Abstract Title

Session S-08B: Stormwater Quality, Impacts, Treatment Solutions

Keywords

Stormwater

Start Date

2-5-2014 8:30 AM

End Date

2-5-2014 10:00 AM

Description

We present preliminary findings of a stormwater retrofit analysis for the Miller and Walker Creeks watershed, located in southwest King County. Miller and Walker Creeks are highly urbanized, with flashy stream flows and impaired stream bug communities; adult coho returning to the creeks experience high rates of pre-spawn mortality. We developed an approach to identify sites where stormwater retrofit projects would provide the greatest potential for stream improvement. The watershed was evaluated for areas with the highest potential for stormwater retrofit based on impervious surface area, critical areas, steep slopes, soil infiltration potential, and other land use considerations. Eighty sites were initially selected for further investigation. Criteria were developed to select up to five sites for stormwater retrofit projects, and pre-design reports will be prepared for those sites. Benefits of the stormwater retrofit mitigation projects were evaluated by using Hydrologic Simulation Program Fortran (HSPF) to compare existing conditions to the predicted responses. Hydrologic metrics (e.g., high pulse count) associated with Benthic Index of Biotic Integrity (BIBI) scores were used to estimate new BIBI scores following retrofit project implementation. This approach attempts to determine the relative improvement that may be gained for aquatic biota by changing the stream flow regime. However, improvements in water quality and physical habitat are among the other factors important to aquatic habitat.

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May 2nd, 8:30 AM May 2nd, 10:00 AM

Using a stream bug index to prioritize areas for stormwater retrofits in an urban watershed

Room 608-609

We present preliminary findings of a stormwater retrofit analysis for the Miller and Walker Creeks watershed, located in southwest King County. Miller and Walker Creeks are highly urbanized, with flashy stream flows and impaired stream bug communities; adult coho returning to the creeks experience high rates of pre-spawn mortality. We developed an approach to identify sites where stormwater retrofit projects would provide the greatest potential for stream improvement. The watershed was evaluated for areas with the highest potential for stormwater retrofit based on impervious surface area, critical areas, steep slopes, soil infiltration potential, and other land use considerations. Eighty sites were initially selected for further investigation. Criteria were developed to select up to five sites for stormwater retrofit projects, and pre-design reports will be prepared for those sites. Benefits of the stormwater retrofit mitigation projects were evaluated by using Hydrologic Simulation Program Fortran (HSPF) to compare existing conditions to the predicted responses. Hydrologic metrics (e.g., high pulse count) associated with Benthic Index of Biotic Integrity (BIBI) scores were used to estimate new BIBI scores following retrofit project implementation. This approach attempts to determine the relative improvement that may be gained for aquatic biota by changing the stream flow regime. However, improvements in water quality and physical habitat are among the other factors important to aquatic habitat.