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Clayton reviews lot-coverage and stormwater policy; consultant recommends stronger technical standards and maintenance reporting
Summary
City staff and consultants recommended shifting to clearer green-space minimums, raising storm-event design standards (to a 100-year, 60-minute event for certain calculations), requiring percolation tests for dry wells, and creating standardized maintenance reporting for BMPs; board asked for real-world examples and further draft code language.
Clayton planning staff and consultant Intuition & Logic presented a set of technical recommendations to update the city's lot-coverage and stormwater rules during the May 5 ARB meeting. The consultants advised separating green-space ratios (neighborhood character) from impervious-runoff calculations (stormwater mitigation) and strengthening technical requirements for new development.
Key consultant recommendations included increasing the storm-event standard used for runoff/detention calculations from the previously used 15-year, 20-minute event to a 100-year, 60-minute event for routine site evaluations, and using a predevelopment all-grass condition for differential detention on larger redevelopment sites (staff suggested applying that all-grass predevelopment assumption for sites disturbing more than five acres). Staff recommended making percolation tests mandatory for dry wells, requiring deed restrictions describing maintenance instructions and creating a standardized reporting form for BMP maintenance to be submitted periodically (for example, every two years) so the city can track ongoing performance.
Staff also proposed creating a green-space minimum (rather than only a maximum impervious coverage) with a sustainability bonus that would allow reductions in mandatory green space if applicants utilize qualified BMPs that treat runoff (dry wells, certain paver systems, rain gardens) and agree to documented maintenance. The board asked staff to return with concrete example projects showing how the new calculations would change design outcomes, and commissioners requested maps and data showing how many lots and which neighborhoods would be affected by new green-space minimums and the proposed five-acre threshold for the predevelopment analysis.
Staff noted that pools would be counted as fully impervious going forward (the recommendation replaces the current convention of counting pool water area at 50%) and that many recent local complaints about persistent yard/sidewalk moisture can be tied to sump pumps, pop-up emitters, and poorly sited discharge points. Next steps described in the meeting: staff will draft specific code amendments and return with worked examples, GIS analysis of affected parcels, and proposed wording for maintenance reporting and deed restrictions.
