King County Road Services - Stormwater Best Management Practices (BMP) sites

Project overview: We are trying to find effective, cost-efficient ways to treat stormwater in roadside ditches. This study is being conducted to test an in-line ditch BMP that, if effective, could potentially be widely used by jurisidictions trying to minimize the impacts of stormwater runoff on surface water bodies and groundwater aquifers. This study is made possible, in part, through funding from the Washington State Department of Ecology and will continue through 2011.

Project location: Ditch along east side of 148th Ave. S.E. just south of S.E. 102nd St.

Drainage basin: Dominated by rural residential properties on the east side of 148th Ave. S.E.; collects stormwater runoff from adjacent properties and the paved roadway; drains to May Creek.

Traffic: Moderate [average daily traffic (ADT) volume of approximately 2,000 vehicles].

BMP type: Water quality.

BMP description: Compost treatment media mixed with washed gravel and wrapped in filter fabric and secured inside a rock check dam (treatment cell). Compost meets Washington State Department of Transportation (WSDOT) specification for use in stormwater treatment projects. Three treatment cells are installed in a section of ditch approximately 100' in length. See BMP design for more information.

Monitoring: Flow measurements and water quality samples are collected upstream and downstream from BMP. Flow composite samples are collected for total suspended solids, total kjeldahl nitrogen, nitrate-nitrite, orthophosphate phosphorus, dissolved metals, and polycyclic aromatic hydrocarbons. Grab samples are collected for total petroleum hydrocarbons and fecal coliform. Water temperature is measured continously in the roadside ditch.

Equipment:

• Flow measurement: Extra-large 60° trapezoidal flumes are placed in the ditch at the upstream and downstream monitoring locations. Isco bubble meters are used in conjunction with the flumes to log data and convert water level to flow in gallons per minute.
• Water quality samples: Upstream and downstream flow composited samples are collected using Isco 6712 autosampler receiving flow signals from the bubble meters. Grab samples are collected by hand. Temperature measurements are collected using a HOBO Onset ProV2 water temperature data logger.
• Rainfall: Rainfall data is obtained from a permanent gage operated by the King County Hydrologic Information Center located at the King County Roads Maintenance Facility in Renton, Washington (approximately 3.5 miles southwest of the 148th Avenue Southeast BMP site). A raingage is also staged at the downstream monitoring site for real-time rainfall records.
• Housing: Utility boxes staged at the upstream and downstream sites are used to secure electronic equipment.
• Power: Group 24-12 volt deep cycle glass-mat batteries with solar panel assist.

Project photos

Downstream monitoring station flume at 148th Ave. S.E. during an October storm looking upstream. (Enlarged view, 137KB .jpg)

Upstream monitoring station flume at 148th Ave. S.E. discharging during an October storm looking upstream. (Enlarged view, 123KB .jpg)

Water quality BMP slowing and filtering stormwater flow within the roadside ditch along 148th Ave. S.E. (Enlarged view, 128KB .jpg)

Metal utility box containing downstream sampling equipment. (Enlarged view, 276KB .jpg)

Have questions?

For more information about this project, please contact:

Information from the Road Services Division's website is available to people with disabilities in alternate formats upon request by calling 206-263-6482 or 711 for the TTY relay service.

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