Formation and evolution of sediment ribbons in open-channel flow

The formation and evolution of sediment ribons over a uniform sediment bed in an open-channel flow was investigated via a stereo-photogrammetric system to measure the bed evolution in combination with a stereo-PIV system to measure the three-component velocity field in a cross-sectional plane above the bed. The formation of ribbons is observed to be triggered by the initially meandering low and high-speed streaks sharing the same spanwise wavelength as the fully-developed ribbons.  When the ribbons are fully developed, the streaks are locked in place with low-speed streaks over the ridges and high-speed streaks over the troughs with strong secondary flows.  The lateral stabilization appears to be facilitated by the stable  streaks near the wall.