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Accueil du site → Doctorat → États-Unis → 1996 → Hydraulic resistance to overland flow on semiarid hillslopes : A physical simulation

State University of New York at Buffalo (1996)

Hydraulic resistance to overland flow on semiarid hillslopes : A physical simulation

Hirsch, Paul J

Titre : Hydraulic resistance to overland flow on semiarid hillslopes : A physical simulation

Auteur : Hirsch, Paul J

Université de soutenance : State University of New York at Buffalo

Grade : Doctor of Philosophy (PhD) 1996

Resistance to overland flow is investigated by performing two sets of flume experiments. One set was conducted in a flume with plane bed and varying concentrations of roughness elements. The relation between friction factor f and flow Reynolds number Re is found to be positive when the elements protrude through the free surface of the flow and negative when the flow overtops the elements. Two models are proposed which partition resistance to overland flow into boundary, form, and wave drag. The models adequately describe the f-Re data up to the point of element submergence and indicate the importance of wave drag. The second set of flume experiments was performed on resin replicas of gravel-covered ground surfaces. These experiments indicate a negative f-Re relation, suggesting that the expected increase in resistance from the progressive inundation of the protruding gravel is outweighed by the decrease in resistance due to (1) greater flow depths over areas of the bed already submerged and (2) the concentration of flow into threads which weave past the roughness elements. The negative trend observed here is similar to that reported in field studies. Frequency distributions of flow depths on the replicas changed from left-skewed to right-skewed as Re increased, due to the progressive inundation of an irregular ground surface and the concomitant decrease in the proportion of the surface covered by shallow flows and an increase in the proportion covered by deep flows. Hot-film anemometry was used to measure flow-velocity profiles on the replicas. One series of experiments explored the shape of the profiles at various locations on the replicas with Re held constant. In relatively open positions the profiles are segmented in a manner similar to that reported by previous investigators studying channel and estuarine flows over rough surfaces, while in the lee of large obstacles profiles tend to be uniform. Another series of experiments examined the change in profile shape with changing Re. Although some profiles became better organized as Re increased, the results make it clear that overland flows on complex surfaces can adjust to changing Re in manifold ways.

Mots clés : Erosion, Applied sciences, Hydrology, Geography, hillslope, Earth sciences Agricultural engineering

Accès au document : Proquest Dissertations & Theses

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