Thermal Refuge Habitat Assessment and Restoration Options for Adult Chinook Salmon in the Sammamish River, WA

We assessed thermal refuge habitat availability and identified and developed appropriate restoration measures in the Sammamish River between Lake Sammamish and Lake Washington for adult migrant Chinook salmon during warm summer and fall months when water temperatures can frequently exceed water quality criteria.  Measurements focused on identifying cooling locations at the confluences of tributaries and in pools that could potentially be used by holding adult salmon.  Detailed elevation and temperature profile data were collected during the warmest portion of the day at ten sites to quantify cool water habitat volumes.  Seven tributaries were identified as having greatest cooling influence, and pool habitat was found to be less useable than suspected.  Two types of measures were evaluateextend d for thermal enhancement at tributary confluences:  construction of physical structures to retard mixing and the cool water plume, and flow augmentation of tributaries.  Candidate sites were evaluated for feasibility and benefits of structural measures, and for potential to expand the cool water plume.  In addition, the relation between flow and temperature was assessed analytically, empirically, and with a numerical model to identify where summer flow augmentation would have meaningful effects.