Standardized description of streams and rivers channel geomorphic units: Qualitative description key and physical measurements.

The direct visual appreciation of geomorphic unit (GU) in running waters is always delicate. Some misinterpretation is frequent among different observers. To standardized the GU description, we proposed a decision key, based on expert' experience. The first discriminative variables are the water depth (limit at D=60 cm) and water velocity (limit at V=30 cm/s). They are easily observable at an average interannual low flow. Else complementary criteria are also argued, particularly the transversal water profile. Any operating advices are also given. In order to link GU and biology, it is advisable to take into account the hydrology as a dynamic physical control factor of the aquatic system. Quantitative measurements are usefull to work with the hydraulic geometry equations. These equations linked width, depth, velocity with discharge, All of them are more pertinent variables to rely physics and biology.