996 resultados para SEDIMENT TRANSPORT
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Mode of access: Internet.
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"March 1984."
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Bibliography: p. 14.
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"April 1980."
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"November 1966."
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"June 1980."
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Mode of access: Internet.
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Prepared in cooperation with the Soil Conservation Service, USDA.
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"October, 1982."
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Bibliography : leaf 33.
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Bibliography: p. 14.
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"December 1996."
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This paper proposes a theoretical explanation of the variations of the sediment delivery ratio (SDR) versus catchment area relationships and the complex patterns in the behavior of sediment transfer processes at catchment scale. Taking into account the effects of erosion source types, deposition, and hydrological controls, we propose a simple conceptual model that consists of two linear stores arranged in series: a hillslope store that addresses transport to the nearest streams and a channel store that addresses sediment routing in the channel network. The model identifies four dimensionless scaling factors, which enable us to analyze a variety of effects on SDR estimation, including (1) interacting processes of erosion sources and deposition, (2) different temporal averaging windows, and (3) catchment runoff response. We show that the interactions between storm duration and hillslope/channel travel times are the major controls of peak-value-based sediment delivery and its spatial variations. The interplay between depositional timescales and the travel/residence times determines the spatial variations of total-volume-based SDR. In practical terms this parsimonious, minimal complexity model could provide a sound physical basis for diagnosing catchment to catchment variability of sediment transport if the proposed scaling factors can be quantified using climatic and catchment properties.
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New experimental laboratory data are presented on swash overtopping and sediment overwash on a truncated beach, approximating the conditions at the crest of a beach berm or inter-tidal ridge-runnel. The experiments provide a measure of the uprush sediment transport rate in the swash zone that is unaffected by the difficulties inherent in deploying instrumentation or sediment trapping techniques at laboratory scale. Overtopping flow volumes are compared with an analytical solution for swash flows as well as a simple numerical model, both of which are restricted to individual swash events. The analytical solution underestimates the overtopping volume by an order of magnitude while the model provides good overall agreement with the data and the reason for this difference is discussed. Modelled flow velocities are input to simple sediment transport formulae appropriate to the swash zone in order to predict the overwash sediment transport rates. Calculations performed with traditional expressions for the wave friction factor tend to underestimate the measured transport. Additional sediment transport calculations using standard total load equations are used to derive an optimum constant wave friction factor of f(w)=0.024. This is in good agreement with a broad range of published field and laboratory data. However, the influence of long waves and irregular wave run-up on the overtopping and overwash remains to be assessed. The good agreement between modelled and measured sediment transport rates suggests that the model provides accurate predictions of the uprush sediment transport rates in the swash zone, which has application in predicting the growth and height of beach berms. (c) 2005 Elsevier B.V. All rights reserved.
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Siliciclastic turbidites represent huge volumes of sediments, which are of particular significance for (1) petroleum researchers, interested in their potential as oil reservoirs and (2) sedimentologists, who aim at understanding sediment transport processes from continent to deep-basins. An important challenge when studying marine turbidites has been to establish a reliable chronology for the deposits. Indeed, conventional marine proxies applied to hemipelagic sediments are often unreliable in detrital clays. In siliciclastic turbidites, those proxies can be used only in hemipelagic intervals, providing a poor constraint on their chronology. In this study, we have used sediments from the Rhône Neofan (NW Mediterranean Sea) to demonstrate that pollen grains can provide a high-resolution chronostratigraphical framework for detrital clays in turbidites. Vegetation changes occurring from the end of Marine Isotopic Stage 3 to the end of Marine Isotopic Stage 2 (from ~30 to ~18 ka cal. BP) are clearly recorded where other proxies have failed previously, mainly because the scarcity of foraminifers in these sediments prevented any continuous Sea Surface Temperature (SST) record and radiocarbon dating to be obtained. We show also that the use of palynology in turbidite deposits is able to contribute to oceanographical and sedimentological purposes: (1) Pinus pollen grains can document the timing of sea-level rise, (2) the ratio between pollen grains transported from the continent via rivers and dinoflagellate cysts (elutriating) allows us to distinguish clearly detrital sediments from pelagic clays. Finally, taken together, all these tools show evidence that the Rhône River disconnected from the canyon during the sea-level rise and thus evidence the subsequent rapid starvation of the neofan at 18.5 ka cal. BP. Younger sediments are hemipelagic: the frequency of foraminifers allowed to date sediments with radiocarbon. First results of Sea Surface Temperature obtained on foraminifers are in good agreement with the dinoflagellate cysts climatic signal. Both provide information on the end of the deglaciation and the Holocene.