Forcing of turbidity currents on the morphological evolution of submarine channel-levee systems: a laboratory study

Erosional and depositional processes that control the morphological evolution of submarine channel-levee systems are poorly understood. One of the key questions is whether internal feedbacks between the flow and channel morphology will always cause a channel to evolve towards an equilibrium shape. Shields scaling allows incorporation of realistic forcing of erosion, bypass, and deposition, which is essential in studying the architecture of channel-levee systems. A series of Shields-scaled experiments have been performed that clarify how channels with different initial dimensions are modified by turbidity currents. A total of five processes have been identified that change channel geometry: levee aggradation, channel aggradation, channel incision, bank erosion and bench formation. Velocity measurements were used to explore the mechanisms behind these processes in terms of bed shear stress and flow-confinement. The five processes combine in three different channel regimes, which are distinguished based on characteristic geometric evolutions and the combination of geometry alternating processes that occur. The equilibrium channel regime consists of channels tending towards an equilibrium geometry. Channels in the incisional regime exhibit an erosional character and are associated with incisional episodes in channel evolution. The high aspect-ratio, oversized regime involves depositional channel infilling. The degree of confinement of the flow by the channel emerged as main controlling factor on what processes occurred and in what regime a channel was located. These three regimes can be mapped on a phase diagram containing channel dimensions. These results might be used in the future to enable qualitative reconstruction of paleo flow conditions based on observed depositional and erosional patterns.