Bedform spurs are formed by helical vortices  that trail from the lee surface of oblique segments of bedform crest lines. Trailing helical vortices quickly route sediment away from the lee surface of their parent bedform, scouring troughs and placing this bed material into the body of the spur. Here’s a video of a single bedform spur:

When present, spur-bearing bedforms and their associated trailing helical wakes exert tremendous control on bedform morphology by routing enhanced sediment transport between adjacent bedforms. Field measurements collected at the North Loup River, Nebraska, and flume experiments described in previous studies demonstrate that this trailing helical vortex-mediated sediment transport is a mechanism for bedform deformation, interactions and transitions between two-dimensional and three-dimensional bedforms. Below is a time lapse image of many spur bearing bedforms. Watch as they pause and surge due to spur-routing of sediment transport.

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