SHORELINE SAND WAVES AND 1D COASTAL MODELLING

摘要

A 1D dynamic equation is obtained for the shoreline planform (small departures from arnrectilinear coastline) which extends the traditional 1-line approach. This is done by considering thernlocal wave-driven hydrodynamics and the local bed changes induced by sediment transport andrnaveraging in the cross-shore direction. The new equation is an advection-diffusion equation withrnsome additional terms coming from the flow distortion produced by the departure from thernrectilinear bathymetric contours. The influence of these terms is still under investigation. It seemsrnhowever that they can be neglected for relatively large wave incidence angles and alongshorernlengthscales of about 1- 15 times the width of the surf zone, XrnXb . The new equation is adequate torndescribe the propagation of shoreline sand waves. Wave propagation is favored by large incidencernangles while the behaviour for very small angles can be complex and even updrift migration canrnoccur. The wave celerity is of the order Q / DrnDb Xb , where Q is the alongshore sediment transportrnrate and DrnDb is the depth at breaking, and it is proportional to (gD gDb)1/2 2. For realistic values of thernparameters the predicted celerities are O(1 km yrrn. Yr-1 -1), so in the good range according tornobservations.rn),