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1. FUrst and H. P. Nachtnebel
1.2 Problems
Beginning in 1992, water quality in the Alte Donau decreased significantly,
leading to massive algae blooms (Oscillatoria redekei Van Goor), and turned the
system into a eutrophic state (Dokulil et al. 1993). The reasons were sought in the
uncontrolled input of nutrients, mainly by underground flow, from various
sources, including incomplete sewage collection, a leaking waste dump site and
overpopulation of water birds. Abatement for several of these sources was
initiated.
However, it was also argued that nutrient inputs were probably even higher in
previous decades, when sewer systems in the surrounding areas and sanitary
facilities at the beaches were less developed. Changes in the hydrological regime
and the dynamics of the Alte Donau, influencing inflow and outflow of
groundwater, had to be considered as additional causes for this deterioration.
These hydrological changes were triggered by several engineering activities
during the past 30 years:
- Construction of the flood bypass channel Neue Donau, which influences the
magnitude and direction of groundwater flow.
- Construction of a main sewer collector near the left bank of the flood bypass.
- Construction of the hydropower plant Freudenau, due to which the
previously free-flowing reach of the Danube was impounded and the water
levels in the Neue Donau were raised.
1.3 Objectives
From 1997 to 1999 a research program was carried out which had to satisfy the
following set of objectives:
- Analysis of the causes and sources of deteriorated surface water quality.
- Analysis of the quantitative, temporal and spatial changes of the
hydrological regime.
- Analysis of the inputs of nutrients by groundwater flow.
Identification of the relationship between the hydrological regime and water
quality, i.e. growth conditions for water plants, depth of water, transparency.
The development of integrated management strategies for ground and
surface water to restore a hydrological regime which is closer to the natural
state and which can support further sustainable rehabilitation measures.
2 Changes in the Groundwater Regime
In the past three decades, the hydrological regime of the Alte Donau has been
substantially modified (Fig. 4). Several construction projects led to partial
1. FUrst and H. P. Nachtnebel
1.2 Problems
Beginning in 1992, water quality in the Alte Donau decreased significantly,
leading to massive algae blooms (Oscillatoria redekei Van Goor), and turned the
system into a eutrophic state (Dokulil et al. 1993). The reasons were sought in the
uncontrolled input of nutrients, mainly by underground flow, from various
sources, including incomplete sewage collection, a leaking waste dump site and
overpopulation of water birds. Abatement for several of these sources was
initiated.
However, it was also argued that nutrient inputs were probably even higher in
previous decades, when sewer systems in the surrounding areas and sanitary
facilities at the beaches were less developed. Changes in the hydrological regime
and the dynamics of the Alte Donau, influencing inflow and outflow of
groundwater, had to be considered as additional causes for this deterioration.
These hydrological changes were triggered by several engineering activities
during the past 30 years:
- Construction of the flood bypass channel Neue Donau, which influences the
magnitude and direction of groundwater flow.
- Construction of a main sewer collector near the left bank of the flood bypass.
- Construction of the hydropower plant Freudenau, due to which the
previously free-flowing reach of the Danube was impounded and the water
levels in the Neue Donau were raised.
1.3 Objectives
From 1997 to 1999 a research program was carried out which had to satisfy the
following set of objectives:
- Analysis of the causes and sources of deteriorated surface water quality.
- Analysis of the quantitative, temporal and spatial changes of the
hydrological regime.
- Analysis of the inputs of nutrients by groundwater flow.
Identification of the relationship between the hydrological regime and water
quality, i.e. growth conditions for water plants, depth of water, transparency.
The development of integrated management strategies for ground and
surface water to restore a hydrological regime which is closer to the natural
state and which can support further sustainable rehabilitation measures.
2 Changes in the Groundwater Regime
In the past three decades, the hydrological regime of the Alte Donau has been
substantially modified (Fig. 4). Several construction projects led to partial