Capillary water

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(4) capillary water

The capillary water is held in the capillaries of the soil (pore diameter up to a maximum of 0.2 µm) through adhesion and cohesion (corresponds to suction tension ).

The capillary water of the upper soil (resulting from precipitation) is called "hanging" and the capillary water of the groundwater is called "sessile". The height of the rising groundwater due to capillary forces is called the capillary fringe ; the area above the groundwater surface that is saturated by capillary water is called the capillary space ; its upper limit is the apparent groundwater surface .

Since the pores of the soil have different shapes and diameters, capillary water rises above the capillary space, but this no longer leads to saturation of all cavities. The smaller the pore diameter, the higher the capillary rise . Clay soils show an unsaturated capillary rise of up to 3 m, sands up to a few dm. Gravels do not have a capillary border or a capillary border of only a few centimeters.

Capillary water ascent from the groundwater can contribute to the water supply of plants. Depending on the type of soil, groundwater can still supply sufficient amounts of water approx. At lower groundwater levels, capillary rise usually no longer contributes significantly to the supply of plants. Plant roots of most plants are not able to survive for long periods in the water-saturated soil without oxygen. Adapted plants such as willow or alder are an exception .