Water storage has increased considerably worldwide since the 1950s. Water is collected and stored in reservoirs to supply towns and cities with drinking water, and for agricultural and industrial purposes, fish farming, leisure activities and low-flow period support. In the late 20th Century, there was a considerable increase in small reservoirs in France, reaching a total of 125,000 by the early 2000s. The creation of new water storage structures continues in parallel with the exploration of water use reduction solutions. These developments raise a whole host of environmental issues, such as the impact of reservoirs on the aquatic environment, particularly in areas where there are already a number of reservoirs and water resources are in high demand. By law, building a new reservoir requires a planning application or government authorization, which require an environmental impact study. Such studies must now assess the cumulative effects of the project together with other known similar projects. The “cumulative” aspect of the impact of water storage structures on a single catchment area is often poorly understood, probably due to a lack of relevant knowledge and methods. Consultants and government services therefore face a lack of operational tools for processing new reservoir applications, which gives rise to other problems around water management planning and the supervision of the development of new reservoirs. In this context, the French Ministry of the Environment, Energy and Marine Affairs (MEEM), supported by ONEMA, requested a joint scientific assessment (ESCo) from Irstea, in partnership with INRA, on the cumulative impact of reservoirs on the aquatic environment. It was produced by around fifteen experts from a range of disciplines and research organizations, and is based on analysis of a thousand or so international scientific articles and reports.

Water storage has increased considerably worldwide since the 1950s. Water is collected and stored in reservoirs to supply towns and cities with drinking water, and for agricultural and industrial purposes, fish farming, leisure activities and low-flow period support. In the late 20th Century, there was a considerable increase in small reservoirs in France, reaching a total of 125,000 by the early 2000s. The creation of new water storage structures continues in parallel with the exploration of water use reduction solutions. These developments raise a whole host of environmental issues, such as the impact of reservoirs on the aquatic environment, particularly in areas where there are already a number of reservoirs and water resources are in high demand. By law, building a new reservoir requires a planning application or government authorization, which require an environmental impact study. Such studies must now assess the cumulative effects of the project together with other known similar projects. The “cumulative” aspect of the impact of water storage structures on a single catchment area is often poorly understood, probably due to a lack of relevant knowledge and methods. Consultants and government services therefore face a lack of operational tools for processing new reservoir applications, which gives rise to other problems around water management planning and the supervision of the development of new reservoirs. In this context, the French Ministry of the Environment, Energy and Marine Affairs (MEEM), supported by ONEMA, requested a joint scientific assessment (ESCo) from Irstea, in partnership with INRA, on the cumulative impact of reservoirs on the aquatic environment. It was produced by around fifteen experts from a range of disciplines and research organizations, and is based on analysis of a thousand or so international scientific articles and reports.

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. Cumulative impact of reservoirs on the aquatic environment. Joint scientific appraisal. Executive summary Nadia Carluer, Marc Babut, Jean Belliard, Ivan Bernez, D. Burger Leenhardt, J.M. Dorioz, O. Douez, S. Dufour, C. Grimaldi, F. Habets, et al.

Le stockage de l’eau a considerablement augmente dans le monde depuis les annees 1950. Les retenues collectent et stockent l’eau, pour l’alimentation des villes en eau potable, a des fins agricoles, industrielles, piscicoles, de loisir ou de soutien d’etiage. En France, les retenues de petites tailles se sont multipliees a la fin du 20ieme siecle. Au debut des annees 2000, on en comptait environ 125 000. La creation de nouveaux ouvrages de stockage se poursuit, parallelement a une recherche de reduction des usages de l’eau. Ces creations soulevent de nombreuses questions environnementales, notamment en termes d’impact sur le milieu aquatique, en particulier dans les zones deja tres equipees et ou les ressources en eau sont d’ores et deja tres mobilisees. La construction d’une nouvelle retenue necessite reglementairement une declaration ou la sollicitation d’une autorisation aupres des services de l’Etat, impliquant de realiser une etude d’impact environnemental du projet. Une telle etude doit dorenavant evaluer les effets cumules avec d’autres projets equivalents. Cette dimension « cumulee » de l’impact d’ouvrages de stockage d’eau sur un meme bassin versant est souvent mal apprehendee, les connaissances et les methodologies etant peu developpees sur cet aspect. Bureaux d’etude et services de l’Etat font ainsi face a un manque d’outils operationnels leur permettant d’instruire les projets de nouvelles retenues. Ces difficultes en entrainent d’autres au niveau de la planification de la gestion de l’eau et de l’encadrement a la creation de telles retenues. Dans ce contexte, le Ministere de l’Environnement, de l’Energie et de la Mer (MEEM), avec l’appui de l’Onema, a sollicite une expertise scientifique collective (ESCo) aupres d’Irstea, en partenariat avec l’Inra, sur l’impact cumule des retenues d’eau sur le milieu aquatique. Cette ESCo a mobilise une quinzaine d’experts de differents organismes de recherche et de disciplines variees. Cette ESCo s’est fondee sur l’analyse d’un millier d’articles scientifiques et de rapports internationaux.