Current and historic stream channel response to changes in cattle and elk grazing pressure and beaver activity

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dc.contributor.authorFouty, Suzanne Catherine
dc.date.accessioned2018-11-05T22:24:25Z
dc.date.available2018-11-05T22:24:25Z
dc.date.issued2003
dc.date.updated2018
dc.description656 pagesen_US
dc.description.abstractLivestock grazing and beaver trapping alter streams hydrologically and geomorphically leading to declines in the quality and extent of stream-riparian ecosystems. The influence of reductions in grazing pressure and fluctuating levels of beaver activity (treatments) on channel capacity was studied at I 08 channel cross-sections, located on eight headwater streams in Montana and Arizona. Cross-sections were surveyed two or three times over a two-to-five year period to determine annual rates of change as a function of treatment. Most cross-sections in the cattle and elk exclosures and grazed areas showed minimal changes in area(< 10 percent). Large decreases in cross-section area were observed in reaches with intact beaver dams, especially near the dams. The beaver ponds reduced channel capacity between 50 to I 00% in most reaches, compared to< 25% in reaches without beaver ponds. The ponds effectively restored the hydrologic connection between the stream and valley floor in less than one year. Upon dam failure, channel capacity increased within a year by 40 percent or more as the ponds drained and sediment eroded. A conceptual model describing geomorphic and hydrologic response of a drainage basin to the entry of beavers and then their removal or abandonment was developed, based on a literature review and field data. The model suggests that the simultaneous existence of discontinuous arroyos and wetlands, observed by Euro-American expeditions to the Southwest prior to settlement, may in fact reflect landscapes transforming due to recent beaver trapping rather than a recent climate shift. Beaver-dam failures would trigger channelization and thus greater flood magnitudes as water was more rapidly routed from upper to lower watersheds. The study suggests that Euro-American trapping and grazing, though temporally and spatially separated, combined with two recent periods of above-average precipitation to transform drainage networks in the West and increase stream ecosystem sensitivity to climatic variability. This transformation pre-dates the installation of stream gages and the data collection that forms the current basis of our understanding hydraulic geometry and fluvial processes. Consequently, current hydraulic geometry relationships and our understanding of stream sensitivity to climatic variability reflect highly disturbed watersheds and ecosystems, not intact systems.en_US
dc.description.versionVersion has slight corrections to the original by the author, as specified in separately attached file Corrections_to_Fouty_2003_PhD_20181810.pdf
dc.identifier.urihttps://hdl.handle.net/1794/23927
dc.language.isoenen_US
dc.publisherUniversity of Oregonen_US
dc.rightsCreative Commons BY-NC-ND 4.0-USen_US
dc.subjectRiver channelsen_US
dc.subjectMontanaen_US
dc.subjectArizonaen_US
dc.subjectRiparian ecologyen_US
dc.subjectEnvironmental aspects of grazingen_US
dc.subjectGeomorphologyen_US
dc.subjectBeaver trappingen_US
dc.subjectEnvironmental aspectsen_US
dc.titleCurrent and historic stream channel response to changes in cattle and elk grazing pressure and beaver activityen_US
dc.typeThesis / Dissertationen_US

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