Quantitative morphodynamic typology of rivers: a methodological study based on the French Upper Rhine basin

This study sought to establish a quantitative functional hydrogeomorphological typology of river reference types in the French Upper Rhine basin that would meet the requirements of the European Water Framework Directive, defined in terms of hydromorphological quality and prospects for river restoration. Four ecoregions (i.e. hydrogeomorphic units ) were delineated by expert opinion and validated by independent variables (i.e. 1·5‐year peak discharge, comparison of 10‐year daily flow and low flow, valley bottom morphology and specific stream power). A data set of 31 quantitative and qualitative variables for 187 field sites was established and analysed. Agglomerative hierarchical clustering (AHC) of the quantitative variables and principal component analysis (PCA) provided hierarchy and grouping of variables. Multiple correspondence analysis (MCA) confirmed these results, discriminating sites into seven groups, but did not lead to a functional typology due to important overlapping between groups and variability within groups. A definitive quantitative typology was obtained through AHC and discriminant analysis with cross‐validation computed separately in each ecoregion. Results for two ecoregions, ‘marly calcareous loess‐covered hills’ and ‘crystalline Vosges mountains’, are given as examples. Finally, the classification of the sites is extended to the whole river network by river sectorization, each homogeneous river section being classified to one category on the basis of the preceding classification of sites. Methodological implications regarding river classification are also given.