Establishing environmental flow regimes in a Mediterranean watershed based on a regional classification

SummaryEnvironmental flow estimation in regulated rivers has become a major issue for watershed management in Mediterranean countries. The lack of regional environmental flow guidelines to protect ecological values of rivers, especially when the environmental flows must be determined at many locations in large basins, has led to the establishment of very simplistic criteria to fix instream flow needs in rivers. These simple hydrological methodologies ignore the site-specific characteristics of natural systems, and therefore should not be used for management practices when maintaining sustainable river ecosystems. We provide different methodological approaches to establish an environmental flow regime for regulated rivers at regional or watershed levels in both gauged and ungauged rivers, depending on the availability of site-specific empirical data and desired accuracy of the results. The types of selected approaches include simple environmental flow values interpolation from calculated values at a discrete set of points with available data, and the development of environmental flow prediction models based on a previous stream-flow classification and regionalization process. A total of 51 hydrological and physical watershed characteristic variables were defined at 46 gauging stations. Variables were classified in five groups, and a Principal Component Analysis (PCA) was conducted on each group of variables in order to reduce the dimension of the data set. Identified PCA axes were used in a Cluster analysis to find similarities among the gauging stations. Results revealed four homogeneous regions in the Ebro watershed, where environmental flow values may be predicted from variables such as the flow equalled or exceeded 347 days per year (Q347), or the average for the period of record of minimum mean monthly flows.