L'abandon des tours d'eau et ses conséquences opérationnelles sur les systèmes collectifs d'irrigation : une approche multi-agents situationnelle appliquée à un canal gravitaire de Moyenne Durance (France)

International audienceThe operation of collective irrigation networks is increasingly constrained by the introduction of new water resource management devices regulating their demand. In France, the 2006 Water Act defined a maximum volume to be withdrawn for irrigation in each river basin where a significant imbalance remains between water supply and demand, leading to a maximum authorized withdrawal for each irrigation structure. In addition, following the 2003 drought, ad hoc drought restrictions were also put in place. These regulatory constraints are in addition to other organizational and operational constraints for farmers. As a result, during an irrigation campaign, the possibilities for operational adjustment of farmers' irrigation schedules are already limited by organizational constraints, and must also take into account new regulatory constraints. Some collective networks are adapting by modifying their organization mode for sharing water between irrigators, by freeing irrigation from the constraints linked to the collective mode of water sharing such as the water daily slot. This is notably the case of the association of irrigators of Aspres-Sur-Buëch, in the Buëch River basin, a tributary of the Durance, which used this mode of sharing for centuries before gradually abandoning it in recent years. This work proposes to study the impact of such a change on the scale of a gravity-fed network that has abandoned the historical mode of sharing by daily slot. The approach mobilizes the WatASit multi-agent model which, based on the affordance concept, allows to integrate a representation of the operational management level during an irrigation campaign. The concept of affordance clarifies the possibilities of action available to actors. Simulation results show that if the abandonment of the water-sharing mode by daily slot effectively allows an increase in irrigation slots, it highlights the inequalities between irrigators in terms of capacity and irrigation abandonment. The change in organization does not impact all irrigators in the same way, depending on the location, especially downstream of the network, and the number of irrigable farm plots of each one.Le fonctionnement des réseaux d'irrigation collectifs est de plus en plus contraint par l'introduction de nouveaux dispositifs de gestion de la ressource en eau visant à réguler leur demande. Certains réseaux collectifs s'adaptent en modifiant leur mode d'organisation pour le partage de l'eau entre irrigants, de manière à rendre l'irrigation plus flexible dans le temps. Cette étude propose d'évaluer l'impact d'un tel changement à l'échelle d'un réseau gravitaire ayant abandonné le mode de partage historique par tours d'eau. L'approche mobilise le modèle multi-agents WatASit qui, basé sur le concept d'affordance, permet d'intégrer une représentation du niveau de gestion opérationnelle durant une campagne d'irrigation. Le concept d'affordance clarifie les possibilités d'actions offertes aux acteurs. Les résultats de simulations montrent que si l'abandon du mode de partage par tours d'eau permet effectivement une augmentation des créneaux d'irrigation, il met en exergue les inégalités entre irrigants en termes de capacité et d'abandons d'irrigation. Le changement d'organisation n'impacte pas tous les irrigants de la même façon, selon la localisation, notamment en aval du réseau, et le nombre de parcelles irrigables de chacun