Groundwater recharge

As groundwater recharge refers to various operations that the supply of groundwater cause.

Types of groundwater recharge

In groundwater hydrology , there are three types of groundwater recharge:

The formation of new groundwater from precipitation , in which the groundwater is fed through the seepage of precipitation ( seepage water ).
The formation of new groundwater from seepage water , in which the groundwater from rivers or lakes is also fed through the seepage (seeping) of surface water. The feeding waters are separated from the groundwater by a layer of soil through which the water seeps through.

Groundwater recharge as influenza (from surface waters). In the case of influenza, the surface water feeds the aquifer directly . The water does not seep away in the event of influenza, but the groundwater is enriched directly because the surface water lies in the aquifer.

For the formation of new groundwater from precipitation, not only the amount of precipitation is important, but also the point in time. Precipitation in summer, because of the higher evaporation, contributes to a lesser extent to the replenishment of the soil water reservoir and subsequently to the formation of new groundwater than in winter, when only little evaporates. The infiltration of precipitation also depends on the water content of the soil. If the soil is dry and therefore has a low water content, then at the same time it has a low hydraulic conductivity and part of the water will run off above ground. If the soil is already damp when it rains, more water can seep away because the soil then has better hydraulic conductivity. The soil has the greatest infiltration capacity when it is completely saturated with water. In winter, ground frost can severely hinder the ability of a soil to absorb water, so that surface runoff occurs.

Determination of groundwater recharge

Based on the water balance equation, the groundwater recharge results in the long term from the precipitation , the surface runoff and the - difficult to determine - evapotranspiration : ${\ displaystyle G}$ ${\ displaystyle N}$ ${\ displaystyle A_ {o}}$ ${\ displaystyle E}$

{\ displaystyle G = N-A_ {o} -E}

In the short term, changes in the groundwater level and the water content of the soil (change in supply) are also taken into account: ${\ displaystyle S}$

{\ displaystyle G = N-A_ {o} -E + S}

Taking into account the underground discharge and supply of groundwater results in: ${\ displaystyle Q_ {from}}$ ${\ displaystyle Q_ {to}}$

{\ displaystyle G = N-A_ {o} -E + S-Q_ {from} + Q_ {to}}

Due to the stronger evaporation in the summer half of the year, groundwater recharge in Germany and countries with a comparable climate mainly takes place in the winter half of the year. The groundwater level is therefore often lowest at the end of summer and highest in spring.

In addition to the determination of the groundwater recharge using the water balance equation, there are other options: dry weather runoff from rivers (in humid climates), weighable lysimeters (actually infiltration), tracers (chloride, tritium), direct measurements in the subsoil (very complex) and model calculations (e.g. . BAGLUVA for Germany).

literature

Ralf Röger / Peter Speth / Uwe Ulbrich / Guido Böllinger / Andreas Krüger: The effect of anthropogenic climate changes on new groundwater formation and the response options of executive power , nature and law 2001, pp. 121–128, ISSN 0172-1631