Flow Dynamics of Sinuous Submarine Channels

Gareth Keevil, Jeff Peakall, and Jim Best
University of Leeds, Leeds, United Kingdom

Submarine channels are considered to be analogous to meandering fluvial channels due to their similar planform geometry. Within fluvial channels secondary circulation has been shown to be an important control of erosion, deposition, lateral sediment transport and overall bend stability. However, there is a lack of direct measurements of velocity and nothing is known about the secondary flow structure within submarine channels.

A series of experiments is presented in which saline gravity currents flowed through a range of submerged, fixed-form, sinuous channel models. The data reveal secondary flow cells in submarine channels are best developed at bend apexes, with the basal component of the flow cell moving from the inside to the outside of the bend, the reverse direction to that expected from fluvial models. The same sense of secondary circulation was found when channel geometry and width:depth ratio were varied. The stability of the results suggests that the direction of secondary circulation is fundamental to all sinuous submarine channels. When a bed of erodible low-density sediment was added to the channel, sediment waves formed on the levee backslope.

This work demonstrates that although submarine and fluvial channels have similar planform geometry they have the opposite sense of secondary circulation. The initiation of sediment waves is intrinsically linked to intra-channel flow processes and distribution of overspill. The sediment waves are formed due to the action of a hydraulic jump within the overspill that induces an undular bore leading to rapid deposition of sediment on the outside of the bend apexes