Minibasins on continental margins trap turbidity currents transporting material downslope, but little is known about the inherently three-dimensional (3-D) mechanics of these confined flows. Utilizing new methodology, experimental results quantify flow dynamics in minibasins for the first time. It is shown that dynamics are dominated by 3-D circulation cell structures, across the fill-to-strip-to-spill transition that are controlled by flow discharge. Measurements of velocity throughout circulation cells indicate vorticity dominates strain rate with fluid rotating into the center of cells where it upwells: this influences minibasin sediment trapping potential and deposit heterogeneity. Flow properties link to depositional patterns on minibasin slopes. Specifically, higher input discharges are correlated with higher fluxes into the center of minibasins and reduced deposit tapering on minibasin slopes. This geometry is linked to the amount of sediment rich flow runup on the distal minibasin wall, where flow and sediment is delivered to circulation cells.

Cohesive properties of clay promote the formation of clay flocs and gels and relatively small suspended clay concentrations can enhance or suppress turbulence in a flow. Flows are naturally non-uniform, varying in space and time, yet the dynamics of non-uniform open-channel clay suspension flows are poorly understood. To research the influence of suspended cohesive clay on changing flow dynamics under non-uniform flow conditions, new experiments were conducted using decelerating and accelerating clay suspension open-channel flows in a recirculating flume. The flows transition between clay flow types, with different degrees of turbulence enhancement and attenuation as the flow adapts to the change in velocity. The experimental results show that decelerating clay suspension flows have a longer adaptation time than accelerating clay suspension flows. The formation of bonds between cohesive sediment particles is a time-dependent process and establishing clay bonds, as in the decelerating flows, requires more time than breaking them, as in the accelerating flows. This hysteresis is more pronounced for higher concentration decelerating flows that pass through a larger variety of flow phases of turbulence enhancement and attenuation. These different adaptation time scales and associated clay flow type transitions are likely to affect erosional and depositional processes in a variety of fluvial and submarine settings.