PERIGEAN Period of time (twice a year) when the moon is at its closest approach to the Earth, and the tidal range is larger than normal.

PERIGEAN SPRING TIDES Coincidence of perigean and spring tidal conditions resulting in the highest high and the lowest low tides, Nor’easters, such as Ash Wednesday Storm of 1962, become even more damaging when they occur during perigean spring high tides.

PERIOD See WAVE PERIOD.

RECESSION Landward movement of the shoreline due to the loss of beach material and/or direct inundation of the land.

REFRACTION The bending of waves by bars and shoals that can cause the concentration of wave energy on a portion of the shoreline, resulting in accelerated beach erosion.

RELATIVE SEA LEVEL RISE The gradual rise in the water level relative to the land surface due to worldwide changes in the volume of seawater and/or local vertical movement of the land.

REVETMENT Facing of stone, concrete or rubble built to protect an embankment or upland against erosion by wave action or currents.

RIDGE A longshore feature that may become exposed at low tide; often formed by a bar moving onshore as a form of post-storm beach recovery.

RIP CURRENTS Strong, localized current flowing seaward from the shore; visible as an agitated band of water, which is the return movement of water piled up on the shore by incoming waves. Rip currents are by far the biggest killers of ocean swimmers.

RIPRAP Layer, facing or protective mound of stones randomly placed to prevent erosion of upland areas. Also the name of the stone so used.

RUNUP Part of the swash action caused by breaking waves.

SAND BAGS Sand-filled cloth or geo-textile bags that can be stacked to provide semi-hard coastal protection and are designed to retain sand while allowing water to flow through.

SAND WAVES Much larger features than cusps that may migrate along the shoreline. Sand waves can locally cause accelerated erosion known as erosion “hot spots.” Also called shoreline meanders, sand humps, or giant beach cusps.

SCARP Vertical drop-off of the dry beach caused by oblique wave attack during stormy conditions; beach scarps can be several inches to over six feet high and disappear by the return of sand onshore during berm accretion. Dunes can also be scarped, forming vertical, wave-cut faces.

SCOUR Removal of beach material by waves and currents such as at the base of a dune or toe of a shore structure.