ASSESSMENT OF THE INFLUENCE OF DISCREPANCY OF THE LOCATION OF GROUNDWATER AND SURFACE WATERSHEDS ON THE QUANTITY OF CALCULATED RENEWABLE RESOURCES, EXEMPLIFIED BY THE P-IX BALANCE REGION IN THE WARTA WATER REGION

Abstract

The article presents the results of research on the renewal of a hydrogeological system that is characterized by a significant discrepancy of the location of groundwater and surface watersheds. The area of the hydrological and hydrogeological studies is part of the P-IX balance region (Warta River from the Prosna to the Mosiński Canal) located south of the Warta River. The evaluation of groundwater renewability has been made using a hydrological method and mathematical modelling. When using the hydrological method, which is a commonly used control method for water balance calculations, it is assumed that the surface and groundwater watersheds are identical. Comparison of the results of water balance calculations obtained with both methods required the assessment of the compatibility of the groundwater catchment and morphological boundaries. This was done by calculating the difference between the quantities of renewable resources determined by two variants of the hydrological method. In the first (standard) variant, renewable resources were determined based on data from water-gauge and hydrometric profiles closing the catchments of the Warta tributaries draining the analyzed water-management regions. In the second (extended) method, they were determined based on data from water gauges controlling the Warta sub-basin. Enlargement of the balanced unit as far as the boundaries of the Warta basin was consistent with the principle that the reliability of calculations of groundwater resources increases proportionally to the analyzed catchment area and the significance of its drainage zone in the regional groundwater circulation (Toth, 1963). The quantity of renewable resources determined by the standard and extended variants of the hydrological method amounted to 107,100 m3/day and 184,000 m3/day, respectively. The difference is 72% of the value determined using the standard method. The article also provides an analysis of the spatial and temporal variability of the nature of the hydraulic relationship between surface water and groundwater, and the influence of this variability on the reliability of water balance calculations, based on stationary observations of surface water flow.