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Anthropogenic changes of wałer conditions..

1975). Significant changes also occurred in the river valleys. Water damming of the ’big’ mili on the Bystrzyca river was lowered by about 1.2 m in 1933, and in the foliowing year a pond on the Czechowka river was liąuidated. In the years 1934—1939, the valleys of both rivers were meliorated. In 1937, a section of the Czerniejowka near the castle was arched, thereby liąuidating the natural element of the hydrographic network and including it into the sewer system (Gawarecki 1975). Municipal building started to encroach upon the river valley bottoms. However, until 1950 the transformation ratę of the water conditions in the city area was relatively smali. In many sections, wetness and meandering as well as weakly-cut in river beds were preserved, which overflowed during inundation. Numerous springs were also preserved, e.g. in Wrotkow, Bronowice and Slawinek.

PRESENT CHANGES IN THE WATER CONDITIONS

In the second half of the 20th century, the demographic development of Lublin has been accelerated; the number of inhabitants increased from 99,0^0 in 1946 to 242,000 in 1970, and 350,000 in 1992. The city area extfcnded from 30 km² to 40 km² in 1955, to 93 km² in 1959, and to 147.5 km² in 1992. The developing city consumed morę and morę water, largely underground. New waterworks intakes were succesively put into operation in the river valleys of the Czerniejowka-’Dziesiąta’, Czechowka-'Slawinek’ and Bystrzyca-Trawiedniki’. Intensified water exploitation resulted in lowering of the underground water table in the water intake regions and the city, forming a regional depression funnel. This has led to accelerated drainage of the primary waterlogged valley bottoms. Ali mili dams have disappeared. The regulated and partially-embanked rivers carry waters from the upper parts of the basin through the city. In the Lublin area they are not supplied with underground water, but only receive waters from storm sewers. In the area of the depression funnel, water losses are found in the rivers which cause seasonal disappearance of water in the lower course of the Czechowka river. Municipal house building has encroached upon the dried river valley bottoms; the valley meadows have also changed to allotments, city parks, sport grounds and communication routes.

In the 50’s the city was supplied with water from two intakes (Fig. 3) and sunk wells, the number of which was about one thousand in that period. In 1950 about 4 million m³ of water were taken from underground resources, and as many as 8.4 million m³ in 1955. The underground water table of 1955 presented in Fig. 3. can still be considered similar to the natural one. The system of hydroisohypses then indicated a generał lowering of the water table towards the Bystrzyca river as well as the strongly-drained Czerniejowka and Czechowka river valleys. Within the valley bottoms the water table was found not to be deep; there still existed