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Berlin Environmental Atlas

02.07 Depth to Groundwater (Edition 1998)

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Groundwater levels in a metropolitan area like Berlin are subject not only to natural factors such as precipitation, evaporation and subterranean outflows, but are also strongly influenced by such human factors as development, sealing of surface, dewatering plants, withdrawals and returns.

The main factors of withdrawal include the groundwater demands of public water suppliers, private water production, and the lowering of groundwater levels at construction sites (cf. Map 02.11). Groundwater recharge is accomplished by precipitation, shore filtration, artificial recharge with surface water and returns of groundwater at construction sites.

In Berlin, there are two groundwater layers. The deeper layer carries salt water and is separated from upper groundwater layer by an 80 m thick layer of clay. The upper layer carries fresh water and has an average thickness of 150 m. It is the source of drinking (potable) and process (non-potable) water supply in Berlin. It consists of a variable combination of permeable and binding loose sediments. Sand and gravel (permeable soils) combine to form the groundwater aquifer, while the clay, silt and mud (binding soils) constitute a groundwater obstructing layer.

The upper surface of the groundwater is dependent on the (usually low grade) gradient of groundwater and the terrain morphology (cf. Fig. 1). The depth to groundwater is defined by calculating the perpendicular distance between the upper edge of the surface, and the upper surface of the groundwater. When the groundwater aquifer is covered by relatively impermeable, binding soil layers (groundwater obstructing layer), the groundwater is unable to rise enough to reach the height of its hydrostatic pressure. It is under these conditions that the groundwater level becomes confined. Only by drilling through the obstructing layer, is the groundwater able to rise on a level with the groundwater pressure area (Fig. 1).

Fig. 1: Depth to Groundwater Shown at Two Different Stages: Free and Confined

The Map of Depth to Groundwater gives an overview of the spatial distribution of areas with the same depth classifications. Areas with a lower depth to groundwater (to about 4 m) are of particular importance. Pollution of soils can quickly lead to deterioration of groundwater in these areas, depending on the nature of the mantle (permeable or non-permeable) above the groundwater. The Map of Depth to Groundwater serves as a basic foundation for the preparation of the Map of Groundwater Vulnerability to Pollution. The spatial overlaying of groundwater depth onto geological characteristics of the covering mantle enables groundwater vulnerability to pollution to be differentiated (cf. Map 02.05).

Knowledge of groundwater depths enables an estimatione of groundwater influence on vegetation. The influence of groundwater on vegetation depends on the root depths of plants and, according to soil type, the capillary climbing capacity of groundwater. The threshold depth at which groundwater can be used by trees is given at 4 m for general Berlin conditions. Vegetation in wetlands depends mostly on groundwater and requires a depth to groundwater of less than 50 cm.

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