Being a unique boundary between land, water, and air, beaches are very dynamic forms of land. Waves continuously operate on the beach, putting beach material into motion. Winds and tides are also important forces acting directly on the beach and causing changes. Also altering the nature of the beach is human interference. Building of breakwaters, piers, jetties, and sea walls can disturb the natural movement of beach material and can cause profound changes.
During the monsoons, very high waves dissipate their energy, causing beach erosion and damage to nearshore landforms and property. During fair weather, low-energy waves help build up beaches by deposition or accretion of sand. One of the important features of wave action near the shore is the generation of nearshore currents (Fig. 27). These water movements, which can be longshore or offshore, are fundamental to the movement of beach material. Also to be noted is the increased intensity of these currents during the monsoon, which would be hazardous for those who venture into the sea for recreational activities. Strong currents directed towards the sea, perpendicular to shore, are called ‘rip currents’ or ‘killer currents’, and one should be careful of them.