Groundwater-related subsidence

Under the lowering of ground water is defined as a desired or undesired lowering of the groundwater table. The opposite is a groundwater recharge.

The lowering of ground water may have natural causes, if the water-bearing layers are changed, for example by earthquakes. But man is responsible for most groundwater level changes. If more water is taken approximately through wells, as the flow of groundwater supplies, groundwater lowering is inevitable.

There is a fundamental distinction between closed and open groundwater lowering. In the open ground-water lowering the water is visible in the reduction. In the closed groundwater lowering, however, the reduction takes place in a closed terrestrial body, ie you can not see the water. The lowering of ground water, thus lowering the size of the funnel, measuring, by means well, such as "well -points" ( needle wells), are determined or calculated (eg after LUCKNER ).

• 2.1 Regulatory ( straightening ) of flowing waters
• 2.2 Public Works
• 2.3 of drinking water in wells

• 3.1 translations
• 3.2 plants

Wanted groundwater lowering

Open-cast mining

When lignite mining a lowering of ground water around the pit mining is necessary because this would otherwise fill with water. The ground water must be lowered to below the degraded coal to (eg conveyor bridge ) to ensure the stability of the thousands of tons of heavy large appliances. The depth of the drop is in Lusatian opencast mines between 50 and 100 meters below ground. Due to this depth and the slightly permeable sand layers it also acts for miles in the surrounding area of the open pit. Increasingly built the mining operation Vattenfall underground cut-off walls in order to limit this effect by a vertical water-impermeable layer is introduced into the ground using special equipment. (Already built: opencast Cottbus -Nord to the north, mining Jaenschwalde westward planned:. . Welzow -south to south, mining Reichwalde ) Where this has not been done, it is required as a protective measure of land owners, water works or environmental organizations. ( Mining Nochten north, mining Jaenschwalde to the north and west)

The Garzweiler mine has probably meant that in the Happelter heath near Brüggen - it lies in the Schwalm -Nette - groundwater has fallen by 75 centimeters. Rhine Brown examines the phenomenon with deep drilling to 250 meters.

"Experts suspect that a Braunkohleflöz in about 250 meters below the Happelter Heath has a gap. Among them is water that normally builds up a pressure upwards. This water column also supports the wetlands of the Schwalm. By Sümpfungen open pit, the pressure reverses, in the depth of water flows from. According to the principle of communicating pipes is reduced where there is a connection to higher layers, the water level. Materialize the assumption Rhine Brown Sümpfungswasser will have to infiltrate from the open pit on the Happel Exploder Heath to restore the natural water level and support. "

Construction work

In order to have a dry pit, a lowering of ground water is at excavation sites, which range into the groundwater is necessary. This can be achieved even with smaller pits that range in a non -yielding groundwater flow, with a sump pump in the pit (open drainage ).

For larger pits that are located in an abundant flow of groundwater, a large-scale groundwater lowering is necessary, which is carried out through wells around the pit. This lowering of ground water in pits is called a closed drainage. It is generally required if the highest groundwater level is more than 50 cm above the bottom of the pit. You must be operated until the sealing work on the building are effective and the finished building parts are no longer vulnerable by buoyancy.

An alternative to lowering of ground water is the closed nature of the excavation through slit or sheet piling. Workers should include up to a water-impermeable layer, otherwise there is the danger of a basic hydraulic fracture.

In tunnel construction work in the flow of groundwater is usually not lowered today, but the groundwater flow diverted through freezing technology.

Agriculture

The lowering of the groundwater table is used to improve the workability of the soil or reclamation of arable land by measures of melioration. The water table is lowered permanently by a network of drainage pipes and ditches. To ensure the security of agricultural yields, an artificial irrigation may be required. Well-known examples of such amelioration measures are the Rhinluch and the Oder.

Unwanted groundwater lowering

Regulation ( straightening ) of flowing waters

River regulation and channelization are interventions that the most dramatic exercise certainly have an impact on the groundwater level. From an ecological perspective, such measures are often serious impacts on the environment is (destruction of habitats such as wet meadows ).

Public Works

Improper planning or execution, it may happen that, for example as a result of line-like civil engineering work, the groundwater flow and thus the water table is changed. This does not always have a reduction result, but can also lead to the exact opposite to the groundwater elevation. Such construction work, for example, Tunnels, sewer lines, or other large underground pipeline routes. There are two main causes for the change in groundwater flow: on the one hand, water-impermeable layers can be penetrated and thus is not a separation of the different groundwater storeys longer available. On the other hand, the preferred groundwater along the line in the sand or gravel bed flow over large distances, thereby changing the water table.

Drinking water in wells

The water that is taken from a well must continue to flow, so that the well does not run dry. This is achieved by the fact that a local groundwater gradient forms around the well shaft, the reduction funnel. The greater the water is drawn, the lower falls of the water table in the well itself is more water removed, as can flow through the flow of groundwater, the water table is falling steadily on.

Effects of groundwater lowering

Especially by large-scale and long-lasting lowering of groundwater may occur in severe damage to the lowering funnel. In neighboring towns damage can occur to buildings.

Subsidence

If the groundwater is lowered, fall soil layers dry, lose buoyancy caused by the water and the soil is more compressed. Technically speaking, the groundwater level lowering increases the buoyancy- free area of the soil and increases the implementation causing effective stresses in the soil skeleton below the original water table. In a groundwater lowering it can also come to flush of fine soil particles from the grain structure of the soil, the suffosion. The coarser grains slump by it. In both cases, depending on soil conditions, a reduction a and these effects may be small scale differently. This fractures can occur in the soil, rich in part to the earth's surface. For buildings uneven settlement amounts can lead to subsidence damage, which usually show up as cracks in the masonry.

Plant

The lowering of ground water can have far- reaching consequences for vegetation. The important for plant capillary fringe shifts to greater depths. Trees and crops lose the natural ground water, deforestation and large-scale drought damage may occur. When meliorative application of groundwater lowering it comes to succession.