Shorerise and bar‐berm profiles on ocean beaches

TLDR

The partitioning of the beach profile into shorerise and bar‑berm reflects distinct forcing modes on either side of the breakpoint. The study develops a beach equilibrium model that treats the outer shorerise and inner bar‑berm portions independently. The model matches the shorerise and bar‑berm portions at the breakpoint‑bar and employs previously unavailable beach profile data. Both portions fit h = A x^m with m ≈ 0.4, and seasonal changes produce self‑similar displacements of the curves, with winter conditions shifting the breakpoint deeper and farther offshore and the berm crest landward.

Abstract

A beach equilibrium model is developed that treats the outer (shorerise) portion of the profile independently from that of the inner (bar‐berm) portion. The two portions are matched at the breakpoint‐bar. The partitioning of the profile in this way is consistent with the different forcing modes on either side of the breakpoint. This formulation utilizes beach profile data not previously available. It is shown that both portions of the profile are well fitted by curves of the form h = Ax m , where h is positive downward and x is the positive offshore coordinate. Surprisingly, the value of m ≈ 0.4 is nearly the same for shorerise and bar‐berm and does not change significantly with seasonal beach changes (summer/winter). The principal difference between seasonal profiles is that in winter (higher waves) the breakpoint‐bar is deeper and farther offshore while the berm crest is displaced landward. Thus the changes in seasonal equilibria are manifested by simple, self‐similar displacements of the bar‐berm and shorerise curves as a consequence of changes in surf zone width and O (1) variations in the factor A .