Open AccessMorphodynamic modeling of an embayed beach under wave group forcing
Author(s) -
Reniers A. J. H. M.,
Roelvink J. A.,
Thornton E. B.
Publication year - 2004
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2002jc001586
Subject(s) - geology , beach morphodynamics , bathymetry , shoal , sediment transport , wave height , surf zone , swash , advection , wave flume , plage , shore , geomorphology , shoaling and schooling , longshore drift , mechanics , breaking wave , wave propagation , sediment , physics , oceanography , thermodynamics , quantum mechanics
The morphodynamic response of the nearshore zone of an embayed beach induced by wave groups is examined with a numerical model. The model utilizes the nonlinear shallow water equations to phase resolve the mean and infragravity motions in combination with an advection‐diffusion equation for the sediment transport. The sediment transport associated with the short‐wave asymmetry is accounted for by means of a time‐integrated contribution of the wave nonlinearity using stream function theory. The two‐dimensional (2‐D) computations consider wave group energy made up of directionally spread, short waves with a zero mean approach angle with respect to the shore normal, incident on an initially alongshore uniform barred beach. Prior to the 2‐D computations, the model is calibrated with prototype flume measurements of waves, currents, and bed level changes during erosive and accretive conditions. The most prominent feature of the 2‐D model computations is the development of an alongshore quasi‐periodic bathymetry of shoals cut by rip channels. Without directional spreading, the smallest alongshore separation of the rip channels is obtained, and the beach response is self‐organizing in nature. Introducing a small amount of directional spreading (less than 2°) results in a strong increase in the alongshore length scales as the beach response changes from self‐organizing to being quasi‐forced. A further increase in directional spreading leads again to smaller length scales. The hypothesized correlation between the observed rip spacing and wave group forced edge waves over the initially alongshore uniform bathymetry is not found. However, there is a correlation between the alongshore length scales of the wave group‐induced quasi‐steady flow circulations and the eventual alongshore spacing of the rip channels. This suggests that the scouring associated with the quasi‐steady flow induced by the initial wave groups triggers the development of rip channels via a positive feedback mechanism in which the small scour holes start attracting more and more discharge.