Computer simulations of flow and sediment transport in the swash zone
on a beach demonstrate that a model that couples local flow accelerati
on and alongshore surface gradient is sufficient to produce uniformly
spaced beach cusps. The characteristics of the simulated cusps and the
conditions under which they form are in reasonable agreement with obs
ervations of natural cusps. The self-organization mechanism in the mod
el is incompatible with an accepted model in which standing alongshore
waves drive the regular pattern of erosion and deposition that gives
rise to beach cusps. Because the models make similar predictions, it i
s concluded that currently available observational data are insufficie
nt for discrimination between them.