River inflows have a major influence on lake water quality due to their input of sediments, nutrients and contaminants. After leaving the river channel, river waters form a plume and interact with ambient lake waters. Strong hydrodynamic changes take place in the nearfield. To determine the nearfield hydro-sedimentary dynamics of the negatively-buoyant Rhône River plume in thermally stratified Lake Geneva, field campaigns were carried out at high and intermediate river discharge. High-resolution full-depth Acoustic Doppler Current Profiler (ADCP) transects were taken at 400, 800, 1,200, and 1,500 m from the river mouth, combined with profiles of temperature, turbidity and particle size distribution. These measurements provided, for the first time in a lake, detailed velocity fields across the full-plume cross-section in each transect. Furthermore, the unique combination of measurement techniques allowed the quantification of entrainment, Suspended Particulate Matter (SPM) concentrations and fluxes. They revealed that the negatively buoyant river inflow intruded into the metalimnion as a laterally unconfined interflow and continued flowing straight out in the streamwise direction, since currents in the lake were weak. At the same time, it mainly spread laterally due to entrainment of ambient water. The size of the interflow core and its velocity progressively decreased with distance from the mouth, as did SPM concentrations and volumes of particles (by a factor of 2–3 within 1,500 m), due to sediment settling and entrainment. The interflow momentum flux remained constant along the pathway, but interflow cross sections and discharge increased 2–3 times (within 1,500 m). The entrainment coefficient was >2 at 400 m and further increased non-linearly along the pathway. These values are much higher than those reported for laterally confined laboratory studies. The particle size distribution in the interflow was dominated by fine particles (<32 μm), which were transported up to 1,500 m from the mouth and most likely beyond, whereas larger particles (>62 μm) almost completely settled out before reaching that distance. The above processes occurred independent of river discharge; their intensity, however, changed with discharge.

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Abstract. Consequences of tidal dynamics on hydro-sedimentary processes are a recurrent issue in estuarine and coastal processes studies, and accurate tidal solutions are a prerequisite for modeling sediment transport, especially in macro-tidal regions. The motivation for the study presented in this publication is to implement and optimize a model configuration that will satisfy this prerequisite in the frame of a larger objective in order to study the sediment dynamics and fate from the Red River Delta to the Gulf of Tonkin from a numerical hydrodynamical–sediment coupled model. Therefore, we focus on the main tidal constituents to conduct sensitivity experiments on the bathymetry and bottom friction parameterization. The frequency-domain solver available in the hydrodynamic unstructured grid model T-UGOm has been used to reduce the computational cost and allow for wider parameter explorations. Tidal solutions obtained from the optimal configuration were evaluated from tide measurements derived from satellite altimetry and tide gauges; the use of an improved bathymetry dataset and fine friction parameter adjustment significantly improved our tidal solutions. However, our experiments seem to indicate that the solution error budget is still dominated by bathymetry errors, which is the most common limitation for accurate tidal modeling.