Efficience économique et financement des solutions fondées sur la nature : le cas du bassin versant de la Brague
Abstract
This paper explores the economic efficiency of flood protection strategies to aid funding decisions of public bodies. The Brague river is a 68 km 2 catchment located on the Mediterranean Sea shore in South East France. It experienced disastrous flash floods triggering costly damages and casualties in the communities of Biot and Antibes. Several possible flood protection strategies using conventional civil engineering measures or Nature-based solutions were tailored mixing engineering and participatory approaches. They were then assessed in terms of i) protection efficacy and avoided damage using numerical modelling, ii) environmental gains or alterations using an indicator on the morphological quality of the river, and iii) willingness-to-pay of the citizens for the various strategies, assessed both by top-down transfer methods, as well as by interviews of about 400 citizens. A dual cost-benefit analysis (CBA) was finally tailored to help the various decision makers involved in the management of the catchment in the context of the Gemapi law (management of aquatic environments and flood protection). A top-down CBA was performed to help national and regional stakeholders decide whether they would support the strategies. In the meantime, a bottom-up CBA was performed to capture the local perception of hazards, the social acceptability of various mitigation measures and to help the basin managers decide on the relevant strategy to be implemented.
Cet article évalue l’efficience économique de stratégies de prévention du risque d’inondation en vue d’éclairer la décision de financement des acteurs publics. Le cas de la protection contre les crues « éclair » (courtes et violentes) de la Brague et des inondations associées de la basse vallée à Biot et Antibes (Alpes-Maritimes) est pris comme exemple. Dans cette perspective, nous proposons une double analyse coût-bénéfice (ACB) dans le contexte particulier de la loi Gemapi (gestion des milieux aquatiques et protection contre les inondations) et des stratégies dites « SFN » (solutions fondées sur la nature). L’ACB top-down éclaire les décisions des acteurs nationaux et régionaux tandis que l’ACB bottom-up répond aux préoccupations des acteurs locaux en évaluant l’acceptabilité sociale des stratégies étudiées.
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