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.