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Whatcom County proposes dredging 150′ of Nooksack River to open side channel

EVERSON, Wash. — Whatcom County Public Works (WCPW) is the lead agency on a State Environmental Policy Act (SEPA) Determination of Nonsignificance (DNS) for a project to open the mouth of an existing Nooksack River side channel in order to reduce the flow of river water that overtops the river’s bank near Everson during flooding events.

Approximate location of project area indicated by arrow

The Nooksack River overtops its north (right) bank upstream of the Everson Road (State Route 544) Bridge in large flood events, and that flow moves north through the cities of Everson, Nooksack, and Sumas as well as adjacent agricultural areas, posing significant risks to people, infrastructure, and land uses. The effects of these overflow events are compounded in the Sumas area by drainage from Johnson Creek and the Sumas River and its tributaries. An interdisciplinary planning and design charette focused on this river “flow split” was held in April 2022 as an initial step to identify both short-term and long-term multi-benefit solutions for reducing flood impacts in the overflow corridor.

One short-term solution that emerged is encouraging a greater amount of flow into a small side channel that runs parallel to the Twin View Levee along the left (south) bank of the Nooksack River immediately upstream of the Everson Road Bridge. This side channel was perennially active a decade ago, but now only has flow conveyance during high-flow events. Preliminary analysis suggests that increased flow down this side channel could lead to a modest increase in local river flow conveyance and an associated reduction in the volume and rate of flow that overtops the river’s right bank during large flood events, thus potentially reducing the severity of flooding in the Everson overflow corridor. Increased flow down the side channel could also potentially provide increased off-channel rearing, refugia, and possibly spawning habitat area for salmonids.

This project will “open up” the upstream end of the side channel to encourage increased river flow into it. The proposed construction work includes:

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• clearing vegetation (but no trees) in an access corridor.
• removal of shrubby vegetation (primarily willows) and floodborne woody material from an approximate 25-foot-wide by 25-foot-long area on the gravel bar at the inlet to the side channel above the ordinary high water (OHW) level of the river. Removed vegetation will be placed on the gravel bar riverward of the side channel.
• excavation of alluvium on the bar extending upstream and downstream (south and northward) from the cleared area, at depths up to 3 feet for a total of approximately 310 cubic yards of excavation (150 lineal feet) and onsite placement of the excavated alluvium along the sides of the channel in between and around existing vegetation
• planting of willow live stakes in areas cleared of vegetation for access to the work area on the bar, and
• erosion and sediment control as well as spill prevention, control and countermeasures to prevent water quality impacts in the river during construction.

Construction equipment access to this side channel work area will occur via the access road on the Twin View Levee. The total area of site disturbance will be no greater than 6,000 square feet.

SEPA DNS proposal SEPA2022-00084 project description

WCPW has determined that no significant adverse environmental impacts are likely as a result of this project. This determination cannot be acted on during an immediate 14-day comment period during which time comments can be sent to Andrew Hicks via email at AHicks@co.whatcom.wa.us.

Appeals to the determination can be made to the Whatcom County Hearing Examiner. Applications for appeal must be filed on a form provided by and submitted to the Whatcom County Current Planning Division located at 5280 Northwest Drive, Bellingham, WA 98226, during the 10 days following the comment period, concluding October 6, 2022.

According to the proposal document, the project is planned for this fall.

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