Feasibility Assessment of Pilot Cold Water Refuge Enhancement Technique

The project team (Lower Columbia Estuary Partnership and Inter-Fluve) researched the potential for a pilot project that would create cold-water (i.e., thermal) refuge habitat for summer-migrating salmonids in the mainstem of the lower Columbia River, at the Horsetail Creek confluence located at river mile 138. If successfully implemented this project would offer critically needed thermal refuge in a 57-mile reach of the Columbia where none is currently present and would also demonstrate the applicability of this enhancement technique to other sites where it could potentially be implemented. This project culminated in a 30% concept design which the project team believes will meet its objectives of creating a thermal refuge with sufficient area, depth, and detectability to attract and retain migrating salmonids, much like larger documented refuge zones currently being utilized in the mid-Columbia. Based on limited stakeholder outreach conducted thus far, no permitting constraints were identified that would jeopardize project construction.

This project will test a promising method for filling a 57-mile gap in cold water refuges in the lower Columbia River by manipulating confluence areas of cold water tributaries to expand their plumes so that they can be detected and are of sufficient size for salmonid use as refuge from mainstem warm temperatures. LCEP manages a comprehensive ecosystem restoration program for the lower Columbia that includes implementing restoration actions, providing technical assistance to our partners, coordinating activities, and filling data gaps important for empirically driven restoration. Our restoration and protection activities, including the efforts of regional partners function as a de facto reserve network for the lower Columbia. To ensure this reserve network is protective of native species and sustainable over the long term, we developed ecologically-based voluntary habitat coverage targets based on standard, widely-used conservation biology approaches. Our Science Work Group and Board of Directors approved the targets in 2015 and 2016, respectively.

We now are applying recent conservation biology research in integrating climate change impacts into our conservation reserve network and species protection planning. We hosted a Science Work Group meeting on the topic in February and presented results to the Columbia River Estuary Conference in April, which included several recommended approaches adapted from Schmitz et al. (2015). This study compiles multiple strategies into six overarching approaches, one of which we are already focusing on - identifying and protecting climate refugia. We began identifying one type of climate refugia - cold water - in 2015, and weve been protecting and restoring these refugia since our restoration work on Horsetail and Oneonta creeks in 2013.

Many returning adult salmon and steelhead temporarily use thermal refuges when mainstem Columbia water temperatures are high. Keefer et al. (2011) identified a series of cool water refuges located along the migration corridor at tributary confluences with the mainstem rivers between Bonneville and John Day dams, where cool-water tributaries draining the Cascade Range enter the mainstem Columbia. The thermal refuges that are most studied are located at tributary confluences, including Herman and Eagle Creeks and the Wind, Little White Salmon, White Salmon, Hood, Klickitat, and Deschutes rivers. The most-used by adults (e.g., up to 70% of adult steelhead) among these have been Herman Creek and the Little White Salmon, White Salmon, and Deschutes rivers. These sites are often 2-7 C cooler than the mainstem, the cold water plumes extend far enough into the mainstem to be detected by migrating salmonids, and the cold water confluences are protected by structures or topography that deflect the mainstem flow away from their plumes (e.g., Herman and Eagle creeks).

Research of cold water refuges below Bonneville Dam by the USEPA and ourselves have identified only a few tributaries that meet the temperature differential criterion established by USEPA for their Columbia River Cold Water Refuges Plan at their confluences with the mainstem. These are the Kalama, Cowlitz, and Lewis rivers and multiple lower Columbia Gorge tributaries (LCEP 2018). However, due to their smaller flows and topographical characteristics, the plumes of the Gorge tributaries are immediately subsumed and diluted upon entering the mainstem Columbia, which limits cold water refuge formation and potential detection by passing salmonids. Additional research to identify mainstem pockets of cold water found only small, isolated pockets near the I-205 bridge and historic outlet of Multnomah Creek. As a result, there are no cold water refuges suitable for use by returning adult salmon and steelhead between the Lewis River and Eagle Creek (Palmer 2017; LCEP 2018). This pilot project tests a new technique to enhance confluence areas to expand extents of cold water to fill that spatia