International audienceA new model for the critical shear stress and the transport of graded sediment is presented. The model is based on the size distribution of the bed surface and can be used to compute sediment transport rates in numerical simulations with an active layer model. This model makes a distinction between unimodal and bimodal sediments. It is assumed that all size fractions of unimodal sediments have the same critical shear stress while there is selective transport for the gravel fractions of bimodal sediments. A recently published laboratory transport data set is used to calibrate our model
Achieving a sustainable management of sediment fluxes in existing or proposed reservoirs is a challenging but essential requirement for dam operators. Such objective is of utmost importance to avoid sedimentation-related consequences. Numerical modelling is of great interest to understand the flow and sediment dynamics in a reservoir, to simulate the long-term evolution of sediment deposits and to evaluate the efficiency of various management strategies. This paper presents recent case studies, which validate the feasibility and relevancy of such technical option. The progresses obtained on essential stages of the numerical modelling of sediments dynamics in reservoirs are particularly emphasized. Concerning the distribution of deposits, a promising field method based on an optimum combination of direct samplings with acoustic measurements and video auscultations is detailed. Feedbacks are then provided concerning an innovative device deployed in the field for a direct measurement of the settling velocity. Issues about the assessment of calibration parameters are also addressed in this communication. Lab experiments performed on deposits sampled in several reservoirs provide practical guidance to evaluate the erosion parameters of sediments. Finally, several examples of sediment dynamics modelling in reservoirs including both cohesive and non-cohesive sediment are presented.
Le colloque SHF-« Transport sédimentaire en rivière et morphologie fluviale » du 31 Mai a été organisé à l'occasion de la publication de l'ouvrage de Philippe Lefort « Morphodynamique fluvialeapproche théorique et expérimentale ». Cet événement a rassemblé dans les locaux d'ARTELIA à Echirolles un auditoire représentatif de l'ensemble la communauté hydrosédimentaire francophone. La centaine de personnes présentes provenait en effet aussi bien d'organismes institutionnels et de la recherche, que de bureaux d'études, de gestionnaires de sites et d'exploitants d'aménagements. Cette diversité des origines et des approches se manifestait aussi au niveau des conférenciers. Ce colloque, par les liens tissés entre scientifiques, ingénieurs et gestionnaires, faisait donc écho à la carrière de Philippe Lefort qui a su établir des passerelles entre ces différentes communautés. Cette dimension transversale est aussi bien sûr en cohérence avec les objectifs de la Société Hydrotechnique de France. La synthèse de ce colloque, proposée cidessous, permet donc de donner un aperçu des travaux et débats en cours dans notre communauté. Les lecteurs souhaitant plus de détails peuvent se référer aux supports des présentations, disponibles sur le site de la SHF.
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