Groundwater Levels 2002

Introduction

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).

Fig. 1: Phenomenology of Underground Water

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).

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).

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.

Geology and Hydrogeology

The present shape of the earth’s surface in Berlin was predominantly the result of the Vistula Ice Age, the most recent of the three great quaternary inland glaciations. The most important morphological units are the Warsaw-Berlin Glacial Spillway, with predominantly sandy-gravel deposits reaching to great depths, and the Barnim Plateau in the north and the Teltow Plateau with the Nauen Plate in the south, which are covered in large part by the thick glacial till or boulder clay of the ground moraines Fig. 4).

Fig. 4: Geological Outline Map of Berlin

The loose sediments dating from the tertiary and quaternary, and averaging approx. 150 m in thickness, are of special significance for the water supply and for the foundation soil. They form the freshwater stock from which all the drinking water and a large part of the process water of the city is drawn.

The tertiary rupelton clay layer beneath it is about 80 m thick, and constitutes a hydraulic barrier against the deeper saltwater tier (Fig. 5).

Fig. 5: Hydrogeological Cross-Section of Berlin

Due to the alternation of aquifers and aquitards, the freshwater stock in the Berlin area is broken down into four separate hydraulic aquifers (Limberg, Thierbach 2002). The second aquifer, which is largely a Saale-glaciation-era aquifer, is known as the main aquifer, since it supplies the predominant share of the drinking water. The fifth aquifer is already in the saltwater tier.

The groundwater conditions in the main aquifer are shown in the isoline map.