Water table

The water table is the balance between the surface pressure of the ground water and the pressure of the atmosphere.

Groundwater levels and surface

The water table approximately follows the curve of the earth's surface and above it rises or falls after heavy rains or during dry periods. Above the water table is the important for plant growth capillary fringe of the groundwater.

If the upper boundary of an aquifer is not confined by impermeable layers prevail unconfined. If the upper limit of a groundwater dielectrics, strained relationships may exist. This means that the so-called hydraulic potential is higher than the actual groundwater surface ( artesian voltage, artesian wells).

Outflows

Naturally, prevail effluente conditions because the water table drops near the river and groundwater flows out of the aquifer in the drainage ditch. Due to special circumstances ( flood, bank filtration ), the water level of an open body of water may be higher than the hydraulic potential of ground water. Then one speaks of influenten conditions ( water flows into the aquifer into ).

When the water table reaches the earth's surface sources or Grundwasserblänken built there ( in arid areas oasis ). Special cases are groundwater withdrawals in the sea, which, however, always occur near the coast.

Measurement

The height of the water table is in groundwater monitoring wells or wells with a well pipe or a water level gauge as Abstichmaß between the top of the pipe and the water table (more precisely, the piezometric surface ) were measured. The resulting calculated amount is given in relation to NN or in meters below ground level ( depth to groundwater ).

Reduction

Through Groundwater pumping it comes to lowering of the water table, it forms an underground lowering funnel. This is done in the drinking water or surface mining permit to.

The lowering of ground water can have far- reaching consequences for vegetation. The capillary fringe is shifted to greater depths. Roots of trees and crops lose the connection to the groundwater, deforestation and large-scale drought damage may occur.

Increase

A groundwater level rise can be caused by decreased groundwater supply, higher groundwater recharge, rising surface water levels or by artificial groundwater recharge or rewetting.

The raising of the water table may have significant negative consequences, such as forest dieback due to the waterlogging of the root zone or moisture damage in buildings. To prevent this, new buildings are now mostly built in a waterproof tray made of waterproof concrete or concrete with additional sealing materials.

• Hydrogeology
• Water production