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Geometrical Constraints on Submarine Channel-Levee System Evolution


Both internal and external forcing may influence the development of aggradational submarine channels, and in particular, their likelihood of avulsion. Simple geometric modelling is used here to show that the channel-levee form is inherently unstable. Thus, given steady input conditions, submarine channel levee systems cannot grow with a fixed geometry, necessitating changes in one or more of: 1) the relative amounts of sediment depositing on the levee vs. in the channel; 2) the outer-levee slope and 3) the channel cross sectional area. It can be shown that any of these changes will ultimately increase the likelihood of system re-organisation via avulsion. Allogenic forcing, expressed by temporal variations in the type of flow entering a channel-levee system, likely modulates the development of the disequilibrium conditions that lead to avulsion. Thus, inspection of the downstream changes in channel levee geometry, and of patterns of avulsion, may permit inferences regarding changes in input conditions, and may ultimately allow better a priori estimates of the patterns of grainsize distribution within channel-levee system sedimentary bodies.