Thurston County commissioners favor hybrid riparian buffer approach; staff to do gap analysis and add meetings

Thurston County Planning Commission commissioners on April 15 signaled support for a hybrid approach to protecting riparian areas and other fish and wildlife habitat conservation areas, directing staff to return with a formal gap analysis and additional meetings before drafting ordinance language.

Staff presented Washington Department of Fish and Wildlife (WDFW) guidance recommending a riparian management zone (RMZ) defined as the channel migration zone plus the site-potential tree height, with a recommended 100-foot minimum RMZ for streams. Staff explained that site-potential tree height is an estimate of how tall dominant tree species on a site could grow over a long-term horizon and that combining it with a channel migration zone produces a buffer intended to protect key riparian functions such as shade, woody debris contribution, root stability and pollution filtration.

Commissioners discussed three broadly described options for buffer calculations drawn from Ecology guidance: option 1 (flexible, site-specific buffers that allow averaging and professional analysis), option 2 (a mid-level prescriptive approach), and option 3 (a simple, large prescriptive buffer with fewer reporting requirements). Several commissioners favored a mix of option 1 and option 3 — effectively allowing property owners either to accept a larger prescriptive buffer for a simpler permitting pathway or to pursue site-specific analysis when development complexity requires it. Staff indicated such a hybrid framework is implementable in code.

There was also extensive discussion about whether protections should treat fish-bearing and non-fish-bearing streams the same. Staff and commissioners cited WDFW rationale that non-fish-bearing streams contribute organic matter, cool water and hydrologic connectivity to downstream fish-bearing waters and that intermittent streams may become fish-bearing during flood events; for that reason WDFW recommends a consistent protection framework for all streams, though jurisdictions sometimes adopt different approaches with documented justifications.

Commissioners and staff emphasized that RMZs are not necessarily absolute no-build zones; rather, they are management zones with standards and best-management practices (BMPs) that can allow some activities if performance standards are met. Staff also discussed using RMZs to prioritize restoration, encourage retrofits (for example, septic upgrades and stormwater improvements), and avoid imposing onerous requirements on low-impact residential changes while reserving stricter mitigation for high-impact commercial or industrial uses.

To strengthen the record and provide defensible policy choices, staff proposed and the commission agreed to add several meetings through October to complete a gap analysis comparing the county’s current code to best-available science and state guidance. The gap analysis will document where code deviates from technical guidance, explain the rationale for any departures, and inform the drafting of ordinance language.

What happens next: staff will prepare a gap-analysis memorandum, consult with biologists where needed (including topics such as riparian pollinators and species of local importance), and bring proposed code language and public outreach materials back to the commission in the coming months; no new ordinance was adopted at the April 15 meeting.