Exergy as a guide to allocate environmental costs for implementing the Water Framework Directive in the Ebro River

Abstract

The Physical Hydronomics (PH) methodology is a tool to properly calculate restoration cost of water resources (regarding to quality degradation of water as well as water quantity losses) in the framework of the Second Law of Thermodynamics. It is based on the exergy, a thermodynamic property that can be understood as the minimum energy needed to restore a resource from its reference environment. An opportunity that methodology brings up is the development of River exergy profiles which can be represented along the length of the river, for different periods and degradation statuses. Focusing on the Water Framework Directive milestones, the most relevant contribution which is presented here is the assessment of restoration cost among diverse water polluters from physicochemical parameters of the river. The case study which is developed is the Ebro basin, a very representative Mediterranean river in Spain. Figures shown that quality restoration costs, found in the agriculture user resulted to be the highest, except for the organic matter component. If degradation is only focused to water consumption, obviously irrigation use obtained the higher figures. Degradation provoked by the hydroelectric user, never taken into account before in the PH assessments resulted to be the lowest, but increases in wet years. Total investments projected in the draft version of the Ebro River Management Plan seem to be enough to fulfill the environmental objectives projected by the Ebro River basin management authorities.