The Concept of Shoreface Profile of Equilibrium: A Critical Review

Abstract

The concept of shoreface profile of equilibrium is the basis for most models used to quantitatively describe and predict profile response on beaches. We question the validity of the concept as used in coastal engineering. The equilibrium shoreface profile concept is based on the following assumptions: (1) underfying geology does not play a role in determining the profile shape; (2) shoreface sediment is moved only by the interaction of wave orbitals with the sea floor, unidirectional current flow is not accounted for; (3) there is no significant net movement of sediment seaward of a so called "closure depth." The equilibrium shoreface profile equation implies: (1) offshore bars do not play an important role in shoreface sediment transport; (2) grain size is the only variable determining shoreface profile shape variability; (3) the shoreface transport system is two-dimentional; and (4) all shorefaces in the world can be described by a single equation with sediment grain size as the only variable. To varying degrees, all of these assumptions fail to be met in real world situations in light of well documented oceanographic and geologic phenomena. A fundamental reexamination of the engineering methods of determining nearshore shoreface evolution is needed. As currently practiced such methods are based on poor oceanographic assumptions.