When Does Flow Splitting Occur in Submarine Channel Bends?

Kyle Straub¹, David Mohrig¹, Jim Buttles¹, Brandon McElroy¹, and C. Pirmez^2
1 Massachusetts Institute of Technology, Cambridge, MA
² Shell International E&P Inc, Houston, TX

A suite of laboratory experiments resolves the governing parameters which determine when flow splitting of turbidity currents occurs in submarine channels. Flow splitting describes a process where a supra-channel portion of a current detaches from its channelized portion at a channel bend. To resolve the influence of channel curvature on the extent of flow splitting we released turbidity currents with similar initial properties into channels with sinuosities of 1.00, 1.05, and 1.32. In the straight channel, levee sedimentation was associated with the supra-channel fraction of the current simply spreading laterally out onto the overbank surface. In the low sinuosity channel, outer bend levee sedimentation was 1-2 times greater than that along the inner levee and the outer bend levees were composed of significantly finer sediment than the channel thalweg deposits. This asymmetry in deposition plus the contrast in grain size of overbank versus channel-bed deposits is consistent with flow splitting. A different scenario was observed in the high sinuousity channel. Outer bend levee sedimentation was 3-4 times greater than that on inner bend levees and there was no appreciable difference in grain size between the levee crest deposit and the channel thalweg, indicating little or no splitting of the current at bends. Our results suggest that flow splitting of thick currents is most likely at channel bends having low-moderate curvature. In contrast, some fraction of the entire current can exit the channel at tight bends due to its large superelevation caused by the high curvature and a low excess density.