Submarine Channel Processes: Implications for ‘Point-Bar’ Development

Jeffrey Peakall¹, Kathryn Amos², James Best¹, Ransome Corney¹, Sanjeev Gupta³, Gareth Keevil¹, and Daniel Parsons^1
1 University of Leeds, Leeds, United Kingdom
² University College, University of New South Wales, Canberra, Australia
³ Imperial College, London, United Kingdom

Intra-channel deposition in sinuous single-thread subaerial channels is dominated by the initiation and development of point-bars at the inside of channel bends. These bars are themselves the product of the complex three-dimensional flow-field within river channels. A key question for understanding the intra-channel architecture of sinuous submarine channels is the nature of deposition at inner bends and the degree of similarity with well-studied and comparatively well understood fluvial systems.

Here we present an integrated set of experimental, analytical and computational fluid dynamic modelling results that reveal that the secondary flow cells in submarine channels are reversed relative to those in subaerial open-channel flows. The models all demonstrate that in gravity currents secondary flows at the bend apex move basal fluid towards the outer bank, produce upwelling at the outer bank, and a return flow higher up towards the inner bank. Secondary flows are known to influence the initiation, development and detailed grain-size sorting of point-bars in river channels. Therefore such a fundamental change, the reversal of the sense of secondary flow, would be expected to influence deposition in gravity currents.

A series of initial experiments are presented where ‘point-bar' like facies are for the first time formed in physical models of submarine channels. The results from these experiments are explored and compared against river channels and engineered compound channels. Implications for submarine channel architecture are then explored.