@article{fdi:010053723, title = {{A}coustic turbulence measurements of near-bed suspended sediment dynamics in highly turbid waters of a macrotidal estuary}, author = {{S}ottolichio, {A}. and {H}urther, {D}. and {G}ratiot, {N}icolas and {B}retel, {P}.}, editor = {}, language = {{ENG}}, abstract = {{S}ediment-turbulence interactions near the bed are still poorly understood in highly turbid estuaries, especially in the presence of fluid mud layers. {T}his results primarily from the difficulty in measuring co-located velocity and suspended sediment concentration ({SSC}) at sufficiently high rate to resolve small turbulent flow scales. {I}n this paper, we show how a set of commercial acoustic and optical bacicscattering systems known as {ADCP}s, {ADV}s and {OBS}s, can be deployed and used in a complementary way to perform large-scale profilings of tidal current and {SSC} combined with high-resolution velocity and {SSC} measurements in the highly turbid near-bed zone. {T}he experiment was done in the {G}ironde estuary ({F}rance) which is well known for its turbidity maximum zone characterized by high {SSC} values, above 1 g l(-1) near the surface. {A} first simple inversion method is proposed to convert the backscattered acoustic intensity measured with {ADV} into {SSC} data in the highly turbid near-bed zone. {N}ear-bed {SSC} data from the {OBS} are used to compensate for the important acoustic sediment attenuation effect at an acoustic frequency of 6 {MH}z. {N}o a priori knowledge of acoustic backscattering properties of mud suspensions is required with this calibration procedure. {W}e obtain an attenuation coefficient for mud suspensions of 0.28 m(2)/kg at 6 {MH}z leading to a good agreement between the {SSC} timeseries from the three {ADV} receivers and the {OBS} over the entire tidal cycle. {T}he obtained {SSC} data are then analyzed with respect to the near-bed velocity, {R}eynolds shear stress and turbulent kinetic energy ({TKE}) timeseries in order to identify the relevant sediment transport processes during the tidal cycle. {S}ignificant differences in bed shear stress and {TICE} levels are found between ebb and flood stages with effects on near-bed sediment dynamics. {D}uring the ebb, maximum levels of tidal current, bed shear stress and {TKE} are associated with a reduction of near-bed sediment concentration (from 400 kg m(-3) down to 100 kg m(-3)). {B}ed liquefaction process is assumed to occur at this moment with the presence of highly concentrated mud layer and a possible lutocline at a distance of less than 20 cm above the bed. {D}uring the first 1.5 h of flood, turbulent activity remains moderate. {T}he near-bed flood current is then inhibited very abruptly while a sudden increase in {SSC} occurred above the bed. {A}ssuming that the {ADV} is able to estimate relevant turbulent erosion fluxes, the co-located velocity and {SSC} are multiplied and compared with settling flux measurements made onboard under quiescent water conditions. {T}he mean sediment settling fluxes (averaged over 3 min) increase with {SSC} and are in relative good coherence with fluxes in quiescent water below the hindered regime, for {SSC} below 15 g l(-1). {R}educing averaging time from 3 min to 30 s allows to increase the range of turbulent fluxes and {SSC} values, up to 99 g l(-1). {A}t this scale, fluxes keep increasing quasi-linearly at higher {SSC}, suggesting the inhibition (delay or reduction) of the hindered settling regime as previously shown by {G}ratiot et al. (2005) from laboratory experiments. {H}owever, the 3-min averaged concentration field remained too low to conclude definitively on the effectiveness of such a process. {F}urther analysis conducted at higher {SSC} regimes and under fully verified equilibrium are necessary.}, keywords = {{ADV} ; {S}uspended sediment concentration ; {T}urbid water ; {T}urbulent flux ; {G}ironde estuary ; {A}coustic inversion}, booktitle = {}, journal = {{C}ontinental {S}helf {R}esearch}, volume = {31}, numero = {10}, pages = {{S}36--{S}49}, ISSN = {0278-4343}, year = {2011}, DOI = {10.1016/j.csr.2011.03.016}, URL = {https://www.documentation.ird.fr/hor/fdi:010053723}, }