Extremes of groundwater level fl uctuation

Abstract

The fluctuation of groundwater level in the period 1960-2000 for 49 measurement stations located in 19 catchements has been analysed. It was observed that extremes were achieved asynchronously in the period studied. Regional co-variability as regards the frequency of occurrence and the duration of extremes, as well as their multi-annual changes during the period studied has been found, in the following types of catchements: mountain, lowland and Mazurian Lakeland, coastal rivers (Pomeranian Lakeland) and, separately, aquifer horizons related to lake systems. No statistically significant tendencies in the changes of high and low levels of groundwater have been observed. The relationship of groundwater extremes to those of surface water is best defined in the upper segments of the mountain valleys. A statistically significant consistency of direction of groundwater and surface water level movements has been observed in the river valleys of lakeland catchements: the delay is at least one week. The fluctuation of extremes in the multi-annual period is periodic; it is consistent with the occurrence of periods of intense precipitation or its deficit