Classification and key for the identification of mountain stream morphodynamic units.

The hydromorphodynamic diversity of 294 units from 15 Pyrenean mountain streams was studied. 6 main groups and 18 secondary groups could be distinguished according to a multivariate analysis. A key for the determination of morphodynamic units in mountain streams is proposed. Five successive quantitative or qualitative discrimination levels allow the determination of 18 types of units. The variability of the biological characteristics of these 18 groups has been tested for trout and redd abundance. These 18 groups explain 45.6% of the total trout biomass variability, and 18.8% of the young-of-the-year trout biomass variability.