Taking into account protective works in land-use planning for mountain torrential floods: state of the art of present French practices

¹ University Grenoble Alps, Irstea, UR-ETGR, 2 rue de la Papeterie - BP 76, F-38402 St-Martin-d’Hères, France
² AgroParisTech, Paris Institute of Technology for Life, Food and Environmental Sciences, Paris, France
³ Ecole Nationale Supérieure des Mines, Saint-Etienne, France
⁴ Office National des Forêts – Service Restauration des Terrains en Montagne des Hautes-Alpes, Gap, France

^a Corresponding author: felix.philippe@irstea.fr

Abstract

In 1995, a law stated a common regulatory natural risk zoning for French municipalities through a land-use planning procedure called Risk Prevention Plan (PPR). In mountain valleys and especially within torrential watersheds, considering protective structures in those plans is an actual concern. Those protections do have an effect on phenomena and modify hazard and risk levels. This paper gives an overview on how torrential protective works are taken into account in present risk prevention plans. To carry out this study, 53 recent risk prevention plans over 11 French mountain departments were selected and analyzed through a common analysis grid. Torrential protection works are taken into account in more than one third of analyzed plans. Protections mostly considered are dikes, bank protections, check-dams and sediment traps. Modalities of integration of these structures vary from one plan to another, influencing both hazard and regulatory zoning. Results also show a wide range of practices between departments and even inside them. Conclusions brought out enhance knowledge about actual practices which were not sufficiently known so far. Findings and new additional recommendations will be included in a future PPR methodological guide exclusively suited for torrential context, which is currently still missing.