Typologie des faciès d'écoulement ou unités morphodynamiques des cours d'eau à haute énergie

Abstract

The microhabitat methodology developped by the CEMAGREF ( LYON ) permlts t o obtain a clear picture of the habitat sultablilty of a trout stream, It consists In linking o n a study reach, représentative of a longer part of the stream, on the one hand a biological model reflectlng connections betv/een the présence an d the relative denslty of a given stage of development of a fish specles ( here the brown trout ) an d the values of the three physical variables characterizing Its habitat ( th e water depth, the stream veloclty an d the sédiment slze ), on th e other hand a n hydraullc model allowlng with one survey, to reconstltute for différent discharges the values of the hydrodynamic variables. To sector a stream, classify It an d choose the study reaches which could give o reliable picture of it, It is necessary to have a good knowledge of the morphological feotures (faciès) types llkely to b e encountered. The Identification of thèse units wlll t>e done In th e fleld using some simple crlterlo such as water depth, stream veloclty, sédiment size, cross section shape, longitudinal profile an d plan vIew. ThIs wlll be carried out during low flow stage In order t o observe the more varled flow conditions, which Is not the case when the discharge Increases an d smoothes the free water surface.