TURBULENT FLOW SURFACE DYNAMICS

The free-surface of shallow flows often appears random to the eye. This paper illustrates that the seemingly complex pattern can be decomposed into a number of fluctuating free-surface disturbances, overlapping and out of phase in both space and time. This new knowledge allows a deeper understanding of the nature of dynamic free-surface roughness patterns. This study considers several flow conditions established in a laboratory flume with a bed composed of uniform river gravel. Laser-induced-fluorescence is used to measure the free-surface dynamics in a vertical streamwise plane along the centerline of the flume. The free-surface fluctuations are examined over space and time, and are shown to influence the near-surface layer of the flow, highlighting a potential interdependence between the free-surface and the underlying flow.