Discrete-Particle Model for Nearshore Bedload Transport
Calantoni, J., and Drake, T.G., 1998, Discrete-particle model for nearshore bedload transport: EOS Trans. AGU, 79(17), Spring Meeting Suppl., S122.
Click here for 3MB Quicktime movie of a simulated sand transport under a broken wave.
Three-dimensional discrete-particle computer simulations of bedload transport of coarse sand under typical nearshore sheet flow conditions predict transport rates that often vary considerably from those predicted by the prevailing nearshore sediment transport models developed by Bowen and Bailard. In particular, the Bowen and Bailard models predict zero net transport for a sawtooth waveform characteristic of broken waves in the surfzone, whereas the simulation predicts considerable net transport onshore. Furthermore, fluid accelerations play an important role in determining bedload transport in the simulations, but are not accounted for in these prevailing models. Time-varying pressure gradients similar to those induced by the passage of surface gravity waves drive the motion of particles and fluid in the model. Particles are spherical grains having quartz density and a distribution of diameters about a mean of 1.1 mm; the fluid is crudely modeled as a series of parallel slabs. Momentum is transferred between slabs using a mixing-length model. Simulated transport rates are typically within 20 percent of rates from physical experiments conducted in an oscillatory flow tunnel by other workers, using quartz sand having the same distribution of sizes. In the simulation, significant grain-size segregation occurs during transport, and always results in larger grains moving up towards the bed surface. Further simulations of transport on a sloping bed will test the significance of gravitational effects in the Bowen and Bailard models, and provide a means of linking sheet flow transport to transport over megaripples and other nearshore bedforms.
Supported by the Office of Naval Research