Estuaries and Coastal Zones in Times of Global Change

With its 625 km2, the Gironde estuary (S-W France) is one of the largest European estuaries. The tidal Garonne and Dordogne Rivers, whose confluence is located at about 75 km from the mouth, form its fluvial section. The Tidal Garonne River (TGR) represents about 2/3 of the freshwater inputs to the Gironde. For a long time it has been accepted the limit of saline intrusion, identified by a salinity higher than 0.5, was nearly at the confluence. In the last decades, there has been a significant decrease of the annual mean TGR discharge, likely to influence marine intrusion. It is often difficult to establish changes in marine intrusion in estuaries due to the limited available data set. This work presents the interest of a multi-sites and high frequency monitoring system, called MAGEST, that records since 2004 four physico-chemical parameters, including salinity, to establish a reference database of water-quality of this large fluvio-estuarine system, in order to address current and future water-quality issues, including saline intrusion. This work presents in details the 14-year time series of salinity along the Garonne-Gironde continuum. Not surprisingly, there are large differences among the instrumented stations depending on their localization. High-frequency salinity chronic at Bordeaux is used to assess the occurrence of saline intrusion in the Tidal Garonne River, revealing marked inter-annual variability in marine intrusion depending of fluvial discharge. The ongoing regional changes suggest an increase of salinity in TGR in the next decades.

In order to discuss the variation of salinity intrusion and mixing types in terms of estuary length, width, depth, and bathymetry, a total of 31 numerical experiments were carried out with a conceptual estuary by using a three-dimensional hydrodynamic simulator, Fantom-Refined. Since sand bars are formed in a river channel, and cyclic variation of the river bed height is found in longitudinal direction, sinusoidal wavy shapes were considered for rough bottom cases to represent the river bed with four different wave amplitudes (0.1, 0.2, 0.3 and 0.4 m) and wavelengths (350, 700, 1400 and 2800 m). In the cases of constant tidal range and discharge with the flat bottom, salinity intrusion length was decreased with increase in estuary length, and mixing condition was changed from salt wedge to well mixed type. On the other hand, salinity intrusion length was increased with increase in width of the channel under constant discharge. Further, the salinity mixing condition was changed from well mixed to salt wedge with the increase in depth of the channel. The salinity intrusion length was increased in the case of funnel shaped estuary when compared with the rectangular shaped estuary. Wavy bottom of the channel had less intrusion length compared with the flat bottom of the constant tidal range and discharge as the bottom friction reduced the velocity of the gravitational flow as well as enhanced vertical mixing. For the constant wavelength, the salinity intrusion length was decreased with increase in wave amplitude. On the other hand, for constant wave amplitude, the salinity intrusion length was increased with increase in wavelength.

The Yangtze Estuary plays an important role in the economic development in the Yangtze River Basin, China. Shanghai is a megalopolis, and more than 70% of its water is supplied from the Yangtze Estuary. Salinity intrusion has become the most restrictive factor for water supply in nature, while the North Branch is the most serious branch compared to others where the salt water in water sources mainly comes from. If the North Branch is properly blocked, construction of tidal gate for example, may alleviate the salinity intrusion. In this chapter, a numerical model is established to study the fresh water distribution characteristic and the impact of the salinity intrusion on the water sources after the North Branch is fictitious blocked. The study shows that salinity intrusion in the Yangtze Estuary is the most serious in January, during which the safety of water sources is likely to be threatened by salt water. The salinity would be greatly reduced in the water sources intake with the North Branch blocked. The salinity of the water intake in the Dongfengxisha Reservoir and Chenhang Reservoir would be close to 0 in any condition while the Qingcaosha Reservoir is still threatened by salt water when continuous northerly wind happens. This study could provide a reference for the discovery of measures for the water source safety in the Yangtze Estuary.

The estuary is a junction of river and sea and is also where freshwater and saltwater meet together. Salinity intrusion may happen when the runoff is relatively weaker or the tidal dynamic is relatively stronger. The Yangtze Estuary is the largest estuary in China. There are some water sources in the estuary to store and provide freshwater. The Dongfengxisha Reservoir is one of these water sources and is constructed in 2014 to provide drinking water for the islanders in the Chongming Island. The water source safety of major islands is most often suffer from the high salinity content of water. For The Dongfengxisha Reservoir, saltwater spilling over from the North Branch is a major threat under natural conditions. To research into how salinity intrusion influence on the water source safety, A two-dimensional tidal-salinity numerical model of the Yangtze Estuary is established to study the relationship between the salinity and the runoff process of the water intake in Dongfengxisha Reservoir. Salinity intrusion in the Yangtze Estuary is the most severe in January and because of its short duration, the water sources safety can be guaranteed. The northeast and northerly wind would increase the salinity of the water intake and northeast wind has a greater influence. The northwest wind would reduce the salinity of the water intake. The sustained north wind would aggravate the intrusion below the South Branch, but it would not affect the water source area. This research can provide reference for the construction of water sources in other islands.

The Qiantang Estuary is characterized by strong tidal bore, high sediment concentration, severe erosion/deposition and frequent human activities. The law of saltwater intrusion is different from other general tidal estuary. This chapter reveals the law of interaction among runoff, channel volume and salinity by means of the analysis of the long-term hydrological and measured salinity data of the Qiantang Estuary. Based on the concept of water, sand and salt mixture density, the muddy water control equations have been derived, and the mathematical model coupling with strong tidal bore-sediment-salinity has been developed as a result, and the model has also been verified, which shows that the result adopting movable-bed numerical simulation model in calculation agrees more with the actual condition.

Deltaic coastal areas are often formed by a piecemeal of transitional wetland environments. These environments consist of wetland-aquifer systems, which commonly react rapidly to climate changes. Direct evaporation from surface water bodies like lakes, wetlands and lagoons will increase due to temperature increase leading to salt accumulation. To understand the hydrological exchanges between the transitional coastal wetlands of the Variconi oasis, the unconfined aquifer of the Volturno River Delta and the Tyrrenian Sea, the contributions of various processes were monitored and assessed. Physical-chemical parameters like salinity, pH, Eh and temperature were monitored during the hydrological year 2016–2017 on a monthly basis. Moreover, the use of groundwater and surface water equivalent freshwater heads, along with hydraulic conductivity tests and the geological architecture, permitted to connect the salinity variations in the wetlands with the degree of the hydraulic connection between the wetlands, the Volturno River, the Tyrrenian Sea and the coastal aquifer. The results show that the permanent wetlands fed by both the Volturno River and the Tyrrenian Sea, show a smoothed salinity peak during the summer season; while the ephemeral wetlands hydraulically disconnected from the aquifer show high salinity peaks during the summer season due to evapoconcentration processes. Spatial mapping of salinity and other measured parameters, highlighted an elevated heterogeneity of environments (from saline to freshwater environments) enclosed in the Variconi oasis. This in turn, induced a large biodiversity of both autochthonous and migratory species. Despite of this, the projected increase in salinity of these wetlands due to coastal erosion, augmented evapotranspiration rates and sea level rise, could be of serious concern for the above-mentioned biodiversity, thus monitoring and management strategies are urgently required to preserve this and other oasis in the Mediterranean area that are key sites employed as stop-over along migratory routes.

Lake Burullus is the second largest coastal lagoon in Egypt, its ecosystem has been deteriorated, due to its central location inside the Nile Delta. The lake receives most of the drainage water of the Nile Delta region through eight agricultural drains. The drainage water which discharged into the lake is mostly nutrient-rich fresh water, polluted with agricultural fertilizer and heavy metals from industry. Lake Burullus is classified as hypereutrophic with bad to very bad environmental conditions. The main objective of this study is to investigate the feasibility of applying different water quality management scenarios to improve the lake ecosystem. A calibrated hydrodynamic and water quality model for the lake was developed using a two-dimensional, vertically averaged, finite difference hydrodynamic and ecological code, MIKE21. This developed model was calibrated with measured field data collected during the period (June 2010–July 2011). Three hydrodynamic parameters and five water quality parameters of the lake were chosen to present the study results. These parameters are: water levels, water temperature, salinity, dissolved oxygen, biochemical oxygen demand, nitrate, Ammonia and ortho-phosphate. Three enhancing water quality scenarios for the lake were investigated: an additional artificial outlet, treatment plants for drains discharge and constructing of radial channels in lake bed. The study results verified that, economically, treatment plants scenario for the two most polluted drains is highly recommended. Constructing of an additional outlet will increase the average lake salinity and is considered as the most effective scenario for enhancing the DO concentrations in the lake. A water quality management strategy is urgently required for the lake ecosystem.

Seawater pumped-storage power station (SPPS), as an efficient large-scale energy storage facility for marine renewable energies, has been incorporated into the key research tasks in the “13th Five-Year Plan” of hydropower development in China. The tailrace surge chamber is very important for the operation safety of the SPPS with a long tailrace tunnel. To determine the conditions under which a SPPS requires a tailrace surge chamber and to account for the time sequence superposition of water hammer vacuum, velocity head vacuum and head loss vacuum, a new setting criterion using the rigid water hammer theory was derived. Then, comparisons among several setting criteria of tailrace surge chambers are conducted. Ultimately, the new setting criterion is investigated and validated by 1D numerical simulation of the hydraulic transient process for a certain pumped-storage power station. The discriminant result obtained by the new setting criterion is consistent with the actual setting condition, and it can be applied as a preliminary setting criterion of tailrace surge chambers for SPPSs and can provide guidance for preliminary engineering design.

Environmental impact assessment (EIA) studies for offshore wind farm projects endeavour to consider the sensitivity of ecological compartments (benthos, fish, birds and marine mammals) to potential pressures/changes occurring in the ecosystem structure and functioning. EIA is expected to be conducted considering an integrated ecosystem approach, which is still a target to reach. In this context, and as a complementary approach to the traditional impact assessments, the objective of the ANR TROPHIK project is to develop an integrated ecosystem approach using several modelling tools for a holistic consideration of the food web. Here, we take into account the case of the Courseulles-sur-Mer offshore wind farm project located in the Bay of Seine. In this project, the potential impacts associated with this planned offshore wind farm are modelled. A model of the food web at the site of the construction was built to test possible reef- and reserve-effects, and to investigate the usefulness of Ecological Network Analysis (ENA) indices in the assessment of ecosystem health state. After the installation of the wind farm, our model showed that the ecosystem witnessed a change in its functioning mainly due to the important increase of the biomass of bivalves with the reef effect related to the installation of hard structures for the OWF. To go further into the integration of these results, we enlarged the description of the ecosystem functioning from a local to a larger spatial scale, where the initial zone was extended to the whole Bay of Seine using a spatial model. Different scenarios were built to test how the association of cumulative impacts, from climate change to fisheries, could affect the ecosystem. Finally, we propose a combined food-web and social network modelling approach to the Courseulles-sur-Mer model. The objectives of this latter analysis are to construct a decision-making process focusing on the network of actors involved, and to couple these social and ecological networks into a qualitative common model for a better understanding of the social-ecological system. Our approach aims to contribute to sustainable development through the analysis of interactions between the different categories of stakeholders groups, and can be applied in other offshore wind farm implementation in European waters.

The Alderney Race is one of the most powerful current in Europe (up to 5 m/s during spring tide). Considering these important currents, this site has been identified to extract energy from the tide with installation of tidal turbines. However, this area is facing open sea to the west and thus strong wind can generate significant wave height interplaying with the tidal currents, which is a critical point for the dimensioning of the tidal turbines. This chapter deals with in situ measurements of waves and currents in Alderney Race.

The fluid dynamics around and inside an OWC-type wave energy device is studied using Direct Numerical Simulations of the multiphase air-water two-dimensional vertical Navier-Stokes equations. A schematic rectangular shaped OWC device placed against the vertical ending wall of the numerical rectilinear wave flume is considered. Owing to numerical constraints, reduced scale simulations are carried out with a focus on the near field of the device over a couple of wavelengths. The power take-off system is simply modelled by an opening through the roof of the device. A parametric study on incident wave period is performed to determine the fluid-structure interactions. Beyond the efficiency predictions, which agree fairly well with different values found in the literature, specific behaviours related with an enhancement of free-surface non-linearities around the resonance frequency are observed. Water flow vorticity is found mainly produced in the vicinity of the end of the semi-immersed frontal wall of the device. Significant energy dissipation results from shear-layer and vorticity associated with the air flow passing through the turbine opening. A one-dimensional vertical analytical model is used to compute the instantaneous bottom shear stress and the induced-bedload sediment transport rate which appears impacted by OWC device.

A simple CFD modeling using force source terms in the momentum equation is implemented, with the aim of computing the performance of a Darrieus turbine in its exploitation area and simulating the wake created behind the turbine. It uses the RANS solution method to reproduce ambient turbulent flow conditions with relatively low computational costs. The force distribution used is three-dimensional and has been calculated prior to implementation using a single URANS simulation of the flow through the real geometry of the turbine. To take into account the velocity and turbulent conditions of the flow impacting the turbine, forces can be corrected by the total forces obtained experimentally on a reduced-scale model for different flow cases. The impact on the turbine of upstream turbulence generated by a grid is studied experimentally. The power coefficient, drag force and transverse component of the force on the turbine are studied, as well as the shape and extension of its wake using Particle Imaging Velocimetry. Simplified models with different levels of detail are compared to the experimental data. The results turn out to be in good agreement in the far-wake, with an underestimation of the flow deficit in the near-wake.

Flood-ebb asymmetry of a tidal flow has important implications for net sediment transport and the potential extractable resource. The asymmetry of the tide in U.K. waters may be understood through the interaction of the M2 (principal lunar) and M4 (first even overtide of the M2) tidal constituents. The interaction of the M2 tide with a tidal-stream turbine will alter the M4 tide, both augmenting and reducing the M4 amplitude, leading to an alteration of flood-ebb asymmetry. In this chapter the impact of a row of tidal-stream turbines on the overtides of the M2 has been investigated through a numerical modelling study. Further, the way that additional turbines alter the way the turbines impact the shallow-water tides individually is explored. The results of the modelling show that when deployed in a row, on average, the peak velocity deficit and change to the current magnitude asymmetry (CMA) per turbine was less than were it deployed alone. The difference between the per turbine impact of turbines in a row and that of an individual turbine grew as the number of turbines in the row, and therefore the row blockage, increased. Additionally, the total area of the model domain experiencing a change to the M2 current and CMA > 1% increased with the addition of turbines to the row, for a row blockage >~10%, but remained similar to the single turbine case for lower blockage values. The implication of the change to the CMA by a turbine in a row for the asymmetry in energy conversion for its lateral neighbours was small as the turbines do not lie within the area of effect of their neighbours. However, the per turbine energy conversion increased as the number of turbines and row blockage increased, in line with theory.

Characterising circulation pathways in tidal stream energy sites is fundamental to evaluate the effects of turbines power extraction on the transport of water-mass and associated particles. The Lagrangian residual currents are commonly considered to assess the displacement of water particles over the tidal period. The associated circulation is, however, characterised by a strong dispersion as water particles may follow different trajectories depending on the release time during a tidal cycle. In order to obtain a synthetic cartography of the Lagrangian Residual Circulation (LRC), Salomon et al. (1988) proposed an original method allocating the residual currents at the barycentre of particle trajectories. This Lagrangian barycentric method was here applied to the Fromveur Strait (western Brittany)—a region with strong potential for turbine farm implementation along the coast of France. A high-resolution depth-averaged numerical model computed the tidal circulation driven by the principal lunar semi-diurnal constituent M2. The initial particle positions were taken at the 14,026 nodes of the unstructured computational grid surrounding the area of interest with a spatial resolution below 50 m. In the strait, the LRC was characterised by a strong asymmetry between (i) a prominent north-eastern pathway with residual currents up to 0.45 ms−1 and (ii) a southward circulation. Both upstream and downstream of the strait, we exhibited furthermore prominent cyclonic and anti-cyclonic recirculations. A close correlation was found between the north eddy and a prominent sand bank. We simulated finally the forces induced by a series of horizontal-axis turbines as an additional bed friction sink term at the scale of the tidal farm. The extraction of tidal stream energy modified the magnitude and direction of the LRC along the current stream emerging from the strait with (i) a tendency for surrounding eddies to get closer to the tidal stream energy site and (ii) potential effects on nearby sandbanks.

In the Seine estuary, maintenance dredging is operated continuously and yearly dredged volumes have the same order of magnitude as natural sediment fluxes at the mouth of the estuary. Prior to 2017, the main dumping site was in the vicinity of the estuarine turbidity maximum (ETM), therefore impacting sediment dynamics in the area. In this context, the aim of our research is to understand and model the contributions of maintenance dredging to the ETM characteristics and to sediment fluxes, and to compare natural fluxes to the anthropogenic ones related to these activities. Our approach relies on a 3D multi-class hydro-sedimentary model validated by (Grasso et al. in J Geophys Res: Oceans 12(3):558–577, 2018), in which dredging and dumping were implemented as processes following rules defined by port authorities of Rouen and Le Havre. Model results are first evaluated regarding the temporal and spatial variability of dredging in the Seine Estuary, and secondly regarding the stability of dumping sites. In order to follow the fate of dredged materials, the latter are numerically marked by assigning them to specific state variables of the model that respect the particle characteristics (gravel, sands or mud). The corresponding concentrations of these new variables can be computed either in the water column (suspensions) or in the layered sediment. Their contributions to the total suspended sediment mass of the estuary and to the siltation rate are evaluated. Results show that most of the dredged material remains in the proximity of the dumping site but the rest contributes to the turbidity and to the siltation pattern in the estuary. The similitude between the global siltation pattern and the distribution of re-deposited dredged material reveals a strong mixing of the latter within the whole estuary mouth. After 3 years of marking, the contribution of dredged sediment to the ETM can be estimated around 1%.

The aim of this work is to present a numerical method for fast evolving flows governed by the two-dimensional shallow water equations semi-coupled with the Exner sediment balance equation for bed evolutions. The method is based on Chorin’s projection, which combines the momentum and continuity equations in order to establish a Poisson-type equation for the water surface level including the bed evolution. The equations are discretized using an unstructured finite-volume technique. In the model, a second-order upwind scheme combined with a Local Extremum Diminishing method is developed to handle convection terms. A comparison with quasi-analytical and existing numerical results are done to test the performance of the used scheme, including the modeling of a dam-break on a mobile bed.

The Jiao (Ling) River is a typical mountainous macrotidal river. The tidal current and runoff jointly guide sediment gathering in a specific section to form the turbidity maximum zone and develop fluid mud. This plays an important role in riverbed evolution. The construction of sluice in the mainstream of the Jiang (Ling) River will greatly change the original flow and sediment movement characteristics of the river channel, forming siltation downstream sluice and producing a big influence on flood control and drainage and navigation. The flow and sediment movement characteristics of Jiang (Ling) River are analyzed and the influence of fine-grained cohesive sediment movement characteristics and salinity considered. A flow and sediment mathematical model for sluice construction in the Jiang (Ling) River is established to simulate the hydrodynamic change and the temporal and spatial distribution characteristics of sedimentation after the sluice construction. The research results show that the sluice construction has an influence on the entire channel downstream sluice. The closer to the sluice site, the bigger the influence will be. At the initial stage of sluice construction, sediment is mainly deposited in a deep trench of 10 km downstream sluice. The siltation downstream sluice will elevate the flood level and low water level, thus affecting flood control and drainage. It will also decrease the water depth of the channel, thus reducing the navigation capacity of the Jiao (Ling) River. The research results have improved the simulation accuracy of sediment transport mathematical model in the estuary with sluice constructed and provided reference for similar sluice construction in estuaries.

Estuaries are complex systems, usually composed by connected subsystems (mostly beaches, dunes, saltmarshes and the main channel), resulting in a complex geomorphology and ecology that makes difficult its study from a comprehensive perspective. In this sense, characterizing the functionality of an estuary is a key element to develop adequate management tools for these environments. Unfortunately, very few studies have focused on the connectivity among their elements, mostly overlooking the derived interactions inherent to them. As an example, San Vicente de la Barquera estuary (Cantabria, Spain) has been selected for this first approach. Considering an estuary as a heterogeneous and continuous system, where system components and processes are interconnected, the present work proposes as methodology the combination of different detailed maps to identify links between morphosedimentary systems and related EU habitats of community interest. The combination of these types of maps allows to drawn up a table of equivalences to relate morphosedimentary units and habitat characteristics from a geographical point of view. In a second phase of this approach, it will be identified physical processes related to morphological systems (i.e., river discharges, water mixing, tidal currents, dynamo-sedimentary models) and biological processes related to ecological systems (i.e., presence and variation of plant communities). Additionally, induced anthropogenic processes will be considered as driving forces acting directly on the previous ones. With the aim of evaluate the global dynamic of the estuary, a set of geo-ecological indicators are proposed to describe the processes and the connectivity established in between their subsystems. The main results of this preliminary study are expected to provide a comprehensive first vision of the estuary functioning, together with the design of a new methodology to improve the environmental characterization of estuaries.

Intensive field surveys (longitudinal and transverse) in the upper region of the Chikugo River estuary (12–14.6 km landward from the river mouth), Japan were carried out in every three or four months during 2009–2011 using a digital sonar system equipped with a differential global positioning system. The primary concern of study was to investigate the spatial and temporal dynamics of bed morphology in relation to semidiurnal and fortnightly tidal variations, magnitude and movement of estuarine turbidity maximum (ETM), and seasonal variations in river discharge in a meandering estuarine channel. The results revealed that the estuary was dominated by tidal discharge for most of the year except for rainy season in which river flow dominates. During the low flow season (September to May), fine sediment was deposited near the inner bank during every semidiurnal tidal cycle and the depth of the inner bank becomes diminished. On the contrary, the outer bank was heavily eroded and becomes steep. As a result, ETM developed at the upstream of the estuary and the channel capacity reduced gradually during this period. However, in the rainy season (June to August), large flood events led to the breakdown of ETM and export the sediment in the upper reach of the estuary to the downstream tidal flat. The seasonal cyclic pattern of erosion and deposition processes were evident at the upstream meander. This cycle of morphological evolution of river bed continues based on the upstream sediment transport by the fortnightly tidal cycles and downstream sediment transport by the river discharge. Hysteretic effects between shear stress and SSC due to the asymmetrical flood and ebb tides as well as the seasonal variations in river discharge are the dominant factors that cause sediment transport and morphological changes in tide dominated estuaries.

The sea-flow driven sediment transport capacity in the Yellow River Estuary is a complicated problem due to the dynamic interaction from river runoff, tidal current and waves. However, it is of a great significance for planning the flow routes into the sea. Two mathematical models for computing sediment transport and current are established based on the MIKE21 model in this chapter. The range of the large model covers the whole Bohai and the validity of the model is calibrated by the harmonic tidal components of observation data. Based on the open boundary conditions from the large model, the tidal currents and sediment transport processes in the Yellow River Estuary are studied by a small model with finer grids. The computational results show that three high tidal current zones exist with maximum current speed reaches 1.7 m/s. The alongshore current from Bohai Bay to Laizhou Bay is the dominant force to transport sediment. The analysis and calculated results show that net fluxes of sediment transported through both sides of 10 km width and into open sea in the routes of Diaokou River, Old Channel, current Qing8 Route, Maxinhe Route, Beicha Route and Shibahu Router are of about 51.04, 39.27, 29.94,17.75, 12.96 and 7.22%, comparing with the amount of sediment in the Lijin station, respectively. In the planning of the available flow routes, the DiaoKouhe Route has the largest sediment transport capacity. Interchangeable use of Qingshuigou routes including Qing8, Old channel and Beicha can be planned in the near future, Diaokou Route is a long-term consideration.

Coastal environments are directly influenced by terrigenous inputs coming from rivers through estuaries. Quantifying the amount of nutrients and contaminants brought by sediment particles from the continental regions to the sea is of major interest for marine resource protection. Estuaries form a transition zone between river and maritime environments and therefore represent dynamic areas in terms of hydrodynamics, hydrology and sediment transport. The hydrodynamics is strongly dominated by asymmetrical tidal currents, modulated by neap and spring phasing. Moreover, the interaction between fresh and saltwater induces salinity gradients, and therefore density gradients, influencing the sediment dynamics. The complexity and the spatial variability of this interface area make it difficult to quantify the actual sediment transfers between the estuary and the ocean, either by in situ measurements, remote sensing or numerical simulation. This study is based on a 3D realistic hydrodynamic model of the Gironde estuary (South–West France) and the continental shelf seaward coupled with a multi-layer process-based sediment model accounting for sand and mud mixtures. In order to better understand the sediment dynamics between the estuary and the continental shelf, the objective is to provide a quantification of suspended sediment mass uncertainties associated with sediment transport parameters. The sensitivity analysis is conducted considering changes in the key sediment transport parameters, such as the settling velocity of the mud class and the sediment initial distribution. A better understanding of the uncertainties associated with simulated sediment transport will enhance the degree of confidence that can be placed in the quantification of the estuarine sediment exchanges with the sea. Such a quantification provides knowledge about the intra-estuarine exchanges with lateral intertidal mudflats, as well as sediment export to the sea, possible trapping in the subtidal muddy areas seaward of the mouth (e.g. the West Gironde Mud Patch) and dispersion along the adjacent coasts.

Tide is influenced due to not only mainly tide generating force but also local wind and weather patterns. The East Asian monsoons cause strong seasonal climatic variations in the Mekong Delta. A two-dimensional, barotropic numerical model was employed to investigate the dynamics of tidal wave propagation in the South China Sea with a particular interest for its characteristics along the Mekong deltaic coast under wind monsoon climate. The results reveal that wind monsoon climate could causes damped or amplified tidal amplitudes around Mekong deltaic coast approximately 2–3 cm due to the changing atmospheric pressure, the tangential stress of wind over the water surface, and wind enhanced bottom friction. The monsoon climate influences rather strongly on the M2 semidiurnal tide system in the eastern Mekong deltaic coast, meanwhile the monsoon climate controls K1 diurnal tide in the western region of Mekong delta.

Based on the analysis of hydrodynamics and sediment transport in the Pearl River Estuary, key techniques for modelling depositional and erosional patterns with physical model are detected. According to the exploration of distinct sediment characteristics and regional setting in Modaomen Estuary, Huangmao Sea and Lingding Bay, different modelling techniques were presented, which aids in the improvement of model results. Since the complex sediment transport process with fluvial and marine hydrodynamics in estuarine regions, key technologies in sediment experiments, including the synchronous simulation of tidal current and wave, automatic control of sediment adding system, were introduced. Additionally, by characterizing the sediment transport and key technical issues in the region, simulations and verifications of currents, waves, and sediments were carried out. Furthermore, the application of physical model in the simulation of sediment erosion and accretion with the impact of the Hong Kong-Zhuhai-Macao Bridge construction were displayed. The results indicated that the model can satisfy the similarity of flow movement and sediment siltation, which provides an important technical support for project construction.

Dredge spoil is commonly disposed in estuarine and coastal waters through submerged pipelines from a barge in the form of concentrated mixture of sediment and water. The discharge resembles a downward dense turbulent plume under the negative buoyancy of the sediment particles. Sediment discharge can increase the turbidity and suspended solid level of coastal water, causing damage the marine ecosystem. It is important to understand the mixing of a sediment plume with the ambient water in order to properly assess the environmental impact of disposal operation. This chapter presents a computational fluid dynamics (CFD) model of a sediment plume in a non-stratified stagnant ambient using the two-phase Eulerian approach. The axisymmetric two-phase continuity and momentum equations are solved with the drag force term accounting for the interaction between phases. The standard k-ε model is used for turbulence closure for sediment-water mixture. The radial turbulent dispersion of particles is modeled by a drift velocity term related to the concentration gradient of the particle phase. The model prediction is validated against experiments of a companion work and independent experimental data, with a wide range of particle sizes (68–1500 μm) and plume sediment volume fraction (maximum of 60%). The model predicted cross-sectional distribution of sediment concentration, plume fluid velocity and the slip velocity of particle to fluid can be well described by Gaussian profiles. The reduction of plume spreading rate with increasing particle size and settling velocity is also well predicted by the model. The CFD model results shed light on the development of a simple integral model for predicting the mixing of sediment plumes.

This study analyzed the shoreline change processes along the Phetchaburi intertidal mudflats with mangroves located on the western portion of the Upper Gulf of Thailand during the period 1953–2017. Historical shoreline positions along the coast were derived from the aerial photographs taken in 1953, 1967, 1976, 1994, 2002 and the satellite imagery in 2006, 2009, 2014, and 2017 using the Geographic Information System (ArcGIS) software. All imagery data were geo-referenced into Universal Transverse Mercator projection with the World Geodetic System 1983 (WGS1983) to eliminate distortion from the aerial photographs and satellite imagery. The shoreline positions along the study area were then digitized for each time period. The outer boundary of the mangrove forest was mainly used as a proxy to define shoreline positions of the muddy beach. The Digital Shoreline Analysis System (DSAS) version 4.4 was used to analyze the changes of shoreline positions in the study area. Results from this study revealed that about 26% of the 30 km Phetchaburi muddy shoreline in the mid portion of the study area had continuously retreated over the past sixty years with an average rate of −6.5 ± 1.8 m/y. The remaining, which was mainly located in the uppermost portion (near the major river mouths) and the lowermost portion (near a natural sandspit) had advanced seaward with the maximum and average rates of 30.0 ± 1.8 and 8.6 ± 1.8 m/y, respectively. Unlike mangrove muddy coasts in other regions, the results of this study suggested that the conversion of mangrove forest to agriculture and shrimp farming had not affected the rate of shoreline accretion of the study area. The variation of shoreline advanced rates likely reflected the changes in river sediment supply from the Phetchaburi River basin and in coastal sediment transport processes of the Phetchaburi coastal system. Meanwhile, the local wave and current conditions and the adjacent shoreline stabilization appeared to be the major factors dominating the shoreline recession of the Phetchaburi coast during the past six decades.

Little understanding on the growth and break-up of mixed sand and gravel spits exists, yet they are associated with estuaries and are often close to settlements and engineering structures, with potential impact and interactions with them. Understanding their behaviour can help manage the environmental and human risk in the future. This chapter reports on the growth, break-up, impact on tidal exchange and interaction with engineering structures of Church Norton Spit over the period 2001–2018 using over 50 topographic surveys, together with tide gauges inside and outside the estuary. During this time, the spit grew over 1100 m in 12 years during which time it rolled back through overwashing but only breached in 2016 due to a series of storms over a period of 3 months. Growth of the supratidal spit is controlled by sediment supply and the presence of an intertidal spit extension/ebb tide delta/intertidal shoals on which to advance. Final breaching results from the complex interaction of a shifting ebb-delta, a curved inlet channel that limits roll-back and a combination of storms and high tides to successively lower the crest through initial overwashing and eventual tidal scouring. Contrary to many studies on sandy inlets, the dramatic increase of the inlet channel length had no impact on tidal exchange in the estuary; this only occurred following breach and the breakdown of the spit. Understanding of the spit dynamics will improve the future management of other shingle spits and of Church Norton spit in case the increased sediment supply that started the growth in ~2003 is continuing and the spit will start to extend again.

The increasing coastal erosion associated with human activities and resulting negative environmental impacts have necessitated the need for improved understanding of the effects of coastal engineering works on coastal processes. Here, the proposed Port of Lekki, situated in the Gulf of Guinea 60 km east of Lagos, Nigeria, is investigated as a case study. Coastal surveys of cross shore profiles and sediment sampling were conducted. Based on investigations of coastal morphology, present erosion and deposition, longshore sediment transport, wave action, beach profile and sediment grain size, a sediment transport and shoreline evolution model was established to exam shoreline evolution and shoreline responses to the proposed port breakwaters. Results indicate that the Lekki coast is wave dominated. Swell waves from the south-southwest induce a longshore current travelling to the east, and leading to eastward longshore sediment transport. The capacities of eastward and westward sediment transport vary between 602,000 m3 a−1 and 963,000 m3 a−1, and between 1000 m3 a−1 and 18,000 m3 a−1, respectively. The eastward net sediment transport capacities were estimated to be between 584,000 m3 a−1 and 962,000 m3 a−1. Under natural conditions, the shoreline near the proposed port is relatively stable. The model predicted that the shoreline to the west of the port will shift a maximum of 442 m, reaching the bend of the main breakwater in approximately 20 years. However, sediment bypassing will begin by approximately 6 years after construction leading to the shore shifting a maximum of 260 m due to longshore sediment transport in the lower surf zone. The shoreline to the east of the proposed port will retreat a maximum of 220 m by 20 years after construction. The maximum erosion is predicted to occur approximately 500 m to the east of the eastern breakwater, and not directly east, due to the effects of the main breakwater on wave propagation. Effective measures to alleviate erosion include the construction of groins and beach fill through dredged sands from the channel and basin.

Cua Dai inlet is a typical microtidal, mixed energy-wave dominated inlet in a tropical monsoon regime in central Vietnam. Both the river flow regime and coastal processes such as induced by waves and tides influence Cua Dai Inlet and its adjacent coasts. Cua Dai Beach, the northern adjacent coast of Cua Dai inlet, has experienced severe erosion since 1995 due to an apparent non-periodic cyclic process, a decrease of sediment supply from the river, estuary and squeeze by coastal developments (Do et al. in J Coast Res 34(1):6–25, 2018). The inlet channel has shifted from North to South which served as an important controlling mechanism for the creation of a new ebb shoal. However, the role of the ebb-tidal delta in relation to the channel shifting and seasonal varying hydrodynamic conditions (river discharge and wave climate) remains poorly understood. Most studies have only considered the impact of waves and tides on the development of the ebb tidal delta. No study has included the impact of a varying river discharge on ebb shoal development and inlet migration. This chapter investigates the seasonal varying hydrodynamics and sediment transport of the inlet and adjacent coasts due to the seasonal varying river discharge and wave climate. The 2DH process-based morphodynamic numerical model (Delft3D) is applied using schematized wave conditions and river discharge. Six simulations with varying dominant wave conditions for the winter and for the summer are executed in combination with varying river discharge classes that corresponding to the dry, wet and flood seasons. There exists an East North East monsoon with a flood season from September to December, an East North East monsoon with a wet season from January to March, and a dry bidirectional South East/East North East monsoon from April to August. We investigate the effect of the seasonal wave climate and seasonal river discharges at Cua Dai inlet by analyzing the effects on the resulting hydrodynamics, sediment transports and potential morphological changes through the inlet and at the adjacent coasts. Primary results indicate that the seasonal variation in the wave climate has a strong influence on the sediment transport patterns in the adjacent coasts. The variation in the river flow dominates the magnitude of sediment transport through the inlet. The results of the simulations show that the inlet generally imports sediment into the estuary except in the case of the flood season. During the flood season the estimated sediment export is significant. Interestingly, the wave direction that varies during summer also influences the magnitude of sediment import into the estuary. Waves coming from the ENE contributes to larger sediment import than waves coming from the SE.

The narrow jetty configuration of Tillamook Inlet functions to constrict tidal flow, increase current speed, and prevent sediment deposition. However, the interaction of strong currents with incoming ocean waves over the inlet’s ebb shoal can amplify and complicate the wave environment at the inlet entrance. In this study, the Coastal Modeling System (CMS) was used to investigate time- and space-varying wave and current conditions affecting boating operations at Tillamook Inlet and quantify the effects of physical processes. Wave simulations with refraction, shoaling, and breaking provided estimates of wave-related parameters of interest to the navigable region at Tillamook. The simulation results showed the winter storms produced larger wave steepness and wave dissipation at the inlet complex, which were also closely associated with the bathymetry of ebb shoal. The flood currents weakened wave dissipation, while ebb currents increased wave dissipation over the ebb shoal and across the USCG recommended south passage in/out of the inlet. The effect of South Jetty shortening was localized to the immediate vicinity of the South Jetty. The calculated wave steepness and wave dissipation indicated that a south passage out of the inlet would be safer than a course straight out passing over the bar or a course turning to NW direction.

The 250,000 dwt Navigation Channel of the Panjin Port is planned to be constructed. Three layout schemes are designed in the project. The hydrodynamics, sediment transport and channel siltation before and after the project under different layout schemes are calculated by numerical model. The results show that for three schemes, the sediment concentration within the waterway show decrease after the construction of the waterway. The annual back-silting thickness is large near the port and small in the offshore area. The total deposition amount and average thickness of scheme 1 is larger than that of scheme 2. In addition, the channel of scheme 3 shows a significant sedimentation at the end of the channel because of the turn of the axis.

For extension project construction of Tianwan Nuclear Power Station (TNPS), China, the sediment suspension and diffusion will be caused in the process of blasting toe-shooting and dredging. The chapter analyzed the motion features of tides, waves, and sediment in engineering sea areas, established a 2-D tidal current and sediment mathematical model and conducted verifications through the actual measurements of tidal level, velocity and sediment concentration in accordance with nuclear safety guide rules and sea area use demonstration. Based on this, the advantageous tide types are selected, the source strength of blasting toe-shooting and mud dredging are determined, the mathematical model is used to study the suspended sediment diffusion scope caused by blasting toe-shooting and dredging respectively.

The wave attenuation service (WAS) literature review over the Bay of Mont-Saint-Michel encompasses saltmarshes, mudflats, seagrasses, shelly cheniers, oyster, honeycomb worm and sandworm reefs, which all together will be named “ecogeosystems” in this review due to their combination of biogenic systems, ecological systems and geomorphological systems (Mury et al. in Geophys Res Abstr 20:2044, 2018). It provides a comparative meta-analysis of the various measurements of wave attenuation induced by “ecogeosystems” across different studies focusing on wave height monitoring. The array of “ecogeosystems” included in this review was firstly identified through a fine-scale mapping of the Bay of Mont-Saint-Michel, then literature research was led using several keywords related to ecosystem services and coastal protection. A total of 32 studies was compiled over six countries. The majority of studies was located on North-Atlantic Ocean coastlines. According to their specificities, “ecogeosystems” were synthetically split into two categories, surface (saltmarshes, mudflats, seagrasses and oyster reefs) and punctual (shelly cheniers), for the sake of the WAS comparability. WAS associated with surface saltmarshes, mudflats, seagrasses, and oyster reefs ranged from 0.25 to 7.86%/m, from 0.01 to 4%/m, from 0.03 to 0.77%/m, from 1 to 64%/m, respectively. The punctual shelly chenier was monitored from 70 to 98%. Honeycomb worm and sandworm reefs have no data about WAS according to our literature review.

A device that is composed of nets is experimented to reduce the erosive currents on estuary banks. A porous environment that generates turbulent dissipation is created by several nets that are assembled in several inverted V in a tepee configuration. The sediments are trapped inside the different layers near the sea bed. The nets are maintained by chains and anchors, whereas the deployment for rising and falling tide is assured by floating buoys. This geometry is completed by vertical nets in order to obtain significant height for the damping of currents behind the nets. The nets were set in November 2014 along the right bank of Authie in a position of groyne. The initial length was 150 m and the initial height was 1 m. The height was raised to 2 m in March 2016. The Bay of Authie is characterised by meanders of the estuary that regularly threaten the right bank in front of dunes in the site named Fir wood. During the last severe erosion in 2011 the meander approached and eroded the dunes so that many trees fell on the beach and were carried away by the flow of the estuary. After a theoretical analysis of the shielding effect of the nets, the sensitivity of the sediment deposit to the net height concludes that it is useless to raise the nets more than 2 m. The monitoring consists in comparing the bathymetry around the nets before and after the last raising and in measuring velocity currents and water height. A deposit of sediment of 1 m due to sand trapping was observed after the last raise in the area around the nets. The results of modelling confirm that the combination of nets is an efficient option regarding the head loss if the inter-nets distance is sufficient. The vertical profiles of current velocity show that the wake effect is observed on a distance of 25 cm downstream and that the reduction of current velocity behind the net can reach 15% up to 5 m downstream.

The evolution of solitary wave along the flume is investigated. Experiments were conducted in a smooth, rectangular sloping flume. Solitary waves are generated using a piston-type wave maker. These type of waves are generated by impulsive mechanism, close to the generation zone, their profile contains both elevation and depression components. These depressions are attached to the main solitary wave along the flume during the propagation. The main hydraulic parameters investigated are: energy damping along the flat bottom, wave height evolution on the slope (shoaling), breaking process and runup heights. It was found that experimental results are almost in good agreement with earlier studies. An empirical formula for runup heights determination is suggested. A good way for tracking the evolution of a solitary wave on flat and sloping bottom is presented thanks to spatiotemporal diagram. It is noted that for better accuracy, especially when investigating breaking, it is better to use camera.

A three-dimensional non-hydrostatic model was presented to simulate solitary wave propagation. A one equation turbulent model (Spalart-Allmaras model) was used to calculate the eddy viscosity. To simulate the bottom boundary layer flow, a high grid resolution was used within the boundary layer. The bottom shear stress was directly calculated using the turbulent model. The model was validated by means of comparing the calculated water elevation with analytical results. Taking a stable solitary wave being simulated in a long numerical flume as the initial condition, we simulated the solitary wave propagation over a trench. The wave profile skewness, the velocity distribution, the local flow separation, and the dissolved mass transportation were elaborately analysed.

Co-oscillating tide, also called odd-tide is a kind of abnormal phenomenon of high tide. It usually comes with storms or big waves, and the associated flood roars on, swifts and clashes on the shore violently. The South Yellow Sea Radial Sand Ridges are featured by a broad beach and large tidal amplitude. The odd-tide happens frequently here. This study tends to find the storm-induced odd-tide in the South Yellow Sea Radial Sand Ridges, with a focus on the historical record analysis. It starts from collecting historical documents, hydrological records, and measured data to identify the storm-induced odd-tides in this area. It parameterizes the waveform and kinematics characteristics of the storm-induced odd-tides. It compares the tropical storms and the winter storm-induced odd-tides, as well as the variations in the south and north wings of the Radial Sand Ridges. Factor tests are operated to find out the sensitivity of the odd-tides to a variety of external elements. Multidimensional regression models will be built to interpret the correlations between the external motivation factors and the characteristic parameters of odd-tide. The investigation tries to make a summary of the local characteristics of space and time, as well as the exploration of the factors and generation mechanisms for the odd-tides.

Experiments are carried out in a flume without slope. Tests are performed for different unidirectional steady flow conditions, varying the initial sediment thickness and recirculating the sediment to ensure a constant supply condition, from an extremely limited sediment supply to an unlimited sediment supply condition. The formation of ripples and dunes is considered from an initially flat bed. The growth rate of the mean wavelength of ripples depends on the sediment supply, whether it is extremely limited or not. In spite of a rapid initial growth when sediment supply is extremely limited, the growth rate is much higher when sediment availability increases. As far as the equilibrium dimensions of the sedimentary structures are concerned, an increase of mean heights of ripples and dunes is pointed out when the sediment availability increases. The similar trend is found for mean ripple lengths but no clear trend is exhibited for dunes which are few and irregular. The empirical law proposed by Tuijnder et al. (2009) in a fluvial context for relative dune heights in the case of sediment limited supply conditions can be used for dunes in a coastal context. However, this formulation cannot be extended to ripple heights for which a dependence with flow conditions is noted. Ripple equilibrium lengths can be described with a relation suggested by Tuijnder et al. (2009) for dunes if an adaptation factor is considered.

The significant defensive role of vegetation in general and mangroves in particular for coastal and estuarine regions has been increasingly recognized. However, understanding the shallow flow field in and around the region of vegetation is still limited. In order to gain more insight, a laboratory experiment of a vegetated compound channel was conducted. The emerged circular cylinders are a representative model for the emergent mangrove forest. Scenarios of different widths and densities of vegetation were considered. Data acquired from Acoustic Doppler Velocimetry (ADV) and force sensors have been analysed. The influences of vegetation on the shallow flow field were clarified by comparing different scenarios with and without vegetation. Furthermore, the results confirm the presence of the large horizontal coherent structures (LHCSs). The large coherent structures formed in the mixing layer at the vegetation interface emerge, promoting the transverse momentum exchange toward the forests. The LHCSs has not only boosted flow penetration into the vegetated floodplain area but also strongly disturbed the flow inside the forest. As the LHCSs move, they cause the fluctuation of the force on the cylinders. The fluctuations are largest at the vegetation edge. Negative values of stream wise forces were also recorded.

In this chapter, the autogenic process of alluvial fan under various discharges and sediment feed rates were studied. Meanwhile, the discharge and sediment feed rate were suddenly changed during some experiments to analyze alluvial fan’s delayed response to external disturbances. The results demonstrate that progradation processes both slow down when water discharge or sediment feed rate is halved separately. When reducing both water discharge and sediment feed rate simultaneously, progradation process become even slower. Widening process of alluvial fan is less sensitive to change of discharge and sediment concentration than progradation process. When sediment feed rate is reduced by half, alluvial fan aggradation processes along flow path slows down obviously. When water discharge is reduced by half, upstream aggradation processes accelerate while downstream aggradation processes decelerate. The alluvial fan fluvial cycle and the channel morphology react to discharge reduction differently with sediment concentration reduction. The rate law can be employed to describe the actual response process of the deposition thickness. Calculated results demonstrate that the response rate of the upper-fan siltation layer is higher than that of the mid-fan and lower-fan. The response rate of the fine-sand alluvial fan is higher than that of coarse-sand. The response of the deposition layer to discharge increase is faster than that of discharge decrease. Alluvial fan development is influenced by both fan reaction mode and the status of fan development.

Local scour around bridge piers can cause significant damage or bridge failure and lead to excessive repairs, loss of accessibility, traffic disruption or even life-threatening incidents. The scouring phenomenon is quite complex and high degrees of uncertainties are associated with the parameters describing this event. Accurate determination of the scour volume and scour area is important in practical decision-making for the control of local scour and the safe design of countermeasures. In the present study, by using three non-uniform sands, a series of large-scale flume experiments have been carried out to investigate the local scour process around four pairs of side-by-side cylindrical bridge piers under conditions of open channel, smooth ice-covered and rough ice-covered flows. Results showed that, under condition of rough ice-covered flow, the scour extent (described by scour areas, scour volumes) is the highest, compared to those under conditions of open channel and smooth ice-covered flows. Finally, empirical relationship between scour area and scour volume have been developed which might be useful for the design of bridge piers.

The Yangtze River Estuary has been the scene of intense human activity in the past two decades. A large number of projects have been implemented to develop waterways and ports, construct bridges, reclaim land, and build reservoirs. During this time, an abundance of monitoring data has been collected. Human activity in natural estuaries often have two major consequences: (1) the dynamic features of the estuary undergo transformation; and (2) engineering activities will change the natural morphology of the ecosystem, harming the integrity of the estuary. Consequently, human activity may lead to the development of a different ecosystem, including the complete filling of waterways with silt, causing serious environmental impacts. This study focuses on the process of the morphological evolution of the Yangtze Estuary. The goal of the present study is to improve our fundamental knowledge of small-scale processes around navigation channels of this estuary, increase our understanding of the large-scale response of estuaries, and explain some complex phenomena, such as the high level of siltation occurring in the North Passage of the Yangtze Estuary. Managers will find the results useful in developing appropriate management plans for the estuary.

Since the completion of Shuikou hydropower station, the process of flow and sediment has undergone profound changes in Minjiang estuary. Under the combined action of hydrodynamic force and sand dredging, the riverbed of Minjiang estuary was cut down sharply. The water level under the hydropower station dam which was 110 km away from Guantou section of Minjiang estuary decreased from 8.80 m in October 1991 to 5.40 m in April 2009, and it also caused shipping suspend during the dry season. Due to the fact that the tail water can not meet the suction height requirement of turbine, the normal operation of the unit has been affected. In addition, the decline of the water level has also led to salinity intrusion, which threatens the safety of urban water intake. The measure presented in this chapter is to replenish flow and sediment of the estuary by means of discharging flood through the combined use of the bottom hole and the surface hole of the hydropower station, so as to restore the riverbed and raise the water level under the dam of Shuikou hydropower station. The flow and sediment numerical model shows that under the condition of 3570 m3/s discharge flow, 2-day duration, and using synchronous measurement of tide level process in the estuary, when the sediment concentration of the discharge is 0.625, 6.25 and 28 kg/m3, the riverbed elevation under the dam of the hydropower station will rise by 0.26–0.32, 0.99–2.16 and 4.71–8.24 m, but as the distance is longer than D20 section which is 7.38 km away from Shuikou hydropower station, the riverbed elevation is of no obvious change. This means that the short-term measure of replenishing flow and sediment only has the repairing effect on the short-distance riverbed of the downstream of the hydropower station. Under the condition of 10-day duration, 6.25 kg/m3 sediment concentration and 308 m3/s basic discharge flow, the lowest water level under the dam of the hydropower station will rise by 7.77 m. Meanwhile, within the distance of about 12.62 km which is located at D1 section to D33 section of the downstream of the hydropower station, the lowest water level will rise by 1.91–7.77 m; among the section of about 27.44 km, which is located at D1 section to D64 Hongwei section, the average riverbed elevation will rise by 4.72 m. The results show that the water level under the dam of Shuikou hydropower station can be restored to the original design level through the measures of replenishing flow and sediment with 0.625 kg/m3 sediment concentration, 3570 m3/s discharge flow, and 4.38-day discharge duration.

To analyze the effect of the project of North Branch Narrowing at Changjiang River on hydrodynamic and sediment transport, a 3D numerical model for Changjiang Estuary was established. The verification of the models shows that they are effectively for simulating tidal current and suspended sediment distribution. The model were then used to simulate the hydrodynamic and distribution of sediment after the north branch narrowing. The results show that, after the narrowing-project, the new shoreline direction conforms with the main current direction of tide, the characteristics of flooding and ebbing tide basically remains unchanged; the project narrows the estuary width of north branch. After the north branch narrowing, the channel and the mouth of the north branch would be narrowed significantly, and tide would be weakened and water level would also be reduced, and tide current would be increased due to the narrowing of channel in the north branch. The concentrations of suspended sediment in the north branch would be reduced along with the reduce of tide level and current speed. The concentrations of suspended sediment reduce 0 to −14.9% after the project construction. It has little impact on the tidal level, current speed and suspended sediment concentration in the south branch in the Changjiang River.

The construction of tide gate at Yongding New River estuary will influence the transportation of water, sediment and pollutant, and these changes at upstream/downstream of sluice will be different under different operation mode, which also in turn restricts the scheduling plan. In order to provide a basis for the selection of tide gate operational modes, the 1-D mathematical model for unsteady flow-sediment-water quality in channel with a sluice has been established, which was used to study the impact of tide gate operation of Yongding New River. The result shows that, comparing with the operation mode which only storing fresh water, the water quality will be better with the operation mode which storing sea water. And the water quality gradually improved with higher storage water level. However, there will be more deposition upstream & downstream of tide gate.

The Authie estuary, located at the eastern part of the English Channel is of environmental, ecological, economic and societal importance. With the intention to better understand the sediment dynamic it is important to better assess the role of sediment dynamics including erosion, stabilization and sediment reworking processes which is challenging in such complex environment. It is also important to consider biogenic components such as the microphytobenthos (MPB) distribution, as the primary productivity may play an important role with the bio-stabilization process. As a consequence, there is a crucial need to provide a synoptic overview of inherent bio-physical characteristics of sediments (i.e., composition, water content, grain-size, and biomass) in estuarine environment by generating precise quantitative maps for predicting in a second step estuarine evolution by including sediment transport, sedimentation rates, coastal flows processes and sea level rise caused by climate change for instance. The use of the remote sensing technology is increasingly used for mapping estuarine and coastal environments by providing a synoptic overview of bio-physical characteristics of sediments. In that sense, the combination between remote sensing imaging, topographic data (LiDAR) and in situ measurements is suitable for improving our understanding of sediment dynamics with respect to physical and biological forcings. The main objective of this study is to demonstrate that the synergy between multispectral (i.e., SPOT 6–7 [1.5 m/pixel]; Sentinel-2, 10–60 m/pixel, 5–10 days)”, hyperspectral [Hyspex, 70 cm/pixel, 160 spectral bands] remote sensing images may be suitable for generating both reliable sedimentary and primary productivity budgets; at least for surficial sediments. All presented data were acquired during the same day (09/21/2017) in the framework TéléEST, CPER MARCO and CNRS-OMPBI projects.

Advances in satellite data, revisit times, computing capacity and processing speed are on their way to deliver a revolution in the monitoring and management of coastal erosion due to systematic remote sensing of the shoreline from space. This represents, and enables further, major progress on a far greater scale than the current state of the art. European public satellites of the Sentinel Constellation (Sentinel-1 and Sentinel-2) of the COPERNICUS program currently offer a revisit time of (i) five days with four satellites under the same viewing conditions, for bathy-topography investigation of the shoreline, i.e. from the continental shelf-break to the foreshore, (ii) a few days at mid latitudes but from different points of view, and (iii) almost daily at higher latitudes. The low resolution (5-to-20 m) of the radar & VNIR components of the time-series is mitigated by high spectral density that allows a true spectral analysis of the earth surface and waters, after appropriate corrections, i.e. removal of atmospheric scattering, sun glint and white caps effects, geometric configuration due to the anisotropic bidirectional soils & waters reflectance distribution function (BRDF). New tools in open source like the SNAP toolbox or interfaces like Coastal Thematic Exploitation platform allow public labs and companies to benefit from this breakthrough in data acquisition, rapid processing or database collection. Via remote sensing techniques, time series of seafloor bathymetry and suspended sediment in the water column can be derived from optical (spectral analysis) and SAR imagery (correlation between radar cross section changes and Bragg scattering of the water-foreshore surface for the assessment of the errors). It complements, when required, Very High Resolution (VHR) surveys made on order with commercial imagery, (or dug out from archives), aerial LiDaR (Light Detection and Ranging) with planes or drones, or depths sounders (on launches) and topographic instrumentation for beach profiling. Yet, the current swarms of nanosatellites such as Planet/Doves give access to systematic VHR cover of the earth. Such work can be carried out in the frame of national programs such as LITTO3D or regional/local programs.

In many domains of application such as sedimentology, remote sensing may be used to fill the gap of field sampling. This gap is often due to unavailable logistics or inaccessible areas. It is recognized that sediment transport directions can be assessed from grain-size parameters of sediment samples, but the determination of transport trend patterns from grain-size remote sensed products has still not been carried out. The main objective of this study was to determine sediment transport trends in the Authie estuary (North of France) using Sentinel-2 data for different periods. This estuary is marked by a critical erosion of the northern shore due to a prograding sandy spit and a general sandfilling. In order to analyse seasonal variations, a set of 4 images were analysed for a period between 2016 and 2018, two during summer and two during winter. A new methodology was developed for mapping sediment transport trend based on grain-size parameters (mean, sorting and skewness) determined from remote sensing data. Three sectors of the estuary were selected according to their main morphodynamics characteristics (e.g. critical erosion and sandfilling sectors). The resulting transport vectors were spatially coherent with sedimentary bedforms (i.e. megaripple) and consistant with known transport directions. Maps of potential sediment transport show spatial variation between summer and storm periods. Our results suggest a changes according the period and some vectors demonstrate a change in direction following the formation of new structures or channel deviations. This study demonstrates that remote sensing combined to grains-size trend analysis can be a useful approach for sediment transport trends determination with a high spatial resolution. Further investigations are needed to identify the role of topographic variations and to obtain a long-term transport trend in order to understand as the spatial variability in sandfilling and erosion processes within the estuary.

From the historical hourly water level data during 29 years, from 1988 to 2016, annual mean water level, annual highest high water level, annual lowest low water level, annual maximum range of tide and some others levels at coastal hydrological stations of the Mekong delta are computed. Results show that at these stations, the annual mean water level and the volume of sea water entering in the delta with tide are increasing; the volume of inland water evacuated to the sea with tide tends to decrease. Evolution of the annual lowest low water level shows an increasing trend, faster in the last 14 years at most of the coastal stations. During 1988–2016 the annual maximum range of tide increases in the eastern coast stations, decreases at Năm Căn, and in the western coast stations except Xẽo Rô, but decreases at most of stations during 2003–2016 except Bình Đại, Xẽo Rô and Rạch Giá. The changes of the water levels at the estuarine areas reported in this chapter are informative for the planning of water regulation works in the Mekong Delta, especially relating to the construction of the sluicegates Cái Lớn and Cái Bé currently under study and the planned ones on the Tiền River branches such as Hàm Luông and Cổ Chiên. Whether and how the changes of water levels highlighted at Năm Căn station are relevant to the confluence and interaction between the tides of the East Sea (South China Sea) and the West Sea (Gulf of Thailand) in the context of global climate change, sea level rise, is an open issue.