and can reduce the frequency and severity of surcharge and basement-backflow incidents during heavy rainfall. Staff said sites roughly 1 acre and larger are generally expected to provide 100-year detention under WRC standards; the county often asks only for 10-year detention for direct connections but the city may require larger detention where feasible.
Engineers and staff discussed practical limits and alternatives. Much of Clawson’s soils are clay-on-clay, limiting infiltration, so solutions that rely on infiltration (permeable pavement, infiltration basins) may not be feasible in many locations. The consultant said alternatives include underground detention systems, rain gardens, bioswales, green roofs and site-specific designs; underground systems require attention to outlet elevations because they cannot be pumped out. Staff warned costs and space constraints make some green options challenging downtown, where parcels are small and parking dominates land use.
Commissioners also asked about homeowner-level remedies. Staff and the consultant recommended homeowners contact county or city staff for site assessments; they noted that backflow valves can help but are not foolproof in extreme overflows and that well-designed French drains and yard-level drainage improvements have resolved recurring problems for some residents.
Next steps: staff told the commission they will develop clearer engineering standards and provide examples of incentive structures (for instance, incentives for green roofs or rain gardens) for the commission and a sustainability subcommittee to vet. Staff said draft engineering standards and incentive examples will be brought back to the commission for discussion before any ordinance language or formal hearings are set.
