Study goals
Stakeholders, including municipal stormwater permittees in Western Washington, want to know how stream health changes over time in small streams as the area urbanizes and stormwater controls are implemented more broadly.
Study design
The Puget Small Streams (PSS) study collects water and sediment chemistry, in-stream and riparian habitat information, benthic macroinvertebrate, and periphyton samples.
Sites are selected following a random probabilistic survey design which allows spatial characterization of large areas across the study region that would not otherwise be possible. It also uses modest funding and resources.
Read the Quality Assurance Project Plan (2020) for detailed information such as study design, plans, and schedules.
Study design adjustment
For studies starting in 2020, we made a few study design adjustments to better answer regional status and trend questions and to improve monitoring efficiency. These include:
- Stream conditions sampled every year at fewer random sites (n=33) to year variability and improve trend detection power.
- Sites are stratified by percent impervious surface of the contributing watershed into four categories to better represent the full range of urban and urbanizing conditions in the region.
- Sites are sampled in the summer only for watershed health (biota, stream, and riparian condition) with targeted water and sediment quality parameters.Monthly water quality was dropped.
- Continuous monitoring of stream water level starting the October before the summer sampling to calculate flows or flow metrics at each site.
Read the study design fact sheet for more information on these changes.
Sampling locations
33 randomly selected sites two reference sites are monitored each year. The sites for 2020 summer sampling are a subset of past 2015 sampling sites that met the new study design criteria and grouped by the percent of impervious cover in contributing watershed.
The United States Geological Survey (USGS) leads the PSS monitoring to provide unbiased regional estimates of status and trends of small, stormwater-receiving streams in the region.
Scope of Work, Quality Assurance Project Plan (2020)
Study objectives
- Implement the probabilistic sampling design that can provide strong status and trends of stormwater receiving water in the region.
- Collect and monitor stormwater-related water and sediment chemistry.
- Continuously monitor stream stage.
- Assess biological conditions in small streams using B-IBI and periphyton.
- Identify key drivers affecting integrated stream health indicators.
- Incorporate existing land use information and other existing data into the status and trends assessment.
Project tasks and key deliverables
- Final sampling list of selected and dropped sites (Note:Check QAPP for finalized site IDs)
- Level logger maintenance and operation: Q1, Q2
- Confirmation of summer sampling completeness and data quality issues for each site
- Annual summary report
Monitoring preparation (completed in 2019)
Watershed basin delineation and land use analysis
The main difference of this long-term stream monitoring is to stratify sampling sites with different amounts of impervious cover within a contributing watershed. USGS provided technical assistance for watershed delineation and land use analysis for each watershed.
- Watershed delineation scope of work
- Delineated watershed basins; master points, including watershed land use information
- Automated watershed delineation tool and guidance
Site evaluation and equipment deployment
After the USGS selected and stratified sampling sites, they conducted site evaluation and deployed sampling equipment. They purchased and deployed pressure transducers (level loggers) to monitor stage continuously at each sampling site. To capture a full year of stage data before chemical and biological sampling occurs in summer, the level loggers need to be installed at each site by October, a year before the summer sampling starts.
Over 100 stream sites were monitored in this large project. It was coordinated by the SAM Coordinator and included staff from King and Skagit counties, San Juan Island Conservation District, U.S. Geological Survey (USGS), Ecology's Environmental Assessment Program, Puget Sound Partnership, and a myriad of laboratories.
Study questions
This first round of stream monitoring evaluated streams in specified urban growth areas (UGAs) and the outside UGAs to understand the status of stream health in the region and identify major stressors causing poor stream conditions.
Study findings
Urban development negatively impacted nearly all of the stream health indicators (B-IBI, periphyton, water and sediment chemistry). Key stressors driving poor B-IBI scores includes physical habitat characteristics, sediment zinc concentration, stream substrate characteristics, and nutrients. This study found that low canopy cover in the watershed is the most important stressors to B-IBI at the regional scale.