Most cost-effective options: what lessons can be learned from the black spots strategy of Agence de l'Eau Seine-Normandie in 1987-1991? | Efficience et obligation de résultats : quelles leçons tirer de la politique points noirs de l'agence Seine Normandie menée de 1987 à 1991 ?

During the period 1987-1991, the French Water Agency of Seine-Normandy basin experimented with a "black spots" strategy in order to restore aquatic sites of very poor quality and of great interest for usages by identifying needed investments and by concentrating funds and communication efforts there. We tried to draw lessons from this policy with an ex-post appraisal of its results. Data collection was an important part of our work given the absence of a Geographical Information System in the Agency. We overcome such constraints with a logical diagram for screening "black spots" out of 8,000 agreements of funding and by digitizing needed data from maps. We built a database of 58 "black spots" which can be considered as well informed case studies with comprehensive financial data and water quality monitoring. We propose indicators to assess the black-spots strategy. We show that, given the general basin-wide quality getting worse, the strategy was effective and efficient. Without any data concerning usage recovery, the weight of the different criteria such as length of restored river or number of restored spots remains subjective. Different variables likely to explain success and failure are tested. Variability of discharges explains partly differences of results. We also enlighten a regional office effect. Such a site-oriented approach illustrates how different causes combine with each other to impact the environment. Therefore the relevance of an overall appraisal remains limited. To assess consistency and effectiveness of any strategy, one should previously list all possible causes of degradation and possible remediation site by site to make them comparable and to understand properly their evolution. Moreover monitoring options may deeply affect scoring results.