Here is a model I made of a beach. It was based on a talk by Alan Brampton at HR Wallingford. Alan explained how various sizes of particles in beaches are moved around by the action of the waves pumping the wet aggregate of sand pebble and rocks. To make it interesting this particular instantiation of the model starts with a stable beach built up after a run-in from an unmixed group of particles. Given a certain set of parameters, after a time, a stable beach is reached and it doesn’t change, it’s basically a gravelly beach which is protected by a veneer of medium particles that have percolated to the surface. Then I added a big pile of pure sand to the beach – perhaps this is what a manager might think would improve the quality and size of the beach. Subsequently, as this model shows, using the same parameters as made the stable beach, the whole thing collapses into the sea and ends up way smaller than before.

The actual rules (all of them) are summed up in the following pictures…