Froehlich, Felix ; Dittmann, Robert ; Muschalla, Dirk ; Ostrowski, Manfred W. ; Pohl, Reinhard (2008)
Re-Operation of Multi-Purpose Reservoirs for Economic and Environmental Benefits.
28th USSD Annual Meeting and Conference. Portland, Oregon, USA (28.04.2008-02.05.2008)
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Kurzbeschreibung (Abstract)

Natural river habitats are subject to continuous changes. The flow regime of a stream affects flow velocity, water depth, sediment transport, water quality and river morphology, as well as the frequency and depth with which floodplains are inundated. The flow regime thus acts as a 'master variable' that influences many aspects of the river habitat. Many aquatic organisms are specialized on being able to cope with the continuously changing environment they inhabit, some are capable of using these circumstances to their advantage and others even depend on them. Reservoir releases that do not imitate the natural flow regime result in changed habitat conditions for organisms inhabiting the affected reaches below the reservoir. In many cases, this leads to an ecological impoverishment of the affected reaches and/or to the invasion of foreign species that are better suited to survive in the changed conditions, in both cases resulting in a changed ecosystem. In order to preserve or restore a natural river habitat, the flow regime of a river that is affected by a reservoir has to imitate the natural flow regime as closely as possible. This concerns properties such as quantity, frequency, duration, timing as well as the rate of change of flow. This paper is a result of an ongoing research project focusing on the reduction of flood risk along rivers regarding both the failure probability of affected structures as well as the damage inflicted upon socio-economic values downstream of reservoirs. At the same time, reservoir releases are modified such that dam-induced hydrologic alteration down-stream is reduced, thus improving downstream habitat conditions. This is achieved by developing tools that allow for improved, model-based reservoir regulation with dynamic releases, producing both economic as well as environmental benefits. A reservoir operation model is used to define dynamic releases which are then optimized with regard to multiple, partly conflicting, objectives (flood protection, dam safety, hydropower production, water supply, hydrologic alteration) using evolutionary algorithms. The methodology is applied to case studies of existing multi-purpose reservoirs in Ger-many and improves existing reservoir operating rules regarding both economic as well as environmental aspects. Compared to conventional operating rules, the dynamic operating rule keeps the reservoir storage levels at a more constant level and produces a more variable reservoir release pattern that follows the natural flow regime. As a result, hydrologic alteration can be reduced significantly, while the storage levels better adhere to the reservoir's flood guide.

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