64
A. Choi´ nski and R. Skowron
erosion base, and variable time of the lake’s incorporation into the hydrographic
network; performance of different hydrotechnical works, both within the lake –
outflow regulation, and within its catchment, e.g. meliorations, as well as natural
factors that can contribute to water level increase, such as landslides or construction
of beaver dams.
The second factor contributing to the decline of lakes, i.e. aggregation of sediments, can occur through: accumulation of biogenic mass, i.e. sedimentation; precipitation of chemical compounds; sedimentation of clastic sediments supplied by
streams, colluvia and deluvia deposited in the lake; effect of aeolian processes.
The course of evolution of a given lake basin depends on many factors, among
others: the genetic type of the basin; location in a given climate zone; individual
features of the basin determining the morphometric parameters; size of the catchment
and the ratio of its size to the surface area of the lake; stability of climate which
determines water balance; effect of human pressure of water relations in the lake’s
catchment.
Three stages of development of lakes are usually designated. The first one is the
youth stage, characterised by the basin’s shape approximate to the original one, with
no evident changes resulting from sedimentation processes. The second stage, i.e.
maturity stage, is characterised by obscuring of depth contrasts as a consequence of
deposition of a high amount of sediments. The final stage, i.e. the old age stage, is
associated with complete disappearance and leads to filling the entire basin with sediments. The evolution of lake basins in some cases does not always follow the above
pattern. Sometimes, with time, lakes not only fail to disappear, but even increase
their surface area, and therefore their water volume. Moreover, in lakes with a very
variable basin, their certain fragments can be in different stages of development due
to their different depths.
In reference to stagnant waters, water resources and their variability can be considered in three aspects, i.e. in reference to lakes (natural water objects >1 ha), tarns
(natural water objects <1 ha), and artificial reservoirs.
5.2 Water Resources of Lakes
Total water resources of lakes in Poland were estimated based on the Catalogue of
Polish Lakes [1], including information concerning surface area for 7081 lakes (above
1 ha). The calculation procedure involved adding up known lake water volumes for
more than 30% of lakes and adding the total water volume of unmeasured lakes.
It was calculated as a product of their surface area and mean depth. Lake water
resources calculated this way equal 19.7349 km
3 . Water resources within particular lake districts are as follows: Masurian Lake District – 10.1183 km
3 (51.27%),
Pomeranian Lake District – 7.1292 km
3 (36.12%), Wielkopolska-Kujawy Lake
District – 2.3535 km
3 (11.93%), and area south of the delineated range of the last
glaciation – 0.1339 km
3 (0.68%). Approximate values were also added in earlier
Polish publications [2].
A. Choi´ nski and R. Skowron
erosion base, and variable time of the lake’s incorporation into the hydrographic
network; performance of different hydrotechnical works, both within the lake –
outflow regulation, and within its catchment, e.g. meliorations, as well as natural
factors that can contribute to water level increase, such as landslides or construction
of beaver dams.
The second factor contributing to the decline of lakes, i.e. aggregation of sediments, can occur through: accumulation of biogenic mass, i.e. sedimentation; precipitation of chemical compounds; sedimentation of clastic sediments supplied by
streams, colluvia and deluvia deposited in the lake; effect of aeolian processes.
The course of evolution of a given lake basin depends on many factors, among
others: the genetic type of the basin; location in a given climate zone; individual
features of the basin determining the morphometric parameters; size of the catchment
and the ratio of its size to the surface area of the lake; stability of climate which
determines water balance; effect of human pressure of water relations in the lake’s
catchment.
Three stages of development of lakes are usually designated. The first one is the
youth stage, characterised by the basin’s shape approximate to the original one, with
no evident changes resulting from sedimentation processes. The second stage, i.e.
maturity stage, is characterised by obscuring of depth contrasts as a consequence of
deposition of a high amount of sediments. The final stage, i.e. the old age stage, is
associated with complete disappearance and leads to filling the entire basin with sediments. The evolution of lake basins in some cases does not always follow the above
pattern. Sometimes, with time, lakes not only fail to disappear, but even increase
their surface area, and therefore their water volume. Moreover, in lakes with a very
variable basin, their certain fragments can be in different stages of development due
to their different depths.
In reference to stagnant waters, water resources and their variability can be considered in three aspects, i.e. in reference to lakes (natural water objects >1 ha), tarns
(natural water objects <1 ha), and artificial reservoirs.
5.2 Water Resources of Lakes
Total water resources of lakes in Poland were estimated based on the Catalogue of
Polish Lakes [1], including information concerning surface area for 7081 lakes (above
1 ha). The calculation procedure involved adding up known lake water volumes for
more than 30% of lakes and adding the total water volume of unmeasured lakes.
It was calculated as a product of their surface area and mean depth. Lake water
resources calculated this way equal 19.7349 km
3 . Water resources within particular lake districts are as follows: Masurian Lake District – 10.1183 km
3 (51.27%),
Pomeranian Lake District – 7.1292 km
3 (36.12%), Wielkopolska-Kujawy Lake
District – 2.3535 km
3 (11.93%), and area south of the delineated range of the last
glaciation – 0.1339 km
3 (0.68%). Approximate values were also added in earlier
Polish publications [2].