Mill Creek staff propose flexible wetland buffers, site-potential tree‑height riparian approach in critical area update

Planning staff presented a suite of proposed changes to Mill Creek’s Critical Areas Ordinance on Oct. 16, telling the Planning Commission that the city must update its code by year-end under the Growth Management Act and that the changes rely on best available science from state agencies.

Justin Horn, planning staff, reviewed a gap analysis prepared with consultant Facet and said staff is drafting code amendments to Chapters 18.04 and 18.06 of the Mill Creek Municipal Code. Horn said the update covers wetlands, fish and wildlife habitat areas (including riparian buffers), geological hazard assessment requirements, and exemptions/exceptions such as for trails. He said the city must “base all of our regulations on the best available science.”

Wetlands: staff presented three options for buffer methodology. Option 1 (staff-preferred) uses buffer widths that vary by wetland category, land-use intensity and a habitat-function score and allows impact minimization measures and buffer averaging in specified circumstances. Options 2 and 3 are progressively more prescriptive and inflexible, with larger fixed buffers in many cases. Horn explained buffer averaging under Option 1—shrinking a buffer in one place and expanding it…