Beaches are the accumulation of sand and shingle. Sandy beaches are often found in sheltered bays where they are called BAY HEAD BEACHES. When waves enter these bays, they tend to bend to mirror the shape of the coast - REFRACTION. This is caused by the water becoming shallower. Wave refraction spreads out and reduces the wave energy in a bay, which is why deposition occurs. Berms are also common, particularly on shingle beaches, as they represent the different tides, such as storm and high tide.