Transport Of Suspended Matter Research Articles

Numerical Investigation of the Sediment Load Exchange between a Coastal Mud Bank and Its Neighbouring Estuary

Muddy coastlines cover much of the world’s shores, yet studies on the interaction between mud-affected coasts and estuaries are limited. This study focuses on the Mahury River estuary and its interaction with the muddy coast of the Guianas, primarily fed by the Amazon. A coupled wave–current–sediment transport model is developed to analyze the sediment exchange in an environment with strong interactions between the waves and the fluid mud. Simulations explore how seasonal changes in waves, mud availability, and tides affect sediment fluxes. The main processes influencing suspended particulate matter (SPM) and sediment transport are well emulated, notwithstanding the complexity of the ambient muddy environment. The results show that during the rainy season, strong wave damping and wave refraction zones cause high SPM resuspension in shallow waters (<5 m). In contrast, during the dry season, wave influence shifts to the estuary mouth. Erosion and sedimentation patterns indicate that ebb currents associated with neap tides during the rainy season represent the most favourable conditions for the alongshore migration of mud banks. Neaptide ebb currents also contribute to sedimentation during the dry season but only in the estuary mouth and the nearby coastal area. The abundance of mud leads to an extension of the estuary’s intertidal area during the dry season.

Physical mechanisms, dynamics and interconnections of multiple estuarine turbidity maximum in the Pearl River estuary

The formation and dynamics of individual estuarine turbidity maximum (ETM) in the Pearl River estuary (PRE) have been investigated but the temporal variability of the ETMs and interconnections among them remain poorly understood. To address these open questions, the distribution and transport of suspended particulate matter (SPM) in the PRE for the period of 2017–2020 are investigated by numerical modeling. The simulated sediment transport flux is decomposed into several major components associated with specific physical processes. Then, the relative contribution of each component to the formation of the ETMs is evaluated. Results suggest the coexistence of three prominent ETMs in the Lingding Bay of the PRE. They are formed by different physical mechanisms and characterized by remarkable seasonality in the spatial extension. In the two ETMs located at the west shoal and middle shoal, advection dominates the sediment transport flux, whilst tidal pumping plays a crucial role in maintaining the ETMs. A sharp bathymetric gradient leads to an entrapment of sediment flux within the bottom layer in the west channel ETM, a phenomenon referred to as topographical trapping. The interconnection analysis shows that the sediment transport between the ETMs varies with seasons, which is attributed to the variation of stratification driven by the monsoon-mediated river runoff. Our results provide new insights into the physical dynamics and interconnections of the ETMs in the PRE, which can serve as scientific base for estuarine sediment management and engineering.

Твердый сток реки Дон и поступление взвеси в дельту при нагонах: статистическое моделирование и сопоставление в период маловодья

Statistical modeling of the Don River solid runoff based on water discharge and turbidity measurements obtained at the hydrological station in the village of Razdorskaya for the twelve-year period 2009–2020 was carried out. The WRTDS (Weighted Regressions on Time, Discharge, and Season) and WRTDSKalman (WRTDS with Kalman filtering) methods were applied. The developed statistical model is aimed at solving the problem of the imbalance between the regularity of collecting data on water discharge and data on the concentration of suspended matter by “restoring” the concentration values on days without measurements based on data on the most “similar” days with measurements in terms of time, discharge and season and does not claim to describe a relationship between the concentration of the constituent of interest and discharge. The quality of the developed statistical model and its modification were checked. The average daily concentrations and fluxes of suspended matter were compared with estimates of the volumes of suspended material deposited during periods of recurring strong surge phenomena. A comparative assessment of sea and river factors contributions to the transport and sedimentation of suspended matter in the Don River delta was fulfilled.

Lagrangian Characterization of Surface Transport From the Equatorial Atlantic to the Caribbean Sea Using Climatological Lagrangian Coherent Structures and Self‐Organizing Maps

AbstractThis study presents an assessment of the transport of suspended material by surface ocean currents, which have a critical role in determining the connectivity and distribution of living and non‐living material. Lagrangian experiments reveal pathways from the Equatorial Atlantic to 10 strategic regions within the Caribbean Sea, determined by considering the space‐time variability of climatological Lagrangian Coherent Structures, which act as recurrent attracting pathways and transport barriers. Due to windage or Stokes drift, wind forcing is a significant factor in determining the spatial locations where particles cluster and the time needed to reach the Caribbean from the Equatorial Atlantic. Pathways shift westward within the Caribbean and take less time to arrive with increasing wind influence. Depending on the wind effect, the particles show higher confluence in different areas of the Caribbean. A case study is presented for the Mexican Caribbean nearshore area, isolated from ocean‐current trajectories. Here, wind weakens the transport barrier responsible for this isolation and causes particle confluence toward that region. Spatial patterns of the Eulerian velocity identified through Self‐Organizing Maps, with time dependence given by their best matching units, can reproduce the characteristic Lagrangian patterns of surface current climate variability. Our study demonstrates the application of tools from dynamical systems and unsupervised neural networks to understand Lagrangian patterns and identify the processes that drive them. These findings improve our understanding of transport mechanisms of suspended material by surface ocean currents in the Western Atlantic and the Caribbean Sea, which is essential for managing and conserving marine ecosystems.

Riverine input of suspended particulate matter controls distribution, partitioning and transport of mercury and methylmercury in the Yellow River Estuary

Riverine mercury (Hg) is the largest global source of Hg in coastal oceans. The Yellow River delivers the majority of Hg to the semi-enclosed Bohai Sea, where Hg contamination adversely affects the surrounding heavily populated provinces in northern China. Mercury distribution patterns in the river-estuary interacting area provides essential information to understand the riverine Hg transport and biogeochemical cycling of Hg in the estuary. Analyzing the spatial distributions of total- (THg) and methyl-Hg (MeHg) in the lower end of Yellow River (∼105 km) and adjacent estuary, we found the dominant role of suspended particulate matter (SPM) in Hg transport, with 99.1% and 86.3% of THg and MeHg being in particulate phase. The SPM dynamics, such as transport, retention, sorting and sedimentation, governs Hg transport with water flow and particle-water partition of Hg. While THg decreased along the water flow to the river mouth with the settlement of particulate THg (about 27.5% onto the riverbed and the rest entering the sea), MeHg and particulate MeHg increased by 110% and 117%, respectively. This study highlights the distinct patterns in THg and MeHg distribution and transport and suggests potential Hg methylation and external MeHg input in the river-estuary mixed zone.

Two-dimensional-one-dimensional splitting scheme for numerical solution of problems of suspended matter transport in coastal systems

This article discusses the problems of numerical solution of non-stationary convection-diffusion-reaction problems using the model problem of suspended matter transport as an example. In the difference scheme proposed by the authors, at each time layer, the original spatial-three-dimensional problem is split along horizontal directions into a chain of two-dimensional and one-dimensional problems. In order to ensure the unconditional skew-symmetry of the convective transfer operator and its energy neutrality, the convective terms are written in symmetric form (half the sum of the non-divergent and divergent forms). The approximation of the initial boundary value problem, to which the suspended matter transport model is reduced, is considered in the Hilbert space of grid functions, which in subsequent discussions will allow us to focus on the use of general results of the theory of stability (correctness) of operator-difference schemes.

The effect of aggregation/disaggregation on suspended particulate matter transport in a tidal strait

Predicting net suspended sediment fluxes in coastal regions is important for promoting good water quality, maritime transport and marine industries. Aggregation and disaggregation of suspended particulate matter responding to spatial and temporal variations in turbulence can control particle size and hence settling speed; little is currently known about how this influences the net suspended sediment flux. A tidal strait, in which the flux is confined to be in one of two directions, makes a good site for observing the effect of changes in particle size on the suspended sediment flux. The Menai Strait in North Wales is a narrow tidal strait in which the flow speeds increase to a maximum in the narrowest central region, the Swellies. Observations at sites on either side of the Swellies show that the median size of suspended particles varies with the speed of the tidal current, but also depends on the direction of the flow, with the smallest particles seen when the current is flowing out of the Swellies. The implication (supported by model results) is that the strong currents in the centre of the strait tear up flocs into small pieces which are then carried out towards both ends of the strait by the tide. Averaged over a tidal cycle, there is a net flux of larger particles into the Swellies and a net flux of small particles out. These results are relevant to the formation of isolated turbidity maxima around a region of strong turbulence.

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 ocean.

Contrasting internal tide turbulence in a tributary of the Whittard Canyon

Submarine canyons that incise continental slopes are considered an important conduit for transport of suspended matter between shelf seas and deep-ocean. However, the exact mechanisms influencing matter transport and deposition are still largely unknown. We present moored observations of current flows, acoustic echo intensity and, in high-resolution, temperature variation from two contrasting mooring sites 6.5 km apart horizontally in 790 and 1130 m water depth in one of the tributaries incising the flank of the easternmost branch of Whittard Canyon, North-East Atlantic Ocean. The shallow site is situated on a steep thalweg slope which is supercritical for semidiurnal internal tides that have >100 m amplitudes and turbulent overturning evenly distributed over the 240 m range of observations, with no particular intensification near the seafloor. In contrast, the deep site is located on an along-canyon slope that is approximately critical for semidiurnal internal tides, with steeper slopes up-canyon and to the sidewalls. The internal tide amplitude at the deep site is about 75 m. In the lower 100 m, flow intensifies and becomes more rectilinear along the canyon axis, together with intensifying mean turbulence dissipation rate and tidally-averaged down-canyon flow. Over a semidiurnal tidal period three episodes of relatively large turbulence are observed. Turbulence is largest when an upslope moving bore passes. Smaller but still relatively large turbulence is associated with a secondary upslope bore and with strong convective overturning during the downslope tidal phase. The convection is clearly distinguished in temperature variance spectra between the buoyancy and Ozmidov frequencies, the range in which anisotropic stratified turbulence is expected. Averaged over the entire depth-time series, mean turbulent kinetic energy dissipation amounts to 4.4 ± 2 × 10-7 m2 s-3, equal for both sites. In the tributary, the first upslope moving bore and the convective overturning at the deep site will affect sediment resuspension most.

Two-Dimensional-One-Dimensional Alternating Direction Schemes for Coastal Systems Convection-Diffusion Problems

The initial boundary value problem for the 3D convection-diffusion equation corresponding to the mathematical model of suspended matter transport in coastal marine systems and extended shallow water bodies is considered. Convective and diffusive transport operators in horizontal and vertical directions for this type of problem have significantly different physical and spectral properties. In connection with the above, a two-dimensional–one-dimensional splitting scheme has been built—a three-dimensional analog of the Peaceman–Rachford alternating direction scheme, which is suitable for the operational suspension spread prediction in coastal systems. The paper has proved the theorem of stability solution with respect to the initial data and functions of the right side, in the case of time-independent operators in special energy norms determined by one of the splitting scheme operators. The accuracy has been investigated, which, as in the case of the Peaceman–Rachford scheme, with the special definition of boundary conditions on a fractional time step, is the value of the second order in dependency of time and spatial steps. The use of this approach makes it possible to obtain parallel algorithms for solving grid convection-diffusion equations which are economical in the sense of total time of problem solution on multiprocessor systems, which includes time for arithmetic operations realization and the one required to carry of information exchange between processors.

Локально-двумерные схемы расщепления для параллельного решения трехмерной задачи транспорта взвешенного вещества

A 3D model of suspended matter transport in coastal marine systems is considered, which takes into account many factors, including the hydraulic size or the rate of particle deposition, the propagation of suspended matter, sedimentation, the intensity of distribution of suspended matter sources, etc. The difference operators of diffusion transport in the horizontal and vertical directions for this problem have significantly different characteristic spatiotemporal scales of processes, as well as spectra. With typical sampling, applied to shallow-water systems in the South of Russia (the Sea of Azov, the Tsimlyansk reservoir), the steps in horizontal directions are 200-1000 meters, the coefficients of turbulent exchange (turbulent diffusion) are (103-104) m2/sec; in the vertical direction - - - steps of 0.1 m-1 m, and the coefficients of microturbulent exchange in the vertical — (0.1-1) m2/sec. If we focus on the use of explicit locally twodimensional - - - locally one-dimensional splitting schemes, then the permissible values of the time step for a two-dimensional problem will be about 10-100 seconds, and for a one-dimensional problem in the vertical direction - - - 0.1 – 1 sec. This motivates us to construct an additive locally-two-dimensional-locallyonedimensional splitting scheme in geometric directions. The paper describes a parallel algorithm that uses both explicit and implicit schemes to approximate the two-dimensional diffusion-convection problem in horizontal directions and the one-dimensional diffusion-convection problem in the vertical direction. The two-dimensional implicit diffusion-convection problem in horizontal directions is numerically solved by the adaptive alternating-triangular method. The numerical implementation of the one-dimensional diffusion-convection problem in the vertical direction is carried out by a sequential run-through method for a series of independent one-dimensional three-point problems in the vertical direction on a given layer. To increase the efficiency of parallel calculations, the decomposition of the calculated spatial grid and all grid data in one or two spatial directions - in horizontal directions-is also performed. The obtained algorithms are compared taking into account the permissible values of time steps and the actual time spent on performing calculations and exchanging information on each time layer.

Impact of Submesoscale Eddies on the Transport of Suspended Matter in the Coastal Zone of Crimea Based on Drone, Satellite, and In Situ Measurement Data

High-resolution measurements by unmanned aerial vehicles (UAVs), satellite and in-situ data are used to study the optical structure of coastal submesoscale eddies and their influence on the transport of total suspended matter (TSM). It is shown that submesoscale cyclones cause intense cross-shelf TSM fluxes and its subsequent accumulation in their cores, similar to what is observed in large mesoscale anticyclones. UAV measurements make it possible to observe intensive dynamic processes on the periphery of eddies, seen as a periodic structure with scales of 20–100 m; the spiral structure of TSM transport; and convergence of TSM in the cores of cyclones. Using UAV guidance, detailed measurements of the distribution of hydrological and hydro-optical characteristics of one of these eddies, with a diameter of about 2 km, were obtained during a scientific cruise in October 2019. Warm brackish water with a high TSM content and the descent of all isosurfaces were observed in the core of this cyclone, located near the topographic slope. We suggest that the probable reason for the convergence in such submesoscale cyclones is the interaction of radial currents with the topographic slope, which causes downwelling in the coastal part of eddies.

Temporal and Spatial Variations in Particle Fluxes on the Chukchi Sea and East Siberian Sea Slopes From 2017 to 2018

Time-series sediment traps were deployed on the Chukchi Sea and East Siberian Sea slopes from August 2017 to August 2018 with the aim of elucidating the temporal and spatial variations in particle fluxes and identifying the main processes affecting those variations. Particle fluxes showed a typical seasonal pattern, with high values in summer and low values in other seasons, and a large inter-annual variation was observed only on the East Siberian Sea slope, where particle fluxes were one order of magnitude higher in early August 2018 than in late August 2017. This large inter-annual variation in particle flux resulted from the episodic intrusion of nutrient-enriched shelf water in the East Siberian Sea, which enhanced biological production at the surface and particle fluxes. The Chukchi Sea slope was influenced by the inflow of Anadyr Water, with high salinity and high nutrient concentrations, which had little annual variability. Therefore, particle flux showed little inter-annual variation on the Chukchi Sea slope. Under-ice phytoplankton blooms were observed in both the Chukchi Sea and East Siberian Sea slopes, and increases in particulate organic carbon (POC) flux and the C:N ratio under the sea ice were related to transparent exopolymer (TEP) production by ice algae. On the East Siberian Sea slope, particle fluxes increased slightly from 115 to 335 m, indicating lateral transport of suspended particulate matter; POC and lithogenic particles may be laterally transported to the slope as nutrient-rich shelf waters flowed from the East Siberian Sea to the Makarov Basin. Annual POC fluxes were 2.3 and 2.0 g C m–2 year–1 at 115 and 335 m, respectively, on the East Siberian Sea slope and was 2.1 g C m–2 year–1 at 325 m on the Chukchi Sea slope. Annual POC fluxes were higher on the Chukchi Sea and East Siberian Sea slopes than in Arctic basins, lower than on Arctic shelves, and generally similar to those on western Arctic slopes.

Исследование формирования и распространения речного плюма Дуная на основе численного моделирования

The relevance of the studied circulation caused by the water river runoff deals with the anthropological impact on the ecological state of the shelf. River waters, entering into the sea, form mesoscale structures in the delta’s area, characterized by low salinity with a high level of suspended matter and dissolved organic matter. Such structures are called “plume” in modern literature. In this case, the inertial motion of the plume is free to form a rounded area or “bulge” like anticyclonic circulation type of flow. The purpose of this work is to investigate the propagation of freshened waters, formed by the river inflow, the formation of the waters hydrological structure regularities, dynamics of the buoyancy current, and thermohaline front formation on the base of numerical modeling. Numerical modeling is used to study the formation of a river plume and downward propagation of buoyancy current on the shelf without taking into account the tides forcing. A three-dimensional σ-coordinate numerical model was used, adapted for the shelf and estuaries. The calculations were carried out for a rectangular box area. The influence of changes in the main parameters of the runoff, the mouth geometry and wind forcing are considered to development of the plume and the alongshore propagation of buoyancy current. The obtained modeling results for the conditions of the Northwestern Black Sea shelf and the Danube discharge are consistent with the estimates of plume characteristics based on the archival hydrological observations data of water temperature and salinity. The results of this work can be used for further study of hydrological processes in the region of river mouths, the peculiarities of the plumes formation and evolution, assessment of the suspended matter, biogenic elements and microplastics transport in the sea and ocean coastal zones.

Human impact on suspended particulate matter in the Yellow River Estuary, China: Evidence from remote sensing data fusion using an improved spatiotemporal fusion method

Transport of suspended particulate matter (SPM) in estuarine waters plays an important role in regulating erosion-accretion and biogeochemical processes. In the Yellow River Estuary (YRE), artificial water and sediment regulation scheme (WSRS) and coastal engineering structures are the 2 typical anthropogenic activities affecting the spatiotemporal dynamics of estuarine SPM. The monitoring of SPM transport affected by such human activities requires SPM mapping at both high spatial and high temporal resolutions. In this study, we presented an improved Flexible Spatiotemporal Data Fusion (FSDAF) strategy with consideration of highly dynamic SPM variations in estuarine waters, and generated 30-m hourly SPM concentrations based on Landsat 8 OLI and GOCI datasets. The new strategy produced higher SPM estimation accuracy than the original FSDAF, with the relative percentage difference (RPD) decreasing from 29.75% to 5.31% using GOCI-derived hourly SPM as reference. With in situ SPM measurements as reference, the fused SPM concentrations had an RMSE of 12.09 mg/L and an RPD of 27.17%. Investigation of interday SPM variations before, during, and after the WSRS in 2018 revealed that the first WSRS significantly increased the SPM concentration and plume extent; new wetland with an area of 12.56 km2 was formed due to sediment accretion near the river mouth. The two groins offshore from the coastlines on the north and south sides of YRE exhibited obvious sediment trapping effects in that higher SPM concentrations on one side of each groin were found regardless of the turbidity modes and diurnal SPM variations; the trapping effects were associated with the number of groins and groin length. Intraday variations of SPM were influenced by tidal currents, with plume direction following the ebb and flooding tidal current direction. The inter- and intraday characteristics of the 30-m hourly SPM dynamics facilitate the detailed analysis of the sediment transport associated with human activities.

Intratidal and spatial variability over a slope in the Ems estuary: Robust along-channel SPM transport versus episodic events

Results from measurements are presented that were collected during a full tidal cycle in the Ems estuary, involving two landers and an anchored research vessel. The conditions were characterized by very weak winds, no wave effects, and low river run-off, so that the state was close to tide-only. We find that the lateral (i.e., cross-slope) transport of water and suspended particulate matter (SPM) much of the time shows a vertically layered structure, which is however subject to sudden transitions. Moreover, even on the small spatial scale of these measurements (i.e., within a distance of 200 m), a strong lateral variability is observed in the circulation patterns. We analyze its dynamics by means of dimensionless parameters. In addition, near-bottom peaks in SPM concentration are observed, notably during early flood. However, these episodic events have little effect on the overall transport of SPM, which involves the whole water column: the measurements show a high vertically integrated SPM signal during late ebb, resulting in an ebb-dominance in the transport at this position in the tidal channel.

Uniqueness of solving the problem of transport and sedimentation of multicomponent suspensions in coastal systems

The present work is devoted to the study of three-dimensional model of transport and sedimentation of suspended matter in the coastal zone. The model takes into account the following processes: advective transport due to the movement of the aquatic environment, microturbulent diffusion and gravitational sedimentation of particles of the suspension, and changes in the geometry of the bottom caused by sedimentation of the suspension or the rise of bottom sediments. The aim of the work was to conduct an analytical study of the uniqueness of the initial-boundary-value problem corresponding to the constructed model. In accordance with the stated aim, an initial-boundary-value problem is considered for a parabolic type equation with lower derivatives in the domain for which a quadratic functional is constructed and the uniqueness of the solution is proved by the energy method.

Indication of size distribution of suspended particulate matter for sediment transport in the South Yellow Sea

The Yellow Sea is a key area for studying source-to-sink sediment transport systems in East China shelf seas. However, the sediment transport and dispersal patterns in the Yellow Sea are not fully understood because of the significant seasonal variation in ocean circulation. In this study, we identify the ocean circulation patterns in the South Yellow Sea based on temperature, salinity and depth data collected from 52 hydrographic stations during the winter of 2016. The mass concentrations and particle size distributions of suspended particulate matter are also determined to decipher the sediment transport pattern in the South Yellow Sea. The results show that particles from the Yellow Sea Coastal Current and Shandong Peninsula Coastal Current display a bimodal size distribution, with peaks at approximately 2.5 μm and 32–64 μm, while particles from the Yellow Sea Warm Current and residual Yellow Sea Cold Water Mass display a trimodal size distribution, with peaks at 2.5 μm, 32–64 μm and 391 μm. The fine and medium particles (<256 μm) are mainly inorganic particles, while the coarse particles (>256 μm) include organic materials. The peak at 391 μm is dominated by organic particles and reflects the influence of the Yellow Sea Warm Current in the surface layer. The Yellow Sea Warm Current enhances the nutrient and temperature conditions in the South Yellow Sea, which facilitates phytoplankton growth under appropriate light conditions. The content of inorganic particles with sizes of 64–159 μm decreases sharply in the central South Yellow Sea, which reflects the transport of suspended particulate matter from the southern study area to the central Yellow Sea mud area. The synthesized evidence suggests that the Yellow Sea Warm Current, as the main driving force, transports particles from the Jiangsu coast or the Changjiang River into the central Yellow Sea mud area in winter.

Consumer movement dynamics as hidden drivers of stream habitat structure: suckers as ecosystem engineers on the night shift

Ecosystem engineering can control the spatial and temporal distribution of resources and movement by engineering organisms within an ecosystem can mobilize resources across boundaries and distribute engineering effects. Movement patterns of fishes can cause physical changes to aquatic habitats though nesting or feeding, both of which often vary in space and time. Here we present evidence of ecosystem engineering by the Sonora sucker Catostomus insignis, a dominant fish in streams of the southwestern United States, and show how cryptic nocturnal movement patterns and bioturbation activities control heterogeneity in benthic substrates, and in sediment and carbon export. Sonora suckers exhibit distinct diel movement patterns, spending daylight hours in refuge habitats (typically deep pools) while moving into shallow habitats at night to feed. Feeding by suckers creates substantial disturbance in soft sediments that are patchy in space and time. These disturbances moved up to 2.4 × 104 cm3 of sediment per square meter per week in locations that are up to hundreds of meters away from sucker daytime refuges. The diel cycles in feeding activity (i.e. nocturnal digging in benthic substrates) caused nighttime pulses in suspended sediment that comprised up to 32% of the daily suspended load and organic matter transport of a stream reach. During the daytime, this particulate transport settles in habitats beyond the location of the initial disturbance, thus redistributing both sediment and organic matter. Our data indicate that cryptic movement by ecosystem engineers can distribute their effects in space and time generating heterogeneity in resources and suggest that habitat modifications restricting consumer movement may alter the impact of engineering activities.

Hydrodynamics and SPM transport in an engineered tidal estuary: The Adour river (France)

The present paper reports on a series of field experiments aiming to characterise the functioning of a man-engineered strongly forced salt-wedge estuary: the lower estuary of the Adour river, France. Bottom-moored velocity measurements and surface boat surveys have been performed under low river discharge conditions, for both neap and spring tides, in order to provide a well-documented reference framework to understand the dynamics of water masses, turbulence and suspended particulate matter (SPM) transport in the lower estuary. An additional campaign has been carried out in high river discharge conditions. This first documented in-situ study of the Adour lower estuary demonstrates its variability in terms of hydrological regimes, from salt-wedge to partially mixed regimes depending on tidal and discharge conditions. Turbulent properties showed a significant response to the variations of salinity structure, with higher values when stratification is minimal. At spring tide, a tidal variation between mixing conditions on the ebb and the flood is revealed by ADCP measurements, with higher values extended up to the surface during the ebb. The link between turbulent mixing and suspended sediment concentration is straightforward during the ebb. During the flood, the suspended sediment concentration (SSC) seems related to the salt-wedge entrance re-suspension and stratification-induced turbulence damping. No stable Estuarine Turbidity Maximum (ETM) has been observed during the field experiment in the lower Adour estuary.