Sediment sorting by size, shape and density during transport and deposition produces characteristic structures used to interpret modern and ancient sedimentary environments. Discrete-particle models which calculate the hydrodynamic, solid contact and body forces on individual grains are one means of elucidating fundamental sedimentary sorting mechanisms. Such phenomena as inverse grading and size-segregation in foreset beds are readily generated by such models. Recent studies of bedload transport under highly unsteady wave- and current-generated flows in the surf zone have shown the importance of fluid acceleration, as well as velocity, on transport rates. Furthermore, the simulations show that fractional transport rates in the surf zone under small waves strongly promote onshore motion of coarser sediment. Many of the ideas embodied in discrete-particle models and other fundamental studies of sediment transport are due to insights provided by John Southard, and inspired by his enthusiasm for research and teaching in the earth sciences.