Defining river types in a Mediterranean area: a methodology for the implementation of the EU Water Framework Directive.

The Water Framework Directive (WFD), approved at the end of 2000 by the European Union, proposes the characterization of river types through two classification systems (A and B) (Annex II of the WFD), thereby obtaining comparable reference sites and improving the management of aquatic systems. System A uses fixed categories of three parameters to classify rivers: three altitude ranges, four basin size ranges, and three geological categories. In the other hand, System B proposes to establish river types analyzing different factors considered as obligatory and optional. Here, we tested Systems A and B in the Catalan River Basin District (NE Spain). The application of System A results in 26 river types: 8 in the Pyrenees and 18 in the Iberic-Macaronesian ecoregions. This number would require the establishment of a complex management system and control of the ecological status in a relatively small river basin district. We propose a multivariant system to synthesize the environmental descriptors and to define river types using System B. We use five hydrological, seven morphological, five geological, and two climatic variables to discriminate among river types. This method results in fewer river type categories than System A but is expected to achieve the same degree of differentiation because of the large number of descriptors considered. Two levels are defined in our classification method using System B. Five "river types," defined at large scale (1:1,000,000), are mainly discriminated by annual runoff coefficient, air temperature, and discharge. This level is useful and could facilitate comparisons of results among European river basin districts. The second level defines 10 "subtypes of river management," mainly discriminated by geology in the basin and flow regime. This level is more adequate at local scale (1:250,000) and provides a useful tool for management purposes in relatively small and heterogeneous river basin districts.