SECONDARY FLOW IN MEANDERING CHANNELS FROM SUBMARINE FANS: IMPLICATIONS FOR CHANNEL MORPHODYNAMICS AND ARCHITECTURE, AN APPLICATION TO THE AMAZON FAN

It has recently been suggested by some authors that the direction of secondary flow of turbidity currents in meandering channels should be reversed compared to rivers. Were this to be the case, the planform geometry of submarine meanders would likely be markedly different from that of rivers. More specifically, the ratio of wavelength to channel width would likely be markedly larger. Yet this ratio has been found to be quite similar for both rivers and channels on submarine fans. The argument for reversed secondary flow is based on the premise that the elevation at which peak streamwise velocity is attained is very low compared to the thickness of the flow. Here it is demonstrated that the position of this peak is strongly dependent upon the densimetric Froude number Frd of the flow. Supercritical Froude numbers (Frd > 1) favor a low elevation of peak velocity. Subcritical Froude numbers (Frd > 1) favor a high elevation of peak velocity. Reconstructions of channel-formative flows on the Amazon Submarine Fan indicate that the flows should have been well into the subcritical range over most of the channel length. The implication is that the sense of the secondary flows should likely have been the same as those of rivers. The magnitude of these secondary flows, however, should have been somewhat weaker than rivers. This conclusion is in concordance with the observed similarity between the planforms of rivers and meandering channels on submarine fans. The conclusion is supported with experimental, theoretical and field data.