Sediment sorting
Swash, the current generated by incoming wave, is strong but of short duration
- It moves coarse debris toward shore
Backwash, the current generated by outgoing wave, is relatively weak & of longer duration
- It move finer material but leaves coarse detritus behind
A beach will have a limited range of sizes of waves that strike it, & so swash zone will be composed of detritus of limited size range
Beaches are usually well sorted