Coastal zone characteristics

Defining the characteristics of the coastal zone will depend on the coastal type. Sand is a common marine sediment producing sandy beaches resulting from littoral transport. It is these hydrographic conditions that determine the appearance of the coastline. In environments that are fairly calm in terms of wave conditions muddy coast tend to be more dominant, in comparison rocky coasts are continually cut back by the sea. Arctic coastlines are those which are exposed to more than 6 months a year freezing. A barrier coast is formed when a lagoon separates a barrier island (which runs parallel to the shore) from the coastline.

Different coastal types:

Sandy beaches

Fig. 1. Sandy coast. Source: DHI

Sand is a very common marine sediment and is transported along the shoreline by littoral transport. Sand transport (littoral transport or littoral drift) is driven by the breaking waves and the longshore currents in the wave breaking zone. The appearance of a natural sandy beach (Fig. 1) is determined by hydrographic conditions and geology. Any interference will cause a reaction in the form of a shoreline response. Therefore, understanding of physical processes is important and the development of suitable solutions required, supported by numerical modelling if needed.

Links:

• Sandy beaches
• Littoral Transport

• Classification of Coastal Profiles
• Shore nourishment

Muddy coasts

Fig. 2. Mangrove coast. Source: DHI

Muddy coasts are only found in environments that are fairly calm with respect to wave conditions; or there is abundant supply of fine sediments. They are normally vegetated e.g. mangroves (Fig. 2) fronted by very flat slopes/tidal flats or a muddy coast with mangrove vegetation which is characterized by a muddy shoreface, sometimes in the form of muddy tidal flats, and the lack of a sandy shore.

Links:

• Characteristics of muddy coasts
• Mud

Rocky coasts

Rocky coasts are continuously cut back by the sea and are characterised by erosional features. They have a slow rate of morphological change, and experience the main erosional processes of: mechanical wave erosion, abrasion and hydraulic action; weathering - physical, salt, chemical and water-layer levelling; bio-erosion - biochecmial and biophysical; and mass movements by rock falls and toppling, slides and flows.

Arctic coasts

Fig. 3. Arctic coast, Photograph by Agata Weydmann

Shores above the North Polar Circle, which are exposed for more than six months of freezing annually are regarded as Arctic coast (Fig. 3). Their characteristic feature is the importance of ice forms (glacial ice – growlers, sea ice – ice pack and winter local ice – ice foot) for their ecology and evolution. Ice act as a limiting factor for the occurrence of infaunal and epifaunal organisms (ice scouring, ice melt and freezing are all stressful processes for coastal macrofauna). Even in the high Arctic, macrofauna and macroalgae can survive winter ice in rocks crevices. In places, with very cold water, where permafrost surface at the intertidal, the specific type of Arctic shore appears – cryolittoral, where freshwater ice forms the seabed, often covered with stones and algal debris (northernmost parts of the Siberian coast and its islands). Soft sediment Arctic coasts are eroding very fast due to the combined effect of ice melt, ice scouring and waves action.

Barrier coasts

Fig. 4. Barrier coast. Source: DHI

Barrier islands (Fig. 4) are parallel to the shore, separated from the mainland by a lagoon. In a profile with a more gentle slope than the equilibrium profile, sediments will be moved onshore, as waves on the shoreface will primarily transport sand towards shore attempting to build up an equilibrium profile. Waves lose their energy over the gentle shoreface and deposition occurs some distance from shoreline, eventually developing into a barrier island due to the cross-shore transport. Transport of sand by longshore transport will add to barrier formation, a combination of sand spit and barrier island processes, normally occurring under type 1 and 2 conditions.

Links:

• Barrier islands
• Slapton barrier beach case study, UK
• Origin and Genesis of coastal barriere systems. Case study from Rømø in the Danish Wadden Sea

See also

Classification of Coastlines

References

Mangor, Karsten. 2004. “Shoreline Management Guidelines”. DHI Water and Environment, 294pg.