Waves are not only capable of transporting material up or down beaches but also along the coastline by the process of longshore drift.
The angle of the swash on a beach is determined by the direction of the winds that created the waves.
The direction of the backwash is always roughly perpendicular to the coastline.
In this way, waves may move material up a beach at an oblique angle but then drag it back down at right angles.
If this process is repeated many times, the beach material moves in a zig-zag pattern along the coast and can be moved many miles.
If, however, wind directions change, it is possible that material may be moved back in the direction from which it came.
On days when the winds blow onshore at right-angles, the material will simply move up and down the beach.
Due to prevailing winds in the UK being from the south-west, the direction of longshore drift along the south coast is west to east. On the east coast, it is from north to south.