10 Flow Seasonality in Two Big Polish Rivers – The Vistula …
201
e.g. greater amplitude of the curve of significant polynomial trend of multiannual
changes.
In both rivers, the difference in flow seasonality was particularly visible in the
1960s and 1970s. IS indices for both Oder gauges were then clearly smaller than
those for both Vistula gauges. The difference ceased to be perceptible later on. Signs
of this regularity can be found when analyzing IS dynamics for the gauges closing
the entire basins (Fig. 10.8c). Again, the index for the Vistula was slightly higher than
for the Oder, but the difference was the most pronounced for the first 30 years. Then
the average flow seasonality indices were similar in both rivers and demonstrated a
similar nature of multiannual changes in relation to years (R = 0.61), year to year
changes and multiannual fluctuations.
10.7 Conclusions
Physico-geographical regions of Poland are divided roughly along latitudinal lines.
Mountains in the south are gradually replaced towards north with uplands, lowlands
and finally lakelands [14]. Two largest Polish rivers follow basically the same course
from south to north as they drain the surrounding regions. It is therefore clear that
their flow seasonality structure shows spatial differences. However, as the courses of
both rivers are similar, greater differences are observed along the rivers than between
their basins. This is confirmed by long-term studies on the variability of their flows
that indicate strong and significant correlation of the Vistula and the Oder SSQ in
their lower sections [16]. The analyses presented above allow for drawing a few basic
conclusions regarding changes in flow seasonality with increasing size of the river
basin.
– Half-flow date (TPO) in the upper sections of the rivers falls roughly two weeks
later than in the lower ones. The average TPOs recorded for these watercourses
occur between 162 and 194 days of a hydrological year and are similar to analogous measures calculated for 12 Carpathian rivers [10, 12]. The difference between
the Vistula and the Oder was insignificant. TPO for the Oder is usually by 4–5 days
earlier than that for the Vistula. The value of TPO is relatively stable along the
course of both rivers, even though it is the highest in the upper sections.
– Flow concentration dates (PK) in the Vistula and the Oder are getting earlier along
their course. The similarity of PK in both rivers is even greater than of TPO. No
major shifts were observed for flow concentration date, which typically occurred
between 153 and 185 days of the hydrological year. This indicated a gradual
transformation of the flow regime downstream from a complex to a simple one.
Average concentration dates for the gauges closing the upper sections of the
Vistula and the Oder were comparable to those computed for the rivers of the
Western Beskids, and those inferred for the lower sections were similar to times
obtained for the rivers of the Eastern Beskids [12].
201
e.g. greater amplitude of the curve of significant polynomial trend of multiannual
changes.
In both rivers, the difference in flow seasonality was particularly visible in the
1960s and 1970s. IS indices for both Oder gauges were then clearly smaller than
those for both Vistula gauges. The difference ceased to be perceptible later on. Signs
of this regularity can be found when analyzing IS dynamics for the gauges closing
the entire basins (Fig. 10.8c). Again, the index for the Vistula was slightly higher than
for the Oder, but the difference was the most pronounced for the first 30 years. Then
the average flow seasonality indices were similar in both rivers and demonstrated a
similar nature of multiannual changes in relation to years (R = 0.61), year to year
changes and multiannual fluctuations.
10.7 Conclusions
Physico-geographical regions of Poland are divided roughly along latitudinal lines.
Mountains in the south are gradually replaced towards north with uplands, lowlands
and finally lakelands [14]. Two largest Polish rivers follow basically the same course
from south to north as they drain the surrounding regions. It is therefore clear that
their flow seasonality structure shows spatial differences. However, as the courses of
both rivers are similar, greater differences are observed along the rivers than between
their basins. This is confirmed by long-term studies on the variability of their flows
that indicate strong and significant correlation of the Vistula and the Oder SSQ in
their lower sections [16]. The analyses presented above allow for drawing a few basic
conclusions regarding changes in flow seasonality with increasing size of the river
basin.
– Half-flow date (TPO) in the upper sections of the rivers falls roughly two weeks
later than in the lower ones. The average TPOs recorded for these watercourses
occur between 162 and 194 days of a hydrological year and are similar to analogous measures calculated for 12 Carpathian rivers [10, 12]. The difference between
the Vistula and the Oder was insignificant. TPO for the Oder is usually by 4–5 days
earlier than that for the Vistula. The value of TPO is relatively stable along the
course of both rivers, even though it is the highest in the upper sections.
– Flow concentration dates (PK) in the Vistula and the Oder are getting earlier along
their course. The similarity of PK in both rivers is even greater than of TPO. No
major shifts were observed for flow concentration date, which typically occurred
between 153 and 185 days of the hydrological year. This indicated a gradual
transformation of the flow regime downstream from a complex to a simple one.
Average concentration dates for the gauges closing the upper sections of the
Vistula and the Oder were comparable to those computed for the rivers of the
Western Beskids, and those inferred for the lower sections were similar to times
obtained for the rivers of the Eastern Beskids [12].