Mukilteo planners recommend WAC-aligned riparian buffers; council questions Brewery Creek approach and legal trade-offs

Planning staff laid out a proposed update to Mukilteo’s critical areas code on March 9 that would align local rules with state definitions (WAC) and update riparian management zones (RMZs) based on "site potential tree height" for Type F streams while using 100 feet as a defensible baseline for some Type N waters.

" This is covered under the Growth Management Act, and it requires us to revisit our regulations every 10 years, " said Christina Shreece (planning staff), summarizing why the city must update its code. She told council the update aims to meet state-mandated thresholds: no net loss of critical-area functions and special consideration for anadromous fish.

Staff explained reasonable-use provisions intended to avoid unconstitutional takings: under the proposal residential reasonable use typically entitles an owner to build a single-family home, and the code would use measured footprint rules (for example, staff described a single-story footprint allowance of up to 2,500 square feet and a smaller allowance for multi-story homes) rather than vague terms such as a 'modest home.'

A central technical change would replace locally designated stream segments with WAC-based Type F (fish-bearing) and Type N (non-fish-bearing) categories and adopt site-potential tree height mapping as the metric for riparian management zones on many Type F streams. Staff said maps are a planning tool but that site-specific reconnaissance and biologist reports would govern final stream typing and buffer extents.

Council members pressed staff on Brewery Creek — several council members said they had walked the creek and questioned whether fish could reach some reaches. Mary Anne Berejikin of the Washington Department of Fish and Wildlife joined the meeting by phone to explain new state science: " We've discovered all streams are important whether they're fish bearing or not, and that has to do with ecosystem services that they provide, not just if it is a fish passable stream, " she said, urging that maps be used as a guide and field verification be required.

Staff warned of legal risk and case law constraints: Snohomish County recently lost an appeal at the Growth Management Hearings Board after adopting smaller setbacks, and staff said departing from best-available-science guidance without documented local analysis could leave the city vulnerable to appeal. Staff offered council two defensible choices: adopt site-potential-tree-height for Type F streams and 100 feet for Type N as a reasonable urban compromise, or pursue an alternative path supported by site-specific science (which would require more study).

Staff said they will continue outreach, keep agencies informed, and return with ordinance language and findings; several council members requested more site-specific information on Brewery Creek and the reports used to classify streams before any final council decision.