Morphologic properties derived from a simple cross-shore sediment transport model

This paper builds on the now classical discussions by Bowen [1980] and Bail ard [1981] on the applicability and implications of Bngnold's [1963] sedime nt transport model to nearshore profile modeling. We focus on the morpholog ic implications of both the strengths and weaknesses of Bagnold's model, is olating the transport terms that are well predicted (i.e., mean flow terms) from those that are not well predicted (i.e., transport due to correlation s between flow and sediment load). We factor Bagnold's model into a dimensi onal transport magnitude and a nondimensional term. The nondimensional term describes the relative importance of transport due to undertow, gravity, a nd correlations between flow and sediment load. The transport magnitude lar gely determines the response time of nearshore profiles. For typical nearsh ore environments this response time was estimated to vary as a function of incident rms wave height (H-rms) from similar to 500 years (H-rms similar t o 0.5 m) to 2 years (H-rms similar to 3 m). The relative importance of comp eting transport mechanisms is shown to depend strongly on the relative wave height (defined as the ratio of the rms wave height to the local depth). S implified nearshore transport parameterizations that are a function of this variable were derived and were interrogated for the existence and form of equilibrium profiles. Several differences from previously computed equilibr ium profiles were noted. First, because the relative wave height saturates in natural surf zones, equilibrium profiles converge to a relatively flat p rofile near the shoreline. Second, under some situations a seaward sloping equilibrium profile may not exist. Third, the long response times combined with unknown stability of an equilibrium profile make it difficult to asses s the physical connection between theoretical equilibrium profiles and prof iles observed in nature.