The coastline is the line that separates the land from the sea. It is located on the middle flood line .
The coastline must not be confused with the baseline , which is the basis for defining territorial waters . Nor should it be confused with the nautical chart zero , which separates the sea from the dry areas . It is also not identical with international borders , these refer to the baseline.
Definition of the coastline
The coastline is determined by the coastal state. In Germany, this task is taken over by the Federal Maritime and Hydrographic Agency (BSH) . Only the actual geographic-hydrographic course is decisive. The coastline is defined differently for the North and Baltic Seas :
At the Baltic Sea, the mean water level (MW) is used as the reference level for determining the coastline. This is calculated as a 20-year mean.
Other calculation methods are sometimes used in other countries. The IHO expresses itself very imprecisely: “The coastline separates the land from the water.” As a result, the coastline would be changeable and would depend on the water level of the tides . To avoid this, more precise definitions are established by the countries.
Importance of the coastline
The coastline separates the sea from the land and thus serves as a case distinction in various laws, for example in the definition of ownership of waters in the tidal area.
“Height” of the coastline
The states use different elevation models and reference levels . Germany has been using the European ETRS-89 since 1991 . Compared to the worldwide WGS 84 there is a height deviation of a maximum of 10 cm if you simply add the current shift of approx. 50 cm towards 41 degrees to the ETRS lat / lon values.
Length of the coastline
- see main article coastline
The length of the coastline depends on the accuracy of the recording. The smaller the radii, the longer the line ( fractal ) becomes . It also depends on how many islands are recorded and from what size. The CIA gives the length of the worldwide coastline (continents and islands) with 356,000 km.
Capture and display
Today, the coastline is marked by georeferenced aerial photographs taken of the Baltic Sea at the time of mean water or of the North Sea of the MHW, which is influenced by the tides . For the sake of simplicity, the lower vegetation limit is often used as a guide for the coastline.
In general maps and on the Baltic Sea, the coastline is shown as a simple line.
At tidal waters, the coast is bounded by two lines: Below or seaward is the line of the lowest possible tidal water level ( LAT = chart zero ). Above or inland is the line of the mean tidal high water (MTHW). In between is the dry area of the tidal water called the tidal flats . It is represented as a special stretch of coastline, with its creeks and sand banks . The line of mean high water is shown as the coastline. Possibly. the baseline is also displayed (further seaward) .
Change of the coastline
Seen in geological time, a coast represents only a snapshot and is constantly changing. The course of the coast changes primarily due to the effects of ocean currents and tides (tides) as well as the erosive force of the surf . In addition, eustatic sea level fluctuations as well as land elevations and subsidence due to isostatic and tectonic processes also play a role.
In addition to the above-mentioned morphological work of the water on the coasts, these are also strongly anthropogenic today through development (e.g. ports, settlements, coastal protection), use for maritime transport (e.g. transport of goods) and economic use (e.g. Fishing, tourism).
The tidal range increases steadily on the North Sea. This leads to stronger wave movements ( orbital movement , flow speed of tidal currents and surf return currents ) and thus increased movement of sand and increased coastal erosion .
Baseline for national border
The coastline serves as the basis for the construction of the baseline , which is used to determine the national border . The baseline is a simplification of the coastline that is administratively determined by the federal states. Curvatures and incisions are straightened and river mouths and bays are connected by straight lines from coastline to coastline. The national border is then 12 nautical miles seaward from the baseline.
- Landmann / Rohmer UmweltR / Faßbender, 81st EL September 2016, WHG § 3 Rn. 20, 41.
- Wolfgang Augath: Contributions from surveying to localization and navigation in transition , Dresden (PDF file; 951 kB)
- CIA factbook
- Investigation of the water levels ( Memento of the original from June 24, 2007 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF; 851 kB)