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UTILIZATION OF IN-STREAM STRUCTURES FOR WET MEADOW STABILIZATION IN THE CENTRAL GREAT BASIN: A PROCESS-ORIENTED APPROACH
Citation:
MILLER, J., D. GERMANOSKI, M. LORD, D. G. JEWETT, J. CHAMBERS, W. TROWBRIDGE, K. STURTEVANT, AND G. S. BAKER. UTILIZATION OF IN-STREAM STRUCTURES FOR WET MEADOW STABILIZATION IN THE CENTRAL GREAT BASIN: A PROCESS-ORIENTED APPROACH. Presented at 2007 International Meeting of the Society for Range Management, Reno, NV, February 12 - 16, 2007.
Impact/Purpose:
To inform the public.
Description:
Wet meadows, riparian corridor phreatophyte assemblages, and high-altitude spring-fed aspen meadows all serve as important habitats in the Great Basin of central Nevada. Geomorphic and biotic characterization of the wet meadow complexes demonstrates that most terminate downvalley in a relatively steep reach which separates the topographically higher meadow from the lower downstream valley floor. The change in elevation creates the potential for meadow degradation through processes of channel entrenchment, and by means of surface piping and pipe collapse. Unentrenched meadows are usually characterized by cyclical episodes of cut and fill associated with channel avulsion, a process driven by the infrequent introduction of coarse bedload. Entrenchment associated with all three processes often leads to lowered water tables and alterations in plant communities. In-stream structures composed of large boulders have been widely used as an ingredient in Natural Channel Design and channel stabilization. In most cases, structures are intended to create a specific channel form by modifying local fluvial processes. Data are rapidly accruing, however, to suggest that such structures are prone to failure, often within a few years of installation. The style of structural damage varies considerably, but is generally related to: (1) flood erosion around the landward side of J-hooks and cross-vanes, accelerating bank erosion locally and stranding the structures as ineffective mid-channel islands; (2) undercutting of footings followed by structural collapse, (3) complete removal of rock materials by floods; and (4) burial by bedload. A different approach is proposed to retard degradation of wet meadow complexes in the Great Basin. In segments of the valley where the valley is wide enough to facilitate channel migration and avulsion the intent is to design structures that are integrated with the existing processes including entrenchment, piping, and avulsion to retard the rate at which those processes occur, while maintaining a deformable channel perimeter. More stable controls are suggested for valley constrictions to strengthen natural baselevel hinge-points.