Lower Cottonwood Creek Instream Restoration Design

The proposed project will take place on private property 2 miles south of the town of Monument, along lower Cottonwood Creek (HUC 1707020209) in Grant County, Oregon. Cottonwood Creek is a 303(d) listed stream for temperature that provides spawning and rearing habitat to ESA listed Mid-Columbia River steelhead. High water temperatures and low summer flows are the primary limiting factors to steelhead populations in Cottonwood Creek, a major tributary to the North Fork John Day River. Smallmouth bass have expanded their range several miles into the Cottonwood watershed, cross competing for habitat resources and adding predation pressure to native species. Land use changes throughout the watershed have modified hydrologic timing, resulting in very efficient (flashy) transport of basin runoff. This project proposes to develop engineered designs for three Points of Diversion (POD), instream habitat and bank stabilization features along approximately 0.7 miles of Cottonwood Creek. The designs will include stable pools for three PODs, low-tech process-based restoration (LTPBR) structures such as beaver dam analogues (BDA) and post assisted log structures (PALS), along with two bank stabilization features. Increased physical complexity within the channel may be utilized by steelhead, but to greater benefit, BDAs are thought to limit the movement of smallmouth bass upstream protecting high quality habitat above the project site. Partners for the project include Kurt Boyer (LO), ODFW, CTWS and Monument SWCD.

Designs for this project will benefit steelhead once implementation begins in the future. Traditional LWD placement along with LTPBR on Cottonwood Creek will facilitate floodplain expansion to enhance riparian vegetation and channel complexity. The project will also facilitate incision recovery, improve stream health and restore ecological function to the stream. The increased physical complexity within the channel will be utilized by migrating steelhead and potentially rearing on longer time scales (this area was used throughout the season by juvenile O. mykiss as early in the past as 2017). The increased wetted extent of the channel during low flow conditions will increase the quantity of habitat available to juvenile steelhead during low summer flow. Added structural complexity throughout the system will help to mitigate changes in hydrologic timing brought on by land use changes. Smallmouth bass are both predators of juvenile salmonids and competitors for instream trophic resources. Small mouth bass are already abundant throughout much of lower Cottonwood Creek with upstream range expansion predicted by 2080 (Rubenson & Olden 2019). Multiple basin partners have hypothesized that BDAs can limit the movement of smallmouth bass. Because small mouth bass are a warm water fish that did not co-evolve with beaver, they are thought to be less adapted to channel spanning structures. BDAs will of course be engineered to meet passage criteria (6 inch max jump height), but will be build as close to natural criteria as possible (highly impermeable). Outcomes from this project can help inform future instream restoration projects across the basin, with similar investigation being conducted within the Thirtymile Creek Watershed.