2003) What kind of water models are needed for the implementation of the European water framework directive? ABSTRACTThe European Water Framework directive (WFD) promotes an integrated management approach, defines the river basin as the relevant management unit, and sets the objective of good ecological status for all waters in Europe before 2015. Based on research activities underway in France, this paper presents five examples of issues related to water modelling for the implementation of the WFD. The new concept of "good ecological status" calls for a necessary shift from a classical biogeochemical modelling to an ecological modelling, and for new kind of models which can describe the biological response of aquatic ecosystems to physical disturbance. The integrated management approach demands new kind of models, based on a more global approach, adapted to the scale of work and management to be done; this is illustrated with the rainfall-runoff models. In the field of hydraulics, the complexity is addressed through the creation of models, consisting of several modules, which are optimised as a function of the application desired. Finally, the need of tools in the process of allocating water resources among several actors in a river basin, as foreseen in the WFD, may be addressed by the use of multi-agent systems. All these examples show clearly that the hydrosystem complexity, the study of which requiring the use of physical, ecological, social and economic sciences, cannot be solved easily with a unique type of water modelling. Research is still needed to address this complexity, but also to provide in the same time tools and results for water managers.

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