Erosion of beaches may be both natural and human-induced and is a result of loss of sediment. Natural erosion is caused by the impact of waves. Beaches are dynamic, with normal fluctuations in sediment levels during the course of a year. Typically, there is ‘natural’ erosion during the stormy months (November to April) with recovery during the calmer period (May to October). These systems are described as being in ‘dynamic equilibrium’. Where recovery does not occur or erosion is exacerbated due to human activities, beaches become unstable and shoreline retreat follows.
The closure zone is demarcated on its seaward margin by an imaginary line beyond which there is no onshore movement of sand. In addition, improper and excessive cross-shore drainage can lead to the migration of sand offshore. Sometimes coastal structures intended to protect property have the unintended effect of exacerbating wave energy and resulting in beach erosion. In addition, it is thought that the extraction of fuels in marine sediments (oil and gas) since the 1960s may have led to the subsidence of nearshore areas and coastal erosion.
In Trinidad the areas most significantly affected by coastal erosion are along the south coast, the southwestern peninsula, and certain sections of the west and east coast. In Tobago however, one of the main influences on coastal erosion is the quarrying of beaches and rivers for construction aggregate. Coastal erosion reduces the aesthetic value of the beaches, hampers tourism and associated recreational activities, weakens bridges and other structures, undermines the stability of coastal roads, and causes loss of habitat.