Salt-wedge Estuary Research Articles

An Earthen Sill as a Measure to Mitigate Salt Intrusion in Estuaries

At a global scale, deltas are vital economic hubs, in part due to the combination of their access to inland regions via river systems with their proximity to sea. However, with the sea in close vicinity also comes the threat of freshwater contamination by saline seawater, especially during droughts. This study explores the potential of a mitigation measure to estuarine salt intrusion, namely the construction of a (temporary) earthen sill—a measure implemented in the Lower Mississippi River near New Orleans (LA, USA). This study suggests design guidelines on how a sill can be used to mitigate estuarine salt intrusion: the design should focus on the longitudinal placement and the height of the sill, and the mitigating efficiency of the sill reduces with increasing tidal range. Overall, a (temporary) sill has great potential to reduce salt intrusion in salt wedge estuaries if there is sufficient water depth available.

Density gradient effect on circulation patterns and mixing processes: Observations at the convergence front of a salt wedge, microtidal estuary

The convergence front in estuaries is a crucial area influenced by dynamic mixing processes which vary from one tidal cycle to another, with density gradients playing a key role in shaping circulation patterns. This significance is particularly pronounced in salt wedge estuaries, where discharge holds greater influence than tides. Despite this, there is a limited amount of research based on high-resolution in-situ data to analyze circulation and mixing processes affected by density gradients in the convergence front of a salt wedge estuary. In this study, continuous measurements of current velocities and CTD profiles were conducted over three tidal cycles to analyze the intratidal variability of circulation patterns (u, v, w) and mixing parameters in the convergence front. Stratification parameter (ηs) and Richardson numbers (RL and Ri) were calculated to analyze the mixing/stratification variability within a tidal cycle. The observations revealed a persistent Subsurface Velocity Maximum (SVM) in the longitudinal component, coinciding with density gradient increases > 4 kg m−3 along the water column. Similarly, lateral circulation patterns were influenced by those increases in density gradient, resulting in eastward-directed currents and the formation of two circulations cells. As expected in a salt wedge estuary, stratification occurs during flood and High Water (HW), when the density gradient increases due to intrusion of the salt wedge. Notably, in the Magdalena River estuary, when the discharge is below 3800 m3 s−1, the salt wedge remains consistently present irrespective of the tidal phase, resulting in a permanently stratified water column with ηs values between 1.60 – 1.95. It is expected that the steady presence of stratified conditions during periods of low discharge leads to an increased accumulation of sediments. These findings provide valuable quantitative insights into the complex interplay of density gradients, circulation patterns, and stratification dynamics in salt wedge estuaries.

Salinity-Various Flow Characteristics Investigation in an Identical Meandering Channel

Estuaries are one of the most productive ecosystems in the world, providing significant resources for humans and animals. However, the influence of various rainfall patterns due to climate change has affected the estuarine system, leading to changes such as salinity intrusion. This study aims to verify how river discharge changes affect salinity mixing within a meandering channel and the effect of flow patterns due to curvature. An experimental hydraulic investigation was conducted at Universiti Teknologi Malaysia (UTM) Johor Bahru. The cross-sectional profiles along the meandering channel are discussed in this paper. The findings prevailed as a typical characteristic of the salt-wedge estuary and indicated the process of estuarine mixing. As the saltwater flow upstream, the salinity level drops due to the dilution process. Additionally, the greater density of seawater compared to freshwater causes it to remain in the lower layers of the water column. The flow pattern in curvature is influenced by the velocity of the inner and outer banks, where velocity has been seen to be higher at the outer bank, allowing the salinity to flow quickly near the inner bank. The present study will be useful in predicting the estuarine salinity response to river inflow.

Spatio-Temporal Patterns of Saltwater Intrusion in A Narrow Meandering Channel

Saltwater intrusion has become a crucial issue for water resources management across the globe. Consequently, this issue leads to problems such as encroachment on water intake zone, loss of freshwater vegetation and also disturbance to aquatic life habitat. Undeniably climate change increases the saline water flow into the river system. The meandering rivers are common, and the hydraulics is more complex than straight rivers. An experimental hydraulic investigation was carried out in the Universiti Teknologi Malaysia to elucidate the hydrodynamic interactions between saline water and freshwater in a narrow meandering channel. The spatio-temporal salinity profiles along the river are discussed in this paper. The findings prevailed a typical characteristic of a salt-wedge estuary and indicated the processes of estuarine mixing. As the saltwater flows upstream, the salinity level drops due to the dilution process. Salinity levels and densimetric Froude number were mainly driven by freshwater discharge in the channel. A variation of dilution rate in a narrow meandering channel were up to 78.9% due to strong velocity forces produced by a high freshwater discharge. Furthermore, the flow resistance induced by the channel boundaries and meander planform itself influenced the salinity intrusion profiles along the channel.

Salt Transport Regimes Caused by Tidal and Subtidal Processes in Narrow Estuaries

AbstractTidally averaged transport of salt in estuaries is controlled by various subtidal and tidal processes. In this study, we show the relative importance of various subtidal and tidal transport processes in a width‐averaged sense. This is done for a large range of forcing and geometric parameters, which describe well‐mixed to salt wedge estuaries. To this end, we develop a width‐averaged process‐based model aimed at conducting and analyzing a large number of experiments (∼40,000). We find that the salt transport is dominated by one of seven salt transport balances, or regimes. Four of these regimes are dominated by subtidal processes, while the other three are dominated by tidal processes. Which regime occurs in a part of an estuary depends on four dimensionless parameters, representing local geometry, and forcing conditions. One of the regimes features salt import by correlations between the depth‐averaged tidal velocity and salinity. While this mechanism was previously only associated with along‐channel geometric variations, we find it can also be a dominant mechanism in a significant part of the parameter space due to river‐induced tidal asymmetry, independent of river geometry. We apply our classification to a case study of part of the Dutch Rhine delta and compare to decomposition results of a fully realistic three‐dimensional model. We find the estuary features two regimes, with import dominated by subtidal shear transport in the seaward part of the estuary and by depth‐averaged tidal correlations in the landward part of the estuary.

Lateral Variation of Tidal Mixing Asymmetry and Its Impact on the Longitudinal Sediment Transport in Turbidity Maximum Zone of Salt Wedge Estuary

The lateral bathymetry in the estuary results in different degrees of tidal mixing asymmetry, which has significant impacts on the longitudinal sediment transport by changing the temporal variation of vertical eddy diffusion. This study focus on the lateral variation of tidal mixing asymmetry and longitudinal sediment transport at the landward boundary of turbidity maximum zone in the North Channel of Yangtze estuary, which is a typical time-dependent salt wedge estuary. A transect survey was carried out in December, 2018; five vertical profiles of flow velocity, salinity and suspended sediment concentration were simultaneously measured covering a spring tidal cycle. Analysis of the data revealed that, after the maximum ebb, the stratification in the main and secondary channel was stronger than that on the shoal. In the channel, during ebb tide, the stronger stratification restrained the turbulent mixing induced by vertical shear, vertical mixing during the flood tide was stronger than that during ebb tide and vertical mixing coefficients ranged from 0.06 to 0.12, showing regular tidal mixing asymmetry over a flood–ebb tidal cycle. Therefore, stronger eddy diffusion caused by vertical mixing resulted in higher suspended sediment concentrations during flood tide, the larger landward tidally averaged sediment transport rate was induced by tidal pumping with the transportation of flood tidal current and the net sediment transport over a flood–ebb tidal cycle in the channel was landward. Meanwhile, on the shoal, under the effect of vertical shear, the vertical mixing during flood tide was weaker than that during ebb tide; vertical mixing coefficients ranged from −0.27 to −0.02, showing the reversed tidal mixing asymmetry. Higher suspended sediment concentration was transported seaward by the ebb current, the tidally averaged sediment transport rate by both tidal pumping and advection was seaward and the net sediment transport was seaward. Furthermore, large river discharge increased the seaward advection sediment flux on the surface layer in the main channel, resulting in the seaward tidally averaged sediment flux. Strong resuspension increased the seaward advection sediment flux near the bottom in the main and secondary channel, resulting in the seaward tidally averaged sediment flux.

Coupling Hydrodynamic and Energy Production Models for Salinity Gradient Energy Assessment in a Salt-Wedge Estuary (Strymon River, Northern Greece)

Salinity gradient energy (SGE) plants generate power from the mixing of salt water and fresh water using advanced membrane systems. In the Strymon River, under low-flow conditions, a salt wedge is formed, developing a two-layer stratified system, which could be used to extract SGE. In this paper, a novel study was implemented by coupling a 3D hydrodynamic model simulating the salt wedge flow, with the SGE model which assesses the net energy produced by a 1 MW SGE plant. Two scenarios were followed: (a) the optimal scenario, operating throughout the year by mixing salt water from the sea (38.1 g/L) and fresh water (0.1 g/L) from the river to produce 4.15 GWh/yr, and (b) the seasonal scenario, utilizing the salinity difference of the salt wedge. Results show that the daily net SGE production varies between 0.30 and 10.90 MWh/day, in accordance with the salinity difference (ΔSsw ~15–30 g/L). Additionally, a retrospective assessment (from 1981 to 2010) of the annual and seasonal net energy production was conducted. This analysis illustrates that the salt-wedge formation (spring to late summer) coincides with the period of increased regional electricity demand. In the future, the emerging SGE could serve as a decentralized renewable energy source, enhancing energy security in the region.

Understanding the circulation in the deep, micro-tidal and strongly stratified Congo River estuary

The Congo River estuary is characterised by a deep canyon that connects the river to the deep ocean by cutting through the continental shelf. Its estuary is influenced by high river discharge and micro-tidal conditions, with a large depth and limited vertical mixing. This restricts the supply of oxygen from the surface waters to the more saline bottom waters, leading to hypoxic and anoxic zones. We study the dynamics of the Congo River estuary by applying the multi-scale baroclinic coastal ocean model SLIM 3D (www.slim-ocean.be) to this topographically challenging environment. By allowing a high degree of flexibility in the representation of both the complex geometry and the strong stratification, SLIM 3D is able to simulate riverine, tidal and gravitational processes that drive the estuarine circulation. Model results compare favourably with in-situ data in the estuary, suggesting that the exchange flow is correctly simulated. The latter is characterised by a two-layer dynamics. The combination of the large river discharge, the strong stratification and the large depth results in a moderate freshwater Froude number and a very small mixing number. It makes the Congo River an outlier in state-of-the-art estuarine classifications, closer to fjords than salt wedge estuaries. Furthermore, using the age as a diagnosis sheds light on the spatial variability of the estuarine waters ventilation. Local maximum of renewing water age located just below the pycnocline is exceeded by old dense oceanic waters which stagnate at the bottom of the canyon for more than two months due to the small vertical mixing. It helps explain the hypoxic and anoxic conditions observed at the bottom of the submarine canyon.

Modeling an arrested salt-wedge estuary subjected to variable river flow

In this study we present an approach to calibrate a three-dimensional hydrodynamic model of a salt-wedge estuary, the Araranguá Estuary, southern Brazil, based on the Delft3D-FLOW model. The calibration was carried out in four steps to predict the vertical salinity structure along the estuary in an efficient and effective way. Skill assessment was used to evaluate the calibration quality. The model is forced by water-level elevation along the offshore open boundary and river-discharge inflows from the two major tributaries. The hydrodynamic model was calibrated using field observation of water level, currents and longitudinal salinity structure. Calibration was performed adjusting vertical grid resolution, bottom-friction coefficient and background eddy viscosity. The model achieves high skill values at water level and currents variations during a 113-day period (in 2008) covering a wide range of river discharge and tidal forcing. Water surface fluctuations obtained from the model are in good agreement with the field data. Modeled depth-averaged currents reproduce the temporal pattern of observed data. Longitudinal salinity structure is also well reproduced, although the vertical structure is more diffusive than the observations. Results also demonstrate that the model predicts the overall measured phenomena and the effects of the flash-flood event, with the discharge affecting water level, currents and salinity.

Adjustment and extension of the Hansen and Rattray estuarine classification diagram

AbstractThe classification diagram developed by Hansen and Rattray (1966, Limnol. Oceanogr.) is one of the classic papers on classification of estuarine salinity dynamics. However, we found several inconsistencies in both their stratification-circulation and estuarine classification diagrams. These findings considerably change the interpretation of their work. Furthermore, while their classification includes salt wedge estuaries, the model used to derive this is only applicable to well-mixed and partially mixed estuaries. Here, we identify and solve these inconsistencies, and we propose new adjusted and extended stratification-circulation and classification diagrams. To this end, we summarise the model of Hansen and Rattray and extend their work to find analytical model solutions and an adjusted stratification-circulation diagram. Using this new diagram, it is shown that Hansen and Rattray incorrectly discussed the behaviour of dispersion dominated estuaries and that several parts of the diagram correspond to physically unrealistic model solutions. This is then used to demonstrate that several estuarine classes identified by Hansen and Rattray correspond to physically unrealistic model solutions and can therefore not be interpreted. A new and extended classification is proposed by using a recently developed model that extends the work of Hansen and Rattray to salt wedge estuaries. This results in an extended estuarine classification including examples of the location of 12 estuaries in this new diagram.

Salt-wedge dynamics in microtidal Neretva River estuary

The Neretva River estuary, located in Croatia, on the eastern coast of the Adriatic Sea, is a typical example of a micro-tidal salt-wedge estuary. Here, the salt-wedge dynamics was investigated based on continuous field measurements and numerical modeling for the period 2015-2018. A two-layer shallow-water numerical model proved to be an accurate and reliable tool for computing the salt-wedge dynamics in the Neretva River estuary. The simulations showed that the river inflow has the strongest impact on the salt-wedge dynamics, whereas sea levels and tides have a much smaller effect, mainly related to daily variations of the salt-wedge length and volume. A set of simple equations were derived, which link the salt-wedge intrusion length, salt-wedge volume, and salt-wedge spread to the river flow rate. It was shown that, during summer, the salt-wedge intrudes more than 20 km upstream from the mouth, exacerbating the salinization of aquifers and soils. The assessment of salt-wedge dynamics in the Neretva River estuary is thus a crucial element for planning, designing, and managing the irrigation system in this coastal region, for sustainable development of agriculture and protection of water resources.

Comparative hydrodynamics of a sub-tropical salt-wedge estuary and a tributary

ABSTRACT The objective of this study is to compare the physical characteristics of circulation, salinity structure and transport in the Itajai-Acu and Itajai-Mirim estuaries. Due to its importance, the Itajai-Acu estuary has been studied in the last decade. However, its main tributary, the Itajai-Mirim has never been assessed, especially as an opportunity to comparatively investigate the flow behavior of salt wedge estuaries with different widths and depths. Field data were acquired during two campaigns that covered the complete semi-diurnal tidal regimes during spring and neap tides. Water level, total transport volume, current and salinity were recorded hourly and synoptically at cross-sections in each estuary. The campaigns were conducted during a prolonged period of low river discharge. The tidal range during the spring and neap tide campaigns were of approximately 1.2 and 0.4 m, respectively. At the Itajai-Acu and Itajai-Mirim cross-sections, the peak ebb and flood currents were -0.8 and -0.6 m s-1 and 0.8 and 0.4 m s-1, respectively, during the spring tide campaign, and classified as well mixed and highly stratified estuaries, respectively. During the neap tide campaign, both estuaries were classified as salt wedge. The dominant mechanism was the salt transport by advection due to fluvial advection in both estuaries and campaigns. The landwards salt transport, which resulted from dispersive processes, was only important during neap tide for the Itajai-Acu estuary.

Circulation and transport processes in a tidally forced salt-wedge estuary: The São Francisco river estuary, Northeast Brazil

The São Francisco river flow is regulated by a series of dams that work in cascade for hydro-power generation, maintaining the flow <1000 m3 s−1 all year long. This caused the dampening of the flood peaks and perpetuated the salt intrusion, changing the function of the system as a material source to the coastal ocean. Here we present an assessment of the estuary salt intrusion, hydrodynamics, mixing processes, and the transport of scalars based on field observations. The mains goal is to evaluate its present role as a sink or source of materials to the adjacent sea. Three tidal surveys were carried out to gather data on the water level, cross-section discharge, current velocity and direction, salinity, temperature, concentration of suspended particulate matter (SPM), dissolved oxygen, and chlorophyll. Data were recorded from moored instrumentations in different locations, from boat-based sampling in a cross-section, and also in along-estuary surveys. The estuary shows a highly stratified salinity distribution, with the salt intrusion excursion of 7 km during the spring tide, reaching ∼11 km at high tide. The salt intrusion is laterally asymmetric, influenced by the system morphology. There is a strong tidal attenuation along the estuary, even though the flow regime is sub-critical (Richardson Number > 0.25). The estuary presented lateral variability of currents modulated by the tide, being horizontally sheared during spring tide and vertically sheared during neap. The transport of scalars was modulated by the tide, and the estuary exported SPM, dissolved oxygen, and chlorophyll both during neap (44.4, 12.9 and 3.6x10−3 kg s−1, respectively) and spring tide (31.8, 7.4 and 2x10−3 kg s−1), despite the severe flow regulation, meaning that the system still functions as a source of materials to the coastal sea.

A Unifying Approach to Subtidal Salt Intrusion Modeling in Tidal Estuaries

AbstractThe salinity structure in estuaries is classically described in terms of the salinity structure as well mixed, partially mixed, or salt wedge. The existing knowledge about the processes that result in such salinity structures comes from highly idealized models that are restricted to either well-mixed and partially mixed cases or subtidal salt wedge estuaries. Hence, there is still little knowledge about the processes driving transitions between these different salinity structures and the estuarine parameters at which such a transition is found. As an important step toward a unified description of the dominant processes driving well-mixed, partially mixed, and salt wedge estuaries, a subtidal width-averaged model applicable to all these salinity structures is developed and systematically analyzed. Using our model, we identify four salinity regimes, resulting from different balances of dominant processes. It is shown that each regime is uniquely determined by two dimensionless parameters: an estuarine Froude and Rayleigh number, representing freshwater discharge and tidal mixing, respectively, resulting in a classification of the regimes in terms of these two parameters. Furthermore, analytical expressions to approximate the salt intrusion length in each regime are developed. These expressions are used to illustrate that the salt intrusion length in different regimes responds in a highly different manner to changes in depth and freshwater discharge. As one of the key results, we show that there are only very weak relations between the process-based regime of an estuary and the salt intrusion length and top–bottom stratification. This implies that the salinity structure of an estuary cannot be uniquely matched to a regime.

Microplastics in a salt-wedge estuary: Vertical structure and tidal dynamics

The abundance and distribution of microplastics in estuaries have been barely documented, and generally without accounting for the vertical structure in the water column. This study presents the very first data on the occurrence and distribution of microplastics in the Adour Estuary, SW France. The experimental data set was complemented by numerical simulations to gain understanding of the behaviour of suspended microplastics. Microplastics were found throughout the water column with a mean abundance of 1.13 part/m3. Films and fragments were the most abundant types of particles collected. Numerical simulations demonstrated that vertical distribution of microplastics in the water column is highly dependent on particle characteristics and on the local hydrodynamics. The main trend is that neutrally-buoyant microplastics are easily flushed out while heavier microplastics are prone to entrapment in the estuary, in particular under low discharge conditions. The present study suggest that estuaries could be a sink of microplastics.

Seasonal Changes in Structure and Dynamics in an Urbanized Salt Wedge Estuary

Hydrographic measurements of salt wedge structure and dynamics spanning a 20-fold seasonal range of river discharges are used to investigate the seasonal variability in the strongly stratified Duwamish River Estuary. The effect of river discharge on salt wedge length, stratification, pycnocline thickness, and intratidal differences in salinity structure are evaluated. The salt wedge decreases in length and becomes more stratified as river discharge increases. The ebb and flood responses to increasing discharge are markedly different; the flood phase structure shows little seasonal dependence, while the ebb structure changes due to an internal hydraulic response that is strongest at two severe lateral constrictions. This response varies with the net barotropic forcing, which is controlled by river discharge. The asymmetry between the structure on ebb and flood is explained using a two-layer hydraulic framework, although spatially, tidally, and seasonally variable vertical mixing also modifies the structure. As a result of the persistent stratification and dominance of hydraulic dynamics, channel constrictions influence circulation and transport during ebb tides. These dynamics also generate a flood/ebb asymmetry in salt wedge structure and circulation that is modulated seasonally through discharge. We hypothesize that these dynamics lead to a seasonally modulated residual circulation.

Influence of estuarine tidal mixing on structure and spatial scales of large river plumes

Abstract. The Yenisei and Khatanga rivers are among the largest estuarine rivers that inflow to the Arctic Ocean. Discharge of the Yenisei River is 1 order of magnitude larger than that of the Khatanga River. However, spatial scales of buoyant plumes formed by freshwater runoff from the Yenisei and Khatanga gulfs are similar. This feature is caused by different tidal forcing in these estuaries, which have similar sizes, climate conditions, and geomorphology. The Khatanga discharge experiences strong tidal forcing that causes formation of a diluted bottom-advected plume in the Khatanga Gulf. This deep and weakly stratified plume has a small freshwater fraction and therefore occupies a large area on the shelf. The Yenisei Gulf, on the other hand, is a salt-wedge estuary that receives a large freshwater discharge and is less affected by tidal mixing due to low tidal velocities. As a result, the low-salinity and strongly stratified Yenisei plume has a large freshwater fraction and its horizontal size is relatively small. The results show that estuarine tidal mixing determines freshwater fraction in these river plumes, which governs their depth and area after they spread from estuaries to coastal sea. Therefore, the influence of estuarine mixing on spatial scales of a large river plume can be of the same importance as the roles of river discharge rate and wind forcing. In particular, plumes with similar areas can be formed by rivers with significantly different discharge rates, as illustrated by the Yenisei and Khatanga plumes.

Assessment of sea-level rise impacts on salt-wedge intrusion in idealized and Neretva River Estuary

Understanding the response of estuaries to sea-level rise is crucial in developing a suitable mitigation and climate change adaptation strategy. This study investigates the impacts of rising sea levels on salinity intrusion in salt-wedge estuaries. The sea-level rise impacts are assessed in idealized estuaries using simple expressions derived from a two-layer hydraulic theory, and in the Neretva River Estuary in Croatia using a two-layer time-dependent model. The assessment is based on three indicators — the salt-wedge intrusion length, the seawater volume, and the river inflows needed to restore the baseline intrusion. The potential SLR was found to increase all three considered indicators. Theoretical analysis in idealized estuaries suggests that shallower estuaries are more sensitive to SLR. Numerical results for the Neretva River Estuary showed that SLR may increase salt-wedge intrusion length, volume, and corrective river inflow. However, the results are highly non-linear because of the channel geometry, especially for lower river inflows. A theoretical assessment of channel bed slope impacts on limiting a potential intrusion is therefore additionally discussed. This findings emphasize the need to use several different indicators when assessing SLR impacts.

Correlation of Remotely Sensed Surface Reflectance With Forcing Variables in Six Different Estuaries

AbstractThis study examines the links between estuarine dynamics and longitudinal distributions of remotely sensed reflectance in estuaries. Reflectance at 655 nm from Landsat‐8 correlates with in situ measurements of surface turbidity. Images collected from 2013 to 2018 are used to investigate the spatial and temporal characteristics of reflectance distribution in six selected estuaries with different dynamics. The results show that the maximum magnitude (C ) and location (X ) of the reflectance are functions of two major forcing variables, the freshwater discharge and tidal stage. Salt wedge estuaries (i.e., the Fraser River, Connecticut River, and Columbia River estuary) are affected strongly by river discharge and are relatively less affected by tidal forcing. In salt wedge estuaries, the C values along the river channel are correlated with river discharge, while the X values generally are not. In partially mixed to strain‐induced periodic stratification (SIPS) estuaries (i.e., Delaware River) and SIPS‐to‐well‐mixed estuaries (i.e., Gironde estuary), the X values are correlated with river discharge, but the C values are not. SIPS‐to‐well‐mixed estuaries (i.e., Gironde estuary) and highly time‐dependent salt wedge to well‐mixed estuaries (i.e., Merrimack River estuary) are affected by tidal forcing. In these estuaries, the C values are correlated with tidal stage. The C values tend to be lower around high tide than low tide. Overall, the results demonstrate that remote sensing observations of ocean color can be utilized to infer subsurface estuarine processes. Satellite ocean color is a potential tool to monitor river discharge and to classify estuaries.

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.