Stability of gravel at artificially created spawning beds in uncontrolled streams Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/9p290d96f

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  • Twenty-five gabion-type structures across the main stem and tributaries of the Siuslaw River in the Oregon Coastal Range, installed to expand the available spawning area for fish, were investigated for their ability to perform gravel control functions such as trapping bedload carried by the stream or holding gravel placed behind the structures. The merits of gravel trapping structures in the main stem Siuslaw River were found to depend largely on channel features in the reach at and above the structures. Factors favoring successful developments were: ample gravel supply, high bed roughness, wide straight reaches, and lateral stream bed slopes deflecting flood water from the structure. Among limiting factors were: the existence of pools immediately upstream of structures, deficient gravel supply, curving stream alignment, and unfavorable lateral stream bed slopes. Main stem reaches with an instantaneous peak discharge exceeding 100 cfs per foot width were found questionable for development. The controlling factors in the tributary streams were found to be approach velocities and stream features such as bedrock smoothness, approach slope, channel alignment, constrictions, lateral bed slope, plunge pools, and lengths of gravel beds. Careful placing of gravel to predetermined slopes was found not to be warranted, as the stream would rework the gravel according to local influences. Reaches where the flow was retarded without widening and reaches where high velocities occurred were found especially unfavorable for gravel stability. Flume studies with simulated gabions and full-size gravel were carried out to study incipient motion and scour from a gravel bed behind a gabion. Scour was found to take place from the upstream portion of the gravel bed, resulting in an adversely sloping bed there. Bed forms of standing-wave type, with changing wave location, were encountered when the flow was in the critical region; subsequent scour would wash the bed waves out. Gravel transport from apparently stable beds subjected to very low flow strengths verified that gravel transport is a statistical phenomenon and that the threshold of motion should include time of observation as a variable. Disruption of the gravel imbrication at the bed surface was found to encourage particle movement. The effect of buried perforated pipes o.n reducing bed siltation was investigated at the time of the stability experiments. No beneficial effect on the siltation pattern could be found when well-graded fine material was added to the flume.
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  • description.provenance : Approved for entry into archive by Patricia Black(patricia.black@oregonstate.edu) on 2014-02-24T21:27:39Z (GMT) No. of bitstreams: 1 Helland-HansenErikA1972.pdf: 2253560 bytes, checksum: f5c06564b0d8a4e4b4906cf02b1ed65c (MD5)
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