9 Flow Regime Patterns and Their Changes
171
Type 3 – the nival well-formed regime. This type of regime is characteristic of
rivers with an average flow of the spring month higher than 180% of the average
annual flow. These rivers are distinguished by the largest changes in flow in the
annual cycle. They are located in the lowland part of the country, from the Greater
Poland Lake District and the South-Silesian Lowland through the Central Mazovian
Lowland, to the majority of rivers in the eastern part of the country, in the Narew
and Bug rivers catchments. Rivers of this type of regime still exist in the KielceSandomierz Upland (in the Kamienna River catchment) and locally in the My´ slibórz
Lake District (the My´ sla River) and on the Szczecinski Coastland (in the Ina River
catchment). These rivers lie in the belt characterized by the lowest flows, which
usually do not exceed 150 mm. A higher flow, over 200 mm, is observed only in the
north-east and in the Kielce Upland. Extremely low flows, below 80 mm, are observed
in the Mogilnica and Flinta rivers in the Greater Poland Lake District and on the
T˛ a˙ zyna River, the left tributary of the Vistula River in Kujawy (60 mm). The volume of
the groundwater supply and the flow variability are also diversified. High variability
of daily flows is characteristic of some rivers of the Kielce Upland (the Koprzywianka
and Czarna rivers), and on the lowlands the Brok River, which is the right tributary
of the Bug River, and the T˛ a˙ zyna River. The latter, like many other rivers of the Great
Poland-Kujawy Lake District (the Sama and Mogilnica rivers), is also distinguished
by high variability of annual flows (Cv > 0.600). At the same time, these rivers usually
have a very low groundwater supply (below 40%). There is a short, intense period
of meltwater feeding in spring and formation of high-water stage on these rivers.
Then, there is a rapid recession of the flood flow and a transition to the low-water
stage in the summer-autumn period. A strongly stable period (March–April) of the
occurrence of floods is observed in many rivers of north-eastern Poland. In the other
rivers, the date of occurrence of the high-water period is stable and earlier (January–
March, February–April). Stable, summer–autumn (July–September) is also the date
of appearance of the low-water period. Rivers with the nival well-formed regime are
distinguished by the most contrasting types of periods with the following sequence:
average low-water (or normal period) → low (or average) high-water → very high
high-water → normal period → deep (or average) low-water.
Type 4 – the nival-pluvial regime. It is characteristic of rivers whose average flow
of the spring month is generally 130–180% of the average annual flow and the flow
increase in the summer months is marked, with at least 100% of the average annual
flow. This type is represented by rivers of the Sudety Mountains and most of the
Carpathian rivers, and by the transit Vistula River up to gauge Puławy, whose regime
in this section is shaped by its Carpathian tributaries. These rivers are characterized
by a large range of annual flows from 100 mm (the left tributaries of the upper Odra
River) to over 800 mm (the upper Vistula River, tributaries of the San River in the
Western Bieszczady Mountains). These rivers are characterized by a small share of
the groundwater supply in the total flow (20–40%) and a large range of variability
of daily flows, from Cv < 1.0 in the lower reaches of the mountain rivers to Cv >
2.0 in the upper reaches. The date of the high-water phase is usually relatively stable
and stable and falls in the spring or the spring–summer period. The least regular date
of appearance of the maxima (relatively unstable type) is usually associated with a
171
Type 3 – the nival well-formed regime. This type of regime is characteristic of
rivers with an average flow of the spring month higher than 180% of the average
annual flow. These rivers are distinguished by the largest changes in flow in the
annual cycle. They are located in the lowland part of the country, from the Greater
Poland Lake District and the South-Silesian Lowland through the Central Mazovian
Lowland, to the majority of rivers in the eastern part of the country, in the Narew
and Bug rivers catchments. Rivers of this type of regime still exist in the KielceSandomierz Upland (in the Kamienna River catchment) and locally in the My´ slibórz
Lake District (the My´ sla River) and on the Szczecinski Coastland (in the Ina River
catchment). These rivers lie in the belt characterized by the lowest flows, which
usually do not exceed 150 mm. A higher flow, over 200 mm, is observed only in the
north-east and in the Kielce Upland. Extremely low flows, below 80 mm, are observed
in the Mogilnica and Flinta rivers in the Greater Poland Lake District and on the
T˛ a˙ zyna River, the left tributary of the Vistula River in Kujawy (60 mm). The volume of
the groundwater supply and the flow variability are also diversified. High variability
of daily flows is characteristic of some rivers of the Kielce Upland (the Koprzywianka
and Czarna rivers), and on the lowlands the Brok River, which is the right tributary
of the Bug River, and the T˛ a˙ zyna River. The latter, like many other rivers of the Great
Poland-Kujawy Lake District (the Sama and Mogilnica rivers), is also distinguished
by high variability of annual flows (Cv > 0.600). At the same time, these rivers usually
have a very low groundwater supply (below 40%). There is a short, intense period
of meltwater feeding in spring and formation of high-water stage on these rivers.
Then, there is a rapid recession of the flood flow and a transition to the low-water
stage in the summer-autumn period. A strongly stable period (March–April) of the
occurrence of floods is observed in many rivers of north-eastern Poland. In the other
rivers, the date of occurrence of the high-water period is stable and earlier (January–
March, February–April). Stable, summer–autumn (July–September) is also the date
of appearance of the low-water period. Rivers with the nival well-formed regime are
distinguished by the most contrasting types of periods with the following sequence:
average low-water (or normal period) → low (or average) high-water → very high
high-water → normal period → deep (or average) low-water.
Type 4 – the nival-pluvial regime. It is characteristic of rivers whose average flow
of the spring month is generally 130–180% of the average annual flow and the flow
increase in the summer months is marked, with at least 100% of the average annual
flow. This type is represented by rivers of the Sudety Mountains and most of the
Carpathian rivers, and by the transit Vistula River up to gauge Puławy, whose regime
in this section is shaped by its Carpathian tributaries. These rivers are characterized
by a large range of annual flows from 100 mm (the left tributaries of the upper Odra
River) to over 800 mm (the upper Vistula River, tributaries of the San River in the
Western Bieszczady Mountains). These rivers are characterized by a small share of
the groundwater supply in the total flow (20–40%) and a large range of variability
of daily flows, from Cv < 1.0 in the lower reaches of the mountain rivers to Cv >
2.0 in the upper reaches. The date of the high-water phase is usually relatively stable
and stable and falls in the spring or the spring–summer period. The least regular date
of appearance of the maxima (relatively unstable type) is usually associated with a