Redmond Paired Watershed Study

Numerous studies have documented the effectiveness of stormwater management practices at the site and parcel scale; however, little information is available on the effectiveness of these practices at a watershed scale. To address this data gap, Herrera is currently working with the City of Redmond to implement a 10-year study to evaluate the effectiveness of watershed rehabilitation efforts for improving receiving water conditions. This study is being funded by the Stormwater Action Monitoring Program for Puget Sound. To support the development of the experimental design for this study, Herrera conducted a literature review to obtain information on past studies that have been implemented to achieve similar objectives. This literature review identified 123 study references that were compiled in an annotated bibliography and synthesized to identify the most effective indicators for documenting long-term improvements in receiving water conditions. Herrera also developed a custom program that performs Monte Carlo simulations for investigating statistical power for detecting long-term trends in time series data given:

1. The significance level;
2. Magnitude of trend;
3. Sample size; and
4. Amount of variation within existing datasets

The experimental design that was subsequently developed involves intensive monitoring in seven different watersheds categorized as follows: three “Application” watersheds that are moderately impacted by urbanization and prioritized for rehabilitation efforts; two “Reference” watersheds that are relatively pristine and not subject to rehabilitation efforts; and two “Control” watersheds that are heavily impacted by urbanization and also not subject to rehabilitation efforts. Monitoring in these watersheds involves routine measurements for the following suite of indicators: water quality, sediment quality, continuous flow, physical habitat, and benthic macroinvertebrates. Compiled data from the benthic macroinvertebrate monitoring are used to compute Benthic Index of Biotic Integrity (BIBI) scores for assessing overall stream health. Using these data, Herrera will prepare trend analysis reports in years 4, 6, 8, and 10 of the study’s implementation to assess improvements in receiving water conditions from ongoing watershed rehabilitation efforts; the study is currently in its 3rd year of implementation. Due to its regional and national significance, Herrera established a technical advisory committee for the study that includes representation from the following agencies: Washington State Department of Ecology, U.S. Environmental Protection Agency, US Geological Survey, Kitsap County, King County, City of Redmond, and City of Seattle.