Environmental Flows in Water Resources Planning - Duero Basin (Spain) Case Study

European Water Framework Directive (WFD) (EC, 2000), demands a more integrated and multidisciplinary approach in the development of water plans. This consideration introduces a higher degree of complexity into the already complex task of integrated water resources management. One of the main and most difficult topics in the development of the current water plans is defining environmental flows. This paper presents a new methodology to define environmental flows by using simulation management models. SIMGES model is used to analyze the possible impact of environmental flows in the reliability of the demands. SIMGES is a simulation program based in network flows optimization. It is part of AQUATOOL, a Decision Support System Shell to develop models for water resources planning and management. A simulation model of the whole Spanish basin of the Duero River was created and calibrated. The model is composed by hundreds of elements such as reservoirs, hydroelectric power plants, agricultural and urban demands, aquifers, etc. The management is simulated with a system of priorities which is later translated to the cost of the network arcs. A range of environmental flows at several points of the basin was obtained from different hydrologic and habitat simulation environmental studies. In order to establish the optimal combination of environmental flows in the basin with an objective of maximum flows with minimum impact in the reliability demands a heuristic optimization approach was developed. This paper explains the optimization approach and the application to a real case, the Duero basin, which helped to define environmental flows taking into account other uses in the basin.