Flow substrate interactions in aggrading and degrading submarine channels

Abstract

ABSTRACT Connecting real-time measurements of current–bed interactions to the temporal evolution of submarine channels can be extremely challenging in natural settings. We present a suite of physical experiments that offer insight into the spectrum of interactions between turbidity currents and their channels, from i) detachment-limited erosion to ii) transport-limited erosion to iii) pure deposition. In all three cases channel sinuosity influenced patterns of erosion and deposition; the outsides of bends displayed the highest erosion rates in the first two cases but showed the highest deposition rates in the third. We connect the evolution of these channels to the turbulence of the near-bed boundary layer. In the erosional experiments the beds of both channels roughened through time, developing erosional bedforms or trains of ripples. Reynolds estimates of boundary-layer roughness indicate that, in both erosional cases, the near-bed boundary layer roughened from smooth or transitionally rough to rough, whereas the depositional channel appears to have remained consistently smooth. Our results suggest that, in the absence of any changes from upstream, erosion in submarine channels is a self-reinforcing mechanism whereby developing bed roughness increases turbulence at the boundary layer, thereby inhibiting deposition, promoting sediment entrainment, and enhancing channel relief; deposition occurs in submarine channels when the boundary layer remains smooth, promoting aggradation and loss of channel relief.