Leslie Wetland Reserve Restoration Project: Phase 1 Alternatives Analysis

In the Coquille watershed, less than 5% of the historic acreage of tidal wetlands remain and a lack of slow-water refugia and off-channel habitat has been identified as a critical limiting factor affecting Oregon Coast ESU coho recovery. The Leslie Wetland Reserve is a 50 acre tidally influence wetland protected under a NRCS easement in Coos County, OR. A project in the 1990’s attempted to revert the 50 acres of bottomland from pastureland to the historic wetland state by removal of tide gates and drainage ditches. However, the majority of the easement is still in poor condition and almost entirely lacks wetland function, including: 1) lack of floodplain connectivity; 2) hydrological constrictions due to undersized culverts; and 3) lack of native plant diversity and a monoculture of reed canary grass. This grant helped CoqWA build a diverse and robust project team, data gathering to inform an alternatives analysis and a preferred alternative was selected for further development.
Engineering for restoration designs was mistakenly reported at proposed. Conducting habitat restoration scoping, particularly developing an alternatives analysis, more accurately describes the work done in this project and has been reported at actual.

Historically coho and Chinook salmon juveniles as well as other species extensively used these tidal wetlands. With the high level of riparian canopy cover shading the channel network and strong tributary cold water input, modeling has suggested that water temperatures and dissolved oxygen levels were satisfactory for year round salmonid rearing. Additionally, these habitats had substantial benefits for fall Chinook and cutthroat trout as well as waterfowl and amphibians. This technical assistance grant will benefit salmon, steelhead and other native fish by laying the groundwork to restore fish access to critical slow-water rearing habitat within the Leslie Creek sub-basin directly connected to the Coquille River. 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. 2011). Additionally, it is estimated that these types of habitats were capable of rearing sufficient number of coho juveniles to produce 11-17 returning coho adults for every acre of high functioning floodplain wetland (Nickelson 2007). Accordingly, restoration of the tidal wetland habitat within the Leslie floodplain will have the capacity to annually produce 385 to 595 returning adult coho. Moreover, upper valleys of the Beaver Hill sub-watershed is anticipated to be able to provide adequate summer rearing temperatures for salmonids, critical refugia for juveniles to have access to when the main-stem Coquille River becomes lethal in the summer due to rising water temperature. The resulting restoration 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, the 270 acre Seestrom Tidelands Restoration Project, the 490 acre Coaledo Drainage District Project, and the Hatch 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 Moreover, recent monitoring in the Lower Coquille indicates that juvenile coho extensively use these off-channel habitats and migrate between sites. Coho have been seen migrating between project sites as far as 7 river miles apart and residing in these sites off the mainstem Coquille for days or weeks at a time. This project is also protected in a NRCS easement, providing habitat for coho and other salmonids in perpetuity.