Surf from breaking swells can erode sand rapidly from the frontal dune at high tide and shift the beach profile to a more gradual slope with a larger offshore sand bar. The offshore sand bar helps to break waves further offshore and reduce dune erosion. The natural shift of sand between the dunes and offshore bars can be reduced by seawalls and shoreline riprap. Tides are important agents of sediment redistribution over the beach. They sort sediments and may cause currents along the shoreline.
Tides also determine the level at which storm waves attack the beach and frontal dunes.
If a storm passes while the tide level is low, most of the wave energy is expended eroding lower portions of the beach and the dunes are preserved. However, many storms last longer than one tidal cycle and at high tide the frontal dune is eroded by waves. Tides are variable along the Maine coast. These tides occur semimonthly when the moon is either new or full and are increased even further when the moon is in perigee, nearest the earth. Currents along the shore can be caused by winds, waves, or tides.