Human impacts to rivers have resulted in increased water temperatures that threaten cold water aquatic species such as salmonids. Higher summer water temperatures and lower winter water temperatures in rivers can lower fish viability by reducing fecundity, increasing morbidity and mortality, and reducing food sources. This can result in localized species extirpation and overall reduction in habitat basin-wide. For cold-water aquatic species recovery programs to meet their long-term goals, they must consider mitigating the impacts of warming waters with “thermal restoration” and creation of thermal refuges.Thermal refuge refers to areas within a stream corridor that buffer, lag, and cool/warm stream temperatures at biologically relevant scales and times . Thermal refuge can be expressed as biologically-available areas within a stream where cooler water temperatures exist at base flow conditions during summer and warmer water temperatures during winter. Thermal refuge restoration refers to physical and biological stream habitat restoration practices that result in creating or enhancing thermal refuges. This may be accomplished by creating and enhancing connectivity between surface and groundwater systems in the hyporheic zone (the interface between surface and groundwater along a river bed and floodplain). Re-vegetating the riparian zone to promote shading can also promote thermal restoration. This study will focus on the former mechanism as it relates to thermal refuges for salmonids including: Chinook salmon, steelhead trout, and bull trout.
