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Anthropogenic changes of water conditions..

maps of 1955 and 1992, occurred in an area of about 68 km² i.e. V₃ of its surface. In the city centre that lowering was about 5 m, and in the neigh-bourhood of the water intakes built after 1960 CSławinek’, ’Prawiedniki’) it exceeded 8 m. Water table lowering in the river valleys disturbed the hydraulic eąuilibrium between underground and top waters. In the areas of lowered underground water table waterlogging and springs of the Czechowka and Czemiejowka river valleys disappeared. Conditions for top waters to escape underground thus emerged.

QUANTITATIVE EVALUATION OF WATER CIRCULATION CHANGES

The evaluation of changes in river flows was madę on the basis of hydrometrie data for the years 1951—1991. The river flows in the Lublin region are checked by two water-gauge stations of the Institute of Meteorology and Water Management (IMiGW) on the Bystrzyca river (Fig. 1); a) in Lublin above dense municipal construction; b) in Sobianowice below the city. In the years 1978—1989, at the commission of the Directorate of Municipal Investments, IMiGW monitored Czerniejowka river flows in Wólka Abra-mowicka and Gluszczyzna. In the years 1981—1991 the Ciemięga river flows were registered in Pliszczyn by the Department of Hydrography of the Maria Curie-Sklodowska University, Lublin. Thus in the last decade 5 water-gauges operated in the Lublin region. After taking off from the Bystrzyca basin area to Sobianowice its area to Lublin, that of the Czerniejowka to Wólka Abramowicka and of the Ciemięga river basin to Pliszczyn, we obtain a differential basin of Lublin; it is 261 km² in area including the whole area of dense municipal construction and the Czechówka river basin. In its area, wastewaters and rainwater from storm sewers are discharged into the rivers. After taking off from the amount of water flowing at Sobianowice the amount of discharged wastewaters and the flows in the three remaining control profiles, we obtain the outflow from the differential basin of Lublin. In the years 1983-1987, negative values for this outflow were recorded, indicating top water escape underground. Since 1988 a limited underground supply of the rivers in this region has been observed. In the years 1982—1991 the unitary outflow from the differential basin was only 0.11 1/s km², with an average of 3.95 1/s km² for the whole Bystrzyca river basin.

From a forty-year-series of flows the hydrometrie data of 1977—1991 recorded an influence of intensive underground water exploitation on river flows in the Lublin region. In the years 1977-1980 the atmospheric supply was higher than normal. Accordingly, river flows were then higher. In the period 1987-1982 the mean annual Bystrzyca river flow at Sobianowice exceeded the long-term mean value for 1951—1990 (amounting to 5.02 m³/s), and in 1981 it reached 9.63 m³/s (Fig. 6). After 1981 the annual amount of precipitation did not reach the normal value. The result was that the mean