The Oregon State University (OSU) team conducted hydro-thermal stream monitoring on the Middle Fork of the John Day River (MFJDR) at the Oxbow and Forrest Conservation Areas from 2008 to 2016. Regulation of temperature within these critical habitats is a primary factor in fish survival. Fiber optic distributed temperature sensing (DTS) monitored about 8,000 meters of river channel per summer with 1 meter and 10 minute resolution to observe peak summer temperatures, supplemented by groundwater contribution, stream discharge, and stream bathymetry across the conservation sites. Diurnal cycles during summer observation ranged from absolute minimum of 9° Celsius (C) to absolute maximum of 26°C. Salmonids are sensitive to stream temperatures above 18°C, resulting in depressed growth and survival, while sustained temperatures above 24°C have directly lethal effects (Bell 1991). Groundwater inputs directly into the MFJDR did not significantly decrease stream temperatures, but did reduce tributary temperatures. The primary cooling mechanism of the MFJDR occurred at the confluence of the mainstem and its tributaries, where tributaries supplied cooler, groundwater rich water into the main channel. Physically-based thermal modeling indicated that solar radiation was the primary driver for gains in stream temperature in the mainstem MFJDR; river surface area change associated with restoration actions of the MFJDR mainstem explained 98% of the change in stream temperature. DTS monitoring of the Phase-2 Oxbow Conservation Area (OCA) restoration project (closing the dredged channel and redirecting all flow to the meandering channel) showed a decrease in mainstem temperature by over 0.6oC (1oF), which model results indicate is due to reduced water surface area. Model results of shade to stream temperature provided by riparian vegetation was shown to be a very slow restoration method, unlikely to provide significant thermal effects within a decade on rivers the size of the MFJDR. Finally, while re-connecting the river with the floodplain has many habitat benefits, model results indicate neither an increase to summer lowflow nor a reduction in summer peak temperatures.
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stream temperature,distributed temperature sensing,fiber optic cable
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