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Density Current Evolution Within an Experimental Submarine Channel


Submarine channels are large geomorphological features which act to control the distribution of large volumes of siliciclastic sediment into deep oceans. The geometry of the associated deposits is controlled by the fluid dynamics of the processes operating within submarine channels. Most recent laboratory and numerical studies have sought to understand the fluid dynamics operating within channels by focusing on the flow processes within single bends. Coherent flow structures are common within submarine channels, but these structures differ significantly from those found within fluvial channels. This paper focuses on the processes of adjustment to a series of bends and the resultant overspill. The results from a series of experiments are presented in which saline gravity currents flowed through a fixed form channel model which comprised 14 symmetrical bend pairs, where the channel model was contained within an elongate flume tank. The dense fluid overspilling the channel was allowed to escape laterally, modelling the likely flow process within aggradational channel systems. The results from the study show that the properties of the flow exhibit a very rapid adjustment to the channel form and then display a relatively constant phase. This adjustment, or flow tuning, occurs over just a few bend pairs and was found to affect flow velocity, discharge and turbulence. Thus the tuning acts to equilibrate the magnitude of the flow with the geometric capacity of the channel. This study reveals in detail the process of flow adjustment to channel form. The variation in overspill seen along the model channel indicates that the rate at which the channel levees are built alters throughout the system. The overspill continues to occur through the system but decreases distally. This matches the observed decrease in channel width and height in natural channel systems. A greater understanding of flow within and overspill from compound submarine channel bends will lead to a better understanding of bend evolution, channel migration, stability and also bed thickness distribution patterns within levees and terminal lobes. This work suggests that the distribution of overbank sediments will be highly complex and controlled spatially and temporally by the interaction of both discharge and channel geometry.