Groundwater level
1. Groundwater; 2. waterproof layers;
3. infiltration zones; 4. artesian well ;
5. water table; 6. Sub-Artesian Well; 7. Source
The groundwater level is the equalization area between the pressure of the groundwater and the pressure of the atmosphere.
In construction projects, the highest groundwater level (HGW) , which is also referred to as the design groundwater level, is often relevant .
Water table and earth surface
The groundwater level roughly follows the course of the earth's surface above it and rises or falls after heavy rainfall or in dry periods. The capillary fringe of the groundwater, which is important for plant growth, is located above the groundwater level.
Unless the upper boundary of an aquifer is limited by impermeable layers, the conditions are unrestrained . If the upper limit is a groundwater non-conductor , tense conditions can exist. This means that the so-called hydraulic potential is higher than the actual groundwater surface (artesian tension, artesian well ).
Drains
Naturally, effluent conditions prevail because the groundwater level sinks near the river and groundwater flows from the aquifer into the receiving water. Due to special conditions (flood, bank filtration ), the water level of an open body of water can be higher than the hydraulic potential of the groundwater. Then one speaks of influential conditions (water flows into the aquifer).
When the groundwater level reaches the surface of the earth, springs or groundwater banks develop there ( oases in arid areas ). Special cases are groundwater outflows in the sea, which, however, always occur near the coast.
Measurement
The height of the groundwater level is measured in groundwater measuring points or wells with a well whistle or a plumb line as a tapping dimension between the upper edge of the pipe and the groundwater level (more precisely: the groundwater pressure surface ). The height calculated from this is given in relation to sea level or in meters below ground level ( floor distance ).
change
Subsidence
Pumping the groundwater causes the groundwater level to drop, and an underground subsurface funnel is formed . This happens when drinking water is obtained (see the current development in Vittel as an example ) or to enable opencast mining .
The lowering of the groundwater level can have far-reaching consequences for vegetation . The capillary fringe shifts to greater depths. Roots of trees and crops lose touch with the groundwater, forest dieback and large-scale drought damage can occur.
rise
A rise in the groundwater level can be caused by reduced groundwater extraction, higher groundwater recharge , rising surface water levels or through artificial groundwater recharge or rewetting .
Raising the groundwater level can also have significant negative consequences, such as forest dieback due to the waterlogging (sometimes also salinization ) of the root area or moisture damage in structures. To prevent this, new buildings are nowadays usually built in a water-impermeable tub made of waterproof concrete or concrete with additional sealing materials, also known as a white tub .
Individual evidence
- ^ Artesian confined groundwater. State Office for Mining, Energy and Geology , accessed on April 19, 2020 .