5 Water Resources of Stagnant Waters
69
Table 5.2 The occurrence of tarns within the designated lake districts (according to [7])
Lake district
Number of tarns
Share (%)
Surface area
(km 2 )
Mean density
per 100 km 2
Pomorskie
36 657
44.6
48 330
75.8
Mazurskie
28 603
34.8
35 928
79.6
Wielkopolsko-Kujawskie
16 916
20.6
31 747
53.3
Summary
82 176
100.0
116 005
70.8
A total of 82 176 tarns were identified in the analysed area. Their highest number
(as well as that of lakes with an area >1 ha) occurs in the Pomeranian Lake District,
i.e. 36 657, constituting 44.6% of their total abundance. Their highest mean density,
i.e. 79.6 tarns/100 km
2 , occurs in the Masurian Lake District, although in terms of
mean density of tarns, the Masurian and Pomeranian Lake Districts are similar. The
Wielkopolska-Kujawy Lake District considerably differs from them in this aspect.
The mean density of tarns in the Lake District is lower by approximately 30%. The
mean density of tarns throughout the analysed area is 70.8 per 100 km
2 . The highest
density of tarns reached more than 300 per 100 km
2 . Zones of the type occurring in
the Kashubian, Drawa, Kraje´ nskie, Gniezno Lake Districts, and north of the Olsztyn
Lake District. An evident tendency of dependency on the number of tarns on the
type of substrate is observed. In zones covered by sands and gravels of fluvioglacial
accumulation, the number of tarns is small and does not exceed 50 per 100 km
2 . In
zones of occurrence of glacial tills, it is several times higher.
The determination of the number of tarns permits the estimation of their total
surface area. It is possible with the assumption of an average surface area of a tarn.
In the case above, the adopted average surface area was 0.5 ha. Therefore, with such
an assumption, the total surface area of tarns was estimated for 41 088 ha. The area
is approximately 4 times larger than the largest Polish Lake ´
Sniardwy.
A procedure analogical to the one described above can be applied in the estimation
of total water resources of tarns. Assuming its previously determined total surface
area of 41 088 ha and mean depth of 0.5 m, the total water volume in tarns can
be estimated for 0.20544 km
3 . The value constitutes 1.0% of water resources of
lakes larger than 1 ha. For particular lake districts, the contribution is as follows:
Pomeranian – 1.28%, Masurian – 0.71%, and Wielkopolska-Kujawy – 1.80%. Total
resources accumulated in tarns determine the retention index within the analysed
area equal to 1.8 mm.
Sebzda [9] analysing topographic maps at a scale of 1:50 000 from the 1970s
determined the number of tarns in the area south of the range of the Baltic glaciation,
i.e. over an area of 195 836 km
2 . Only 10 676 tarns were identified there, corresponding to a mean density of only 5.5 per 100 km
2 . With assumptions analogical to
the previous ones, their total surface area can be estimated for 5 338 ha. It is therefore approximate to the surface area of Lakes Jeziorak and Jamno and constitutes
1.9% of Polish lakes larger than 1 ha. Their water resources can be estimated for
0.02669 km
3 , which corresponds to only 0.13% of lake water resources in Poland. In
69
Table 5.2 The occurrence of tarns within the designated lake districts (according to [7])
Lake district
Number of tarns
Share (%)
Surface area
(km 2 )
Mean density
per 100 km 2
Pomorskie
36 657
44.6
48 330
75.8
Mazurskie
28 603
34.8
35 928
79.6
Wielkopolsko-Kujawskie
16 916
20.6
31 747
53.3
Summary
82 176
100.0
116 005
70.8
A total of 82 176 tarns were identified in the analysed area. Their highest number
(as well as that of lakes with an area >1 ha) occurs in the Pomeranian Lake District,
i.e. 36 657, constituting 44.6% of their total abundance. Their highest mean density,
i.e. 79.6 tarns/100 km
2 , occurs in the Masurian Lake District, although in terms of
mean density of tarns, the Masurian and Pomeranian Lake Districts are similar. The
Wielkopolska-Kujawy Lake District considerably differs from them in this aspect.
The mean density of tarns in the Lake District is lower by approximately 30%. The
mean density of tarns throughout the analysed area is 70.8 per 100 km
2 . The highest
density of tarns reached more than 300 per 100 km
2 . Zones of the type occurring in
the Kashubian, Drawa, Kraje´ nskie, Gniezno Lake Districts, and north of the Olsztyn
Lake District. An evident tendency of dependency on the number of tarns on the
type of substrate is observed. In zones covered by sands and gravels of fluvioglacial
accumulation, the number of tarns is small and does not exceed 50 per 100 km
2 . In
zones of occurrence of glacial tills, it is several times higher.
The determination of the number of tarns permits the estimation of their total
surface area. It is possible with the assumption of an average surface area of a tarn.
In the case above, the adopted average surface area was 0.5 ha. Therefore, with such
an assumption, the total surface area of tarns was estimated for 41 088 ha. The area
is approximately 4 times larger than the largest Polish Lake ´
Sniardwy.
A procedure analogical to the one described above can be applied in the estimation
of total water resources of tarns. Assuming its previously determined total surface
area of 41 088 ha and mean depth of 0.5 m, the total water volume in tarns can
be estimated for 0.20544 km
3 . The value constitutes 1.0% of water resources of
lakes larger than 1 ha. For particular lake districts, the contribution is as follows:
Pomeranian – 1.28%, Masurian – 0.71%, and Wielkopolska-Kujawy – 1.80%. Total
resources accumulated in tarns determine the retention index within the analysed
area equal to 1.8 mm.
Sebzda [9] analysing topographic maps at a scale of 1:50 000 from the 1970s
determined the number of tarns in the area south of the range of the Baltic glaciation,
i.e. over an area of 195 836 km
2 . Only 10 676 tarns were identified there, corresponding to a mean density of only 5.5 per 100 km
2 . With assumptions analogical to
the previous ones, their total surface area can be estimated for 5 338 ha. It is therefore approximate to the surface area of Lakes Jeziorak and Jamno and constitutes
1.9% of Polish lakes larger than 1 ha. Their water resources can be estimated for
0.02669 km
3 , which corresponds to only 0.13% of lake water resources in Poland. In