Surface water

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The Aubach (Wiehl) in Reichshof, as an example of a flowing surface water.

Surface waters , also called surface waters or open waters depending on the context, are inland waters with the exception of groundwater . They include both still waters (also called standing or standing waters) as well as flowing waters . As part of the global water cycle , surface waters are in constant exchange and connection with underground groundwater as well as with the oceans . Their exact delimitation and definition is therefore fuzzy and dependent on the context, whereby scientific, hydrological , hydrogeological and limnological definitions and legal terms do not always match. Cases of doubt concern some forms of karst waters , wetlands or estuaries (river mouths) and marine , shallow water areas near the coast.

Legal Regulations

The status of a “body of water” is legally linked to various obligations and is therefore defined in national and international regulations.

  • Water Framework Directive : In the Water Framework Directive, "surface waters" are inland waters with the exception of groundwater, as well as transitional waters and coastal waters (transitional waters are waters near estuaries that have a certain salinity but are mainly influenced by freshwater currents). According to the Water Framework Directive, coastal waters are therefore surface waters.
  • Water Management Act : In the German Water Management Act, "surface waters" are water that is constantly or temporarily flowing in beds or standing or flowing wildly from springs. Together with the coastal waters and the groundwater, they form the body of water as a whole. To protect surface waters, the Surface Waters Ordinance was issued in 2016 , the definition of which follows the Water Framework Directive. Surface waters are the surface waters including transitional waters plus coastal waters (§ 2: Definitions).
  • The Swiss Water Protection Act defines surface water: water bed with bed and embankment as well as animal and plant colonization , in contrast to this, underground water is groundwater.

Comparable regulations, but with different detailed provisions, can be found in most national legal systems.

It should be noted that individual bodies of water legally defined as surface water or surface water (in connection with the Water Framework Directive we speak of water bodies ) retain this status even if they are piped. A piped flowing water , or a piped section of such, remains legally a surface water. The sewer network ( sewer system ) serving to dispose of wastewater is not a body of water in the legal sense.

Scientific definitions

The term surface water is often used in scientific works without being as sharply defined as in the legal context. Limnologists and hydrologists define it primarily as negative in relation to groundwater. Groundwater is "underground water that is drip-free (not capillary bound), forms a coherent body of water and whose movement is determined by gravity and frictional forces" or "underground water that continuously fills the cavities of the earth's crust and whose movement is exclusively or almost exclusively the force of gravity and the friction forces triggered by the movement itself are determined “The terms underground water and groundwater are (largely) congruent. Accordingly, surface or open waters are all bodies of water that do not count as groundwater. For practical reasons and for reasons of the history of science, inland waters and marine waters are almost always treated separately. Although there are both groundwater and water-filled cavities such as marine caves under the seabed, the terms open water or surface water are not common in connection with marine waters (both above and below ground there are also cases of doubt here that can be precisely defined withdraw like e.g. the anchialine waters).

Above-ground waters and groundwater as underground waters are related in the context of the water cycle. Groundwater emerges in springs and forms surface water (the springs are usually included here). The bottom of surface waters mostly depends on the height of the groundwater level, so that the watercourse forms the groundwater receiving water, but it can also be in the unsaturated zone, whereby the waterway gives off water to the groundwater via seepage. Since groundwater is the habitat of its own groundwater fauna, limnologists differentiate both areas, in addition to the hydrological definition, partly also according to the community.

In case of doubt karst waters

In karst areas , the solubility of the rocks in water creates extensive subterranean cavity systems, some of which are also accessible to humans as caves . Extensive caves are not completely filled with water, but form extensive air-filled cavity systems (the so-called vadose zone ). The permanently water-filled cave systems are counted as groundwater. Cave lakes and cave rivers that are in contact with the air, especially those cave rivers that penetrate from the surface into karst cavities and only flow a certain distance underground, have hydrological and ecological properties that are more similar to those of surface waters and, in case of doubt, are more likely to be combined with them classified.

Position in the water cycle

The volume of water in inland surface waters is relatively small compared to the other reservoirs in the system. Together, flowing and standing waters have a water volume of around 178,000 to 360,000 cubic kilometers. This is only a few percent in relation to groundwater, the amount of water fixed in the ice or the content of the oceans. The supply of fresh water in Germany is estimated at 188 billion cubic meters, 49 billion of which is groundwater. Globally, around 4.6 million square kilometers are covered by surface water, which is slightly more than three percent of the land surface.

Individual evidence

  1. ↑ Directive 2000/60 / EC of the European Parliament and of the Council of 23 October 2000 on the creation of a framework for Community measures in the field of water policy , Article 2: Definitions.
  2. ↑ Law on the regulation of the water supply (Water Management Act - WHG) , § 3: Definitions
  3. ↑ Federal Act on the Protection of Waters (Water Protection Act, GSchG) , Article 4: Terms.
  4. ↑ Wilfried Schönborn, Ute Risse-Buhl: Textbook of Limnology. 2nd edition 2013. Schweizerbart Verlag, Stuttgart, ISBN 978-3-510-65275-4 , on page 17.
  5. ↑ DIN 4049, Part 1: Basic hydrology terms. Edition 12.1992
  6. ↑ Susanne I. Schmidt & Hans Jürgen Hahn (2012): What is groundwater and what does this mean to fauna? - An opinion. Limnologica 42: 1-6. doi: 10.1016 / j.limno.2011.08.002
  7. ↑ Groundwater in Karst. in John Gunn (editor): Encyclopedia of Caves and Karst Science. Fitzroy Dearborn, New York and London, 2004. ISBN 1-57958-399-7 .
  8. ^ David C Culver, Tanja Pipa: Subterranean Ecosystems. In Simon A. Levin (editor): Encyclopedia of Biodiversity, Volume 7, 2nd edition 2013 ISBN 978-0-12-384719-5
  9. ↑ Chris Groves, Joe Meiman: Flooding. David C. Culver, William B. White: Encyclopedia of Caves. Elsevier, Amsterdam etc. 2005. ISBN 0-12-198651-9
  10. ↑ Kevin E. Trenberth, Lesley Smith, Taotao Qian, Aiguo Dai, John Fasullo (2007): Estimates of the Global Water Budget and Its Annual Cycle Using Observational and Model Data. Journal of Hydrometerology 8: 758-769. doi: 10.1175 / JHM600.1 (open access)
  11. ^ Moustafa C. Chahine (1992): The hydrological cycle and its influence on climate. Nature 359: 373-380.
  12. ↑ Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (publisher): Groundwater in Germany. Environmental Policy Series, August 2008.
  13. ↑ JA Downing, YT Prairie, JJ Cole, CM Duarte, LJ Tranvik, RG Striegl, WH McDowell, P. Kortelainen, NF Caraco, JM Melack, JJ Middelburg (2006): The global abundance and size distribution of lakes, ponds, and impoundments. Limnology and Oceanography 51 (5): 2388-2397. doi: 10.4319 / lo.2006.51.5.2388 (open access).