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: West shoulder of 276th Ave. S.E. between S.E. 208th St. and S.E. 216th St.

Drainage basin: Dominated by rural residential properties on the west side 276th Ave. S.E.; collects runoff from adjacent properties and the paved roadway; ditch drains to a stream that crosses 276th Ave. S.E. just north of S.E. 208th St., flowing west toward Issaquah Creek.

Traffic: Relatively high [average daily traffic volume (ADTV) of approximately 12,700 vehicles (2007)].

BMP type: Flow control.

BMP description: Coarse washed sand media wrapped in filter fabric and secured inside a rock check dam. Ten BMPs have been installed along a section of roadside ditch approximately 340 feet in length.

Monitoring: Stormflow is continuously monitored upstream and downstream of the BMPs. Rainfall data is collected from county maintained gages.

Rainfall: Rainfall data is obtained from a permanent gage station (Hobart Rain Gage #31z) operated by the King County Hydrologic Information Center located on S.E. 208th St. (approximately one mile east of the 276th Ave. S.E. BMP site).

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 level in stilling wells attached to the flumes, Campbell CR800 loggers record data and convert water level to flow in gallons per minute.

• Housing: Small pole-mounted utility boxes staged at the upstream and downstream sites secure equipment.

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

Project photos

Looking upsteam at a series of flow control BMPs toward the upstream 276th Ave. S.E. monitoring station. (Enlarged view, 146KB .jpg)

Looking downstream toward the downstream 276th Ave. S.E. monitoring station. (Enlarged view, 150KB .jpg)

King County Road Maintenance crews place rock on top of the flow control BMP cell at 276th Ave. S.E. (Enlarged view, 208KB .jpg)

Looking upstream at the flow control BMPs installed along 276th Ave. S.E. (Enlarged view, 188KB .jpg)

Stormwater being conveyed through study area prior to BMP installation, looking upstream. (Enlarged view, 126KB .jpg)

Weir insert installed in culvert. (Enlarged view, 198KB .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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