Graduate Thesis Or Dissertation

 

Summer stream temperatures and channel characteristics of a southwestern Oregon coastal stream Pubblico Deposited

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/r207tr48q

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  • The Elk River Basin drains 93 sq ml of steep forested terrain on the west side of the Klamath Mountains in Southwest Oregon. This river and its tributaries support a diverse and abundant population of anadromous fish; a hatchery located at river mile 13 (km 21) supplements these native populations. Clear weather in combination with dry summers and low streamflow produce warm water temperatures. Historical data indicate that summer stream temperatures as high as 76°F (24.4°C) have occurred in the mainstem of the Elk River. This study was undertaken to evaluate summer stream temperatures and to what extent they were affected by natural factors and land use. In selected tributaries and along the mainstem of the Elk River, measurements were made on canopy cover, stream surface width, and thalweg depth during the summers of 1984 and 1985. Recording thermographs and maximum/minimum thermometers were used to determine the overall temperature pattern of the basin. In genera.l, maximum stream temperatures appear to be declining since 1970, following a period of increased landslide activity in the basin. The trend of decreasing maximum temperatures was not associated with changes in summer streamflow or summer precipitation patterns, suggesting that a recovery of streamside vegetation and/or change in channel morphology is proceeding within the basin. Tributaries with relatively large width / depth ratios (exceeding 14 or more), generally exhibited large diurnal fluctuations in temperature indicating solar heating was occurring. For drainages of similar size, large diurnal temperature fluctuations were associated with large surface area to volume ratios. Tributaries found to be especially low in maximum temperatures generally flow subsurface as a result of channel aggradation. In the 1984 and 1985 field seasons, maximum stream temperatures in the tributaries never exceeded the maximum temperature of 69°F (20.6°C) found in the mainstem. The upper reaches of the mainstem, which is wide and aggraded, was the portion of the basin found to have the highest maximum stream temperatures. Five pools were sampled to determine vertical profiles of temperature and dissolved oxygen. Temperatures and dissolved oxygen concentrations did not vary with depth.
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