Bi-objective dynamic programming for trading off hydropower and irrigation

Reservoir management is examined from the bicriterion viewpoints of hydropower generation and irrigation. Specifically, a decision support system is developed which includes constructing the set of non-inferior solutions, using the constraint, penalty and weighting methods. The reservoir operation model, as well as the optimization and simulation software, were initially provided by the R & D Division of the French Electrical Utility (Electricité de France) ; the method is based on a Stochastic Dynamic Programming - SDP - model with daily time steps, using 50 annual values of daily historical inflows and marginal electricty production costs. The water requirement for irrigaton is taken either as preset using a demand curve, or as a soil reservoir model based on SDP running simultaneously with the resevoir model. The model yields trade-off curves of electrical production losses versus, respectively, irrigated surface area, crop yield, and agriculture benefits. A numerical application illustrates the methodology in the French case of the Bort reservoir, in the Dordogne valley. The model reveals releasing water for irrigation could present economic advantages within certain constraints on maximum irrigated surface area and minimum water price. Consequently, the current economic justification of single purpose reservoir management for hydropower ought to be changed. Negotiation should be initiated for the purpose of selecting one of the non-dominated reservoir management policies, hereby minimizing the distance of the " most preferred " solution point from the ideal one or by using the Nash cooperative game solution. Multicriterion decision-making seems to be a promising operational management tool for hydrosystems. La gestion d'un barrage est étudiée avec pour double objectif la production électrique et l'irrigation. Afin de déterminer l'ensemble des solutions non-inférieures, un modèle est développé utilisant successivement la méthode des contraintes, la méthode des pénalités et la méthode des pondérations de critères. Le modèle initial de gestion de barrage, ainsi que le programme d'optimisation et de simulation, proviennent du centre de recherche d'EDF. Ce modèle utilise la programmation dynamique stochastique au pas de temps journalier, la valeur des débits d'entrée journaliers observés au cours des 50 dernières années et le coût marginal de la production électrique donné par le service économique d'EDF. La demande en eau d'irrigation est estimée soit à p