9 Flow Regime Patterns and Their Changes
173
groups of rivers having different scales and causes of modification of the hydrological regime [14]. Rivers with the largest changes in the flow regime caused by
human activity are found in different regions of the country. These include: the Kłodnica, Brynica and Czarna Przemsza rivers in the Silesian region, the Oława River
in Lower Silesia, the Ner River flowing through the Łód´ z agglomeration, rivers
in the hydrographic system of the Drw˛ eca, Ina and Drawa river catchments in the
Pomeranian Lake District, and rivers of Przymorze – the Wieprz and the Łupawa.
These rivers are distinguished by a decrease in flow in the years 1951–1970 and an
increase in 1971–1990. Observed changes usually occur in the winter period (from
mid-December to mid-February) and in the summer-autumn season (from mid-June
to the end of the hydrological year). In the summer and autumn seasons, a higher
flow was also observed in 1981–2000 (from mid-June to the end of the hydrological year). The different nature of changes in the flow regime is presented by other
rivers transformed by the human activity in Silesia: the Brynica and Biała Przemsza,
but also the lower Nysa Kłodzka River, the upper Warta with the Ole´ snica, Barycz,
Pilica, Łasica, Rawka rivers, the upper Note´ c River with the G˛ asawka and Wierzyca
rivers, the Wda and Brda rivers in the lower Vistula basin. Until 1985, higher, and
after that year, lower flows than the average were observed. The biggest changes
usually occur at the beginning of the hydrological cycle, that is in November and
December. In the years 1961–1980, these rivers were characterized by an increase,
and in the years 1983–2002 a decrease in flow. In 1961–1980 a higher flow was also
observed from mid-April to early July, and in some rivers even up to the end of the
hydrological year. The more stable flow regime is represented by rivers located in
the north-eastern part of the country – in the Narew River catchment (except for the
Bug River), some rivers of Przymorze (the Rega, Pars˛ eta and Słupia rivers) and the
lake-district Gwda River. However, in 1951–1970 usually lower than average flows
were observed in these rivers, especially in the winter season (in the Narew River
from January to March). In turn, in the years 1970–1989 higher flows occurred in the
summer-autumn period, and in the years 1975–2000 also in winter. Other regularity
can be observed in the case of the majority of rivers in the middle and lower Warta
River catchment, in the middle and lower reaches of the Odra basin and in rivers in
the Pilica catchment. In the years 1961–1990, these rivers were characterized by a
clear increase in flows from December to the beginning of February, as well as from
May to July. At the scale of the whole country, the most stable features of the flow
regime are represented by rivers of the upper and middle Vistula basin together with
the Bug River and the Sudety Mountains tributaries of the Odra River. Exceptions
include the Dunajec River at gauge Czorsztyn, the Nysa Kłodzka River, and the
Wieprz River at gauge Zwierzyniec.
Rivers with similar changes in flow conditions, except from those with transformation of water relations caused by the human activity, also represent similar
physical and geographical regions. This indicates the importance of climatic conditions in the modification of the characteristics of the flow regime, and the spatial
diversity of these changes results from the local variability of the flow caused by
the environmental conditions of the catchment. Certain evidence of the influence of
climatic conditions on changes in the flow regime in the winter-spring period may be
173
groups of rivers having different scales and causes of modification of the hydrological regime [14]. Rivers with the largest changes in the flow regime caused by
human activity are found in different regions of the country. These include: the Kłodnica, Brynica and Czarna Przemsza rivers in the Silesian region, the Oława River
in Lower Silesia, the Ner River flowing through the Łód´ z agglomeration, rivers
in the hydrographic system of the Drw˛ eca, Ina and Drawa river catchments in the
Pomeranian Lake District, and rivers of Przymorze – the Wieprz and the Łupawa.
These rivers are distinguished by a decrease in flow in the years 1951–1970 and an
increase in 1971–1990. Observed changes usually occur in the winter period (from
mid-December to mid-February) and in the summer-autumn season (from mid-June
to the end of the hydrological year). In the summer and autumn seasons, a higher
flow was also observed in 1981–2000 (from mid-June to the end of the hydrological year). The different nature of changes in the flow regime is presented by other
rivers transformed by the human activity in Silesia: the Brynica and Biała Przemsza,
but also the lower Nysa Kłodzka River, the upper Warta with the Ole´ snica, Barycz,
Pilica, Łasica, Rawka rivers, the upper Note´ c River with the G˛ asawka and Wierzyca
rivers, the Wda and Brda rivers in the lower Vistula basin. Until 1985, higher, and
after that year, lower flows than the average were observed. The biggest changes
usually occur at the beginning of the hydrological cycle, that is in November and
December. In the years 1961–1980, these rivers were characterized by an increase,
and in the years 1983–2002 a decrease in flow. In 1961–1980 a higher flow was also
observed from mid-April to early July, and in some rivers even up to the end of the
hydrological year. The more stable flow regime is represented by rivers located in
the north-eastern part of the country – in the Narew River catchment (except for the
Bug River), some rivers of Przymorze (the Rega, Pars˛ eta and Słupia rivers) and the
lake-district Gwda River. However, in 1951–1970 usually lower than average flows
were observed in these rivers, especially in the winter season (in the Narew River
from January to March). In turn, in the years 1970–1989 higher flows occurred in the
summer-autumn period, and in the years 1975–2000 also in winter. Other regularity
can be observed in the case of the majority of rivers in the middle and lower Warta
River catchment, in the middle and lower reaches of the Odra basin and in rivers in
the Pilica catchment. In the years 1961–1990, these rivers were characterized by a
clear increase in flows from December to the beginning of February, as well as from
May to July. At the scale of the whole country, the most stable features of the flow
regime are represented by rivers of the upper and middle Vistula basin together with
the Bug River and the Sudety Mountains tributaries of the Odra River. Exceptions
include the Dunajec River at gauge Czorsztyn, the Nysa Kłodzka River, and the
Wieprz River at gauge Zwierzyniec.
Rivers with similar changes in flow conditions, except from those with transformation of water relations caused by the human activity, also represent similar
physical and geographical regions. This indicates the importance of climatic conditions in the modification of the characteristics of the flow regime, and the spatial
diversity of these changes results from the local variability of the flow caused by
the environmental conditions of the catchment. Certain evidence of the influence of
climatic conditions on changes in the flow regime in the winter-spring period may be