Skagit Forks Off-Channel Restoration & Feasibility

Category Overview

The State Lands Restoration and Enhancement category provides funding to two state agencies to help repair damaged plant and animal habitat. These grants focus on resource preservation and protection of public lands. Projects in this category help bring important natural areas and resources back to their original functions by improving the self sustaining and ecological functionality of sites.

Project Highlights

The project consisted of three discrete but related restoration concepts; Lower Cottonwood Slough Mouth, Cottonwood Slough Inlet, & Skagit Forks Wetland. Lower Cottonwood Slough Mouth was a design and construct project and the other two were design only. Specifics for each are as follows. Lower Cottonwood Slough Lower Cottonwood Slough consisted of the removal of an abandoned road crossing that isolated Cottonwood Slough from being backwatered by the Skagit River during most flows. The project final design was prepared by Washington Department of Fish and Wildlife (WDFW) engineers in conjunction with an engineer from the Skagit Conservation District (SCD). A cultural resources report was completed for the site and we acquired a Hydraulic Project Approval from WDFW and a Nationwide Permit 33 from the Army Corps of Engineers. The project was approved by WDFW to be a fish enhancement project and therefore all other local permits were exempt. The project was successfully constructed by a WDFW construction crew during the fall of 2015. The project removed one (1) fish passage blockage improving access to 0.20 miles of off-channel delta habitat in low flows and to as much as 0.80 miles of habitat in higher flows. Cottonwood Slough Inlet The Cottonwood Slough Inlet design was based upon earlier designs evaluating re-opening the nearly one mile long slough to Skagit River flow. Northwest Hydraulic Consultants (NHC) was contracted to perform hydraulic and geomorphic analysis of the site to evaluate restoration potential. Physical data of the site was collected in conjunction with many partners including; Bathymetric and topographic survey of the Cottonwood Slough inlet, North Fork, South Fork, and main stem Skagit River, data collected by NHC with contributions from United States Geological Survey (USGS), a 2011 NHC project at the site, LiDAR from Skagit River System Cooperative (SRSC), and survey data collected by SCD & WDFW. Water surface elevation was collected using piezometers and water stage recorders. Data was collected by NHC and WDFW. A groundwater evaluation was conducted to evaluate the rate of groundwater movement into the slough. The data was collected with the installation of piezometers at the mouth of the slough and 1700 feet downstream of the mouth. The evaluation was performed by Shannon and Wilson with the addition of data collected by SCD. Subsurface geology was evaluated with samples taken from borings near the mouth of the slough. Shannon and Wilson modeled the groundwater flux for each of three design alternatives. With the information as described above NHC modeled three restoration alternatives; a flow through channel, a backwater channel, and a backwater channel augmented with groundwater. The selected preferred alternative was the backwater channel. This alternative provides high quality habitat without near term sedimentation that would reduce habitat quality and access. A preliminary design was created by SCD. Skagit Forks Wetland In 2007 WDFW acquired property on the left bank of the Skagit River directly across from Cottonwood Island. Contained within the property is a large open water wetland that has been disconnected from the river. The objective of this project was to evaluate and design reconnecting the wetland to the Skagit River to provide access to juvenile fish. Topography of the site was evaluated with a site surveys conducted by NHC, SCD, & WDFW, and with LiDAR from Skagit River System Cooperative. Hydrology in the wetland was determined by SCD by deploying level loggers in the Skagit River, in the wetland, and in Britt Slough on the upriver edge of the property. Water quality in Britt Slough was evaluated by taking a grab sample in the slough immediately downstream of where it is pumped through the dike upstream from the confluence with the Skagit River. The sample was tested for various water quality parameters typically present in agricultural runoff. NHC modeled hydrology, hydraulics and sediment transport in the Skagit River at the project site to inform the selection of design alternatives. With the information described above, four alternatives were considered; an outlet channel to the Skagit River to provide backwater habitat; reconnection to the river, creating flow through the wetland and back into the river; a filtration gallery creating flow through the wetland from a groundwater source; and the re-alignment of Britt Slough to flow through the wetland. The preferred alternative selected was to re-align Britt Slough. This alternative re-establishes a connection between the wetland and the river while maintaining a flow that will prevent sediment deposition from isolating the habitat. A preliminary design was created by SCD. Each of the above projects is more completely described in design documents submitted as attachments in PRISM.

Quick Facts

WWRP Applicant: Fish & Wildlife Dept of Category: State Lands Restoration & Enhancement WWRP Grant: $55,650.60 Applicant Match: $0.00 Project Type: Planning & Restoration County: Skagit Legislative District: 10 Status: Closed Completed RCO Project # 13-1053

Location Details

From Mount Vernon, WA take Division Street across the Skagit River, turn left on S. Wall street and continue on to McLean Road, in about 1/2 mile turn left onto Penn Road, follow the road to the end and turn left onto the revetment. Park at the Cottonwood Island Access Area.

What is the WWRP

The Washington Wildlife and Recreation Program (WWRP) is a state grant program that creates and conserves local and state parks, wildlife habitat and working farms. The Washington State Recreation and Conservation Office administers WWRP grants, and the legislature funds the program.