Implementing Environmental Flows in Complex Water Resources Systems Case Study: The Duero River Basin, Spain

Abstract

European river basin authorities are responsible for the implementation of the new river basin management plans in accordance with the European Water Framework Directive. This paper presents a new methodology framework and approach to define and evaluate environmental flow regimes in the realistic complexities that exist with multiple water resource needs at a basin scale. This approach links river basin simulation models and habitat time series analysis to generate ranges of environmental flows (e-flows), which are evaluated by using habitat, hydropower production and reliability of water supply criteria to produce best possible alternatives. With the use of these tools, the effects of the proposed e-flows have been assessed to help in the consultation process. The possible effects analysed are impacts on water supply reliability, hydropower production and aquatic habitat. After public agreements, a heuristic optimization process was applied to maximize e-flows and habitat indicators, while maintaining a legal level of reliability for water resource demands. The final optimal e-flows were considered for the river basin management plans of the Duero river basin. This paper demonstrates the importance of considering quantitative hydrologic and ecological aspects of e-flows at the basin scale in addressing complex water resource systems. This approach merges standard methods such as physical habitat simulations and time series analyses for evaluating alternatives, with recent methods to simulate and optimize water management alternatives in river networks. It can be integrated with or used to complement other frameworks for e-flow assessments such as the In-stream Flow Incremental Methodology and Ecological Limits of Hydrologic Alteration.