MORPHODYNAMIC MODELS FOR THE CONSTRUCTION OF SUBMARINE CHANNEL LEVEES AND IMPLICATIONS FOR THE HYDRAULIC GEOMETRY OF SUBMARINE CHANNELS (Invited Presentation)

Levees are the primary elements of self-formed submarine channels, yet in comparison to channel thalwegs little is known about their morphodynamics. Motivated by observations of levee stratigraphy in seismic data and levee morphodynamics observed in physical experiments we have developed a levee growth model. This model couples a simple advection settling scheme for suspended sediment with a vertical suspended sediment profile for partially-channelized turbidity currents. Use of an advection-settling scheme is supported by small advection length scales for settling sediment in overbanking flows compared to most levee widths. The channelized (parent) suspended sediment concentration profile in our model is defined for multiple grain sizes using a two-layer method. Suspended sediment concentration below the height of the velocity maximum is defined by the Rouse equation, while the concentration above this height is defined by a near-Gaussian relationship. In our model only the current fraction situated above the elevation of the levee crest is used in the advection settling calculation. As a result early levee growth is associated with coarse and relatively stratified overbanking flow compared to later periods of growth when channel relief is greater. We use this model to link channelized flow properties to the evolution of channel relief, levee morphology and texture. The evolution of levee morphology, specifically levee taper, is shown to depend on the Rouse number of the parent flow with high Rouse number flows corresponding to steep levees. Initial exploration of levee texture has focused on the distribution of particle diameters in the parent flows. We find that a flow composed of a narrow distribution of particle diameters results in a coarser levee than a flow with the same median grain size but broader particle size distribution.