Of the total of 105 groundwater measuring points on which the map of the expected highest groundwater level is based, 67 still existed in 2014. That is, for 38 measuring points, no or no sufficient groundwater level data are available for calculating the required MHGL for the period 2002 to 2014, but for the period 1990 until 2001 data are available, at least with some restrictions (e.g. lower measuring frequency). In order to obtain a grid of sampling points as dense as the one for the EHGL map, the MHGLs of these 38 measuring points were estimated for the period 2002 to 2014. By means of correlation analyses between different quantities obtained from the hydrographs, a significant relationship between the EMHGL for the period 2002 to 2014 (EMHGL 02-14), the mean value of the measurements between 1990 and 2001 (MGL
90-01) and the standard deviation of the measurements between 1990 and 2001 (s 90-01) was found.
With an increment of 20 cm selected to account for the uncertainties inherent in this procedure, the following formula for calculating the desired EMHGL 02-14 is obtained:
EMHGL 02-14 = 2.43 * s 90-01 + 0.13 + MGL 90-01
EMHGL 02-14 :desired expected mean highest groundwater level
s 90-01 :standard deviation of the measurements between 1990 and 2001
MGL 90-01 :mean value of the measurements between 1990 and 2001
According to this method, the MHGL values for the 38 groundwater measuring points mentioned above were estimated by calculation. As desired, the MHGL values for 105 measuring points are thus available.
Based on these 105 MHGL values and on another 15 sampling points that were specified at the border to the EMHGL map for the glacial valley in order to ensure consistent continuity with that map, the distribution of the EMHGL was calculated (without taking the surface waters into account) by means of the software system SURFER and was represented in the form of EMHGL isolines. The calculation method is the same as the one used for the current map ‘Groundwater Levels’ (Hannappel, Hörmann & Limberg 2007).