Shorelines can switch between erosional and constructional processes rapidly in both time and space. Well developed beaches tend to form in areas with high sediment supply and high wave energy. They are constructional features. Tidal range and climate can vary and will affect the geometry of a beach, but beaches can form in a full range of conditions. Wave action is critical to beaches.
Waves come in off the ocean, and start to feel the shore, especially on the upper shore face.
Wave ripples form here, as well as other cross stratification from storms and tidal channels. In shallower water, the sand and rocks are washed back and forth almost continuously which produces well rounded and well sorted grains. The grain sizes present depend on the wave energy and can range from cobbles to fine sand. In the zone where waves break, the erosional force is particularly strong due to high flow speeds and abundant sediment suspended in the water. The eroded sediment is washed up onto the foreshore and deposited as the water drains back into the ocean.