Field observations of swash zone infragravity motions and beach cusp evolution

Fluid flows consistent with low‐mode edge waves were evident in video observations of swash motions during a field experiment in which beach cusps developed on an initially smooth beach. As beach cusps grew, energy lying along low‐mode dispersion curves increased. The most energetic edge‐wave propagation direction changed from upcoast to downcoast as the orientation of the cusp horns rotated. These observations suggest a coupling between morphodynamics and hydrodynamics, and are evidence that beach cusp evolution might control low‐mode edge wave dynamics.