Proposal of Environmental Flow Assessment Criteria for Exceptional Hydrologic Situations

Abstract

One of the difficulties with habitat simulation methods for environmental flow determination is how to choose the minimum commitment point on the weighted usable area (WUA)–flow (Q) curve. For decades, considerable efforts have gone into finding a method that is objective and has biological sense. In Spain, the regulatory hydrologic planning code suggests taking a flow that produces a fixed percentage of the maximum WUA. Given the generalistic nature of this instruction, an evaluation based on environmental criteria needs to be considered. This paper proposes a test to assess the results obtained with the Instrucción de Planificación Hidrológica (IPH) criterion that can also be used to assess the results provided by other flow selection methods. The proposed test is based on the potential of the defined flows to allow fish movements. The results question the validity of applying a fixed percentage of the maximum WUA to determine the minimum flow on any river reach. They also allow the studied river reaches to be classified in groups with channels and basins of similar physical characteristics that can be taken into account for management purposes.