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Highway 520 Bridge Storm Water Runoff Study

The Highway 520 Bridge Storm Water Runoff Study is a data collection effort that is part of the Sammamish-Washington Analysis and Modeling Program (SWAMP). SWAMP is a water quality and quantity monitoring and modeling project that was initiated in 2000 to support a variety of potential water resource decisions for the majority of the Greater Lake Washington watershed. The continued expansion of urban and suburban development and associated hydrological changes affecting flow and degrading riparian habitat arguably make this watershed one of the most highly altered on the West Coast (Kerwin, 2001). SWAMP provides a comprehensive evaluation of current and future water quality conditions in the study area.

Watershed modeling is an integral part of the SWAMP program. During development of the SWAMP workplan it was determined that water quality loadings from a limited access highway were needed for watershed model calibration in the Lake Washington watershed. Consequently, the primary purpose of this project is to assess the quality and quantity of storm water runoff from the 520 Bridge and to estimate contaminant loadings to Lake Washington.

The 520 Bridge was chosen for several reasons, including:

  • Contaminant loadings from the bridge to the lake have not been directly measured.
  • Contaminant sources to the road surface are assumed to be limited almost exclusively to those associated with vehicle traffic; few other potential contaminant sources are likely present on the bridge deck to confound results.
  • Results will also be used to better understand the contaminant characteristics of bridge runoff to Lake Washington.
  • Results will be used to calibrate/validate watershed models developed in the Lake Washington watershed.

View the report

    Highway 520 Bridge Storm Water Runoff Study (426.00 KB)

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