A new model is described that simulates the paths taken by a large number of identified ('tagged') sand grains in coastal areas in response to waves and currents. A number of practical applications require such a Lagrangian approach, as distinct from the more traditional Eulerian calculations of the transport rates of bulk quantities of identical, non-tagged, grains. Such applications might include studies on the dispersal of dredged spoil, or on the release of contaminated particulate material.The particle-tracking algorithm determining the movement of tagged grains takes account of the following processes: 9 burial and re-emergence 9 initiation of motion and entrainment by combined waves and currents 9 bedload transport 9 suspended transport 9 turbulent diffusion.

A model, SandTrack, has been established to simulate movements of sand-sized particles in coastal waters within a Lagrangian framework. The model can be applied to assess the dispersal of contaminated particulate material, such as may be associated with industrial discharges, or the dispersal of dredged spoil. For such applications, the Lagrangian approach is essential, as the identity of the particles is important. Although Lagrangian models existed previously which could simulate fine sediment constantly in suspension, there are certain applications, such as dealing with the movement of bed particles, in which intermittent physical processes are critical. SandTrack has been tested against field observations from the coastal waters near Dounreay, United Kingdom. The tests strengthened confidence in the model predictions, and enabled appropriate values of some of the model's main physical parameters to be set. Some features of the particle distributions simulated by SandTrack are consistent with field observations, and are not achievable with simpler sediment transport models. The model's run times are sufficiently short for simulations of particle movement in moderately large coastal areas over several decades to be practical.

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