Graduate Thesis Or Dissertation
 

Stream temperatures, riparian vegetation, and channel morphology in the Upper Grande Ronde River Watershed, Oregon

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/qf85nd82c

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  • The Upper Grande Ronde River Watershed in northeastern Oregon is considered important habitat for threatened stocks of chinook salmon (Oncorhynchus tshawytscha). Documented reductions in channel complexity and riparian vegetation within the watershed have increased concern over loss of viable habitat. An important component of salmonid habitat is stream temperature during critical summer periods. In general, annual maximum stream temperatures and diurnal fluctuations in the Upper Grande Ronde River were found to reflect local reach characteristics, position in the drainage, and large-scale changes in valley shape. Stream temperatures on the Grande Ronde River at a distance of 71 km from the watershed divide exceeded 14°C, the "upper preferred temperature" for chinook salmon, more than 90% of time in July of 1991 and in July and August of 1992. While the occurrence of temperatures above 14°C were less common in the headwaters of the Grande Ronde River, downstream of a large meadow (i.e., Vey Meadow) (29 km from the divide) 14°C was exceeded at least 60% of the time during the same three month period. Seven-day maximum stream temperatures on the Upper Grande Ronde River ranged between 17.9°C and 26.6°C in 1991 and between 19.1°C and 26.7°C in 1992. Diel fluctuations on the mainstem were greatest immediately below Vey Meadow (about 12°C) but tended to stabilize at approximately 8°C at distances of over 49 km from the divide. Maximum stream temperatures in tributaries of the Upper Grande Ronde River varied by as much as 11°C (during 1992), reflecting large differences in stream cover, aspect, and flow. The timing of annual maximums seemed to be strongly linked to aspect during 1992. In addition, the high-elevation, forested tributaries had annual maximum stream temperatures and diel fluctuations which were 3°C lower than those associated with more open, low-elevation sites. Relationships between stream temperatures, riparian vegetation, and channel morphology characteristics were evaluated for 11 tributary reaches. Differences in stream cover, average flow velocity, bankfull depth and percent undercut bank were found to be significantly (p <0.1) related to maximum stream temperatures and/or average August diel fluctuations based on linear regression models. A stream temperature prediction model (i.e., TEMP-86) was found to be an accurate predictor of average hourly strew temperatures through short 250-m long reaches. An average WSTAT (a measure of model accuracy) of -0.18°C was calculated based on 11 reaches though two reaches led to consistent over- and under-predictions of downstream temperatures. A series of temperature simulations using TEMP-86 and combinations of wetted width and percent stream cover suggest that lower maximum daily stream temperatures would be observed through altered reaches if concurrent changes in both parameters occurred.
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