Facies

Morphodynamic unit of a stream having longitudinal homogeneity in the slope of the water surface and in the distribution of water levels, in the velocities of the flow and in the particle size of the substrate. The length of a facies can vary from one to several times the width of the wet bed. For example, we can mention three major types of contrasted facies: wet (relatively low slope, high water levels, low velocities); fast (high slope, high flow velocities, substrate mainly composed of large blocks ); and flat (average slope, average and uniform velocities, water level rather low, symmetrical and regular cross profile, medium and homogeneous particle size).