2949775696

93

Anthropogenic changes of water conditions..

To document long-term trends for flow changes, a curve of total annual Bystrzyca river flows in Lublin was plotted in comparison to those at Sobianowice (Fig. 7). It shows the flow relationships between these water-gauges. On this curve a trend for flows to decrease in Lublin is found from 1982. For the period 1982-1991 the total ’deficit’ of flows in this section was almost 182 million m³ in all. This value corresponds to almost a four-year exploitaton of underground water to satisfy the needs of the city. A trend for flows to decrease was also found in the Wolka Abramowicka profile on the Czerniejowka river.

Fig. 7. Totals of annual mean flows of the Bystrzyca river in the years 1977-1991 in Lublin (1),

and in the years 1979-1989 at Wólka Abramowicka (2) (calculated in relation to those at

Sobianowice). Dotted linę shows the trend till 1981; continuous linę — real sums of flows

Losses of river flows in the area of the Lublin depression funnel are caused by decreasing underground supply and escaping top waters (Los, Michalczyk 1984, 1989). Series of flow measurements madę at Iow flows of 1990—1992 in 10 hydrometrie sections point to non-natural changes in the amount of flowing water (Fig. 1). Five measurement series were carried out in rai.iless periods by workers of the Department of Hydrography, Maria Curie-Sklodowska University and the Municipal Company for Water Supply and 'freatment in Lublin (Table 1). Despite the basin enlargement of the Bystrzyca river and its supply by the Kręzniczanka river, a decrease in its flow is found. A similar situation is in the river basins of the Czerniejowka and Czechówka rivers, where flows are decreasing in their lower courses. The Bystrzyca river below the city is supplied with wastewaters on average of 1.51 m³/s, thus regaining its normal flow. Unitary outflows calculated from tie given mean flows also indicate the escape of top waters underground.