INFLUENCES OF TEMPERATURES WITHIN THE NORTH FORK JOHN DAY RIVER, CENTRAL OREGON

Temperatures exceeding the optimum range for viable fish habitat have been observed in the North Fork John Day River by forward looking infrared (FLIR) imaging. This project investigates the sources of temperature input to the river system and relative significance of each source by employing a multi-disciplinary approach, specifically targeting the extent (or lack thereof) of the hyporheic zone within the system. Temperatures of strategic river reaches between Monument and Kimberly, Oregon, were monitored at high temporal (10 min. interval) and spatial resolutions during low-flow conditions in September 2005. A digital representation of temperatures with respect to time was modeled using a combination of Matlab, Argus, and ArcGIS. River parameters, including hyporheic capacity, were compared to the temperature representation to investigate parameter significance. In addition, the surrounding geologic environment and geomorphic processes were mapped to provide an environmental control on the extent of formation for the rivers hyporheic zone. Preliminary results show a faster stream temperature response to atmospheric temperature fluctuations in river sections containing less hyporheic material. This may result in an overall increase in thermal loading during summer months. In addition, sections with increased return flow due to summer irrigation generally show a slower response to atmospheric temperature fluctuations, possibly resulting in a decrease in overall thermal loading during summer months.