You will need a large shallow tray. Put sand in it to form a thin layer.

Now put two bricks in the tray so they jut out from one side. These represent headlands.

Add water slowly so that it does not disturb the sand.

Now make waves in the tray by moving a long ruler up and down in the water. You will see that a regular movement soon makes quite big waves. Look to see what happens to the sand around the headlands and in the bay (the space between the headlands).