The Development of Leveed Channels by Turbulent, Plane Jets: Laboratory Modeling of Floodplain Tie Channels

Rowland, Joel C.¹, Mark Stacey¹, William E. Dietrich¹ (1) University of California - Berkeley, Berkeley, CA

Leveed channels represent a common and fundamental element of distributary systems. Floodplain tie channels, which transfer sediments from rivers to floodplain lakes, comprise one of the simplest distributary systems found in terrestrial settings. Tie channels are essentially a single-thread deltaic channel that forms and propagates as a sediment-laden jet debouches into a lake. Field studies of tie channels across lowland river systems ranging from the arctic to the wet tropics reveal a characteristic leveed channel form that scales in size the main stem river. Using tie channels as prototypes, we have conducted scaled laboratory experiments to document the morphodynamics of levee channel formation by a sediment-laden jet entering a body of still water. Detailed velocity measurements using an acoustic doppler velocimeter (ADV) were made of a turbulent, plane jet entering into a 3 x 8 m basin of water. The hydrodynamic properties of the jet were compared to the location and morphology of levees formed by sediment with varying settling velocities under the same flow conditions. Our results show that variations in lateral diffusive transport create local convergences that, when coupled with an analysis of the local sediment resuspension by turbulent stresses, accurately predict the position of levees along the perimeter of the jet. A scaling for the levee width is introduced based on the lateral diffusion coefficient, the local depth and the settling velocity and is validated by the laboratory measurements.