Author(s): Klaus Jorde; Ivo Scherrer
Linked Author(s): Klaus Jorde
Keywords: Stream temperature; Temperature modeling; Solar radiation; Streamside vegetation; Thermal restoration; Energy budget; Fish habitat
Abstract: High stream temperatures are a limiting factor for salmonid species in many rivers and streams in the Western United States. Increased temperatures often result from land use changes, such as deforestation or mining operations, that leave wide and shallow river beds. Restoration efforts to improve the ecological integrity of rivers and streams have to include thermal aspects. A physical process based temperature model was developed for Red River in central Idaho within a large scale restoration project to help quantify the energy balance of the river and to explore different options for thermal restoration. The model uses three tributaries as the upstream boundary, and includes two open meadows connected by a canyon reach, each comprising reaches with a variety of different morphological/hydraulic properties, shading from trees or topography etc. The model was calibrated with data from an on-site weather station and numerous stream temperature gauges and was then used to evaluate different options to lower the temperatures in the downstream meadow, a Chinook salmon spawning and rearing site, which is suffering from elevated temperatures. Results show that short wave solar radiation is the predominant component of the energy flux and signals from a reforested upstream watershed would be mostly lost by the time the water reaches the lower meadow, and that thermal restoration efforts will be most effective if focused on streamside vegetation within the meadow itself.