Author(s)

M. M. Portela

Abstract

One of the environmental issues related with the numerous dams of the Alqueva irrigation system (South of Portugal) was, and still is, the definition of the ecological regimes. Besides other features, those regimes must account for the extreme water scarcity that characterizes the region. For the 12 dams of the Alqueva system (either existing or new ones) several methods aimed at defining the ecological flows were applied. The comparison of the ecological flows thus predicted revealed the inadequacy of the different methods, suggesting the need for a new approach capable of providing comparable ecological flows under similar hydrologic constraints. In the previous scope a new method supported by hydrologic and hydraulic criteria was developed. The hydrologic criteria account for the water scarcity and for the temporal irregularity of the natural hydrologic regime and the hydraulic criteria, for the geometry of the cross sections and of the river reaches. The method is briefly described and the ecological flows achieved for 12 case studies are presented. Keywords: ecological flows, hydrologic-hydraulic method, hydrologic regime, hydraulic characteristics, cross section, mean flow velocity. 1 Introduction: scope of the study In the next few years an intense agricultural development is expected in Alentejo (South of Portugal) as result of the construction of the Alqueva dam, located in the Guadiana River and providing a huge reservoir, in fact, the largest artificial

Keywords

ecological flows, hydrologic-hydraulic method, hydrologic regime, hydraulic characteristics, cross section, mean flow velocity.