As falling dry a naturally occurring phenomenon is called, is water from the countryside retreats in temporarily or permanently, respectively, of the body of water is increasingly free.
Falling dry on coasts
Dry traps denote the phenomenon that sandbanks and shallow seabeds off the coast lie above current sea level for a certain time when the water level is low .
Areas that fall dry are a nautical problem and therefore tinted green on nautical charts , the number of depth information is underlined and indicates how high the corresponding point is above the temporary water level at low water. The nautical chart zero (elevation reference of nautical charts) usually shows the astronomically lowest possible tidal water level ( LAT ) on tidal coasts , so that the contour lines indicate the dangers of agglomeration.
The dry areas form a special habitat for flora and fauna , the Wadden Sea being an example.
In the case of areas that have fallen dry, there is a risk that people who have entered these areas will have their way cut off when the water runs up, since differences in height cannot be seen in large areas that have fallen dry. The returning water creates strong currents that make swimming impossible. It can also be very difficult to walk on dry land. A person can sink in unexpectedly, especially in the mud flats because such places are not visible in the mud flats. It is therefore recommended that dry areas and sandbanks only be entered with an experienced mudflat guide .
Inland waterways falling dry
Rivers and lakes suffer from dry traps in the event of prolonged drought , i.e. lack of precipitation . In the process, the water is increasingly narrowing, and flowing water can dry up completely, and still water can dry out. With strong karstification , such as B. on the Swabian Alb , waters can also fall dry at low tide due to sinking .
From an ecological point of view, drying out in freshwater is a catastrophe that has serious effects on flora and fauna. In those areas where low water levels or even dry runs occur regularly, the organisms are usually adapted. Water bodies that regularly dry out are called intermittent , and a distinction is made between periodic (regular) and episodic (occasional) dry-falling: The water type that the puddles (the paints) fall dry differs from lake and pond .
Skippers can against strong low tide only by dredging of the navigation channel or by construction of impoundments manage. The problem of water abstraction and the amount of water remaining at dams is also a problem for water management .
Drying out water points
Drying out fresh water is also critical for the water supply . Both direct water points and neighboring groundwater levels sink, wells dry up and the vegetation withers. Extraction wells may dry out when the delivery rate remains higher than the yield is.
The cause of this can also be the clogging of the well filter , e.g. B. due to ocher formation , or the hydrogeological conditions do not allow permanent production in the scope of the initial production due to insufficient permeability .
Falling dry through geophysical processes
In the geological sector, coastal areas or entire stretches of land can dry up due to tectonic shifts or earthquakes triggered by them . For example, a scientist from the University of Utrecht assumes that the entire Mediterranean Sea dried up about 5 million years ago due to evaporation. The inflow of water from the Atlantic did not occur because the land mass under the Strait of Gibraltar had risen above sea level. This condition regressed after about 170,000 years.
Cold periods bind such large amounts of water as ice that entire straits fall dry, this also applies to the question of the Bering Strait and the settlement of North America , or the islands of Southeast Asia , or the contact of the British Isles with the mainland instead of the English Channel and the southern North Sea.
The earthquake off Crete 365 , for example, raised the harbor basin of the ancient city of Phalasarna several meters above sea level.
In the winter of 1848, Niagara Falls fell dry for a few hours. The cause here was the lack of water masses due to an ice build- up upstream.
It is also known to fall dry during a tsunami . This is the wave crest , the following wave trough leads to abnormally low water level. Depending on the triggering process, a wave crest or a wave trough hits land first: The dry fall can appear as a sign and is then the highest alarm signal, otherwise between two single tsunamis. Since the 2004 tsunami, it has been known worldwide that in the former case, the curious often go into the dry area, which can mean the greatest danger for those affected.
Watercraft drying out
Watercraft drying out refers to the process in which a watercraft hits a flat spot or anchors at a shallow spot when the water is running out, so that the vehicle lies dry on the seabed when the water is low. On coasts with a strong tidal range , entire ports sometimes dry out, so that ships that want to stay in port have to be designed to dry out.
- ↑ Springer-Verlag, Heidelberg: Scinexx from February 12, 2009 - Rising earth crust made the Mediterranean fall dry , queried on July 20, 2010.