Water Management in the Neste System (France)

Abstract

For over thirty years the Compagnie d’Aménagement des Coteaux de Gascogne (CACG) has been in charge of the water management of the complex hydrographic system of the Neste. This system makes it possible to divert a part of the river Neste natural flow for the benefit of the Gascony rivers which are completely dry in the summer and often so in the autumn. Despite this natural disadvantage, Gascony rivers provide irrigation water to 40 000 hectares, drinking water to 200 000 people and keep a satisfactory level of quality as far as the Garonne confluence: this was made possible not only through the increase of water resources by building reservoirs on these rivers but also thanks to constant efforts to make the best possible use of the existing water resources, thus leading, year after year, to the development of specific management techniques with the following main characteristics: (1) perfect knowledge of demands, both in terms of quantity and quality; (2) regular coordination and discussion with the main water users to define at the beginning of each summer the volumes to be diverted; (3) weekly adjustments of demand satisfaction according to the level of reservoirs and natural inflow predictions (strategic management); (4) automatic real time modulation of released dam water (tactical management).