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This study examines the local, intratidal effects of suspended sediment concentrations (SSCs) on the hydrodynamics and vertical mixing in the Ems Estuary, located on the border between Germany and The Netherlands, during summer and winter seasons when the estuary turbidity maximum (ETM) is located upstream and adjacent to the study site, respectively. Measurements of density, SSCs, turbulent kinetic energy dissipation, and current velocity were collected and analyzed over a semi-diurnal tidal cycle in August of 2018 and January of 2019 as part of the collaborative Ems-Dollard Measurement (EDoM) campaign. During August, the estuary turbidity maximum was located 25 km upstream from the measurement site and local SSCs were low. Results revealed that under these conditions, suspended sediment minimally impacted vertical mixing by stabilizing density near-bottom during flood tide, while typical salinity-induced tidal straining patterns dominated. During January, the ETM was located only 5 km upstream of the measurement site leading to higher local sediment concentrations. Salinity-induced straining of the density occurred on early flood tide, creating stratification that suppressed vertical mixing. The suppression was enhanced by the contribution of vertical gradients in SSC to density, as signified by the gradient Richardson number. Suppression of vertical mixing by sediment-enhanced stratification was most significant within the hour following maximum flood currents when elevated velocity shear occurred. The variability observed between the local dynamics during August and January were attributed to greater sediment concentrations due to the ETM proximity in January. The intratidal asymmetry of vertical mixing observed under higher SSCs likely has implications for sediment transport.

Many coastal monitoring programmes have been carried out to investigate in situ hydrodynamic patterns and correlated physical processes, such as sediment transport or spreading of pollutants. The key point is the necessity to transform this growing amount of data provided by marine sensors into information for users. The present paper aims to outline that it is possible to recognize the recurring and typical hydrodynamic processes of a coastal basin, by conveniently processing some selected marine field data. The illustrated framework is made up of two steps. Firstly, a sequence of analysis with classic methods characterized by low computational cost was executed in both time and frequency domains on detailed field measurements of waves, tides, and currents. After this, some indicators of the hydrodynamic state of the basin were identified and evaluated. Namely, the assessment of the net flow through a connecting channel, the time delay of current peaks between upper and bottom layers, the ratio of peak ebb and peak flood currents and the tidal asymmetry factor exemplify results on the vertical structure of the flow, on the correlation between currents and tide and flood/ebb dominance. To demonstrate how this simple and generic framework could be applied, a case study is presented, referring to Mar Piccolo, a shallow water basin located in the inner part of the Ionian Sea (southern Italy).

The Seto Inland Sea (SIS) is a critical semi-enclosed coastal sea in Japan, characterized by intricate coastlines and narrow straits that give rise to various fronts. Despite extensive research on tidal fronts, knowledge gaps persist regarding their spatiotemporal dynamics, particularly in certain poorly documented regions. Additionally, the understanding of thermohaline fronts, which emerge during winter, requires further investigation. We aimed to enhance our understanding of tidal and thermohaline fronts in the SIS by analyzing their dynamic processes, including intra-tidal and spring–neap tidal cycles, seasonal variations, and anomalous frontal variability. Using a gradient-based algorithm with an advanced contextual feature-preserving median filter, we processed the high-resolution sea surface temperature dataset to detect and quantify tidal and thermohaline fronts. Our analysis revealed the presence of numerous tidal fronts, predominantly influenced by the M2 tide, across the SIS, with substantial spatial variations in amplitude due to complex coastlines and narrow straits. Intra-tidal movements of tidal fronts corresponded to ebb and flood currents, while spring–neap tidal cycles and seasonal shifts influenced frontal positions and intensities. Additionally, thermohaline fronts were identified in certain regions during winter, characterized by large horizontal temperature and salinity gradients. This study enhances the understanding of tidal and thermohaline fronts in the SIS, emphasizing the importance of intra-tidal and wind-driven influences on frontal dynamics. However, limited observational coverage and resolution emphasize the need for further research to explore long-term temporal changes and better grasp the influences of ambient currents and wind patterns. Such insights are vital for effective coastal management and environmental monitoring in the SIS region.

Purpose The nearshore area of many sandy beaches exhibits morphological patterns which are rhythmic along the coast. Most studies on submerged sandy bedforms have focused on their morphodynamics in the deeper part of the nearshore due to operational limitations when performing bathymetric measurements. Along part of the macrotidal Belgian west coast, a remarkable field of coast-normal submerged dunes is found in a very shallow area that partly emerges at low tide. Methods For the first time, the morphology, volumetric budgets and evolutionary trend of these large transverse submerged dunes have been investigated using high resolution multibeam bathymetric surveys performed over an observation period of 9 years and returned at intervals from daily to a few years. Results The morphological analysis indicates the presence of seven large transverse sharp-crested sandy dunes with a height of 1–2 m and a spacing up to 200 m, extending from the beach to 2.7 km offshore. Their morphodynamic patterns show a remarkable rhythmicity along the coast with a persistence over time. The large dunes are an integral part of the coastal system contributing to the long-term natural beach accretion. They migrate at a rate of 36 m yr −1 in the direction of the longshore sediment transport towards NE mostly driven by flood currents. The morphology of the large dunes is also controlled by storm-wave action depending on their depth below sea level. Storm-waves do not influence the dune mobility. Their morphology is forced by the bathymetric context as well as the presence of coastal engineering structures such as groynes. Conclusions The morphodynamics and evolution of the large transverse dunes suggest complex morphosedimentary interactions of a shallow nearshore area, where a constant large natural sand supply interferes with strongly fluctuating coastal hydrodynamics.

Tidal-scale wave modulation is a critical yet complex process in macro-tidal estuaries. This study investigates semidiurnal wave modulations in the Changjiang River Estuary (CRE) using unique, long-term in situ observations and high-resolution ADCIRC–SWAN coupled simulations. Pronounced semidiurnal signals are identified in significant wave height (Hs), mean wave period, and wave direction. Observational results demonstrate that the modulation intensity is highest in Hangzhou Bay and the CRE mouth, decreasing gradually offshore. A key finding is that semidiurnal Hs maxima systematically coincide with peak flood currents and precede high water by approximately three hours. Long-term records confirm that this modulation persists year-round and intensifies during energetic events such as typhoons. The expression of the tidal signal depends on wave composition: wind-sea-dominated conditions exhibit stronger period modulation, whereas swell-dominated conditions favor coherent Hs modulation as kinematic tidal effects remain more apparent in the absence of strong local wind forcing. Numerical sensitivity experiments demonstrate that tidal currents are the primary driver of the observed wave modulation, while water-level effects are largely confined to shallow shoals. The results highlight that accurately reproducing the observed frequency–directional structure requires the inclusion of current-induced Doppler shifts and refraction. Beyond the classical following-current effects, the analysis suggests that the spatial deceleration of currents along the wave path acts as a kinematic trap that focuses wave action and sustains Hs intensification. This mechanism provides a physically plausible explanation for the observed phase relationship and points to the non-local nature of estuarine wave dynamics, where the wave state appears as an integrated response to cumulative current gradients along the propagation path. These findings emphasize the necessity of incorporating wave–current coupling in future coastal modeling and hazard forecasting.

Based on a comprehensive study of the Tina Mayor estuary, a conceptual morphosedimentary model is proposed for one of the best-preserved limestone sectors of the Iberian Peninsula. This mesotidal and rock-bounded estuary consists of a significant proportion of quartzitic gravel fractions, which is distinctive compared to the other nearby estuaries of Northwest Spain on the Iberian Peninsula. Fluvial discharges allow for high coarse fraction inputs to be distributed to all the geomorphological estuarine zones, particularly the mouth, the bay and the inner areas. Moreover, the narrowing of the rocky boundary affects the outermost sector of the mouth of the estuary, developing two coarse grain spits; the inner being much more extensive, while tidal flats occupy a greater reclaimed area than the natural ones. The dominant sedimentary flow regime was established based on tidal and current records during a tidal cycle. The flood currents crossing the bay change trajectory at the mouth boundary as a result of rocky narrowing from the western mouth to the eastern inner side in a reverse response to the Coriolis effect. Estuarine morphosedimentary units are mapped, including the large and minor bedforms in each estuarine zone. These have been characterised according to the average values of the granulometric parameters (coarsest 1-percentile grain size or centile, mean size, sorting, skewness and kurtosis), as well as the carbonate (bioclast) percentage, including the trend maps of the mean size, sorting and biogenic carbonate content. Furthermore, taking into account the mean tidal amplitude and mixing waters (QF/QT), a suitable classification can be established for any type of estuary, including the characteristics of the confinement of the estuary mouth.

The intertidal patterns at the inlet of three coastal lagoons (Agiasma, Porto Lagos, and Xirolimni) in Northern Greece were investigated by combining in situ samplings and computational efforts. These lagoons are Mediterranean, microtidal coastal systems, connected with the adjacent open sea (Thracian Sea) through their inlet canals and are highly affected by the lagoon–sea exchange processes. Limited freshwater enters their basins, mostly due to precipitation and agricultural drainage. An intense monitoring program of water flow and quality at the mouth of the three lagoons was carried out, aiming to quantify the transport mechanisms of water, salt, and nutrients across the inlet canal under different tidal/meteorological conditions. Ebb currents were recorded higher than flood currents, and the temporal variability of the longitudinal velocity was characterized by asymmetries. Residual currents were important to the water exchange, with the Eulerian water, salt, and nutrient fluxes being an order of magnitude larger than the Stokes drift. Eulerian transport and tidal pumping are considered as important mechanisms for salt and nutrients exchange through the inlets. The return flow factor varied from 1 to 17.5% of the water exiting the lagoons in ebb, while the residence time ranged from 0.7 days to 4.2 days.

Due to remarkable reduction of sediment supply, the vulnerability of Yellow River deltaic system increased and ecological impacts occurred to some extent. To have a comprehensive and quantitative understanding of the morphological evolution of deltas, surficial sediments of tidal flat along the abandoned southern Yellow River sub-delta and two adjacent coastal units were systematically collected and evaluated by grain-size analysis in the study. The results reveal that surficial sediments of the abandoned southern Yellow River sub-delta have been coarsening significantly since the 1980s, as characterized by a decrease in both the mud content and the clay/mud ratio. In particular, the transition from cohesive to non-cohesive sediment was completed between 2007 and 2013. With a sharp decrease in sediment flux from the Yellow River estuary, the flood currents from the submarine coastal slope carry few fine particles into the tidal zone, whereas the ebb currents with reverse direction remove some fine particles from the tidal flat. This is a major cause of sediment coarsening in the tidal flat. As sediment coarsening, the coastline of the abandoned southern Yellow River sub-delta has remained stable. The significant change in the grain size of the tidal flat surficial sediments may have a profound impact on the future coastal geomorphic evolution.

This paper presents the mud dynamics in the harbor basin of Zeebrugge in the Southern North Sea based on an analysis of field data. Mud is typically transported into and within the harbor basin through advection of suspended particulate matter (SPM). Three important timescales have been identified. On the intratidal timescale, sediment import occurs from 2 h before high water to high water. Flood currents in the North Sea (directed northeastward along the Belgian coast) drive the primary gyre in the harbor mouth which is advected into the basin during rising tide. This results in water inflow near the eastern breakwater and outflow near the western breakwater. Because of sediment settling in the harbor, this results in a net import of SPM. During spring tide, the SPM flux into the harbor basin is two to four times higher than during neap tide. However, the volume of sediment removed from the port by maintenance dredging is kept constant over the spring-neap cycle, causing the amount of mud in the harbor basin to grow around spring tide conditions. On the seasonal timescale, mud volume within the harbor basin is larger in winter and reaches a minimum at the beginning of autumn. Moreover, the measured densities within the deposited mud layers are lower in winter than in summer. The most shallow point of the 210-kHz reflector is also more shallow in winter. Finally, the profile of the interface of the mud layer in the sheltered Albert II dock is more horizontal in winter than in summer, suggesting seasonal variations in the strength of the mud layer. The question to what degree the seasonal variation of thickness and density of the fluid mud layer is related to differences in the suspended sediment input, to differences in the settling rates of suspended flocs, or to the mud consolidation rate remains open however. The data do not show a strong influence of meteorological conditions (waves, freshwater inflow) on siltation rates in the harbor basin.

Albemarle‐Pamlico Sound (APS) is a shallow lagoonal estuary connected to the Atlantic Ocean through narrow inlets. The circulation dynamics and salt balance in this estuary are investigated using a numerical model. Although the vertical stratification is weak, the mean flow features a two‐layer gravitational circulation with speeds reaching several centimeters per second. Analysis of the momentum budget shows a primary balance among the barotropic pressure gradient as a result of sea level slope, the baroclinic pressure gradient due to horizontal salinity gradients, and stress divergence. The salt budget for APS is determined by the balance between river flow and salt exchange through the inlets. At the inlets, the salt flux resulting from estuarine shear flow is much weaker than that due to tidal pumping and subtidal barotropic transport. Tidal pumping produces a net influx of salt into APS: Strong flood currents push oceanic water into the estuary through a propagating density front, whereas ebb currents advect lighter estuarine water over denser bottom water. The salt flux due to the subtidal barotropic transport across the inlets shows large temporal fluctuations associated with wind events. This transport can be either a source or sink of salt to APS and correlates well with the sea level difference across each inlet. Higher–sea level on the shelf leads to an intrusion of oceanic water into APS whereas higher–sea level inside APS leads to a withdrawal of estuarine water to the shelf. Key Points The mean flow in the lagoon features a two‐layer gravitational circulation Tidal pumping salt flux is large and works through a propagating density front Subtidal salt flux correlates well with sea level difference across each inlet