IWRA World Water Congress 2008 Montpellier France
1. Water availability, use and management
Division of Water
Institute for Water Quality and Waste Management (ISAH),
Am Kleinen Felde 30,
D - 30167 Hannover, Germany,
phone: +49 (0)511 762 19477,
+49 (0)511 762 19413,
reservoir operation, environmental sustainability, ecology, water quality, IWRM
A multitude of factors impacts on the
environment and thereby on the freshwater resource.
Despite the influence of human societies that modify their
environment to their needs, global warming is strongly impacting on precipitation, flow regimes, and the frequency
and intensity of extreme events.
Regulating rivers by dams modifies directly and significantly natural river flow
regimes and, since their operating rules and policies determine the amount and timing of releases, they are an
important starting point for securing water quality, quantity and environmental sustainability.
operation (enrop) is a concept for operating reservoirs by adapting the inflow and release patterns considering water
quantity and quality dynamics, and including environmental aspects.
This paper discusses the
application of enhanced reservoir operation (enrop) as a management concept supporting the improvement of
IWRM in water deficient regions. The development of operation schemes by adapting reservoir inflow and releases
addressed the provision of downstream water supply and ecological requirements. The extended understanding of
the interactions between specific reservoir operations and the provided water quality and quantity will support
satisfying the potential conflicting needs of humans and ecosystems.
For integrating enhanced
reservoir operation into IWRM mainly information on the reservoir inflow quality and quantity dynamic as well as
release pattern need to be known. Using reservoir water quality models, like the 1D reservoir model Lac or the 3D
model Mohid, the changing status of the water body is investigated and following the needed information on release
quality is gained. Based on this, site adapted reservoir operations will be developed.
From the vast of existing
methods for assessing environmental flow, e. g. hydraulic rating methods, habitat simulation methods, and holistic
methodologies (Arthington et al., 2006, Dyson et al. 2003, Tharme 2003), predominantly building on a natural flow
paradigm (Poff et al., 1997), will be reviewed and pre-selected against their potential to be linked to the enrop
concept. Environmental requirements will be then incorporated into developed enhanced operation schemes, as they
give thresholds for the water released by the dams and these in turn set boundary conditions for the management of
the reservoir inflow.
The intrinsic natural variability of the environment plays a central role in the
investigation of improved IWRM measures for integrating environmental aspects into enhanced reservoir
The alteration of the natural flow regime variability by dams is cannot be reconditioned completely.
Studies carried out in regulated streams mostly come to the conclusion that the optimal flow regime to be provided
should be fairly the same as the natural one given before the dam was built, what is completely/eventually not
possible due to the far-reaching changes caused by the dam
It is therefore needed that the assessment of
ecological flow regimes needs to be based on the current state. Investigating different discharge dynamics by
adapted dam operation, it can be stated that the more a flow regime approaches the natural flow, the higher its
potential for assuring environment relevant requirements.
There is the pressuring need of
improving water resources management in order to secure water quality, quantity and environmental
Enhanced reservoir operation allows environmental aspects to be incorporated into water
management by optimising reservoir storage in terms of quantities and quality.
Combining such operational
choices with important issues concerning water resource management the proposed method helps to develop a more
holistic approach to environmental sustainability, avoiding past limits imposed by considering only quantitative
aspects (e.g. minimum flow approach), but implying the understanding of downstream ecosystem needs.
method further supports decision makers in the overall water management for determining adaptive reservoir
operation schemes aiming for an improved water quality and quantity for civil use and aquatic ecosystem