The EU water framework directive (WFD) provides a template for sustainable water management across Europe. The WFD requires the development of procedures to ensure appropriate mitigation of anthropogenic impacts on river ecosystems resulting from water abstraction and impoundments. It is widely acknowledged that alterations to flow regime impact on riverine ecosystems. As a result, hydromorphology, which includes the hydrological regime, is embedded within the WFD as a supporting element to achieve good ecological status (GES). Environmental flow releases from impoundments such as reservoir dams will need to be implemented to mitigate impacts from their construction and operation. This paper outlines the process involved in the analysis of available scientific information and the development of guidance criteria for the setting of environmental flow release regimes for UK rivers. The paper describes two methods-developed by round-table expert knowledge and discussions and supported by available data-for implementation of the WFD for rivers subject to impoundments. The first is a method for preliminary assessment of a water body to determine if it is likely to fail to achieve GES because of changes to the flow regime (indexed by simple flow regime statistics) in systems where appropriate biological assessment methods are limited or currently unavailable. The second is a method for defining an environmental flow regime release based on the requirements of riverine ecological communities and indicator organisms for basic elements (building blocks) of the natural flow regime.

Under the European Union Water Framework Directive, Member States must put in place a river basin planning framework to determine what measures are necessary to maintain and improve the ecological status for all surface water bodies. The governmental organisations legally responsible for implementing the Directive in the UK have recognised that an appropriate river flow regime is fundamental to maintain a healthy river and, as a result, they need to regulate abstractions and effluent discharges and ensure sufficient water is released from impoundments. This paper reports on the process of producing environmental standards that define the maximum abstraction allowable from UK rivers, to leave sufficient flow to maintain a healthy river ecosystem. As there are currently insufficient data available to determine the relationships between river flow and ecological status empirically, expert knowledge was captured through a series of workshops at which leading UK freshwater scientists defined maximum levels of river flow regime alteration that would achieve ecological objectives for different river water body types. For the least ecologically sensitive rivers, maximum abstractions in the range 15-35% of the natural flow were proposed, depending on the flow magnitude and time of year. For the most sensitive rivers, the maximum abstraction proposed was in the range 7.5-25%. The knowledge was used by the responsible UK authorities to develop environmental standards. The authorities subsequently used the environmental standards to determine regulatory standards that could be implemented within practical constraints and current licensing policies.Key words Water Framework Directive; environmental standards; abstraction management; rivers; expert panel; environmental flows; ecohydrology; hydro-ecology Développement de standards environnementaux sur les prélèvements d'eau en rivière au Royaume Uni pour la mise en oeuvre de la directive cadre sur l'eau de l'Union Européenne Résumé La directive cadre sur l'eau de l'Union Européenne impose aux Etats membres de mettre en place un cadre de gestion des bassins versants afin de déterminer les mesures nécessaires au maintien et à l'amélioration de l'état écologique des eaux de surface. Les organismes gouvernementaux légalement responsables de la mise en oeuvre de la directive au Royaume Uni ont reconnu qu'un régime hydrologique approprié est fondamental pour la bonne santé d'une rivière et que, en conséquence, ils doivent réglementer les prélèvements et les rejets et assurer un débit suffisant en sortie des retenues. Cet article porte sur le processus de production de standards environnementaux définissant les prélèvements maximaux possibles dans les rivières britanniques en vue du maintien de la bonne santé des écosystèmes de cours d'eau. Etant donnée l'insuffisance des données disponibles pour déterminer empiriquement une relation entre débit de rivière et état écologique, la connaissance experte a été capturée à travers une série d'ateliers lors desquels les principaux s...