Groundwater Management Strategies to Improve Surface Water
263
reveals, however, that they are rather parallel, not admitting significant
fluctuations of lake volume. The previously typical rise from spring to summer is
either shifted in time or much less visible. In the period from April to August,
increases are between 0.5 and I million m 3 , starting from already high levels
above 3 million m 3 • This means that the effect of renewal and dilution by filtered
groundwater is significantly reduced.
The separate consideration of the water balances in the three compartments
indicates significantly slower renewal in the upstream part and acceleration in the
downstream part. To balance the deficit in the upstream part and the surplus in the
downstream part, a surface flow in the Alte Donau from downstream to upstream
is necessary (Fig. 8).
3.3 Summary of Changes in the Hydrological Regime
Due to construction of the flood bypass channel Neue Donau and associated
measures, the hydrological regime of Alte Donau changed significantly (Fig. 8):
1. An analysis of the hydrographs of surface and groundwater levels revealed
that parameters of groundwater dynamics were reduced by about 50% after
construction of the Neue Donau.
2. Low water levels in spring are missing, reducing the effect of dilution and
renewal by the increase of the water level to the summer maximum in the
Alte Donau.
3. The fluctuations of groundwater inflow were reduced and spatially
homogenised although total inflow increased. Seasonal reversals of flow
direction in the downstream part are completely eliminated.
4. The main flow direction from Neue Donau to Alte Donau became rather
uniform over the year.
5. Main inflow shifted from the upstream area to the downstream area,
inducing a slow upstream current in the Alte Donau.
57~600
~
ltOO-3800
I 3607
/'!.o(}'S200 mld I '~332P *
' " " "
1.0~.5900 mld
~
140(}'2900
~
~
2400·3200
230-1900
10600·12100
1971-73 ~(}'74fJ0 1993-96
~ 5900·6700
3600·4400
Fig. 8. Schematic flow-chart of mean inflow and outflow of groundwater for the periods
1971-1973 and 1993-1996
263
reveals, however, that they are rather parallel, not admitting significant
fluctuations of lake volume. The previously typical rise from spring to summer is
either shifted in time or much less visible. In the period from April to August,
increases are between 0.5 and I million m 3 , starting from already high levels
above 3 million m 3 • This means that the effect of renewal and dilution by filtered
groundwater is significantly reduced.
The separate consideration of the water balances in the three compartments
indicates significantly slower renewal in the upstream part and acceleration in the
downstream part. To balance the deficit in the upstream part and the surplus in the
downstream part, a surface flow in the Alte Donau from downstream to upstream
is necessary (Fig. 8).
3.3 Summary of Changes in the Hydrological Regime
Due to construction of the flood bypass channel Neue Donau and associated
measures, the hydrological regime of Alte Donau changed significantly (Fig. 8):
1. An analysis of the hydrographs of surface and groundwater levels revealed
that parameters of groundwater dynamics were reduced by about 50% after
construction of the Neue Donau.
2. Low water levels in spring are missing, reducing the effect of dilution and
renewal by the increase of the water level to the summer maximum in the
Alte Donau.
3. The fluctuations of groundwater inflow were reduced and spatially
homogenised although total inflow increased. Seasonal reversals of flow
direction in the downstream part are completely eliminated.
4. The main flow direction from Neue Donau to Alte Donau became rather
uniform over the year.
5. Main inflow shifted from the upstream area to the downstream area,
inducing a slow upstream current in the Alte Donau.
57~600
~
ltOO-3800
I 3607
/'!.o(}'S200 mld I '~332P *
' " " "
1.0~.5900 mld
~
140(}'2900
~
~
2400·3200
230-1900
10600·12100
1971-73 ~(}'74fJ0 1993-96
~ 5900·6700
3600·4400
Fig. 8. Schematic flow-chart of mean inflow and outflow of groundwater for the periods
1971-1973 and 1993-1996