The occurrence of coastal erosion is dependent upon the balance between the resistance, or erodibility, of the coastline and the strength, or erosivity, of the waves and tides affecting the area.
These conditions are, in turn, reliant upon a number of factors, including topography, the composition and structure of the geological formations exposed at the coast, the state of man-made coastal defences, local currents and tidal range, wave climate (as characterised by wave height, period, direction and fetch), groundwater, sediment supply, and relative sea level.
Consequently, rates of coastal erosion and accretion are very variable at regional, national and international scales.
Coastal erosion typically results in a landward retreat of the coastline. This can increase the risk of coastal flooding and result in loss of land and damage to buildings, infrastructure and agricultural land.
Sudden coastal erosion events, particularly those in the vicinity of coastal cliffs, may directly endanger the lives of people. The movement of salt-water into freshwater areas (saline intrusion) can occur during coastal flooding and can impact upon the biodiversity of previously freshwater or terrestrial ecosystems.
It has been estimated that across England and Wales 113,000 residential properties, 9,000 commercial properties and 5,000 hectares of agricultural land are within areas potentially at risk of coastal erosion, which translate to a capital value of assets at risk of approximately £7.7billion for England and Wales (DEFRA, 2001).