Basin influence on natural variability of rivers in semi-arid environments

Scientific evidence indicates that freshwater aquatic ecosystems can be protected or restored by recognising that dynamic flow patterns must be maintained within the natural range of variation to promote their integrity and sustainability. An evaluation of the required conditions for healthy functioning needs to begin with a description of natural streamflow patterns. In order to characterise the flow regimes of a group of rivers located in central Spain, data was taken from 25 gauging stations in a major river basin to establish a hydrological grounding upon which to base biological studies. A number of basin variables were also obtained, and this paper considers the relationships that exist between relevant ecohydrological indices and these basin characteristics. Special importance has been attached to low flow characterisation, since these situations are important determining factors for the development and evolution of biological populations. The results show a significant relationship between one of the low flow indices and basin lithology, evapotranspiration and river basin size. Finally, two models have been found which allow low flow volume values to be estimated from these river basin variables. These models can be used to obtain low flow values in river basins where gauging stations do not exist.