Reference statistics for the structure of measurement series of groundwater levels (Wielkopolska Lowland,western Poland)

Abstract

This study analyses the statistical and dynamic properties of time series of mean annual groundwater levels for the years 1961–2000, with the purpose of preparing reference statistics for the study period. Data came from 62 measurement stations of the groundwater observation network of the Institute of Meteorology and Water Management—the National Research Institute IMGW-PIB—located across the Wielkopolska Lowland (western Poland). Station-grouping criteria were as follows: the availability of a 40-year measurement series, spatial location, as well as separation of the aquifer from the surface. For estimating the time series structure of groundwater levels, the following stationarity tests were conducted: the augmented Dickey-Fuller (ADF) test and the Kwiatkowski-Phillips-Schmidt-Shin (KPSS) test, with positive results in 44% of the stations, the majority comprising a group that represents confined aquifers. Their non-stationarity was attributed to the presence of a long-term stochastic trend. In the majority of cases the groundwater-level frequency distributions were within the group of platykurtic distributions, right asymmetrical. In the period studied, 62% of the series showed a downward tendency of groundwater levels, including 45% for which the trend was statistically significant; a rising trend was only statistically significant in half of the series. The masking effect of anthropogenic factors was indicated as a fundamental element interfering with the statistical properties of the groundwater observation series in the period 1961–2000 in the Wielkopolska Lowland. This information can be of use for the management and protection of water resources and in prognostic studies on modifying aquiferous systems with recorded water deficits.

Editor D. Koutsoyiannis; Associate editor T. Ouarda