Expected Highest Groundwater Level (EHGL) 2018
The EHGL map for the Berlin glacial valley,the Panke valley as well as the Teltow Plateau and the Nauen Plate (2018) covers about three quarters of the area of the State of Berlin. The expected highest groundwater level is represented by lines of equal height in metres above sea level. The difference in height between groundwater isolines is 0.1 m. Thus, the map shows the distribution of the observation well levels in the EHGL case. In the areas of the glacial valley and the Panke valley, the uppermost groundwater is predominantly unconfined, in the area of the plateaus it is confined or covered. It is evident from the course of the contour lines that the Spree and the Havel and their tributaries form the receiving waters for the groundwater close to the surface. The groundwater flow direction lies perpendicular to the contour lines from the higher to the lower level. The EHGL varies between about 58.7 m above sea level in the northern Panke valley on the state border and 30.1 m above sea level where the Lower Havel exists the state area in the southeast. The closer clustering of the contour lines in the Panke valley, the Teltow Plateau and the Nauen Plate shows that the height gradient of the groundwater is larger here than in the glacial valley, as expected. Thus, the course of the EHGL isolines shows a plausible picture for the case that neither groundwater extractions nor artificial groundwater replenishments occur. In particular, this map provides realistic EHGL values in the area of the large cones of depression of the Berlin waterworks, which could hitherto only be estimated very roughly without the groundwater levels calculated using the model (cf. current groundwater levels maps, on which the cones of depression are visible).
On the digital map, the EHGL value for a certain location can be displayed on screen by a mouse click.
In the vicinity of the shores of the Spree, the upper Havel and Tegel Lake, there are lateral riparian strips (see also Methodology). These areas are marked with different colours according to the EHGL value and can also be queried with a mouse click.
Thus, the user receives an EHGL value for his respective question in a simple manner.
The following should be noted:
The map value applies to the groundwater level of the uppermost aquifer. In the area of the glacial and Panke valley, the uppermost aquifer is predominantly unconfined. Thus, the map value generally specifies the height of the groundwater surface here, which is for instance relevant for dimensioning waterproofing for buildings.
However, in some places – more often in the plateau areas – overlying layers with low water conductivity, such as boulder clay and boulder marl, clay, silt and organic soils, cause the groundwater to be confined (e.g. in the area of a boulder marl “island” in Charlottenburg designated on the map). In these cases, the map does not specify the height of the groundwater surface, but rather that of the piezometric surface of the confined groundwater.
In these cases, shallow groundwater (in the sense of the groundwater definition of DIN 4049) may form – possibly only temporarily – above the confining layers. This so-called stratum water is also water under pressure in a constructional sense and must be taken into account in corresponding contexts.
Due to the scale and the rather heterogeneous individual sedimentation conditions, the two possible deviations from the usual hydrogeological configuration that were mentioned are not, or not completely, representable in the Geological Outline provided. However, they can be recognized in the framework of a subsoil expertise, which is principally required for construction activity. In addition, in concrete cases the strata-log sheets from the database of the State Geological Service can be accessed on the Internet [only in German].
It should also be noted that the EHGL may lie above ground level. In this case, the formation of groundwater ponds cannot be excluded.
Near surface waters, in addition to high groundwater levels, short-term local flooding may occur, which cannot be inferred from the EHGL map. Information in this regard is available under Hochwasser [floods, only in German].
The current groundwater level can be accessed for the month of May on the Internet.
Should the current groundwater level at a certain location lie only slightly below the value of the EHGL map, or even above, which is very unlikely in the glacial valley but cannot be entirely excluded, this may be due to the different statistical basis of the maps. In these cases, more detailed information may be requested from the Berlin Groundwater Service.
In the Panke valley, in particular in its northern part, the groundwater measuring points are sometimes relatively far apart in view of the heterogeneity of the aquifer and the mostly large natural groundwater gradient. As a result, the EHGL map is more fraught with uncertainty here than in the area of the glacial valley. This also applies to areas in the immediate vicinity of surface waters (the Panke and its small tributaries). While this was accounted for by the abovementioned increments, localised deviations of the map value from an actually occurring highest groundwater level cannot be entirely excluded. If new investigations (drillings, groundwater level measurements) yield results in such areas that clearly contradict the EHGL value of the map (current groundwater level above the map value or within metres of it), the EHGL should be locally modified by an expert. In such cases, the Berlin Groundwater Service kindly requests to be notified.
The hydrogeological conditions in the area of the Teltow Plateau and the Nauen Plate are considerably more complicated than those in the glacial valley and the Panke valley. Therefore, the mathematical EHGL estimate, applying the method described above is fraught with somewhat higher uncertainties. To be on the safe side, the map was thus developed to indicate EHGL values that are rather on the high side compared to those that may actually occur. It was deemed a reasonable approach in construction planning. It should also be noted here that the probability of locally-occurring stratum water atop confined layers at heights above the indicated EHGL values is greater than in the glacial valley. Should you detect contradictions to the map in the framework of future investigations (e.g. a subsoil expertise), please also inform the above-mentioned authority.It is envisaged that the map will continue to be checked and possibly modified based on the results of the Berlin Groundwater Service and new scientific findings. The intent is to recognize and take into account possible changes in the hydrological conditions that cannot currently be foreseen (e.g. due to general changes in the climate) as soon as possible.