HYDRAULIC GEOMETRY OF SINUOUS CHANNELS: A COMPARISON BETWEEN SUBMARINE AND SUBAERIAL ENVIRONMENTS

Submarine channels are a very common feature of continental margins across the globe, acting as conduits through which sediment is transported from continental shelves into deep-sea basins. Striking similarities exist between these submarine channels and subaerial river channels, especially regarding the development of a sinuous planform geometry, the construction of levees, and the process of bend cutoff. In spite of these similarities, there are few, if any, systematic comparisons of the channel cross-sectional geometry of rivers and submarine channels across a variety of scales. In this study, we compare the width, depth, and slope of 180 submarine channel cross-sections to that of 250 river cross-sections. The results show that submarine channels have cross-sectional dimensions that can exceed the dimensions of the largest rivers on earth by an order of magnitude. Indeed, “small” submarine channels (width < 20 m) are entirely absent from this database of submarine channel dimensions. Additionally, we find that for channels of a given width or depth, the slope of a submarine channel can be up to two orders of magnitude greater than the slope of a river. We also use a Chezy-type formulation to calculate bank-full discharge at each submarine channel cross-section and apply a hydraulic geometry analysis. The results of the hydraulic geometry analysis indicate that channels follow power law relationships between discharge and channel dimensions that are similar to the power law relationships determined for rivers. We conclude that the difference in channel size and slope between rivers and submarine channels is linked to the non-negligible buoyant force in the submarine environment. Turbidity currents must be sufficiently deep and/or flow over a sufficiently steep bed gradient for the driving force of flow (the force of gravity acting on suspended sediment) to overcome both frictional resistance and the buoyant force.