Détermination d'une recirculation par aDcp, LS-PIV et modélisation 2Dh

[Departement_IRSTEA]RE [TR1_IRSTEA]RIE / TRANSFEAUDownstream connection of abandoned channels during floods is a key process for the assessment of water exchange, sedimentation rate and biodiversity in oxbow-lakes. The flow-induced morphological evolution of the confluence (stability, occlusion, scour) governs the frequency and the intensity of downstream submersion. Recirculating flow patterns at the junction between a former meander and the Ain river, France, have been investigated for different discharge values through detailed in situ measurements: acoustic Doppler current profiler (aDcp) and image-based velocimetry (LS-PIV). Detailed topographic data have been collected in order to feed a 2Dh hydraulic model representative of the study reach, using the Rubar20 code. Post-processing tools were developed in order to get the mean velocity patterns from aDcp and LS-PIV data. Then observed velocity fields were compared to Rubar20 outputs. The simulated distribution of velocity vectors in the natural dead-zone is quite in agreement with field measurements: the main flow pattern is a large plane recirculation in the mouth of the former channel. However the recirculating flow intensity is underestimated