Wednesday Oct 17, 2018

Definitions of the coastal zone

It is important, in order to ensure a sound communication, to define the coastal terms that are used in coastal engineering and shoreline management. Therefore, the definition of the coastal term s for the form elements and processes in the coastal area given in the following, see also the coastal profile in fig 1.

Fig.1. Definition of coastal terms, mainly from Shore Protection Manual, 1984

 

 

 

 

 

 

 

Fig.1. Definition of coastal terms, mainly from Shore Protection Manual, 1984

 Definition of coastal terms:

 COASTAL AREA: The land and sea areas bordering  the shoreline.

  COAST: The strip of land that extends from the coastline inland to the first major change in terrain features. The main types of coast features are the following:

-          Dune areas

-          Cliff areas

-          Low laying area, possibly protected by dikes or seawalls etc.


  COASTAL HINTERLAND: the land that extends landward of the coast and which is not influenced by coastal processes.

 

 COASTLINE: Technically the line that forms the boundary between the COAST and SHORE, i. e. the foot of cliff or the foot of the dunes. Commonly, the line that forms the boundary between the land and the water.

  SHORE or BEACH: The zone of unconsolidated materials that extends from the low water-line to the line of permanent vegetation (the effective limit of storm waves).The shore can be divided into the foreshore and the backshore. The foreshore, also called the beach face, is the area between mean low water spring and mean high water spring plus the uprush zone. In the case of a high tidal range the foreshore can be very wide, in which case the the foreshore is sometimes referred to as a TIDAL FLAT. The backshore is the part of the shore which is dry under normal conditions. The backshore is often dominated by berms and it is whithout vegetation. The backshore is only exposed to wave action during extreme events; the width of the backshore depends on the beach material, the magnitude of the storm surge, and the wave exposure provide the conditions for a wide backshore; the width of the backshore , however, also depends on the geology at the site. The landward limit of the backshore toward the COAST is the place where there is a marked change in material or physiographic form, e.g. the foot of a cliff, the foot of the dunes, or the line of permanent vegetation. A shore of unconsolidated material (sand) is usually called BEACH.

 

 SHORELINE: The intersection between the mean high water-line and the shore.

  SHOREFACE or LITTORAL ZONE: The zone extending seaward from the low water-line to some distance beyond the breaker-zone. The littoral zone is the zone in which the littoral processes take place; these are mainly the long-shore transport, also referred to as the littoral drift, and the cross-shore transport. The width of the instantaneous littoral zone of course depends on the wave conditions.

  

 BREAKER-ZONE or SURF-ZONE: There is no clear definition of the breaker-zone, but it can be defined as the zone extending seaward from the shoreline that is exposed to depth-limited breaking waves. The outer limit of the breaker-zone is called the BREAKER-LINE. The instantaneous width of the surf-zone varies of course with the instantaneous wave condition. In this context we will defined the surf-zone as the zone valid for the yearly wave climate defined by significant wave height HS, 12h/y which is the wave exceeded 12 hours per year. The width of the breaker/surf-zone can thus be defined as the width of the zone within which HS,12h/y breaks. The breaker/surf –zone is somewhat narrower than the littoral zone, as the transport starts at greater depth than the breaking. It is evaluated that 80 to 90% of the yearly littoral transport takes place within the breaker or surf-zone. The depth at the outer limit of the breaker-zone is closed to the 1.8 times HS,12h/y.

  NEARSHORE ZONE: The zone extending seaward from the low water-line well beyond the breaker-zone; it defines the area influenced by the nearshore currents. The nearshore zone extends somewhat further seawards than the littoral zone.

 CLOSURE DEPTH: the depth beyond which no significant longshore and crossshore transports take place due to littoral transport processes. The closure depth at the seaward boundary of the littoral zone

 OFFSHORE ZONE: The offshore zone is not well defined. In relation to beach terminology, it is thus not clear if it starts from the littoral zone, from the breaker or from the nearshore zone. In the present context the offshore zone is defined as the zone off the nearshore zone..