Changes in water conditions in the Racławka and Szklarka drainage basins in 1933-1998

Autor omawia zmiany, jakim uległy stosunki wodne w wyżynnej zlewni w południowej części Wyżyny Krakowskiej. Przedstawia zestawienie kilku serii pomiarów dokonanych w tej zlewni w okresie ostatnich 35 lat, mających na celu ustalenie położenia zwierciadła wód podziemnych i wydajności źródeł, analizując różnice pomiędzy nimi, jak również przedstawia to zjawisko w przestrzeni i wyjaśnia jego przyczyny. Na przykładach ukazuje ścisłe powiązania między systemem krążenia wód podziemnych a zasilanym przez nie systemem wód powierzchniowych oraz zmiany obiegu wody w zlewni.

The author discusses changes in water conditions that took place in the drainage basins Racławka and Szklarka (62,7 km2) in 1933-1998. These drainage basins are representative of the areas built of rocks which are strongly fractured and subjected to karstification. A primary goal of the work is to examine the depth of ground water table, determine discharge of springs, and verify stream lengths. Then, the obtained results are compared with the records registered in documentary materials originating mainly from the 1960s. Moreover, determination of a direction of changes in water conditions, their intensity as well as explanation of their reasons have been attempted. In order to determine the depth of ground water table a.s.l., water level in wells (hydrogeologic boreholes), which are sparse especially on the summit area, has been measured twice. What is more, to find the influence of the changing level of ground water table on functioning of a surface water system, discharges of 40 springs have been gauged twice. The performed study allow to state that the ground water table has been lowered in three regions of the drainage basins due to industrial activity of man (mining, exploitation of rock resources, exploitation of ground water) and due to a natural factor which was a water deficit occurring in 1978-1993. This lowering of the ground water table altered the natural direction of water outflow and caused destabilisation of surface runoff regime. Moreover, the discussed water table lowering resulted in weakening of ground water fluxes that, in turn, led to disappearance of several springs recharging permanent streams. Drying of streams in river head areas as well as other springs discharging to the rivers brought about shortening of hydrographic network by 3.1 km, and a decrease in stream runoff as well as lack of rapid floods in 1979-1997. Just heavy precipitation in 1997 and 1998 caused floods again.