Tidal Straining Research Articles

Tidally-modulated stratification in a channel-shoal estuary

This study integrates field observations and numerical simulations in the Delaware Estuary. The geometry of the Delaware Estuary is similar to that of South San Francisco Bay, the German Wadden Sea, and the mouth of the Changjiang Estuary. Both the observations and model results demonstrate that the water column was stratified (Δs > 15 psu), in contrast to the prior designations of the Delaware Estuary as a “weakly-stratified” estuary (Garvine et al., 1992). This study implements the salinity variance method to qualify the contributions of different mechanisms to initiating estuarine stratification. The analysis indicates that the tendency for stratification is initialized by the interplay between tidal straining and mixing from the end of spring tides. Although the longitudinal straining decreases during flood tides, the lateral straining contributes to a positive tendency for estuarine stratification. The lateral salinity gradient is not significant under the annual mean discharge condition. The strong vertical shear of flow and deviation from the mean salinity are favorable for the generation of lateral tidal straining. In contrast, a prior study showed that strong lateral salinity gradients enhance vertical stratification during the flood. The lateral straining at the end of the flood provides initial stratification, resulting in enhanced the longitudinal tidal straining during the early ebb due to the inhibition of turbulence and thereby enhanced tidal shear.

Contrast of fine sediment dynamics between shoals and channels in a microtidal estuary with mixed semi-diurnal tides

Estuaries usually feature complex bathymetries, where shoals and channels are co-existent. Due to the differences in water depth, current, density gradient and therefore stratification, sediment dynamics on the shoal and in the channel demonstrate significant variations. In this study, field measurements were carried out during spring and neap tides in both wet and dry seasons in the Huangmaohai Estuary, a microtidal estuary located in the southwest of the Pearl River Delta. Harmonic analysis was conducted for the timeseries data of current and suspended sediment concentration (SSC) for each deployment. Sediment transport flux was decomposed into an advective component, and tidal pumping fluxes by different tidal constituents. During the neap tides, sediment transport is primarily controlled by the advective flux, whereas during the spring tides, tidal pumping fluxes become comparable to, sometimes even exceeding, the advective one. For a 25-hr period, the M1 component of SSC usually denotes the maximum SSC associated with the highest bottom stress, while the M2 component signifies the two highs of the SSC. The M4 component is generally insignificant. The M1 and M2 components can be induced by both the advection and bottom resuspension. For the resuspension part, the M1 component is mostly induced by tidal velocity asymmetry, while the M2 component is generated by tidal straining effect. Sediment transport at the shoal is mostly controlled by the advective flux and the tidal pumping due to tidal velocity asymmetry, while that in the channel is dictated by advective transport and the tidal pumping due to tidal mixing asymmetry.

The Impact of Tidal Straining and Advection on the Stratification in a Partially Mixed Estuary

Stratification and mixing of the water column is an important dynamic process in the estuary, which plays a significant role in the estuarine circulation, mass transport and energy exchange. Based on the multi-station synchronous observation data from 26 February to 6 March in 2011 during dry season in the North Channel of the Changjiang Estuary, the Richardson number, the Simpson number and the potential energy anomaly of water were calculated to analyze the tidal variation of the mixing and stratification processes. The roles of the depth-mean straining, longitudinal advection, non-mean straining and tidal stirring in the processes of mixing and stratification of the water column were analyzed by calculating the contribution terms of the time-derivative of potential energy anomaly. The results show that the mixing and stratification of the water column in the North Channel have significant spatiotemporal variation. Stability of the stratification gradually decreases from neap tide to spring tide. In the reaches of salt wedge migration, permanent stratification develops during neap and mean tide, with stability increasing on the flood and decreasing on the ebb, which is dominated by longitudinal advection. During spring tide, periodic stratification develops, with development of stratification on the flood and its breakdown on the ebb, which is dominated by longitudinal advection and tidal stirring. In the main reaches of saltwater intrusion, permanent stratification develops during neap tide, with stability increasing on the ebb and decreasing on the flood, which is dominated by depth-mean tidal straining. During mean and spring tide, periodic stratification occurs, with development of stratification on the ebb and its breakdown on the flood, which is controlled by depth-mean tidal straining and assisted by tidal stirring. In the North Channel, tidal advection is the main stratifying agent in the salt wedge migration reaches, and tidal straining is the main stratifying agent in the main reaches of saltwater intrusion.

On the mechanisms controlling near-coast circulation in the southern Colombian Pacific at tidal, seasonal, and interannual time scales

This research analyzed the near-coastal circulation along 300 km in the southern Colombian Pacific, a meso-tidal region formed by Tumaco Bay and the Mira River Delta. The interaction between tidal dynamics and the Mira River plume stratification and dispersion is not well known. Moreover, the combined effects of tide and density gradients on the circulation patterns in Tumaco Bay have rarely been studied. The region was investigated using the Delft3D hydrodynamic model, calibrated and validated using field data. The results show that Tumaco Bay is ebb-dominated, and the tide and bottom shape are the dominant forces in the circulation patterns inside the bay. The weak horizontal density gradient induced by Mira River did not show a substantial effect on the circulation of the bay. Near the mouth of the Mira Delta, the water column was predominantly partially mixed, but stratification changed within the tidal cycle, presenting tidal straining along the minor axis of the plume. This may generate strongly stratified conditions in the water column during flood periods. Although tidal straining is very common along the major axis of tide-dominated estuaries, it is not as common in coastal river plumes. The analyzed system provides additional evidence about this phenomenon in a tropical delta. • Hydrodynamics of Mira River and Tumaco Bay as an integrated system is studied for the first time using 3D modelling. • Tumaco Bay is ebb-dominated, and the bottom shape dominates the circulation patterns. • Tidal straining is observed along the minor axis of the Mira River plume. • Cross-shore tidal straining in the plume of tropical rivers has been barely reported previously.

Investigating tidal river dynamics in a longitudinally varying channel geometry

Examining the flow dynamics in a tidal river, particularly downstream, is of great importance to consider the substantial interaction between river runoff and tidal waves. Previous studies have investigated flow dynamics in tidal rivers mainly concentrated on the lateral structure of the estuarine dynamics, with limited consideration of the impact of geometrical variation of the tidal channel, which has an enormous effect along the longitudinal direction. The aim of this study is to offer a comprehensive understanding of the dynamics of a tidal river with longitudinally varying channel geometry. To accomplish the aforementioned aims, this study provides a spatiotemporal analysis of water current and density for a fortnight period of a mesotidal estuarine channel that encompasses both curved and straight channels in the streamwise direction. Moreover, a quantitative analysis of the governing mechanisms for estuarine dynamics was performed to determine the alteration of driving mechanisms due to channel geometry variation. The longitudinal velocity profile indicates the existence of tidal asymmetry where the ebb currents are dominant over flood currents. The asymmetry, which is induced by the interaction between the channel curvature and density gradient, is observed to be more enhanced in the curved channel than in the straight channel. Moreover, the across-channel bathymetry difference between the curved and straight channels leads to different patterns of lateral flow in those channels. Additionally, the longitudinal and lateral velocities averaged for the spring/neap tides reveal that the channel with a higher curvature degree has greater residual circulation. On the other hand, the periodically varying density distribution denotes the existence of tidal straining, which is slightly modified by the variation in geometry. The notable findings of this study are as follows: (i) the variability in channel geometries introduces different responses of tidal straining and tidal stirring; (ii) the river effect (river-induced shear) in the curved channel substantially increases significantly compared to the straight channel over a certain threshold of river runoff. We believe that the findings of this study deepen our understanding of tidal river dynamics in a longitudinally varying channel geometry.

Numerical Investigation of the Sediment Hyperpycnal Flow in the Yellow River Estuary

Sediment hyperpycnal flow is one of the most important processes for mass transport, which is essential to coastal morphodynamics. Herein, we studied the generation and maintenance of the sediment hyperpycnal flow in the Yellow River Estuary (YRE) using a three-dimensional finite volume coastal ocean model (FVCOM). The model considered the effect of sediment-laden water on density stratification, and was validated by field hydrodynamic and sediment data. Numerical results revealed that the hyperpycnal flow shows periodic characteristics with tidal cycles where the flow is weakened during flood tides and enhanced during ebb tides. A high suspended sediment concentration (SSC) of about 30–40 kg/m3 constitutes an important factor in the formation of hyperpycnal flows. High river discharge with high SSC is essential for maintaining the hyperpycnal flow in the YRE. The Simpson potential energy theory was applied to study the processes of estuarine circulation, tidal straining, and tidal stirring in the YRE. The tidal straining is the main control factor of the periodic stratification-mixing process of hyperpycnal flows in the YRE. Along the axis of the river mouth, the momentum balance is mainly dominated by the pressure gradient and advection.

ADCP Observations of Currents and Suspended Sediment in the Macrotidal Gulf of Martaban, Myanmar

The Ayeyarwady and Thanlwin Rivers, which drain Myanmar, together form one of the largest point sources of freshwater and sediment to the global ocean. Combined, these rivers annually deliver an estimated 485 Mt of sediment to the northern Andaman Sea. This sediment contributes to a perennially muddy zone within the macro-tidal Gulf of Martaban, but little is known about the processes that dominate dispersal and trapping of sediment there, as very few water column observations are available. A research cruise in December 2017 provided a rare opportunity to obtain Acoustic Doppler Current Profiler (ADCP) data along transects from the Gulf of Martaban and adjacent continental shelf. Two transects were obtained from the outer portion of the Gulf of Martaban in water depths that ranged from about 20–35 m. These showed very fast currents, especially during flood tide conditions, exceeding 1.5 m/s. The backscatter record from the ADCP indicated asymmetries in distribution of suspended sediment during the ebb versus flood phase of the tide. During ebb tidal conditions, the backscatter record indicated that sediment was transported in either a surface advected layer, or fairly well-mixed throughout the water column. In contrast, during flood tidal conditions, sediment was confined to the bottom boundary layer, even though the velocities were faster during flood than the ebb conditions. The vertical structure of the currents during flood tide conditions indicated the presence of sediment–induced stratification because currents within the near-bed turbid layers were relatively slow, but speeds increased markedly above these layers. This albeit limited dataset provides an exciting glimpse into the dynamics of sediment transport within the muddy, macrotidal Gulf of Martaban, and implies the importance of tidal straining and bottom nepheloid layer formation there.

Observations of Multiple Internal Wave Packets in a Tidal River Plume

AbstractRemotely sensed images document the occurrence of multiple packets of internal solitary waves (ISWs) in the Rhine River plume at the same time. We use a combination of field observations, and non‐hydrostatic and hydrostatic modeling to understand the processes that lead to the generation and retention of multiple ISW packets within the Rhine plume. Previous numerical modeling shows that the tidal plume front is trapped in the mid‐field plume for more than one tidal cycle due to tidal straining and recirculation within the plume, resulting in the presence of multiple fronts in the near‐and mid‐field plume regions. In this work, we show how variations in the strength of these fronts can lead to the release of ISW packets. We conclude that the retention of the fronts in the mid‐field region of the plume and modulation in the strength of the fronts can explain the presence of multiple ISW packets. A frontal Froude number analysis shows that fronts generated during the previous ebb tide can release ISWs in addition to the newly released tidal plume front.

The Evolution of Plume Fronts in the Rhine Region of Freshwater Influence

AbstractThe Rhine region of freshwater influence (ROFI) is strongly stratified, rotational, relatively shallow and has large tides, resulting in a dynamic field of fronts that are formed by multiple processes. We use a 3D numerical model to obtain a conceptual picture of the frontal structure and the processes responsible for generating this multiple front structure in the Rhine ROFI. The horizontal salinity gradient and numerical tracers are used to identify three different types of fronts: outer, inner, tidal plume and relic tidal plume fronts. Tidal plume front (TPF) trajectories together with the tracers demonstrate that TPFs exist for longer than one tidal cycle. A Lagrangian frontogenesis analysis shows that the fronts are strengthened mainly as a result of increased convergence, which is observed to occur at times when tidal straining is large. Additionally the alongshore tidal excursion and the dominance of the tidal currents over the intrinsic frontal propagation speed, trap TPFs within 20 km from the river mouth. Trapping and re‐strengthening maintain several fronts at a time in the mid‐field region, resulting in a multi‐frontal system. The observation of a complex river plume system is expected to be important for cross‐shore exchange, transport and coastal ecology.

Unravelling spatio-temporal patterns of suspended microplastic concentration in the Natura 2000 Guadalquivir estuary (SW Spain): Observations and model simulations

Microplastics (MPs) patterns in a weakly-stratified estuary were investigated using a combined approach of observations and modeling. The study was conducted in the Guadalquivir River Estuary, which is of high environmental value, yet significantly altered by human activities. The study aims to contribute to understanding and quantifying the land-ocean transport of MPs. Mean concentrations of MPs in the estuary were 0.041itemsm−3, with maximum values up to 0.20itemsm−3, in agreement with the range reported in other estuaries. Polyethylene floating MPs were predominant. Relationships between increases in MP concentration and local rainfall events were identified in the middle estuary when there were no significant discharges from the head dam. Modeling results mimicked observations and revealed the effects of tidal straining, density-driven, and river flow-induced circulation on the net transport. Convergence of transports favors the MPs trapping in the vicinity of Doñana National Park, overlapping the location of the Estuarine Turbidity Maximum.

Determining the subtidal flow at a stratified tidal junction by a novel repeated measurements method

The division of freshwater into separate channels at tidal junctions plays an important role in determining the hydrodynamics and material transport in multichannel estuaries. To obtain a better understanding of the net material transport, it is essential to precisely measure the residual flow near the tidal junction. In this study, the phase-averaging method (PAM) was applied to investigate the residual current and freshwater division at the lower reaches of the Modaomen Estuary (ME), China. This is the first PAM-based quantitative evaluation of the freshwater division at the tidal junction, which controls the freshwater division between the mainstem of the ME and the Hongwan Waterway (HW). The accuracy of the PAM results was examined by comparison with the subtidal flow obtained at a moored site near the estuary mouth. The results showed that the HW received freshwater discharge from the ME during both spring and neap tides. The stratification in the HW was determined by water masses advected from the mainstem of the ME. During the spring tide, the ME had a stronger longitudinal salinity gradient. Via interaction with the vertical shear of the along-channel velocity, the tidal straining tended to enhance the vertical salinity gradient, which generated more vigorous stratification in the channel during the spring tide than during the neap tide. In accordance with the stratified and longitudinal salinity gradient, the mainstem of the ME exhibited a stronger exchange flow during the spring tide. Harmonic analysis and error estimation showed that the PAM can effectively remove the tidal signals. The accuracy of our results suggests that the PAM can be applied to survey other tidal junctions.

Transport processes in the Santa Cruz Channel, Brazil

The Santa Cruz Channel is part of the Itamaracá–Itapessoca estuarine system in Brazil’s Northeast region. It presents a complex geometry and receives the debouches of several small streams. Here we present an assessment of the hydrodynamics of the Santa Cruz Channel and its role on the suspended sediment transport. A field campaign was carried out when water level, cross-sectional flow, current velocity and direction, salinity, and turbidity were recorded during a complete semi-diurnal tidal cycle during the peak of the wet period when the freshwater and river-borne suspended sediment are highest. Longitudinal distribution of salinity and turbidity were also recorded along a transect starting at the adjacent sea up to the upper estuary (salinity = 0). Tides are the main driver of the transport processes, even considering that the observations were during the peak of the rainy season. The salinity displayed intra-tidal stratification, increasing to the low water and vanishing to the high water, which can be explained in terms of the tidal straining effect. So, the Santa Cruz channel behaves as a ‘Strained Induced Periodic Stratified’ (SIPS) system. The horizontal density gradient producing gravitational circulation seems to have a minor role in producing exchange flows. The suspended sediment input by the local river drainage dispersed along the systems displaying a conservative behavior. However, the hydrodynamic condition favors the retention of the river-borne sediment in the system, which has a high trapping efficiency.

Processes of Stratification and Destratification During An Extreme River Discharge Event in the German Bight ROFI

AbstractProcesses of stratification and destratification in the German Bight region of fresh water influence (ROFI) are investigated following an extreme river discharge event in June 2013. For this purpose, a high‐resolution baroclinic ocean model is set up and validated against field data. The model results are used to study the temporal and spatial variability of stratification and the duration of persistent stratification in 2013. The relevant processes affecting stratification are investigated by analyzing the potential energy anomaly budget, with a focus on mixing and tidal straining. It is shown that the stratification in the German Bight is highly affected by the spring‐neap tidal cycle, with generally less stratification at spring tides due to dominant tidal mixing. It is also shown that the location of the river plume can modify this pattern. During spring tides, if the river plume is confined to the eastern region, stratification decreases significantly, as expected, due to the dominance of mixing over tidal straining. On the other hand, if the river plume moves toward deeper regions at spring tides, strong tidal straining becomes present. In this condition, mixing is weak, and the dominant tidal straining results in persistent stratification.

海底斜面上のtidal straining と懸濁物質の輸送過程

海底斜面上のtidal straining と懸濁物質の輸送過程

The Formation of Turbidity Maximum Zones by Minor Axis Tidal Straining in Regions of Freshwater Influence

AbstractThis study investigates the influence of tidal straining in the generation of turbidity maximum zones (TMZ), which are observed to extend for tens of kilometers along some shallow, open coastal seas. Idealized numerical simulations are conducted to reproduce the cross-shore dynamics and tidal straining in regions of freshwater influence (ROFIs), where elliptical current patterns are generated by the interaction between stratification and a tidal Kelvin wave. Model results show that tidal straining leads to cross-shore sediment convergence and the formation of a nearshore TMZ that is detached from the coastline. The subtidal landward sediment fluxes are created by asymmetries in vertical mixing between the stratifying and destratifying phases of the tidal cycle. This process is similar to the tidal straining mechanism that is observed in estuaries, except that in this case the convergence zone and TMZ are parallel to the shoreline and perpendicular to both the direction of the freshwater flux and the major axis of the tidal flow. We introduce the term minor axis tidal straining (MITS) to describe the tidal straining in these systems and to differentiate it from the tidal straining that occurs when the major axis of the tidal ellipse is aligned with the density gradient. The occurrence of tidal straining and the coastal TMZ is predicted in terms of the Simpson (Si) and Stokes (Stk) numbers, and top–bottom tidal ellipticity difference (Δε). Based on our results, we find that SiStk2 > 3 and Δε > 0.5 provide a limiting condition for the required density gradients and latitudes for the occurrence of MITS and the generation of a TMZ.

Observation of the sediment trapping during flood season in the deep-water navigational channel of the Changjiang Estuary, China

After the construction of the Deep-water Navigational Channel (DNC) in the North Passage of the Changjiang Estuary, siltation in the channel became severe during the flood season in the navigation channel. To investigate the causes, field observations of tidal current, salinity and suspended sediment concentration (SSC) were conducted by 16 anchored boats in the navigation channel of North Passage during spring tide in the flood season. The across-channel differences of salinity, SSC, and near bottom residual sediment transport at the high siltation area of the DNC were observed and analyzed. The results show that the near bottom SSC presented a south-to-north decreasing trend during the flood tide at the lower reach of the North Passage. During the ebb tide, a suspended sediment cloud of extremely high concentration was detected within the channel. The observed longitudinal sediment trapping was not only shown as the turbidity maximum (TM) trapped within the moving salinity front but also as the longitudinal convergence of the residual sediment transport at the middle reach. The mechanism for the longitudinal sediment trapping was due to the tidal asymmetry in mixing. The observed lateral sediment trapping was prominent at the most severe siltation area of the DNC in the section #2. The lateral sediment trapping at the across-channel section #2 was not only shown as the lateral transport of the sediments from the channel flanks during the flood slack but also as the lateral convergence of the residual sediment transport during the entire spring tidal cycle. The mechanism for the lateral sediment trapping was dominated by the advective transport. The lateral impact on the channel sediment trapping was not negligible in view of the depth-mean lateral tidal straining on the water stratification. The observed convergences of both the longitudinal and the lateral residual sediment transports were responsible for the severe channel siltation in the North Passage.

Secondary circulation in shallow ocean straits: Observations and numerical modeling of the Danish Straits

In this paper, we explore the secondary flows in the Danish Straits using observations and numerical simulations performed with the unstructured-grid hydrodynamic model SCHISM covering the North Sea and Baltic Sea. The straits are resolved on scales of up to ∼100 m. Given that large-scale atmospheric variability dominates the transport in these straits, we focus on the processes with subtidal time scales. Similarities and differences between the in- and outflows in the straits and flood and ebb flows in estuaries are analyzed. Contrary to the tidal straining in estuaries, the Danish Straits feature substantial differences in the stratification stability during the outflow and inflow phases. With a resolution of ∼100 m, new transport and mixing pathways that were previously unresolved appear fundamental to the strait dynamics. The variety of the strait morphology leads to high variability in the appearance of secondary circulation. Helical cells, often with a horizontal extension of ∼1 km, develop in the deep parts of the channels. A comparison between the high-resolution simulation and a simulation with a coarse grid of ∼500 m in the straits suggests that the coarser resolution overestimates the stratification and misrepresents the transport balance; the axial velocities and transport through the Sound are underestimated by ∼12%. These differences are explained by the missing secondary circulation when the coarse resolution is used (approximately two grid-points per cell instead of ten grid-points per cell in the fine resolution model), along with the resulting changes in mixing along the straits. In conclusion, the use of ultrafine resolution grids is essential to adequately resolve secondary flow patterns and two-layer exchange. Thus, the problems caused by the failure to resolve the secondary circulation in straits appear similar to the problems caused by the failure to resolve mesoscale eddies in ocean models.

Response of Stratification Processes to Tidal Current Alteration due to Channel Narrowing and Deepening

AbstractStratification in estuaries has received much focus due to its importance in estuarine hydrodynamics and material transport. By utilizing a well‐calibrated numerical model, in this work we investigate the changes in stratification in the deepened and narrowed North Passage of the Changjiang Estuary. Before channel narrowing and deepening, lateral straining, generated by the interaction between vertical shear in lateral flow and transverse salinity gradient, is the dominant factor that controls stratification. A two‐layer structure of the lateral flow strains the isopycnal transversely, resulting in rapid stratification from late flood to early ebb tide. Thus, maximum stratification occurs during the early ebb. Then, the stratification was suppressed by the vertical mixing and the less stratified water advected from upstream, even the vertical shear in along‐channel flow continued to strain the isopycnal. After channel deepening and narrowing, the salinity in the upper water column experienced a sharp vertical gradient during the entire tidal cycle, while the transverse salinity gradient and lateral flow are profoundly reduced. The impact of lateral straining on stratification becomes minor. The enhanced stratification results in a sharp decrease in turbulent mixing within the pycnocline. The water movement in the upper layer is in a free‐stream status and the tidal current speed increases significantly. The alteration of the vertical current structure enhances the along‐channel tidal straining and stratification is most vigorous on late ebb tide.

Observations of Restratification after a Wind Mixing Event in a Shallow Highly Stratified Estuary

In stratified estuaries susceptible to wind mixing events, the changes in stratification have important implications for estuarine dynamics. Understanding the timescale associated with these mixing events and indirect wind impacts is dependent on estimating the restratification timescale. Bay-wide stratification observations, turbulence time series, and long-term data were examined to quantify the response mechanisms and restratification times in Mobile Bay. Observations showed moderate increases in stratification occurred over 2–3 days after the mixing event and were spatially variable. Turbulence data and model results that further highlight the period of returning stratification had changes in the relative contribution of tidal straining and gravitational exchange for the residual circulation in the estuary. Estimates of dissipation for the two ADVs averaged 2.6–3.1 × 10−5 m2 s−3 prior to the mixing event and increased to 1.4–8.5 × 10−4 m2 s−3 after the mixing event. These changes showed with increasing stratification; the turbulent dissipation decreased. These results highlight initial high returns in stratification are slowed over time as the exchange and mixing in the bay develop, and stratification returns to its premixed state.

Suspended particulate matter concentration in response to tidal hydrodynamics in a long mesotidal floodway

Analyses of seasonal data obtained using acoustic Doppler current profilers provide an understanding of the behavior of suspended particulate matter concentration (SPMC) toward different forcings in tide-controlled floodways. In this work, the relative contributions of external forcings on SPMC variability were quantified in a tidal river system using singular spectrum analysis (SSA). The main environmental features affecting SPMC were identified as i) spring-neap tidal oscillation, ii) the ebb/flood velocities, and iii) tidal straining. Large SPMC fluctuations occurred under strong mixing states and were directly related to the sediment resuspension stirred up by spring-neap tidal cycles (73.6%–81.9%) and ebb/flood velocities (9.6%–19.5%). On the seasonal scale, river discharge is the key variable explaining the downstream flushing and promoting the occurrence of a convergence zone at the floodway. Upstream from the floodway (greater than 4.8 km from the river mouth), the spring-neap tidal oscillation dominated the suspended particulate matter (SPM) mobility under low river discharge. Two interesting findings were revealed in this work: (i) the SPMC/SPM transport variation responses to tidal forcing (tidal asymmetry) were dominated and modified by river discharge and (ii) the effect of river discharge on the SPMC/SPM transport did not result in a uniform state along the floodway. It is believed that these findings provide further understanding of the dynamics of suspended sediments in shallow tidal systems.