Relations among mean flow, turbulence, and mixing at a small stream confluence

Stream confluences are important locations for mixing in river systems. This study examines the relations among the mean flow, turbulence, and lateral mixing at a small stream confluence. Advective effects associated with secondary motion of the mean flow dominate mixing in the channel downstream of the confluence. Detailed analysis of velocity and turbidity time series at a location corresponding to the time-averaged position of the mixing interface shows that the exact location of the mixing interface is unsteady and dominated by pulses of interacting fluid from each tributary. These pulses of interacting fluid reflect the passage of coherent turbulent structures, generated by lateral shear between the flows, past the point of measurement.