Groundwater Levels of the Main Aquifer and Panke Valley Aquifer 2020

Introduction

Exact knowledge of the current groundwater levels, and hence also of the groundwater resources, is crucial for the State of Berlin, since the water for the public water supply of Berlin (233 million m³ in the year 2019) is provided from groundwater. The groundwater is pumped at nine waterworks, almost entirely within the city area, with the exception of the waterworks Stolpe. It is located on the northern outskirts of the city and pumps water from wells that are located in Brandenburg (approx. 9 % of the total annual pumping volume) (Fig. 1).

Fig. 1: Location of the waterworks which supply Berlin with drinking water, as of May 2020

Additionally, groundwater is pumped from individual wells (like garden wells) and for industrial use, but also in the context of construction sites, groundwater remediation projects and for geothermal usage. In Berlin, numerous cases of soil and groundwater contaminations are known and the information about the hydraulic situation is fundamental for their remediation.

The map of the groundwater levels for the month of May, with the highest groundwater levels throughout the year is published in the Environmental Atlas.

Definitions Regarding Groundwater

Groundwater is underground water (DIN 4049, Part 3, 1994) which coherently fills out cavities in the lithosphere, and 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 sediment particles in the loose sediments. Precipitation water which percolates (infiltrates) into the ground first fills these pores. Only that part of the percolating water which is not bound as adhesive water in the non-water-saturated soil, nor used up by evaporation, can percolate to the phreatic surface and form groundwater. Above the phreatic surface, capillary water is present within the unsaturated soil zone; it can rise to various heights, depending on the type of soil (Fig. 2).

Fig. 2: Types of appearance of subsurface water

Aquifers consist of sands and gravels, and, as incoherent material, make the storage and movement of groundwater possible.

Aquitards consist of clay, silt, peat clay and glacial till and, as cohesive material, hinder water movement.

Aquicludes consist of clay which is virtually impermeable to water.

If the potentiometric surface lies within an aquifer it is known as free or unconfined groundwater. The phreatic and the potentiometric surfaces coincide. In cases of confined groundwater however, an aquifer is covered by an aquitard so that the groundwater cannot rise as high as it might in response to its hydrostatic pressure. Under these conditions, the potentiometric surface is located above the phreatic surface (Fig. 3).

If an aquitard (e.g. a layer of glacial till) is located above a large coherent aquifer (Main aquifer), shallow groundwater may develop in sandy segments above the aquitard and in islands within it, as a result of precipitation. This is unconnected with the main aquifer, and is often called stratum water. If an unsaturated zone is located below the glacial till, it is called floating groundwater (Fig. 3).

Fig. 3: Hydrogeological terms

Typically, groundwater flows with a small gradient into rivers and lakes (“receiving channel”) and infiltrates into them (effluent conditions; Fig. 4a).

Fig. 4a: Groundwater infiltrates into the surface waters (effluent conditions)

In times of flooding, the water surface is higher than the groundwater surface and surface water infiltrates into the groundwater (influent conditions). This is known as bank infiltration (Fig. 4b).

Fig. 4b: Bank-filtered water caused by flooding: Surface water infiltrates into the groundwater (influent conditions)

If pumping of groundwater in the vicinity of surface water bodies is leading to a drop of the phreatic surface drops below the water table of the surface water body, the body of water will also feed bank-filtered water into the groundwater (Fig. 4c). The amount of bank filtration is between 50 and 80 % of the total water obtained in Berlin, depending on the location of the wells.

Fig. 4c: Bank-filtered water caused by discharge of groundwater: due to the drop in the groundwater caused by wells, surface water infiltrates into the groundwater

The groundwater flow velocity in Berlin is approx. 10 to 500 m per year, depending on the hydraulic gradient and the transmissivity of the aquifer. However, in the surrounding flow field of the well galleries, these low-flow velocities can increase significantly.

Morphology, Geology and Hydrogeology

The present surface of Berlin is mainly a result of the Weichselian glaciation, the most recent of the three major quaternary inland glaciations. It has determined the morphology of the city (Fig. 5): the low-lying Warsaw-Berlin glacial spillway and its side valley, the Panke Valley, which consists predominantly of sandy and gravelly sediments; the neighbouring Barnim Plateau to the north; and the Teltow Plateau with the Nauen Plate to the south. Both plateaus are covered in large parts by the thick glacial till and boulder clay of the ground moraines (Fig. 6). The morphological appearance is supplemented by the depression of the Havel chain of lakes (Fig. 5 and Fig. 6). For more information on the geology, see Limberg & Sonntag (2013) and the Geological Outline.

Fig. 5: Morphological map of Berlin

Fig. 6: Geological map of Berlin

The unconsolidated quaternary and tertiary sediments show a thickness of approx. 150 m and the pore volume is often filled with groundwater up to ground level. These layers build the freshwater reservoir that is used for the public water supply for the city state of Berlin. Numerous waterworks (see also Fig. 1) and other pumping stations have lowered the groundwater table in Berlin for more than 100 years in some areas.
The clayey Oligocene layer from the Septarienton Formation (“Rupelton”) is situated in a depth of 150 to 200 m below ground level and is approx. 80 m thick. It serves as a hydraulic barrier against the underlying saltwater aquifer (Fig. 7).

Fig. 7: Schematic hydrogeological cross-section of Berlin, from south to north

Due to the alternation of aquifers (green, blue, brown and yellow in Fig. 7) and aquitards (grey in Fig. 7), the freshwater reservoir in the Berlin area is broken down into four distinguishable hydraulic aquifers (Limberg, Thierbach 2002). The second aquifer is built up predominantly by sediments of the Saalian glaciation and is known as the Main Aquifer, since most of the water for the public water supply is pumped from it. The fifth aquifer is found below the Septarienton Formation and is a saltwater aquifer.

The groundwater conditions of the Main Aquifer (Aquifer 2) are shown in the groundwater contour map in violet; in the Panke Valley Aquifer (Aquifer 1) in the north-western area of the Barnim Plateau, they are shown in blue. The Panke Valley aquifer is situated above the main aquifer and is separated from it by the glacial till of the ground moraine (Fig. 7 and Fig. 8).

Fig. 8: The unconfined Panke Valley Aquifer (Aquifer 1) in the north-western area of the Barnim Plateau is situated above the Main Aquifer (Aquifer 2), which is confined in this area

In the north-western area of the Barnim Plateau, the ground moraines are so thick that no main groundwater aquifer exists, or occurs only in isolated places, with a thickness of a few meters. For those parts of the Berlin city area, no groundwater contours can be shown.