Conceptual Approaches, Methods and Models Used to Assess Abstraction Limits for Unconfined Aquifers in France

Abstract

This chapter presents a review of methods an tools used in France to assess groundwater abstraction limits in unconfined aquifers. The experience gained from over 30 studies shows that the estimation of Maximum Permissible Volume (MPV) is complicated by numerous uncertainties. The first prerequisite is a good knowledge of the dynamics of the hydrosystems and abstraction volumes, but unfortunately this is rarely achieved. Moreover, both the calculation methods and modelling tools that aim to conceptualize these complex systems have limitations due to the simplifying assumptions required for their application. Technical recommendations are proposed for a proper assessment of such uncertainties. In many cases, the calculated maximum permissible volumes were much lower than the previously authorized volumes. Therefore, many of the results were contested by affected users. Such disputes concerned not only the economic consequences of reduced abstraction, but also the scientific basis of the studies in view of the known uncertainties and limitations. The last section of this chapter discusses this phase of negotiations, specifically based on examples from the Adour-Garonne water basin in southwest France.