Hydraulic geometry of stream reaches and ecological implications
Géométrie hydraulique des cours d'eau et conséquences écologiques
Résumé
The hydraulic geometry (width- and depth-discharge relationships) of stream reaches (length = tens of width) is a key physical description for predicting the ecological impact of physical constraints at a range of spatial scales. Downstream and at-a-reach hydraulic geometry relationships make it possible to estimate reach-averaged hydraulic variables across reaches and within reaches when discharge rate changes. Reach-averaged hydraulics govern the frequency distribution of point hydraulic variables (velocity, shear stress, water depth) in stream reaches. Therefore, the hydraulic geometry of reaches is linked to the diversity of microhabitat conditions, which constrain aquatic organisms. As a consequence, reach-scale responses of populations and communities are also related to the hydraulic geometry. Some of these relationships are very general; for example, a number of functional descriptions of fish and macroinvertebrate communities (describing size, shape, behaviour, reproduction patterns) show similar responses to hydraulics in stream reaches of independent basins or continents. The hydraulic geometry of reaches provides a tool for predicting the ecological impacts of stream restoration (discharge modifications, other hydraulic changes) over large scales. An example of application is the estimation of suitable flow rates for populations over whole river networks.
La géométrique des cours d'eau met en évidences des propriétés des caractéristiques hydrauliques moyennes des cours d'eau partagées en différentes régions du globe. Or les caractéristiques hydrauliques moyennes des cours d'eau sont également liées à la diversité des microhabitats hydrauliques, aux prédictions des modèles d'habitat et aux réponses biologiques effectives. C'est pourquoi la géométrie hydraulique est particulièrement intéressante à connaître et modéliser en écologie aquatique.