Ocean Color Remote Sensing of Suspended Sediments along a Continuum from Rivers to River Plumes: Concentration, Transport, Fluxes and Dynamics

This study investigates the capability of high and medium spatial resolution ocean color satellite data to monitor the transport of suspended particulate matter (SPM) along a continuum from river to river mouth to river plume. An existing switching algorithm combining the use of green, red and near-infrared satellite wavebands was improved to retrieve SPM concentrations over the very wide range (from 1 to more than 1000 g.m−3) encountered over such a continuum. The method was applied to time series of OLI, MSI, and MODIS satellite data. Satisfactory validation results were obtained even at the river gauging station. The river liquid discharge is not only related to the SPM concentration at the gauging station and at the river mouth, but also to the turbid plume area and SPM mass estimated within the surface of the plume. The overall results highlight the potential of combined field and ocean color satellite observations to monitor the transport and fluxes of SPM discharged by rivers into the coastal ocea

Particle assemblage characterization in the Rhone River ROFI

International audienceAn innovative experiment was carried out in the vicinity of the Rhône River mouth in February 2014. An instrumentalpackage, composed of a CTD, a LISST-100 type B (1.25–250 μm), and a LISST-HOLO (20–2000 μm), wasused to characterize the hydrological parameters and suspended particles properties (concentration, size, composition,shape, and effective density) in the region of freshwater influence (ROFI) of the Rhône River. Besides,a coastal SLOCUMglider, equipped with a CTD and optical backscattering sensors at severalwavelengths,was deployedto detail the spatial description of the hydrological parameters and some particle properties. Large riverdischarge (annual flood ~5000 m3 s−1) and strong wind conditions favored the dispersal of the river plume onthe shelf. Surface suspended particulate matter concentrations decreased rapidly seaward from 20 mg L−1next to the river mouth to 1.5 mgL−1 at the shelf break. A persistent bottomnepheloid layerwas observed acrossthe shelf with concentrations decreasing from8 mg L−1 at the coast to 1 mg L−1 at the shelf break. Observationsshowed that most of suspended particles were mainly flocculated in micro and macro-flocs (30–400 μm) ininner-shelf waters. The particle assemblage in the Rhône River plume and in the bottomnepheloid layer becameprogressively finer seaward and the associated effective density increased from 370 to 1600 kgm−3. Outside theplume, planktonic organisms increasingly contributed to the total volume concentration. Finally,we demonstratedthe ability of gliders, equipped with optical backscattering sensors at severalwavelengths, to describe the finescale distributions of suspended particles, and provide an index of their size distribution

MORPHODUNES, a new project dedicated to the 3D morphodynamics of sub-marine sand dunes for safety and maritime activities

International audienceHere is presented a new project, MORPHODUNES, dealing with the sub-marine sand dune morphodynamics. It is funded by Shom (French Navy) to develop a fully-coupled 3D hydro-morphodynamic model able to simulate the dune migration over the continental shelf according to the metocean forcings, sediment characteristics and seabed morphology. The first part of the project is related to the physical modelling of an idealized and realistic field of dunes at laboratory scale. The laboratory measurements of the flow characteristics and bed topography will be used to validate and calibrate the hydro-morphodynamic model for some specific processes (e.g. sur-imposed bedforms and impacts). The second part of the project is devoted to the analysis of field data. These data are recorded by Shom in Iroise/Celtic sea, near the Brest harbour during the project. Sedimentary fluxes, bed morphology and thickness of the mobile zone, sediment response of the hydrodynamic conditions will be determined from this analysis. The third part is dedicated to the set-up, validation, and calibration of the hydro-morphodynamic model for the study site thanks to the in-situ data and their analysis. This work will be based on several diagnoses for hydrodynamics and morphodynamics (e. g. flow characteristics, wavelength and height of dunes, asymmetry index, crest sinuosity). At the end, the model should be as much as possible independent of the site conditions to be used to simulate dune morphodynamics in 3D at another location in the world for the marine safety and navigation

MORPHODUNES, a new project dedicated to the 3D morphodynamics of sub-marine sand dunes for safety and maritime activities

International audienceHere is presented a new project, MORPHODUNES, dealing with the sub-marine sand dune morphodynamics. It is funded by Shom (French Navy) to develop a fully-coupled 3D hydro-morphodynamic model able to simulate the dune migration over the continental shelf according to the metocean forcings, sediment characteristics and seabed morphology. The first part of the project is related to the physical modelling of an idealized and realistic field of dunes at laboratory scale. The laboratory measurements of the flow characteristics and bed topography will be used to validate and calibrate the hydro-morphodynamic model for some specific processes (e.g. sur-imposed bedforms and impacts). The second part of the project is devoted to the analysis of field data. These data are recorded by Shom in Iroise/Celtic sea, near the Brest harbour during the project. Sedimentary fluxes, bed morphology and thickness of the mobile zone, sediment response of the hydrodynamic conditions will be determined from this analysis. The third part is dedicated to the set-up, validation, and calibration of the hydro-morphodynamic model for the study site thanks to the in-situ data and their analysis. This work will be based on several diagnoses for hydrodynamics and morphodynamics (e. g. flow characteristics, wavelength and height of dunes, asymmetry index, crest sinuosity). At the end, the model should be as much as possible independent of the site conditions to be used to simulate dune morphodynamics in 3D at another location in the world for the marine safety and navigation