Stormwater Retrofit Analysis and Recommendations
for Juanita Creek Basin in the Lake Washington Watershed
The Stormwater Retrofit Analysis and Recommendations for Juanita Creek Basin in the Lake Washington Watershed focuses on a tributary stream to Lake Washington covering the City of Kirkland. The publication identifies a retrofit strategy or strategies that would meet the project goal -- improving flow and water quality to support aquatic life, including use by fish.
As of 2012, Juanita Creek basin is nearly 70% developed with stormwater facilities that are critically lacking or undersized relative to current stormwater standards.
In developing retrofit strategies, a 'multiple lines of evidence' approach was used to evaluate the effectiveness of each mitigation scenario, using metrics that included a biological indicator (Benthic Index of Biotic Integrity–BIBI ) estimated from regression relationships with hydrologic metrics, frequency of gravel disturbance, water-quality exceedances relative to Washington State standards (e.g., dissolved copper) and reductions in pollutant loads for water quality parameters with no regulatory thresholds (e.g., total suspended solids).
The best performing mitigation scenario combined the flow control standards for low-flow (low impact development (LID) performance standard) and high-flow (standard requirement) proposed by Ecology in the draft Phase 1 Municipal National Pollutant Discharge Elimination System (NPDES) permit with effective date of August 1, 2013. To meet the standard requires not only LID best management practices applied to most impervious surfaces, but also conventional end-of-pipe flow control and treatment facilities. The modeling results indicate that this scenario, if implemented, would achieve the project goal.
This publication was produced in partnership between King County, City of Kirkland, and Washington State Departments of Ecology and Transportation (external links).
Stormwater Retrofit Analysis and Recommendations for Juanita Creek Basin in the Lake Washington Watershed is provided in Adobe pdf format. For help using Acrobat files, please visit our Acrobat© help page.
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For more information about the Stormwater Retrofit Analysis and Recommendations for Juanita Creek Basin in the Lake Washington Watershed, please contact Jeff Burkey, hydrologist, King County Science and Technical Support Section.