Abstracts
Résumé
La mobilité de la charge de fond de trois affluents de la Drôme (Barnavette, Béoux et Esconavette) a fait l’objet d’un suivi événementiel entre 1997 et 2002, au moyen d’un dispositif de terrain relativement simple permettant de mesurer les phénomènes de creusement et de remblaiement du lit, ainsi que la mise en mouvement des particules. Trois stations de mesure comprenant un ou plusieurs profils en travers pour le suivi topographique, un ensemble de chaînes d’érosion, des traceurs colorimétriques et un équipement d’enregistrement des hauteurs d’eau maximales ont été installés à proximité de l’exutoire des trois affluents. Cet équipement a permis de caractériser la fréquence du charriage (6 à 7 crues mobilisatrices par an en moyenne), les distances de transport de la charge de fond (en moyenne entre 450 et 470 m par an) et les seuils de mise en mouvement. Les résultats obtenus sont en adéquation avec les valeurs communément observées dans les rivières à forte pente, avec des forces tractrices critiques adimensionnelles comprises entre 0,031 et 0,076.
Abstract
Event-based bedload mobility of three tributaries to the Drôme River (Barnavette, Béoux and Esconavette) was monitored between 1997 and 2002, with field devices allowing the measurement of scour and fill processes, and individual particles displacements. Three field sites including one or two resurveyed cross sections, a set of scour chains, painted tracers and one crest stage gauge were installed near the outlet of the streams. This equipment allowed the characterization of the frequency of bedload transport, the hydraulic conditions for incipient motion and the distances of transport of individual grains. We observed that an average of 6 to 7 competent flow events per year occurred during the study period. The annual distances of transport of coarse particles range between 450 and 470 m. The thresholds of motion for bedload transport are similar to the values published for small gravel-bed rivers, with dimensionless critical shear stress between 0.031 and 0.076.
Appendices
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