10 Flow Seasonality in Two Big Polish Rivers – The Vistula …
197
rivers indicates significant changes at those sites (Figs. 10.4 and 10.5). Moreover,
the first two gauges (Jagodniki and ´
Scinawa) roughly close the parts of the basins
featuring mountain river regimes (Western Beskids – the Vistula; Sudetes – the
Oder). The flow regime at the next two gauges (Warsaw and Poł˛ ecko) is considerably
modified by waters supplied from the areas where many rivers show regimes typical
of central Poland uplands. The last two gauges (Tczew and Gozdowice) close nearly
the entire basins of the largest Polish rivers. The observed changes and oscillations
in the seasonal structure of flow may reflect fluctuations and large-scale changes in
flow regimes in Poland. Data obtained at the selected water gauges cover the same
time interval of 1951–2016, which allows for reliable comparisons of the recorded
changes and regularities.
Multiannual changes in two different seasonality aspects in six selected water
gauges are analyzed based on the concentration date (PK) and seasonality index
(IS). The other two investigated parameters (TPO and GMO) closely correlate with
the previous two (Figs. 10.2 and 10.3).
Analysis of variability and covariability of average flows in the Vistula and the
Oder at the selected water gauges (Fig. 10.6) seems to be a good starting point
for assessing multiannual changes in their seasonality. The correlation coefficients
between the pairs of the water gauges are R(SQs÷SQj) = 0.74; R(SQp÷SQw) =
0.69; R(SQg÷SQt) = 0.81. All are significant for α = 1% (Student’s t-test). The
greatest convergence of multiannual changes in average flows occurred for the entire
basins of the Oder and the Vistula, and the smallest for the gauges closing the mountain and upland sections of both basins. All gauges showed multiannual, sinusoidal
fluctuations with phases and relative amplitudes for individual periods not identical
but close regarding the dates of maxima and minima. The amplitude of changes in
average flow at the gauge closing the upper part of the Oder basin ( ´
Scinawa) was
greater than at the corresponding gauge for the upper Vistula in Jagodniki. A reverse
situation was observed at downstream water gauges. Relative dynamics of changes
in the Vistula flows was larger than that for the Oder. This was observed for both
year to year and multiannual fluctuations.
Multiannual changes in the concentration date (PK) at the six water gauges at
the Oder and the Vistula irregularly oscillated around average values, and average
PK for the three pairs of gauges were nearly identical (Fig. 10.7). Changes in the
concentration dates for the Oder and the Vistula flow at the gauges closing the upper
sections of their basins ( ´
Scinawa and Jagodniki) were too irregular to identify any
correlation (R = 0.14). PK extrema (local minima and maxima) concerned the same
years (1974, 1983, 1997), or occurred in different years (Fig. 10.7a). There were
years when the concentration date was very late in the upper Vistula and very early
in the upper Oder or the other way round (1958, 1978, 2009). In the years 1951–
1983 PK oscillation rate in both rivers was more rapid than later, and a declining
trend in the upper Oder that began in the 1980s caused the concentration date to fall
increasingly early.
For the other two pairs of water gauges (Poł˛ ecko÷Warszawa and
Gozdowice÷Tczew), correlation of PK parameters over time was higher and significant (α = 1%), although in some years late concentration date in the Vistula was
197
rivers indicates significant changes at those sites (Figs. 10.4 and 10.5). Moreover,
the first two gauges (Jagodniki and ´
Scinawa) roughly close the parts of the basins
featuring mountain river regimes (Western Beskids – the Vistula; Sudetes – the
Oder). The flow regime at the next two gauges (Warsaw and Poł˛ ecko) is considerably
modified by waters supplied from the areas where many rivers show regimes typical
of central Poland uplands. The last two gauges (Tczew and Gozdowice) close nearly
the entire basins of the largest Polish rivers. The observed changes and oscillations
in the seasonal structure of flow may reflect fluctuations and large-scale changes in
flow regimes in Poland. Data obtained at the selected water gauges cover the same
time interval of 1951–2016, which allows for reliable comparisons of the recorded
changes and regularities.
Multiannual changes in two different seasonality aspects in six selected water
gauges are analyzed based on the concentration date (PK) and seasonality index
(IS). The other two investigated parameters (TPO and GMO) closely correlate with
the previous two (Figs. 10.2 and 10.3).
Analysis of variability and covariability of average flows in the Vistula and the
Oder at the selected water gauges (Fig. 10.6) seems to be a good starting point
for assessing multiannual changes in their seasonality. The correlation coefficients
between the pairs of the water gauges are R(SQs÷SQj) = 0.74; R(SQp÷SQw) =
0.69; R(SQg÷SQt) = 0.81. All are significant for α = 1% (Student’s t-test). The
greatest convergence of multiannual changes in average flows occurred for the entire
basins of the Oder and the Vistula, and the smallest for the gauges closing the mountain and upland sections of both basins. All gauges showed multiannual, sinusoidal
fluctuations with phases and relative amplitudes for individual periods not identical
but close regarding the dates of maxima and minima. The amplitude of changes in
average flow at the gauge closing the upper part of the Oder basin ( ´
Scinawa) was
greater than at the corresponding gauge for the upper Vistula in Jagodniki. A reverse
situation was observed at downstream water gauges. Relative dynamics of changes
in the Vistula flows was larger than that for the Oder. This was observed for both
year to year and multiannual fluctuations.
Multiannual changes in the concentration date (PK) at the six water gauges at
the Oder and the Vistula irregularly oscillated around average values, and average
PK for the three pairs of gauges were nearly identical (Fig. 10.7). Changes in the
concentration dates for the Oder and the Vistula flow at the gauges closing the upper
sections of their basins ( ´
Scinawa and Jagodniki) were too irregular to identify any
correlation (R = 0.14). PK extrema (local minima and maxima) concerned the same
years (1974, 1983, 1997), or occurred in different years (Fig. 10.7a). There were
years when the concentration date was very late in the upper Vistula and very early
in the upper Oder or the other way round (1958, 1978, 2009). In the years 1951–
1983 PK oscillation rate in both rivers was more rapid than later, and a declining
trend in the upper Oder that began in the 1980s caused the concentration date to fall
increasingly early.
For the other two pairs of water gauges (Poł˛ ecko÷Warszawa and
Gozdowice÷Tczew), correlation of PK parameters over time was higher and significant (α = 1%), although in some years late concentration date in the Vistula was