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Hydrological conseąuences of human action..

from coal exploitation near a region of smali resistance to anthropopressure (Wilgat 1973, 1975; Wilgat and Fijałkowski 1974).

The coal deposits occur in a Carboniferous formation which is covered by Jurassic and Cretaceous carbonate sediments of varying resistance and plasti-city. Hydrological studies have shown 4 water-bearing horizons associated with formations of: a) the Quaternary and Upper Cretaceous, b) the Lower Cretaceous (Albium) and Upper Jurassic, c) the Jurassic, and d) the Carboniferous periods. Besides the first horizon, waters of the others are confined. Since the beginning of coal-mine building, waters of the Jurassic and Carboniferous formations have been pumped intensively to protect it from flooding. As a result, separate cones of depression transgressing the central coal region have been formed in both formations. A pressure decrease in Jurassic and Carboniferous waters changing the conditions of their circulation and feeding. Do these changes effect the surface water relationships? This problem is approached from two points of view. Some are of the opinion that poorly-permeable Cretaceous rocks constitute a good barrier for waters of the Quaternary-Cretaceous upper water horizon, which should protect the hydro-graphic conditions of the Lakę Region against the conseąuences of pumping waters from Jurassic and Carboniferous beds. Others think that the inten-sification of water percolation from the upper horizon will be possible due to the opening of fissures during rock subsidence. At present there is not enough evidence to confirm the reality of such threats.

As a result of mining work in the Lublin Coal Basin, there is land subsidence caused by decreasing confined waters of the Jurassic and Carboniferous formation and coal exploitation by the Tali’ method. At present surface subsidence exceeding 0.2 m has been found in an area of about 20 km² in a mining field in the neighbourhood of the shafts, largely over the coal deposits exploited sińce 1982. Coal beds 2.5-3.3 m thick are mined at a depth of 815-920 m. Local depressions of the land surface in the exploitation region near Bogdanka and Nadrybie have already exceeded 1.5 m. They will deepen and widen with developing coal exploitation.

Depressions up to 2.8 m are expected to have been formed by 2010 after the exploitation of two coal beds. In the further futurę land deformations will be still bigger. Land subsidence results in changes of water occurrence and circulation, largely in the first horizon, but slow changes of deeper waters are not excluded.

Land deformations in areas of shallow groundwater lead to the formation of depressions filled with water or excessively moistured. From the natural point of view it would be most advisable to leave such depressions and not attempt to dry them. However, naturalists’suggestions are difficult to realize, largely because of private ownership and agricultural utilization of the land. Thus earlier drainage works are planned consisting in regulating and deepening the Świnka river channel and other rivers even by 5 m (Drainage study... 1986). This would cause a considerable increase of the draining role of rivers, followed by a decrease of the undergroud water table, local ground