9 Flow Regime Patterns and Their Changes
167
conditions), a high lake density and a large number of closed depressions. Upland
rivers have balanced flows due to significant retention capabilities of heavily fissured
and karstified carbonate rocks, while those in industrial areas due to the human interference in the water cycle. The Przymorze and lake-district rivers are characterized by
the smallest variability of flows as well as their extreme irregularity. These rivers are
also distinguished by high total flow, over 200 mm, and in the case of the Przymorze
rivers even over 300 mm, and the largest share of the groundwater supply in the total
flow, which in many rivers is higher than 80% (Table 9.1). The date of occurrence of
high water in the rivers of Przymorze and on individual rivers of the Masurian Lake
District is relatively stable and occurs in the winter–spring season. In the majority
of rivers, the first minimum of monthly flows has a relatively stable or stable date of
occurrence, usually in the summer or the summer–autumn period. A strongly stable
date of the appearance of a period of low flows is characteristic only of the Brda
River (June–July). On the other hand, relatively unstable minima occur in individual
rivers, mainly transformed by the human activity, for example in Silesia, and their
date falls in the summer–autumn (the Bytomka River) or the autumn–winter (the
Brynica River) period. Due to the low variability of flows, these rivers are characterized by the low-contrasting hydrological periods, with the following sequence in
the annual cycle: normal period → low high-water → normal period → low lowwater (Fig. 9.2). In extreme cases, in rivers with changes in flow conditions caused
by human activity, only one normal hydrological period is observed with very even
flows (the Brynica River).
Type 2 – the nival moderately formed regime. This is represented by rivers
whose average flow of the spring month is from 130 to 180% of the average annual
flow. Rivers with this regime are located in:
– the northern part of the country, e.g. in the western part of Przymorze (the Rega
and Pars˛ eta rivers), in the Masurian Lake District (the Łyna and Omulew, Czarna
Ha´ ncza and Supra´ sl rivers),
– in the central part – the transit rivers, e.g. the Vistula, Odra and Warta rivers with
the Note´ c River,
– in the upland belt – rivers located between the Warta and Vistula rivers, the Lublin
Upland rivers in the Wieprz catchment.
These rivers are characterized by average flows (100–200 mm), only the riparian
and coastal rivers are distinguished by the flow of over 200 mm or even 300 mm.
Rivers in the northern part and in the Wieprz catchment are also characterized by a
high share of the groundwater supply (60–80%), which in the other rivers of this type
of regime is 40–60%. The date of the high-water phase is usually relatively stable
and stable and falls in the winter–spring or the spring period. In most rivers, the
low-water phase has a relatively stable or a stable date of occurrence, usually in the
summer–autumn or the summer period. In comparison with the previous type rivers
with the nival moderately formed regime are characterized by greater variability
of flows, but the types of hydrological periods and their sequence are similar. The
following ones can be distinguished in the yearly cycle: normal period → high-water
(from low to high) → normal period → low low-water.
167
conditions), a high lake density and a large number of closed depressions. Upland
rivers have balanced flows due to significant retention capabilities of heavily fissured
and karstified carbonate rocks, while those in industrial areas due to the human interference in the water cycle. The Przymorze and lake-district rivers are characterized by
the smallest variability of flows as well as their extreme irregularity. These rivers are
also distinguished by high total flow, over 200 mm, and in the case of the Przymorze
rivers even over 300 mm, and the largest share of the groundwater supply in the total
flow, which in many rivers is higher than 80% (Table 9.1). The date of occurrence of
high water in the rivers of Przymorze and on individual rivers of the Masurian Lake
District is relatively stable and occurs in the winter–spring season. In the majority
of rivers, the first minimum of monthly flows has a relatively stable or stable date of
occurrence, usually in the summer or the summer–autumn period. A strongly stable
date of the appearance of a period of low flows is characteristic only of the Brda
River (June–July). On the other hand, relatively unstable minima occur in individual
rivers, mainly transformed by the human activity, for example in Silesia, and their
date falls in the summer–autumn (the Bytomka River) or the autumn–winter (the
Brynica River) period. Due to the low variability of flows, these rivers are characterized by the low-contrasting hydrological periods, with the following sequence in
the annual cycle: normal period → low high-water → normal period → low lowwater (Fig. 9.2). In extreme cases, in rivers with changes in flow conditions caused
by human activity, only one normal hydrological period is observed with very even
flows (the Brynica River).
Type 2 – the nival moderately formed regime. This is represented by rivers
whose average flow of the spring month is from 130 to 180% of the average annual
flow. Rivers with this regime are located in:
– the northern part of the country, e.g. in the western part of Przymorze (the Rega
and Pars˛ eta rivers), in the Masurian Lake District (the Łyna and Omulew, Czarna
Ha´ ncza and Supra´ sl rivers),
– in the central part – the transit rivers, e.g. the Vistula, Odra and Warta rivers with
the Note´ c River,
– in the upland belt – rivers located between the Warta and Vistula rivers, the Lublin
Upland rivers in the Wieprz catchment.
These rivers are characterized by average flows (100–200 mm), only the riparian
and coastal rivers are distinguished by the flow of over 200 mm or even 300 mm.
Rivers in the northern part and in the Wieprz catchment are also characterized by a
high share of the groundwater supply (60–80%), which in the other rivers of this type
of regime is 40–60%. The date of the high-water phase is usually relatively stable
and stable and falls in the winter–spring or the spring period. In most rivers, the
low-water phase has a relatively stable or a stable date of occurrence, usually in the
summer–autumn or the summer period. In comparison with the previous type rivers
with the nival moderately formed regime are characterized by greater variability
of flows, but the types of hydrological periods and their sequence are similar. The
following ones can be distinguished in the yearly cycle: normal period → high-water
(from low to high) → normal period → low low-water.