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: Southwest shoulder of S.E. Petrovitsky Road between house #17201 and #17235.

Drainage basin: Low density rural residential properties (zoned RA-5) and City of Seattle’s Lake Youngs Watershed on the southwest side of S.E. Petrovitsky Road; collects runoff from adjacent properties and the paved roadway; ditch drains southeast to Shady Lake, which outfalls to Honey Creek.

Traffic: Relatively high [average daily traffic volume (ADTV) of approximately 17,060 vehicles (2007)].

BMP type: Flow control

BMP description: Coarse washed sand media wrapped in filter fabric and secured inside a rock check dam. Five BMPs have been installed along a section of roadside ditch approximately 287 feet in length.

Monitoring: Stormflow is continously monitored upstream and downstream of the BMPs.

Rainfall: Rainfall data is obtained from a permanent gage operated by the King County Hydrologic Information Center located on S.E. 196th St. (approximately 2 miles east of the Petrovitsky BMP site). An Isco rain gage installed at the lower monitoring station is used as a secondary source for precipitation information.

Equipment:

• Flow measurement: Extra-large 60° trapezoidal flumes placed in the ditch at the upstream and downstream monitoring locations. Instrumentation Northwest (INW) 5 psi pressure transducers record water level in stilling wells attached to the flumes and Campbell CR800 loggers record data and convert water level to flow in gallons per minute.

• Rainfall: An Isco rain gage is installed at the downstream monitoring station that is used as a secondary source for real-time rainfall records and as a back-up source of rainfall information for the primary rainfall gage.

• Housing: Large electrical utility box staged at the upstream site and a small pole-mounted utility box staged at the downstream sites secure equipment.

• Power: Small 12 volt deep cycle glass-mat batteries.

Project photos

Looking upstream at the upstream monitoring station on S.E. Petrovitsky Road. (Enlarged view, 198KB .jpg)

Looking upstream at the downstream monitoring station on S.E. Petrovitsky Road. (Enlarged view, 109KB .jpg)

Looking upstream at a series of flow control BMPs toward the upstream monitoring station. (Enlarged view, 113KB .jpg)

Stormwater being conveyed through study area prior to BMP installation, looking upstream. (Enlarged view, 168KB .jpg)

Monitoring equipment housed in metal utility box. (Enlarged view, 87KB .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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