2949775608

138

T. Wilgat et al.

attention was given to the decline of lakes. Many forms indicating shrinking of the shore linę have remained and their short-lived existence allows us to conclude that the changes occurred relatively recently, largely by the end of the 19th c. and at the beginning of the 20th c. The disappearance time of some of them can be defined from few data in the literaturę (Roztworowski 1882) and interviews with people.

I

years

Fig. 12. Water level of Piaseczno Lakę

The Department of Hydrography, Maria Curie-Skłodowska University, Lublin, has carried out field studies on a large scalę sińce the 50’s. To obtain an extensive knowledge of water conditions the method of hydrographical survey according to the instruction of Polish geographers was used (Instrukcja.... 1954, II ed. 1959, III ed. 1964). In 1964, a 1:100,000 hydrographical map was madę by T. Wilgat for a large part of the Lakę Region. Censorship did not allow its printing. The one proof-sheet saved is a document of the region’s water conditions at that time preceding the changes connected with the building and functioning of the Wieprz-Krzna canal (Fig. 13 and 14). In the following years a hydrographical survey was repeated for large fragments of the Lakę Region (Wilgat et al. 1984; Michalczyk, Bartoszewski et al. 1993). From successive maps presenting the state of the groundwater table it results that from the early 60’s no change occurred in the course of the main watershed of groundwaters and runoff directions, but the depth of the water table and the rangę of wetlands changed. On comparing maps