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Accueil du site → Doctorat → États-Unis → 1985 → ANNUAL BEHAVIOR OF SAND-BED CHANNELS (HYDRAULIC GEOMETRY, MINIMUM VARIANCE, MEGAWAVES, GEOMORPHOLOGY, EPISODIC BEHAVIOR)

Colorado State University (1985)

ANNUAL BEHAVIOR OF SAND-BED CHANNELS (HYDRAULIC GEOMETRY, MINIMUM VARIANCE, MEGAWAVES, GEOMORPHOLOGY, EPISODIC BEHAVIOR)

BUCHANAN, JOHN PETRELLA

Titre : ANNUAL BEHAVIOR OF SAND-BED CHANNELS (HYDRAULIC GEOMETRY, MINIMUM VARIANCE, MEGAWAVES, GEOMORPHOLOGY, EPISODIC BEHAVIOR)

Auteur : BUCHANAN, JOHN PETRELLA

Université de soutenance : Colorado State University

Grade : Doctor of Philosophy (PhD) 1985

Résumé
Annual variations of channel morphology in sand-bed braided-stream systems is controlled largely by hydraulic and hydrologic parameters, upstream sediment availability and sediment characteristics. Scrutiny of data from six stream-flow gaging stations indicates that the bed-load channel morphology of reaches in Red and Canadian Rivers display great temporal and spatial variability. Adjustment behavior is inconsistent, in direction and magnitude, along channel reaches between gages on the same river at a given time, and at the same gage through time. At-a-station hydraulic geometry varies on an annual basis, where the major component of short-term adjustment is in the width exponent (b). Ephemeral-stream channel reaches are characterized by erratic adjustments of the exponent set from one year to another, whereas reaches experiencing more perennial flow reflect more consistent adjustment patterns through time. Minimum variance theory is inapplicable for channels developed in loose, noncohesive materials that adjust cross-sectional geometry frequently to each discharge event. In these channels, the hydraulic geometry exponent set adjusts unequally through time, in fact, adjustment is usually described by a single exponent. Statistical analyses suggest that ephemeral-stream reaches adjust primarily in response to changes in mean-annual and peak flows and the duration of mean flows from one year to another. That is, the current year discharge magnitude and duration controls channel dimensions and hydraulic geometry relationships for that year. River reaches that experience more perennial flows are shaped by prior year hydrologic regime. Discharge fluctuations during the current year in these channels have little effect on channel geometry and development for that year. Evidence for the migration of sediment waves was obtained in that relationships between morphologic variables at the study gages displayed episodic behavior patterns through time. However, supporting evidence from time-sequenced aerial photography and longitudinal profile data was not obtained. Relationships between sediment supply, channel morphology and flow hydraulics are complex ; the relationships change through time, and with location along the channel. Thus, generalizations regarding annual behavior of sand-bed channels should not be attempted without consideration of geomorphic relationships in such dynamic systems

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