Illabot Creek is a highly productive tributary of the upper Skagit River that supports relatively large populations of Chinook, chum, coho, and pink salmon, native char, and steelhead trout. Due to its importance in providing spawning and rearing habitat, much of the watershed has already been protected or restored. However, there is an approximately half-mile reach of Illabot Creek that is heavily degraded.
Skagit River System Cooperative (SRSC) completed a feasibility study (Smith and Ramsden 2006) that evaluated habitat conditions and restoration alternatives in the lower portion of Illabot Creek. This study determined that straightening and diking of Illabot Creek near the Rockport-Cascade Road has had a significant negative effect on habitat conditions by creating a steeper gradient, reducing channel area and habitat complexity, increasing bed scour, and degrading riparian conditions. Restoration alternatives included: 1) relocating the Rockport-Cascade Road and bridge to the historic crossing further upstream on Illabot Creek and removing all riprap bank armoring in the floodplain reach, 2) constructing an additional bridge span at its present location to accommodate an historic secondary channel and removing most of the riprap upstream and downstream of the bridge, or 3) removing some of the excess riprap (270 m in length) downstream of the current bridge crossing.
A preferred alternative was selected in the Feasibility Study, identifying a project that would restore Illabot creek to its historic channel, remove all or most of the dikes along the existing channel, construct a two new bridges and maintain the existing bridge on Rockport-Cascade Road, install log jams as habitat features, and provide erosion protection for existing powerline towers and the county road. Construction for this project was broken into two phases, with Phase I work downstream of the Rockport-Cascade Road having been constructed in 2013. Phase I included removal of 900 linear feet of dike and rip-rap material, installing log and rock structures to protect the existing powerline towers, excavating pilot channels on the alluvial fan to encourage channel development, and installing log structures to improve habitat conditions.
We are currently pursuing funds for final design and construction of Phase II. Phase II includes work at and upstream of the Rockport-Cascade Road, including construction of two new bridges, dike removal, pilot channel excavation, and installation of log structures to improve habitat conditions. Modeling and design work has been completed to a 90% level, and bridge design has been completed to a 30% level, and reviewed and approved by engineering staff from Skagit County.
A Feasibility Study for this project was completed in 2006. Phase I construction, including dike removal, pilot channel excavation, and installation of log and rock structures, was completed in 2013. We are currently pursuing funding for final design and construction of Phase II of this project.
Primary Project Contact
Devin Smith – Senior Restoration Ecologist
SRFB – Salmon Recovery Funding Board
Skagit River System Cooperative
Seattle City Light