Groynes are cross-shore structures designed to reduce longshore transport on open beaches or to deflect nearshore currents within an estuary. On an open beach they are normally built as a series to influence a long section of shoreline that has been nourished or is managed by recycling. In an estuary they may be single structures.
Sandy shorelines are some of the most extensive intertidal systems worldwide, representing both excellent recreational assets and buffer zones against the sea. Despite their initial barren and sterile appearance, many sandy littoral localities might even be considered as highly productive.
There are several conspicuous parts to a beach that relate to the processes that form and shape it. The part mostly above water (depending upon tide), and more or less actively influenced by the waves at some point in the tide, is termed the beach berm. The berm is the deposit of material comprising the active shoreline. The berm has a crest (top) and a face — the latter being the slope leading down towards the water from the crest.
The sand deposit may extend well inland from the berm crest, where there may be evidence of one or more older crests (the storm beach) resulting from very large storm waves and beyond the influence of the normal waves. At some point the influence of the waves (even storm waves) on the material comprising the beach stops, and if the particles are small enough (sand size or smaller), winds shape the feature. Where wind is the force distributing the grains inland, the deposit behind the beach becomes a dune.
Dunes are a dynamic, but fragile coastal landform. The changes brought about by the natural processes of winds, waves and tides are rarely gradual or predictable. Rather they are episodic, with periods of little or no change followed by times of intense activity, most obviously during storms when dunes may be eroded rapidly, their seaward faces receding many metres in a few days. Often these events go unnoticed by local residents or land-owners, with subsequent re-building of the dunes by wind action in the following weeks and months. However, when damage occurs with little or no natural restoration of the dunes over a period of several years, then concern arises, especially if there are important assets at risk to the landward. It is usually as a result of such events that intervention works are undertaken, sometimes later proving to be unnecessary or damaging to the natural beach/ dune system.
From the perspective of coastal management dunes protect low lying coastal areas from flooding and also act as a buffer against erosion: they form a reservoir of sand, replenished when beach levels are high and released to nourish the foreshore during storm erosion. They are also areas of considerable scientific, conservation, landscape and recreational value. Because of these attributes they are important to a wide range of human activities, and their management is seen as an important objective in planning and usage of the coastal zone.
The development of the beach as a popular leisure resort from the mid-19th century was the first manifestation of what is now the global tourist industry. The first seaside resorts were opened in the 18th century for the aristocracy, who began to frequent the seaside as well as the then fashionable spa towns, for recreation and health.
Beaches and dunes are changed in shape chiefly by the movement of water and wind. These movements can lead to coastal erosion and coastal flooding. Coast erosion is the process of wearing away material from the coastal profile due to imbalance in the supply and export of material from a certain section. It takes place in the form of scouring in the foot of the cliffs or in the foot of the dunes. Coast erosion takes place mainly during strong winds, high waves and high tides and storm surge conditions, and results in coastline retreat. The rate of erosion is correctly expressed in volume/length/time, e.g. in m3/m/year, but erosion rate is often used synonymously with coastline retreat, and thus expressed in m/year.
Although the sediment balance can be disturbed by natural causes (depletion of the source, a change in the mouth of a river or estuary, gradual shift in wave climate), it is often the result of human activities along an adjacent frontage or nearshore area. These may include dredging, construction of harbour breakwaters, protection of eroding cliffs or construction of beach control structures such as groynes or breakwaters. Erosion in these cases is not natural.
More information on impacts of tourism in coastal areas here.