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Dam operations can influence spatial and temporal thermal heterogeneity in rivers, yet quantity and distribution of cold-water refuges for salmonids in large impounded rivers have not been well studied. 

Researchers examined thermal heterogeneity across space and time and identified potential cold-water refuges for salmonids in the Pend Oreille River in northeastern Washington. They used thermal infrared imagery from a sensor attached to a helicopter, in-stream water temperature loggers, and high-resolution 3-D hydraulic mapping using acoustic Doppler current profilers deployed from boats. Results showed that water temperature in the main stem of the Pend Oreille River increased as water moved downstream, but tributaries and depth created thermal heterogeneity in the river and provided potential cold-water refuges for salmonids. Modeling results support mechanistic understanding of the interactions of physical river attributes to explain the complexity of thermal patterns in impounded rivers. Findings also highlight the importance of using multiple approaches to describe a river’s thermal heterogeneity in longitudinal, lateral, and vertical dimensions to develop management and restoration strategies.


Mejia, F.H., Torgersen, C.E., Berntsen, E.K., Maroney, J.R., Connor, J.M., Fullerton, A.H., Ebersole, J.L., Lorang, M.S., 2020, Longitudinal, lateral, vertical, and temporal thermal heterogeneity in a large impounded river- Implications for cold-water refuges: Remote Sensing, v. 12, no. 9, p. 1386,

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