Utilities staff explain watershed management plan, monitoring program and how results guide stormwater system planning

Eric LaFrance, utilities planning manager, and Brianna Pierce, senior environmental technician and environmental data scientist, briefed the commission on June 5 about progress on Bellevue’s Watershed Management Plan and the environmental monitoring program the city is using to measure stream health.

LaFrance framed the watershed plan as focused on stream-health objectives and described how that work will feed into a broader storm-and-surface-water system plan now under way; the system plan will assess service levels, policies and funding needs and is expected to proceed through 2025–26 with completion targeted in early 2027. LaFrance told commissioners the watershed plan alone could not resolve competing infrastructure and environmental priorities, so staff are using the system plan process to evaluate trade-offs and financing.

Pierce described the environmental monitoring program’s structure: indicators mapped to a ‘‘stream functions’’ pyramid (hydrology, geomorphology, chemistry and biology), continuous flow and temperature gauges, monthly water-quality sampling, annual benthic macroinvertebrate surveys and fish/habitat surveys on a multi-year cadence. Monitoring stations are prioritized in three tiers: Tier 1 (highest priority) includes Coal Creek, Kelsey Creek and Lewis Creek; tiering guides where staff focus the most intensive monitoring.

Pierce said most urban stream sites scored poor to very poor on the benthic macroinvertebrate index, but that some long-term sites show promising trends: three long-running stations in Bellevue — including a Coal Creek site — have statistically significant improving scores, and one Coal Creek site reached the highest score Bellevue has recorded. She attributed those improvements to long-term stormwater infrastructure and best-management practices while cautioning that broad recovery remains slow and that establishing trends requires multi-year data.

Commissioners asked whether the monitoring program diagnoses causes of poor stream health or only measures condition. Pierce said the program primarily measures status and trends and supports inference about drivers; detailed cause-and-effect monitoring (effectiveness monitoring) can be added to evaluate specific projects. LaFrance said watershed assessment reports and watershed improvement strategies synthesize monitoring data to identify probable drivers (for example, older neighborhoods with limited stormwater treatment) and to recommend targeted actions.

LaFrance noted ongoing efforts such as WSDOT culvert replacements that should improve fish passage and said staff are coordinating monitoring and system planning so that the watershed recommendations are not lost in system-level trade-offs. He also described the city’s participation in the National Flood Insurance Program’s Community Rating System and said Bellevue’s floodplain regulations translate into discounts for a small number of covered properties.

No formal decisions were taken; staff said they will continue monitoring, produce synthesis reports on a four-year cycle, and bring policy-level system-plan discussions to the commission this fall.