Résumé
In numerous river basins, the implementation of the Water Framework Directive challenges the administrative authorization delivered for agricultural withdrawals. In such a context, farmers demand public subsidies for building water reservoirs filled in winter for summer use (substitution reservoirs) in order to compensate the water quota reduction and prevent drop in income. We here present a financial and economic assessment method for such projects and highlight how it is possible to support the decision in assessing profitability thresholds. This method combines classical project economic analysis and microeconomic modelling. It is implemented in the Boutonne River basin, where an 84% agricultural water quota reduction is planned. Our calculation shows that this quota reduction could lead to a drop of 3.2Msin agricultural income at the basin scale and creation of a 15.5 Mm3 water reservoir could offset the 19.6 Mm3 quota reduction. However, this creation of a water reservoir for irrigation is not feasible without state aid. Economical and financial criteria alone do not make it possible to decide on creating the reservoir, but they are usable for determining the impacts of public subsidize rates.