High Resolution Thermal and Fluvial Habitat Data Inform River Restoration for Cold-Water Fishes.
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Restoring thermal heterogeneity in degraded lotic systems requires initial assessment of the thermal and geomorphic riverscape to identify stressors and determine riverine features that can be enhanced. We identified potential cold-water refuges and characterized channel morphology by floating the lower 70 km of the Lower Priest River in northern Idaho (USA). We produced longitudinal profiles of thermal patterns, water velocity, and depth with temperature probes and acoustic doppler current profiling (ADCP). We complemented these spatially continuous data with (1) in-situ thermographs placed every 2 km and at selected pools and tributary junctions, and (2) physical measurements of channel morphology and instream and riparian cover. Preliminary results revealed that water temperature decreased in a downstream direction due to groundwater and surface water exchange and tributary inflows. We observed localized downstream warming in low-velocity reaches where travel time was greater and net solar radiation was relatively high, whereas high velocity reaches showed less warming in a downstream direction. Cover for fish (e.g., overhanging vegetation, large woody debris) and large, deep pools were limited, and cold-water areas associated with tributary junctions were localized. Restoration efforts can be focused on restoring and enhancing these riverine features at specific locations. These preliminary findings highlight the importance of high-resolution, spatially extensive assessments of the ecohydraulic landscape to help prioritize the selection of sites for restoration.