50
Z. Michalczyk and J. Sposób
The outflow module is the most accurate estimate of water resources. Its value
constitutes the difference between atmospheric precipitation and evapotranspiration. The amount of outflow is calculated based on multiannual observations and
hydrometric measurements performed in river channels where both very high and
extremely low flows can occur. Precipitation falling on the land surface in the country
determines the development of own water resources. In the environmental cycle,
precipitation water can directly flow to rivers, return to the atmosphere in the process
of evaporation and transpiration, or can be retained in the soil cover, and then retained
in the bedrock. The contribution of precipitation water in particular phases determines
the rate of water inflow to river channels.
Almost the entire area of Poland is located in the catchment of the Baltic Sea
(99.7% of the area), and only small fragments are incorporated in the catchment
of the North Sea (0.1%) and Black Sea (0.2% of the territory of the country). The
surface of catchments of the Oder and Vistula Rivers constitute 89.6% of Poland’s
territory, and the remaining part is occupied by those of rivers of the Pomeranian
and Masurian Lake Districts [8], draining water directly to the Baltic Sea or to the
catchment of the Neman and Pregolya River [9]. Water resources of the territory
of Poland are associated with the amount of mean outflow from the area of the
country, i.e. 312,677 km
2 . They develop as a result of alimentation with atmospheric
precipitation as own renewable resources. Own resources are increased by internal
resources, i.e. by the volume of water introduced through rivers to the territory of
Poland, where part of catchments is located outside the national borders. After adding
the parts of catchments located in the neighbouring countries, the area from which
Polish rivers collect water occupies 351,208 km
2 , i.e. it is 12.3% larger than the
territory of Poland.
Amounts of outflowing water are calculated based on daily water gauge observations and flow measurements performed in the scope of the network of the Institute of
Meteorology and Water Management. The data are collected in water gauge profiles
established in river channels. The number of water gauges and way of registration of
water stages changes with technical progress. At the beginning of the current century,
daily water stages and discharges were determined in 611 water gauge stations [7]
distributed on Polish rivers. Their catchment areas occupy from several tens to 194
thousand km
2 .
Discharge of Polish rivers fluctuates in annual and multi-annual periods. Cyclical
occurrence of years with high and low discharges is registered, and seasonal discharge
fluctuations are observed. According to calculations performed by IMGW, mean total
water outflow in Polish rivers in the twentieth century was 61.5 km
3 , whereas outflow
from the area of the country equalled 53.9 km
3 [7]. The difference between mean
river outflow and outflow from the area of Poland equals 7.6 km
3 . It results from
the outflow of water introduced by rivers inflowing to the territory of Poland, i.e.
they are resources developed outside of the national borders. Total annual outflows
showed a series of several years with high or low discharges, and following annual
values showed a significant level of autocorrelation. This points to significant environmental conditions of development of water resources, and particularly to the way
of alimentation of rivers with a high contribution of the groundwater component. The
Z. Michalczyk and J. Sposób
The outflow module is the most accurate estimate of water resources. Its value
constitutes the difference between atmospheric precipitation and evapotranspiration. The amount of outflow is calculated based on multiannual observations and
hydrometric measurements performed in river channels where both very high and
extremely low flows can occur. Precipitation falling on the land surface in the country
determines the development of own water resources. In the environmental cycle,
precipitation water can directly flow to rivers, return to the atmosphere in the process
of evaporation and transpiration, or can be retained in the soil cover, and then retained
in the bedrock. The contribution of precipitation water in particular phases determines
the rate of water inflow to river channels.
Almost the entire area of Poland is located in the catchment of the Baltic Sea
(99.7% of the area), and only small fragments are incorporated in the catchment
of the North Sea (0.1%) and Black Sea (0.2% of the territory of the country). The
surface of catchments of the Oder and Vistula Rivers constitute 89.6% of Poland’s
territory, and the remaining part is occupied by those of rivers of the Pomeranian
and Masurian Lake Districts [8], draining water directly to the Baltic Sea or to the
catchment of the Neman and Pregolya River [9]. Water resources of the territory
of Poland are associated with the amount of mean outflow from the area of the
country, i.e. 312,677 km
2 . They develop as a result of alimentation with atmospheric
precipitation as own renewable resources. Own resources are increased by internal
resources, i.e. by the volume of water introduced through rivers to the territory of
Poland, where part of catchments is located outside the national borders. After adding
the parts of catchments located in the neighbouring countries, the area from which
Polish rivers collect water occupies 351,208 km
2 , i.e. it is 12.3% larger than the
territory of Poland.
Amounts of outflowing water are calculated based on daily water gauge observations and flow measurements performed in the scope of the network of the Institute of
Meteorology and Water Management. The data are collected in water gauge profiles
established in river channels. The number of water gauges and way of registration of
water stages changes with technical progress. At the beginning of the current century,
daily water stages and discharges were determined in 611 water gauge stations [7]
distributed on Polish rivers. Their catchment areas occupy from several tens to 194
thousand km
2 .
Discharge of Polish rivers fluctuates in annual and multi-annual periods. Cyclical
occurrence of years with high and low discharges is registered, and seasonal discharge
fluctuations are observed. According to calculations performed by IMGW, mean total
water outflow in Polish rivers in the twentieth century was 61.5 km
3 , whereas outflow
from the area of the country equalled 53.9 km
3 [7]. The difference between mean
river outflow and outflow from the area of Poland equals 7.6 km
3 . It results from
the outflow of water introduced by rivers inflowing to the territory of Poland, i.e.
they are resources developed outside of the national borders. Total annual outflows
showed a series of several years with high or low discharges, and following annual
values showed a significant level of autocorrelation. This points to significant environmental conditions of development of water resources, and particularly to the way
of alimentation of rivers with a high contribution of the groundwater component. The