Interplay between turbulence and periphyton in rough open-channel flow

During the low flow period, important development of periphyton occur in rivers. The understanding of the mutual 'periphyton-flow' influences have induced, through recent studies, conflicting conclusions which underlined the particular complexity of these interactions. An experimental flume has been build to show that the near-bed regime (which depends on the water discharge, the nature and form of the substrate, the presence or absence of blowing,...) and the development of the periphyton are strongly dependent on each other. Indeed, different experiments show that the periphytic characteristics differ depending on the hydrodynamic conditions and that the flow properties are modified by the presence of the periphytic matrix. The periphyton induces a smoothing of the roughness of the bottom which is significant depending on the thickness of the periphytic matrix. This thickness has been taken into account in terms of a gap of the y-axis in the interpretation of measurements of the hydrodynamic parameters, contrary to recent papers.