Résumé
This report presents the first part of the audit of the State concessions of the Neste system commissioned to Irstea by the Ministry of Agriculture, in view of their transfer to the Occitania and New Aquitaine Regions. The report begins with an executive summary. The introduction positions these concessions in the yarrow of water territories in Gascony. The first chapters deal with the state of the hydraulic heritage, the maintenance policies and the hydraulic regulation of the works (Neste canal and its gullies, dam-river systems and pressurised networks). They conclude that the general state of the works is good, even if further investment in their renovation is required. The following chapters deal with the dynamics over 30 years of the withdrawals (agriculture, raw water for drinking water, industry) from rivers and pressurised networks. The tariffs and revenues generated by these abstraction uses are presented. The increasingly marked economic imbalance is highlighted and options for reform are outlined. One of these options would be to make non-drawing uses contribute, including low-water support and the replenishment of the headwaters of the basin to ensure the health of these rivers subject to a high risk of intermittence. The last chapter presents an initial assessment of the volumes involved and the quality of service indicators for these non abstraction uses. These points should be examined in greater depth in the second part of the audit, which focuses on the prospects for this complex hydraulic system.