Beaches
A beach has four zones - offshore, nearshore, foreshore and backshore.
- The backshore doesn't normally get hit by waves, except during severe storms
- The foreshore is the area between high tide and low tide
- The nearshore is where breaking waves form
- The offshore is out past the breaking waves
Beach Processes
Waves
- Waves are created by the wind blowing over the surface of the sea. The friction between the wind and the surface of the sea gives the water a circular motion.
- The effect of a wave depends on its height and fetch. The fetch is the distance over which the waves are built up. The height depends on the wind speed.
- As waves appraoch the shore they break. Friction with the sea bed makes the wave motion more elliptical. The crest of the wave rises up and then collapses onto the beach.
- Water breaking onto the beach is called the swash. Water washing back towards the sea is called the backwash.
- There are two types of wave. Surfing breakers have short wavelength, and are high and steep. They are destructive, pounding onto the beach and removing material from it. Surging breakers have a long wavelength, and are low and gentle. Surging breakers are constructive carrying material up the beach.
Currents
- Currents are the general flow of water in one direction.
- Currents move material towards and along the coast - this is called the longshore drift.
- Swash carries sediment up the beach, parallel to the prevailing wind. Backwash caries sediment back down the beach, at right angles to the shore line.
- When there an angle between the prevailing wind and the shore line, a few rounds of swash and backwash move the sediment along the shore.