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Berlin Environmental Atlas

02.12 Groundwater Levels (Edition 2002)

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Overview

The exact knowledge of the current ground-water levels, and hence also of groundwater stocks, is imperative for the State of Berlin, since 100% of the drinking-water supply (approx. 220 million m³ in 2001) is obtained from groundwater. This groundwater is pumped at nine waterworks, almost entirely from the city’s own area. Only the Stolpe Waterworks on the northern outskirts obtain water from Brandenburg, but also supply Berlin.
Moreover, groundwater reserves are tapped for in-house and industrial use, as well as for major construction projects and heating-related purposes. Numerous instances of soil and groundwater contamination are known in Berlin, which can only be rehabilitated on the basis of exact knowledge of groundwater conditions.

Definitions Regarding Groundwater

Groundwater is underground water (DIN 4049, Part 3, 1994) which coherently fills out the cavities in the lithosphere, the movement of which is caused exclusively by gravity. In Berlin, as in the entire North German Plain, the cavities are the pores between the rock particles in the loose sediments. Precipitation water which seeps (infiltrates) into the ground first of fills out these pores. Only that part of the infiltrating water which is not bound as adhesive water in the non-water-saturated soil, or used up by evaporation (evaporating transpiration), can seep to the phreatic surface and form groundwater (Fig. 1).

Figure 1
Fig. 1: Phenomenology of Underground Water (from Hölting 1996)

Aquifers are made of sands and gravels, and, as incoherent material, make the storage and movement of groundwater possible.
Aquitards consist of clay, silt, gyttja and glacial till and, as cohesive soils, hinder water movement.
Aquicludes are made of clay which is virtually impermeable to water.

Groundwater the phreatic surface of which lies within an aquifer, i.e., whose phreatic and piezometric surfaces coincide, is known as free or unconfined groundwater. If however, an aquifer is covered by an aquitard, the groundwater cannot rise as high as it might in response to its hydrostatic pressure. Under these conditions, the piezometric surface is above the phreatic surface of the groundwater, which is then referred to as confined (Fig. 2).
If an aquitard is located over a large coherent aquifer, such as a glacial till, perched groundwater may develop temporarily in sandy segments (Fig. 2).

Figure 2
Fig. 2: Hydrogeological Terms

As a rule, groundwater flows at a low incline into the rivers and lakes (receiving bodies of water) and infiltrates into them (effluent conditions; Fig. 3a). If in the neighborhood of these surface waters groundwater is discharged, e.g. through wells, so that the phreatic surface drops below the level of that body of water, the surface water infiltrates into the groundwater as bank-filtered water. This is known as an influent condition: (Fig. 3b).

Figure 3
Fig. 3: Infiltration: a) Effluent condition, b) Influent condition

The groundwater velocity of flow in Berlin is about 10 to 500 m p/a, depending on groundwater incline descent and the permeability of the aquifer. However, near well facilities, these low flow velocities can increase significantly.

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