What’s the difference between a swash and a backwash?

The swash and backwash are both types of wave movement that influence the structure of a beach. The swash helps to build up the beach, loosing its energy and depositing its load of sand and silt onto the beach. The backwash scours out the beach as moves back down towards the sea scraping with it and picking up material as it goes. When a wave has a strong swash and a weak backwash the beach will build up and often become steep. When the wave has a strong backwash but a weak swash the beach has a flat profile and is constantly being degraded.