Analyse des récentes sécheresses du Sud-Ouest

Analysis of the recent droughts in the south-west of France

¹ Ingénieur en Chef des Ponts et Chaussées, Chef du Service Navigation de Toulouse, Délégué du Bassin Adour-Garonne
² Délégation de bassin Adour-Garonne

Abstract

The drought of Autumn 1986 was all the more difficult since it followed that of 85 which lasted until quite late. Winter and Spring of 86 saw a return to normal rainfall but the month of May saw the beginning of a new dry period which was to last until the beginning of Winter.

The succession of these two exceptionnally dry periods led to rapid consummation of water level reserves from 1986 onwards. In 1986 the phenomenon is more rigourous than in 1985 and much more so than in 1976: You have to go back to 1949 to find an equivalent drought.

This led the Basin Delegate to set up a "crisis cell" to follow the development of the phenomenon and to propose to the Basin Coordinating Prefect a series of actions followed by effects: reduction of the flow delivered by the Neste canal, limitation of the supply flow rate of the canal parallel to the Garonne, releasing of water from EDF reserves, and finally stopping of pumping for irrigation.

The succession of these two worrying periods also enabled all partners to become aware of the problems, and triggered off the development programme approved of by the Committee for the Ardour-Garonne Basin, and plans for construction work over 10 years to provide a total capacity of 300 million cubic meters for a total cost of 1480 million francs.