Coaledo Drainage District Tidegate Replacement and Fish Passage Project Phase 2 Final Designs

The Coaledo Drainage District tide gate is located in Coos County, OR along Beaver Slough, a major salmon rearing tributary of the lower Coquille River. In the Coquille watershed, slow-water and off-channel habitats have been converted to pasture using tide gate infrastructure to the extent that less than 5% of the historic acreage of wetlands currently exists. This project will address this limiting factor by finalizing designs to restore fish passage to a 9,100-acre sub-watershed containing 11.4 miles of coho habitat and 490 acres of tidal wetland habitat, of which 289 acres are a natural wetland managed by ODFW. This TA project has resulted in final designs for the tide gate and channel enhancements, an approved water management plan, additional cultural resource investigations, permitting, and continued coordination among stakeholders. This fish passage project and working landscapes initiative is now 100% ready for implementation pending funding.

This technical assistance grant will benefit salmon, steelhead and other native fish by improving fish access to critical slow-water refugia, rearing habitat and spawning habitat within the Coaledo Drainage District. The failing tidegates are currently limiting fish access to Beaver Slough, Beaver Creek, Dufoe Creek and several other unnamed sub-watersheds. In total, these watersheds contain 11.4 miles of coho habitat and 13.6 miles of steelhead habitat. This technical assistance grant will result in a fish passage restoration project that will enhance fish access to a large quantity of spawning habitat beyond the lowlands. In addition to using upstream reaches for spawning habitat, juvenile coho and other anadromous fish use tidal wetland habitats for feeding, rearing and as a source of slow water refugia during high winter flows. Studies have shown smolt growth rates are often 1.5-2.0 times greater for off-channel and tidal wetland habitats compared to stream locations (Nickelson 2012, ODFW, unpublished 2014). Final technical designs and secured permits funded by this technical assistance grant will facilitate the replacement of the Coaledo Drainage District tidegates and will address downstream hydrological constrictions in lower Beaver Slough. This will improve fish passage to 490 acres of tidally influenced habitat, of which 289 acres exist as natural tidal wetlands owned and protected as part of ODFW’s Coquille Valley Wildlife Area. The aim is to enhance lower Beaver Slough and the tidegates to mimic natural tidal conditions as much as possible. Nickelson (2007) estimated that these types of habitats historically were capable of rearing sufficient number of coho juveniles to produce 11-17 returning coho adults for every acre of high functioning floodplain wetland. Accordingly, the tidal wetland habitat within the Coaledo Drainage District will have the capacity to annually produce 5,390 – 8,330 returning adult coho. Lastly, this project builds on several tideland projects undertaken in the Coquille Valley to restore floodplain and off channel habitat connectivity including the 1,700 acre Winter Lake Restoration Project (completed 2018), 280 acre Seestrom Tidelands Restoration Project (projected completion 2022), and 40 acre Hatchet Slough Fish Passage Project. These four projects alone are estimated to annually produce an additional 27,610– 42,670 returning adult coho in the Coquille watershed.