The internal structure of deposits emplaced under upper plane bed / sheet flow transport conditions: Laboratory experiments and numerical modeling

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The internal structure of deposits emplaced under upper plane bed/sheet flow transport conditions: Laboratory experiments and numerical modelingEnrica Viparelli, EAR-1250641, University of South CarolinaABSTRACTRock deposits emplaced by storms and turbidity currents can be characterized by a lower erosional boundary underlying a massive unit followed in ascending order by a parallel laminated unit and a cross laminated unit. Such deposits are interpreted to be emplaced by waning energy flows. Massive units are macroscopically structureless, i.e. there is not a visible organization of sediment particles within the deposit. In the laminated units, sediment particles of different size are deposited with visible patterns.The main objective of this research is to investigate and model flow and sediment transport conditions that are responsible for the emplacement of massive and parallel laminated units. Laboratory and field studies demonstrate that parallel laminated units are emplaced under sediment transport conditions known as upper plane bed regime. These conditions are characterized by i) a moving bedload layer one or two grain diameters thick, and ii) downstream migrating low amplitude bedforms. As the parallel laminated unit is deposited under upper plane bed regime, the basal unit has to be emplaced under more intense transport conditions. The central hypotheses of the proposed research are that i) those intense transport conditions correspond to sheet flow, which is a mode of bedload transport characterized by a bedload layer 10-100s grain diameters thick, ii) the sheet flow layer can suppress the formation of parallel laminations, and iii) this suppression results in a tendency to homogenize the grain fabric of the emplaced deposit under conditions of continued deposition. It must be acknowledged that sheet flow is not the only mechanism that produces massive deposits, but the conditions for it to operate can be commonly met at field scale.Based on the results of preliminary laboratory experiments, an experimental and numerical program is proposed to characterize the deposition of massive versus parallel laminated deposits. Open channel, i.e. river-like, laboratory experiments will be performed to build a deposit under upper regime plane bed and sheet flow transport conditions. The choice of this experimental setting is dictated by the need to induce sediment deposition in the sheet flow regime at laboratory scale. However, the experiments will be specifically designed to model intense and net-depositional subaqueous flows. The numerical program is centered on the development of a model that is able to reproduce the grain fabric of the deposits emplaced under upper plane bed and sheet flow transport conditions. The model will be validated against the experimental results. The results of the laboratory and numerical work will provide the necessary information to i) characterize the mechanics of upper plane bed and sheet flow transport regimes in general, and ii) relate the grain fabric of the deposit to the characteristics of the flow and the sediment transport. They are thus expected to have a transformative impact on the communities studying subaqueous sedimentary processes, coastal and deep-water engineering. One graduate student will take the lead in the performance of the experimental and numerical work to pursue his PhD research. He will also be responsible for the organization of the laboratory and numerical data and for their timely dissemination through the CDSMS and the NCED repositories. Four undergraduate students will be hired in three years to prepare them for graduate studies via undergraduate research projects that will be directly supervised by the PI.