Summertime water temperature trends in Steamboat Creek Basin, Umpqua National Forest Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/bn999986t

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  • The Steamboat Creek basin drains 227 mi² (588 km²) of steep forested terrain into the North Umpqua River of Southwest Oregon, 39 mi (63 km) northeast of Roseburg. Summer base flows for Steamboat Creek average 83 cfs (2.35 m³/sec). Steamboat Creek and its tributaries are considered important to the production of summer-run steelhead; the basin has been closed to angling since 1932. Harvesting has occurred in every subdrainage of the Steamboat Creek basin. Trees were routinely removed from riparian areas when harvesting in the basin began in 1955. Since the mid-1970s to early-1980s, however, buffer strips were left adjacent to streams. In addition, the floods of 1964-65 caused significant damage to riparian vegetation in the basin. This study was undertaken to: (1) determine long-term trends over the period 1969-90 of summertime water temperatures in the mainstem of Steamboat Creek, selected tributaries, and in Boulder Creek, an unharvested control stream in an adjacent watershed and (2) evaluate spacial patterns of maximum water temperatures in the Steamboat Creek basin during the summer of 1990. Significant (P≤0.10) trends of decreasing maximum daily summertime stream temperatures on Steamboat Creek and tributaries occurred from 1969-90. In contrast, an unharvested control stream showed a small, but nonsignificant, increasing trend in stream temperatures. The largest decrease in maximum stream temperatures (7 to 11°F, 3.9 to 6.1°C) occurred on small streams with summer base flows less than 6 cfs (0.17 m³/sec). These streams also had the highest proportion of stream length adjacent to harvesting activities before 1974. The smallest decrease in maximum stream temperatures (0 to 3°F, 0 to 1.7°C) occurred on streams with little or no history of timber harvest activity along riparian areas, or at locations where summer base flows were greater than 15 cfs (0.42 m³/sec). Since no trends in either air temperature or streamflow were apparent over the 1969-90 period, regrowth of riparian vegetation that was previously removed by flooding, debris torrents, or streamside harvesting, appears to be the major cause of trends in decreasing maximum summer stream temperature. Regrowth of riparian vegetation provides shade over small streams, decreasing energy input to the stream from solar radiation. Maximum daily stream temperatures in lower Steamboat Creek did not change significantly during the 1969-90 study period and stream temperature data in 1960 indicates that maximum stream temperatures in lower Steamboat Creek have historically been high. Any cooling effects by groundwater or tributaries are largely negated by the large volume of water in the main channel. Also, the large stream width renders riparian vegetation relatively ineffective in protecting the stream from solar radiation. Minimum stream temperatures decreased during the 1969-90 study period for all of the long-term stations in the Steamboat Creek basin while the control stream showed a slight increasing trend. Similarly, diurnal stream temperature fluctuations decreased for several tributaries.
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  • description.provenance : Approved for entry into archive by Laura Wilson(laura.wilson@oregonstate.edu) on 2008-11-20T21:29:21Z (GMT) No. of bitstreams: 1 Holaday, Steven A_1999_MS.pdf: 870356 bytes, checksum: cacd8df479e91963b62267d04cdca0af (MD5)
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