70
M. Rz˛ etała
is greater than 80%. An exception is water bodies without surface inflows where all
water comes from precipitation and groundwater supply.
In the case of many water bodies, surface outflow is determined not just by the
amount of water released or flowing naturally out of the body of water in question,
but also by the amount of water sourced from the basin to meet the water needs
related to economic activity. Total surface outflows (including artificial releases and
the water sourced) account for more than 90% of water loss in most water bodies
(with the exception of the so-called endorheic water bodies where water losses are
mostly caused by evaporation and sometimes by significant underground outflow as
well).
The loss of water caused by evaporation is on average around 440 mm. Water losses
due to evaporation are higher where thermal pollution is present [18, 21] or the water
body exhibits intensive overgrowth resulting in increased evapotranspiration [22].
Nevertheless, the amount of water evaporating from the surface of the vast majority
of flow-through water bodies is usually estimated at just a few percent of the water
lost, although in the case of endorheic bodies of water it is the most important item
depleting the amount of water retained.
The amount of water retained in the basin varies widely for individual water bodies
in Poland; the maximum value is 472.4 million m
3 for the Solina Reservoir. The
water retained is also replenished in various ways. In this respect, the Dzie´ ckowice
Reservoir is exceptional. The most important source of water supply to this lake
since the very beginning of its operation has not been its own river catchment but
rather water transfers from the Carpathian tributaries of the Vistula River, i.e. the
Soła and Skawa Rivers. In annual terms, this type of supply accounts on average
for 86% of the total water supplied to the reservoir [23]. Precipitation, inflow from
the river catchment and from the direct catchment of the reservoir and underground
supply account for around 14% on average. In the 1970s, around 20 hm
3 of water
were supplied annually by way of such transfers. In the next few years, this amount
varied from 30 to more than 50 hm
3 per year. In the late 1980s and in the early
1990s, an increase in water supply to nearly 70 hm
3 followed. The maximum level
of water supply from the Soła River to the reservoir was reached in the mid-1990s
(in 1995, it was 92 hm
3 ). From the very beginning of its operation, the main user
of the Dzie´ ckowice Reservoir was the Katowice Steelworks, which also transferred
water from the reservoir to other external users such as the coking plant and water
treatment plants using its own water transfer system.
4.5 Selected Limnic Processes
The functioning of water bodies involves limnic processes. These are processes
characteristic of stagnant waters which result in changes in the physical, chemical
and biological conditions within water bodies. These include variations in water
cycle conditions, water mass dynamics, water temperature and oxygenation and
M. Rz˛ etała
is greater than 80%. An exception is water bodies without surface inflows where all
water comes from precipitation and groundwater supply.
In the case of many water bodies, surface outflow is determined not just by the
amount of water released or flowing naturally out of the body of water in question,
but also by the amount of water sourced from the basin to meet the water needs
related to economic activity. Total surface outflows (including artificial releases and
the water sourced) account for more than 90% of water loss in most water bodies
(with the exception of the so-called endorheic water bodies where water losses are
mostly caused by evaporation and sometimes by significant underground outflow as
well).
The loss of water caused by evaporation is on average around 440 mm. Water losses
due to evaporation are higher where thermal pollution is present [18, 21] or the water
body exhibits intensive overgrowth resulting in increased evapotranspiration [22].
Nevertheless, the amount of water evaporating from the surface of the vast majority
of flow-through water bodies is usually estimated at just a few percent of the water
lost, although in the case of endorheic bodies of water it is the most important item
depleting the amount of water retained.
The amount of water retained in the basin varies widely for individual water bodies
in Poland; the maximum value is 472.4 million m
3 for the Solina Reservoir. The
water retained is also replenished in various ways. In this respect, the Dzie´ ckowice
Reservoir is exceptional. The most important source of water supply to this lake
since the very beginning of its operation has not been its own river catchment but
rather water transfers from the Carpathian tributaries of the Vistula River, i.e. the
Soła and Skawa Rivers. In annual terms, this type of supply accounts on average
for 86% of the total water supplied to the reservoir [23]. Precipitation, inflow from
the river catchment and from the direct catchment of the reservoir and underground
supply account for around 14% on average. In the 1970s, around 20 hm
3 of water
were supplied annually by way of such transfers. In the next few years, this amount
varied from 30 to more than 50 hm
3 per year. In the late 1980s and in the early
1990s, an increase in water supply to nearly 70 hm
3 followed. The maximum level
of water supply from the Soła River to the reservoir was reached in the mid-1990s
(in 1995, it was 92 hm
3 ). From the very beginning of its operation, the main user
of the Dzie´ ckowice Reservoir was the Katowice Steelworks, which also transferred
water from the reservoir to other external users such as the coking plant and water
treatment plants using its own water transfer system.
4.5 Selected Limnic Processes
The functioning of water bodies involves limnic processes. These are processes
characteristic of stagnant waters which result in changes in the physical, chemical
and biological conditions within water bodies. These include variations in water
cycle conditions, water mass dynamics, water temperature and oxygenation and