Stream channel adjustments following elimination of cattle grazing
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Authors: F. J. Magilligan, and P. F. McDowell
Date: 1997
Journal: Journal of the American Water Resources Association
Volume: 33
Number: 4
Pages: 867-878
Summary of Methods: Stream channel geomorphic adjustments following the removal of cattle grazing in four gravel-bedded, steep alluvial streams in eastern Oregon was examined with cattle exclosures greater than 14 years old. Exclosure reaches (Reach B) were compared to adjacent grazed reaches (Reach A- upstream, Reach C-downstream reach) at each location. Each reach was divided into habitat units (pool, glide, riffle, and step) and each habitat unit thalweg length, water surface width, bankfull width, and water depth were measured. Maximum pool depth was also recorded in pool habitats. Five to eight channel cross-sections were surveyed at each reach and width-depth ratio, bankfull width, bankfull depth and bed-sediments were measured at each cross-section to characterize the stream.
Article Summary / Main Points: Cattle removal from the riparian zone decreased both bankfull width (10-20%) and low flow width. Bed mobilization occurred as pool area increased in ungrazed reaches as compared to grazed reaches. Morphologic adjustments of the channel at four sites occurred through two mechanisms: reworking of bank sediment during lateral migration and reduction of wetted perimeter by sediment deposition with little or no migration. Most of the geomorphic properties measured did not demonstrate riparian recovery with 14 years of livestock exclusion.
Vegetation Types: Riparian and Wetlands
MLRA Ecoregions: Unknown
Agrovoc Control Words: Riparian zones Grazing Streams
Article Review Type: Refereed
Article Type: Experimental Research
Keywords: grazing, fish habitat, exclosures, channel adjustment, riparian disturbance
Annotation: These findings are widely applicable to riparian stream areas where vegetation is grazed by cattle. Though results may vary as grazing intensity levels and periods were not described in the study. The limitation of this study is that all the properties measured did not explain riparian recovery; therefore, a detailed long-term study designed to capture the conditions at the time the exclosure was constructed and changes over time would be beneficial.
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