Zmienność wieloletnia i sezonowa występowania minimalnych stanów wód podziemnych na wybranym obszarze nizinnym

Abstract

Seasonal and long-term variability of monthly minimum groundwater levels in selected lowland area.A b s t r a c t. The study undertakes investigations of the seasonal and long-term variability of monthly minimum groundwater levels of unconfined aquifer within selected lowland areas of Wkra and Skrwa Prawa catchments. Data were collected at four locations, monitored within the national groundwater monitoring network run by the Polish Geological Institute – NRI and cover a period of 39 years (1976–2014). Analysis performed within the study includes descriptive statistics, autocorrelation coefficients for delays from 1 to 450 months and the indicator of minimum groundwater level; results are presented using contour graphs. Data demonstrate very strong autocorrelation and internal inertia. A specific long-term irregular periodicity of monthly minimum levels’ fluctuations dominating over seasonal changes has been revealed. The study also shows, that seasonal variability of monthly minimum levels within the catchments corresponds to the continental type of groundwater fluctuations. The highest monthly minimum levels occur in spring (predominantly in April), and the lowest – in autumn (October and November). The analysis indicates no obvious overall change in the structure of seasonal monthly minimum groundwater levels within the investigated period. However, in one location within the Skrwa Prawa drainage basin, the period with the highest monthly minimum levels was brought forward from April to earlier months.