What does groundwater mean



  Groundwater is the water that forms a body of water in cavities under the earth's surface.

Basics and definition

Groundwater is defined according to DIN 4049 as underground water, which fills the cavities of the earth's crust continuously and whose movement is determined exclusively or almost exclusively by gravity and the friction forces triggered by the movement itself.

Groundwater is therefore only subject to the force of gravity and hydrostatic pressure. It moves (flows) mainly horizontally through the cavities of the subsurface.

The underground water of the unsaturated soil zone, which is hygroscopic, bound by surface tension and capillary effects, does not count as groundwater (Soil moisture, Adhesive water). Also that which moves mainly vertically Seepage water in the unsaturated soil zone does not belong to the groundwater.

Real groundwater comes from precipitation, fake groundwater comes from seepage from surface waters (rivers, lakes, etc.).

Those mentioned in the definition Cavities in the earth's crust are, depending on the geological nature of the subsoil: pores (clastic sediments and sedimentary rocks such as sand, gravel, silt), fissures (solid rocks such as granite, quartzite, gneiss, sandstones) or large cavities created by solution ( e.g. limestone). A distinction is made accordingly: Pore ​​groundwater, Cleft groundwater and Karst groundwater.

Groundwater takes part in the water cycle. The residence time ranges from less than a year to many millions of years. Very old groundwaters are also called fossil water referred to, e.g. B. that under the Sahara.

Hydrogeological terms

The rock in which the groundwater resides and flows is that Aquifer (from Latin also: Aquifer). It is bounded at the bottom by a rock that is impermeable to water or can be regarded as impermeable to water, a Groundwater non-conductor (Aquiclud). In the case of a vertical sequence of several aquifers and aquifers, several superimposed Groundwater storeys (Horizons) are available.

The upper limit of the groundwater in an aquifer is that Groundwater surface. If the groundwater surface is exposed, for example in a well or a groundwater measuring point, it is referred to as Groundwater level. The distance between the surface of the terrain and the groundwater surface is the distance from the ground or the groundwater. If the geological unit lying above the aquifer, the Groundwater cover, is not a water-impermeable layer, prevail relaxed conditions in front. If the groundwater cover is impermeable, you can tense conditions exist, which means that the hydraulic potential is higher than the actual groundwater surface (artesian confined groundwater, Artesian well).

Like surface water, groundwater also follows gravity and flows in the direction of the greatest gradient. This can be determined from maps on which standpipe level heights are shown as isohypses (groundwater level plan). The greatest gradient and thus the direction of the groundwater flow or the groundwater flow lines are always at right angles to the groundwater levels. In contrast to surface water, groundwater mostly flows at much lower speeds (difference between filter speed and distance speed). In gravel (grain sizes 2-63 mm) the transit time is between 5-20 m / day (maximum values ​​are 70-100 m / day), in fine-pored sediments such as sand (grain sizes 0.063-2 mm) only about 1 m / day, as capillary and pore suction forces reduce the usable pore volume.

Groundwater flows into you Receiving waters (Channels or depressions) or enters swell to the surface of the earth.

In hydrological and hydrogeological terminology, the confusing term Water vein not used.

Groundwater recharge

Groundwater is created when precipitation seeps away or water in the bank area of ​​surface waters through filtration (Bank filtrate) or other enrichment infiltrated into the subsoil.

In the long-term soil passage, the groundwater is changed by physical, chemical and microbiological processes; a chemical and physical equilibrium is established between the solid and liquid phase of the soil or rock. For example, the uptake of carbon dioxide (from the respiration of soil organisms) and its reaction with the calcite and dolomite create the hardness of the water. If the retention time is long enough, pathogenic microorganisms (bacteria, viruses) can be eliminated to such an extent that they no longer pose a threat. From a water management point of view, these processes are predominantly positive for the quality of the groundwater and are therefore collectively referred to as self-cleaning.

However, when very acidic water seeps away, for example from residual opencast lakes, considerable amounts of aluminum can also be released from crystalline rock. Acidic groundwater can also contain high levels of iron.

Threats to groundwater and groundwater protection

Human activities can have a qualitative and quantitative negative impact on groundwater.

In Germany, quantitative bottlenecks due to excessive groundwater abstraction are only of local importance. In semi-arid or arid regions with little groundwater recharge, excessive abstraction of groundwater leads to a large-scale lowering of the groundwater surface and to corresponding environmental damage. In the event of a gross violation of applicable laws, criminal proceedings are often initiated against so-called environmental offenders.

Dangers to the groundwater quality are, for example, the deposition and soil passage of air pollutants, the excessive application of fertilizers and pesticides by agriculture or highly concentrated pollutant plumes from contaminated sites.

The preventive (curative) and restorative (remedial) groundwater protection is therefore very important in environmental protection. The designation of water protection areas in the catchment area of ​​waterworks is part of the preventive groundwater protection. The remediation of groundwater damage is usually expensive and time-consuming.

literature

  • G. Mattheß & K. Ubell: Textbook of Hydrogeology, Volume 1: General Hydrogeology, Groundwater Balance. 1983, Gebr. Borntraeger, Berlin / Stuttgart, ISBN 3-443-01005-9.
  • Hölting, B. & Coldewey, W. G. (2005): Hydrogeology - Introduction to General and Applied Hydrogeology. - 6th edition, 326 p., 118 figs., 69 tab .; Munich (Elsevier), ISBN 3-8274-1526-8.
  • Kinzelbach, W. & Rausch, R. (1995): Groundwater modeling: an introduction with exercises.- 284 p., 223 fig., 15 tab., 2 diskettes; Berlin, Stuttgart (Borntraeger), ISBN 3-443-01032-6.
  • Gudrun Preuß, Horst Kurt Schminke: Groundwater is alive! Chemistry in our time 38 (5), pp. 340 - 347 (2004), ISSN 0009-2851,ISBN 3-527-28527-X.
  • R. Schleyer & H. Kerndorff: The groundwater quality of West German drinking water resources. 1992, VCH, Weinheim, ISBN 3-527-28527-X.
  • Werner Aeschbach-Hertig: Climate archive in the groundwater. Physics in Our Time 33 (4), 160 - 166 (2002), ISSN 0031-9252.
  • Frank-Dieter Kopinke, Katrin Mackenzie, Robert Köhler, Anett Georgi, Holger Weiß, Ulf Roland: Groundwater purification concepts. Chemie Ingenieur Technik 75 (4), pp. 329 - 339 (2003), ISSN 0009-286x
  • Hardhof groundwater works in Zurich (pictures)
  • Research projects on substance transport in the soil and groundwater at Forschungszentrum Jülich
  • Institute for Groundwater Ecology of the GSF Research Center for Environment and Health, Neuherberg
  • Groundwater protection information service of the State Office for Mining, Energy and Geology, Hanover
  • Salt and groundwater salinization on the Upper Rhine

Category: water