Quantifying the morphology and growth of levees in aggrading submarine channels

Abstract

Levees are the primary elements of self‐formed submarine channels, yet little is know about their morphodynamics. We present field observations of static levee morphology and stratigraphy in addition to laboratory experiments that link levee morphodynamics to turbidity current flow properties. These observations are used to motivate a levee growth model. Using a three‐dimensional seismic volume, we mapped the depositional patterns associated with a network of submarine channels defined by prominent levees on the continental slope offshore Brunei. Levee taper increases rapidly as channel depth increases from 5 to 50 m and then increases at an ever diminishing rate for channels between 50 and 72 m of depth. A similar relationship between levee taper and channel relief was observed in a set of laboratory experiments. We released turbidity currents into a straight channel positioned within a larger experimental basin. The currents were able to interact with the overbank environment and therefore construct channel bounding levees. We link periods of rapid change in levee growth in our experiments to the vertical structure of suspended sediment in turbidity currents. Our field and laboratory observations suggest that the most important parameters controlling levee morphodynamics are the degree of channel confinement and the vertical structure of suspended‐sediment concentration profiles. Our levee growth model couples a simple advection settling model for currents with a vertical sediment concentration profile defined by the Rouse equation. The model reproduces our field and laboratory observations of levee growth and provide a method to estimate current thickness from levee stratigraphy.