Tidal Dynamics Research Articles

Exponential inequalities for exit times for two dimensional stochastic tidal dynamics equations

In this work, we consider two dimensional stochastic tidal dynamics equations in bounded domains. We establish the exponential estimates on certain exit times associated with the solution trajectory of the tidal dynamics system. Using contraction principle, we study these exponential estimates of exit times in the context of a Wentzell-Freidlin type large deviations principle.

Coastal circulation and water transport properties of the Red Sea Project lagoon

The Red Sea Project (RSP) is based on a coastal lagoon with over 90 pristine islands. The project intends to transform the Red Sea coast into a world-class tourist destination. To better understand the regional dynamics and water exchange scenarios in the lagoon, a high-resolution numerical model is implemented. The general and tidal circulation dynamics are then investigated with a particular focus on the response of the lagoon to strong wind jets. Significant variations in winter and summer circulation patterns are identified. The tidal amplitude inside the lagoon is greater than that outside, with strong tidal currents passing over its surrounding coral reef banks. The lagoon rapidly responds to the strong easterly wind jets that occur mainly in winter; it develops a reverse flow at greater depths, and the coastal water elevation is instantly affected. Lagrangian particle simulations are conducted to study the residence time of water in the lagoon. The results suggest that water renewal is slow in winter. Analysis of the Lagrangian coherent structures (LCS) reveals that water renewal is largely linked to the circulation patterns in the lagoon. In winter, the water becomes restricted in the central lagoon with only moderate exchange, whereas in summer, more circulation is observed with a higher degree of interaction between the central lagoon and external water. The results of LCS also highlight the tidal contribution to stirring and mixing while identifying the hotspots of the phenomenon. Our analysis demonstrates an effective approach for studying regional water mixing and connectivity, which could support coastal management in data-limited regions.

Origin and evolution of tidal depressions in a tidal flat and their role in carbon sequestration in the Bahía Blanca Estuary (Argentina)

Tidal flats play an essential role in the global carbon cycle. Intertidal environments are very dynamic and have several erosive landforms such as tidal depressions (TD), although TD genesis is still poorly understood. The tidal flats of the Bahía Blanca Estuary (BBE) are ideal for TD’s study since they are hardly altered by human activity. In this site is possible to distinguish a gradation from a non- bioturbed zone to one dominated by erosive landforms. This preliminary study aims to determine the origin and evolution of TD in tidal flats and evaluate their role as carbon sinks based on an integrated sedimentological and geomorphological study. We found that the origin of TD in siliciclastic tidal flat is associated with the activity of the Neohelice granulata crabs. N. granulata selects finer particles and organic matter to build burrows; also alter the physical properties of the sediment. The loss of sediment structure by the increase in the density of excavations added to the tidal dynamics favour the burrows's collapse giving rise to the tidal depression. Tidal dynamics affect sediment stability by exerting a hydrostatic pressure on the burrow when flooding and emptying of burrows. The effect of N. granulata in the sediment record is clearly identifies by an increase water content with a decrease in the sediment density. Furthermore, it is possible to identify changes in the grain size distribution curves of the typical tidal flat facies as a second mode at 10 μm. These features can be recognised and used as a tool to identify TD in the geological record. TD with occluded crab burrows can be important organic carbon sinks due to the organic matter fixation under suitable conditions that delay its decomposition. Due to the large number of TD (of the order of 35 million), we estimated that the C sequestration by these landforms might be of the order 1.8 × 10–3 Gtn without considering that may be stored directly on the tidal flats themselves.

Internal tidal waves and deep-water renewal in a tropical fjord: Lessons from Ambon Bay, eastern Indonesia

Seasonal-varying internal tidal dynamics have a critical role in deep-water renewal in tropical shallow-silled fjords (e.g. Ambon Bay, Indonesia). Seasonal- and tidal-based longitudinal CTD casts from the slope of outer Ambon Bay (OAB) to the sill of Ambon Bay coupled with bottom-mounted current meters at the sill and in inner Ambon Bay (IAB, the fjord basin), were employed to investigate the internal tidal-sill slope interaction and the characteristics of deep-water inflow. Weaker stratification in the easterly monsoonal season than the transitional monsoonal season (dT/dz = ~0.02 °C/m cf. dT/dz = ~0.06 °C/m) drives the predominant sub-critical slope condition at the OAB slope causing more frequent tidal upwelling events in the easterly monsoonal season (13 events in a spring-neap sequence) than in the transitional monsoonal season (5 events). The magnitude of tidal upwelling in Ambon Bay, as measured by the depth from which water upwells, is stronger in the easterly monsoonal season (up to 200 m) than in the transitional monsoonal season (maximum: 115 m). The influx of upwelled water across the sill was controlled by the tidal excursion of the deep-water plume in the easterly monsoonal season and by the deep-water/sill density difference in the transitional monsoonal season. A series of deep-water renewal events in IAB within a spring-neap sequence (~2 weeks) in the easterly monsoonal season supplied a total inflow volume of 0.09 ± 0.02 km3 which can replenish approximately 80% volume of the IAB deep layer. This total inflow volume was smaller in the transitional monsoonal season (0.05 ± 0.01 km3), hence, only flushing 40% volume of the IAB deep layer. The knowledge of internal tidal waves and deep-water inflow in Ambon Bay presented here will be a key reference for future studies focused on water transport in Ambon Bay and other shallow-silled tropical fjords.

Tide-Induced Variability and Mechanisms of Surface Suspended Sediment in the Zhoushan Archipelago along the Southeastern Coast of China Based on GOCI Data

The variations and dynamics of suspended sediment in the coastal waters around the Zhoushan Archipelago are complex due to strong tidal dynamics. This study aims to delineate the tide-induced variability of surface suspended sediment and reveal its mechanisms in the Zhoushan Archipelago based on Geostationary Ocean Color Imager (GOCI) data. Suspended sediment concentration (SSC) estimations through the ultraviolet wavelength atmospheric correction (UV-AC) algorithm and a tuned empirical inversion algorithm using extensive in situ measurements are presented. GOCI-processed remote sensing reflectance (Rrs) is validated using field data and is cross-validated with Landsat 8 Operational Land Imager (L8/OLI) measurements, respectively. The estimated SSC is validated with independent datasets. The validations reveal that GOCI-processed Rrs is reasonable and that the GOCI-retrieved SSC is accurate and can be used to quantify SSC distributions and variations in the Zhoushan Archipelago. The variations of the SSC in the study area are closely related to the temporal variations of the tidal level. High SSCs often occur in the middle of ebb or flood tides due to large tidal discharge and high tidal velocity. Significant hourly variations of the SSC are mainly controlled by tidal forces. Dynamic mechanism analysis indicates that during neap and middle tides, the local high SSC is mainly attributed to the sediment resuspension process driven by tidal currents; in addition, during the spring tide, the variations of the SSC are simultaneously modulated by sediment resuspension and horizontal advection processes.

Response of tidal flow regime and sediment transport in North Malé Atoll, Maldives, to coastal modification and sea level rise

Abstract. Changes to coastlines and bathymetry alter tidal dynamics and associated sediment transport processes, impacting upon a number of threats facing coastal regions, including flood risk and erosion. Especially vulnerable are coral atolls such as those that make up the Maldives archipelago, which has undergone significant land reclamation in recent years and decades and is also particularly exposed to sea level rise. Here we develop a tidal model of Malé Atoll, Maldives, the first atoll-scale and multi-atoll-scale high-resolution numerical model of the atolls of the Maldives and use it to assess potential changes to sediment grain size distributions in the deeper atoll basin, under sea level rise and coastline alteration scenarios. The results indicate that the impact of coastline modification over the last two decades at the island scale is not limited to the immediate vicinity of the modified island but can also significantly impact the sediment grain size distribution across the wider atoll basin. Additionally, the degree of change in sediment distribution which can be associated with sea level rise that is projected to occur over relatively long time periods is predicted to occur over far shorter time periods with coastline changes, highlighting the need to better understand, predict and mitigate the impact of land reclamation and other coastal modifications before conducting such activities.

Impacts of coastal reclamation on tidal and sediment dynamics in the Rui’an coast of China

Coastal reclamation projects have been extensively constructed along the coastline of the East China Sea over the past decades. To investigate the impact of reclamations on the Rui’an coastal zone, regional tidal and sediment dynamics were studied by combining field data and numerical modeling. Field data of tidal elevation and currents, suspended sediment concentration (SSC), and bottom erosion were obtained during both spring and neap tides from 2014 to 2019. Data analysis suggested that the reclamation and construction of the dike reduced the currents in the tidal flat and subsequently reduced the SSC values. The sediment was mainly deposited in the tidal flat after construction. The largest annual deposition rate was approximately 1 m, occurring in the southern part near the dike, while the deposition rate was only 0.08 m/a in the middle part of the tidal flat. In addition, the results of the numerical experiment proved that the reclamation and dike construction contributed to the variations in currents and SSC, thus altering the deposition in the tidal flat. It is suggested that the construction of coastal works and social facilities in macro-turbid coastal zones, such as the Rui’an coast, require the evaluation of possible impact on sediment dynamics.

Assessing the Influence of Shoreline Adaptation on Tidal Hydrodynamics: The Role of Shoreline Typologies

AbstractIn coastal embayments, tidal dynamics are influenced by mean sea level and shoreline configuration. As sea levels rise and coastal communities modify their shorelines to mitigate future flooding, spatial patterns of inundation, tidal amplitude, and tidal phase will change in response. Here we apply a hydrodynamic model to systematically investigate the effect of local‐scale, spatially refined shoreline protection on regional tidal dynamics and peak water levels in San Francisco Bay, California. We find that individual shoreline protection scenarios produce relatively small changes in tidal amplitudes at 50 and 100 cm of sea‐level rise but can result in amplification of the M2 tide by up to 40% at 200 cm of sea‐level rise. Protection of shorelines with gradually sloping topography and space for floodwater accommodation generally has the largest influence on tidal response, both locally and regionally. In the northern part of San Francisco Bay, tides down‐estuary of protected shorelines move closer to a standing wave, while up‐estuary tides become more progressive. In the southern part of the bay, which is already close to a standing wave, effects are more localized and variable. Overall, the tidal response to shoreline protection is a function of both the geographic location within the embayment as well as the geomorphic characteristics of the local landscape that is protected. Understanding the relative influence of local shoreline modifications on tidal dynamics under a range of sea‐level rise scenarios is critical to developing effective shoreline adaptation alternatives that maximize flood mitigation.

Spatiotemporal Distribution Characteristics of Nutrients in the Drowned Tidal Inlet under the Influence of Tides: A Case Study of Zhanjiang Bay, China.

The tidal dynamics and the characteristics of pollutant migration in the drowned-valley tidal inlet, a typical unit of coastal tidal inlets, are strongly influenced by geomorphological features. Along with the development of society and the economy, the hydrodynamic and water quality environment of the tidal inlet is also becoming more disturbed by human activities, such as reclamation of the sea and the construction of large bridges. In this study, a typical drowned-valley tidal inlet, Zhanjiang Bay (ZJB), was selected for the establishment of a model via coupling of a tidal hydrodynamic model and water quality numerical model. This model can be used to simulate the migration and diffusion of pollutants in ZJB. The spatial and temporal variation processes of water quality factors of the bay under the influence of special geomorphic units was simulated at the tidal-inlet entrance, the flood/ebb tidal delta, and the tidal basin. The results show that ZJB has strong tidal currents that are significantly affected by the terrain. Under the influence of the terrain and tidal currents, the phosphorus and nitrogen concentration at the flood-tide and ebb-tide moments showed obvious temporal and spatial differences in the ebb-tide delta, tidal-inlet entrance, flood-tide delta, and tidal basin. In this study, we analyzed the response mechanism of the water quality environment to the drowned-valley tidal inlet, and this can provide theoretical guidance and a basis for decision-making toward protecting the ecology and water security of ZJB.

Integrating a Three-Level GIS Framework and a Graph Model to Track, Represent, and Analyze the Dynamic Activities of Tidal Flats

Tidal flats (non-vegetated area) are soft-sediment habitats that are alternately submerged and exposed to the air by changeable tidal levels. The tidal flat dynamics research mainly utilizes the cell-level comparisons between the consecutive snapshots, but the in-depth study requires more detailed information of the dynamic activities. To better track, represent, and analyze tidal flats’ dynamic activities, this study proposes an integrated approach of a three-level Geographic Information Science (GIS) framework and a graph model. In the three-level GIS framework, the adjacent cells are assembled as the objects, and the objects on different time steps are linked as lifecycles by tracking the predecessor–successor relationships. Furthermore, eleven events are defined to describe the dynamic activities throughout the lifecycles. The graph model provides a better way to represent the lifecycles, and graph operators are utilized to facilitate the event analysis. The integrated approach is applied to tidal flats’ dynamic activities in the southwest tip of Florida Peninsula from 1984 to 2018. The results suggest that the integrated approach provides an effective way to track, represent, and analyze the dynamic activities of tidal flats, and it offers a novel perspective to examine other dynamic geographic phenomena with large spatiotemporal scales.

Spatio-temporal distribution of diatoms and dinoflagellates in the macrotidal Tanintharyi River estuary, Myanmar

The spatio-temporal distribution of diatoms and dinoflagellates composition and abundance were analyzed to investigate their seasonal and neap–spring tidal dynamics in the tide-dominated tropical Tanintharyi River estuary (TRE), Myanmar in 2019. The salinity showed significant variations between seasons (F=32.86, P < 0.001) and the maximum salinity was found in the lower estuary. The turbidity was highest in the mid-upper estuary during spring tide in both seasons. Eighty-two species of microphytoplankton (Fifty-nine species of diatoms and twenty-three species of dinoflagellates) were observed and summarized as 15 groups based on their similarity in cell shapes and sizes. Diatoms were dominant over dinoflagellates in both seasons. The density of diatoms was maximum during the intermediate tide in both seasons. The density of dinoflagellates was maximum during the neap tide in the dry season while during the intermediate tide in the wet season. Spatially, abundances of both diatoms and dinoflagellates were maximum in the lower part of the estuary, which corresponds to high salinity. The abundance of diatoms was significantly different between seasons (F=4.14, P < 0.05). Further, chain-forming diatoms and surface extension dinoflagellates were the dominant groups throughout the estuary. The study indicates that the salinity, turbidity, and mixing driven by the seasons and the neap–spring tidal cycle can influence the distribution and abundance of diatoms and dinoflagellates in the TRE. The cell shape and size promote most aspects of their survival strategy.

Mapping coastal salt marshes in China using time series of Sentinel-1 SAR

Salt marshes provide crucial ecological functions and services and are experiencing rapid losses and degradation under global climate changes and high-intensity human activities in coastal zone. However, mapping salt marsh distributions and compositions with high accuracy on the national or global scale remains challenging. Here, we used Sentinel-1 time-series data and knowledge-based automatic decision tree classifiers to produce a 10-m map of the salt marshes in China coastal zones. We established annual synthetic aperture radar (SAR) composite features to address seasonal variations and tidal dynamics in salt marshes and created five partitioned-region classifiers according to the climatic and environmental characteristics. In total, 1729 Sentinel-1 images in 2019 and 3418 in situ sites were included for the classification. The results showed that (1) the annual mean SAR composite is more stable and practical than the seasonal composite for salt marsh classification along the China coastal zones in terms of these features addressing variations in tidal fluctuation, climate zones, and salt marsh compositions; (2) SAR surface roughness can effectively separate salt marshes into sparse density and red phenotype salt marshes; (3) the total area of Chinese coastal salt marshes was 127,477.37 ha with an overall accuracy of 87.30%, it included 48.30% Spartina alterniflora, 29.19% Phragmites australis, 13.76% Suaeda spp. and 8.75% Scirpus spp., and more than 85% of salt marshes were distributed from Shandong Province to Zhejiang Province. This study showed the potential application of time-series Sentinel-1 SAR data, annual composite data and knowledge-based classifiers for large-scale coastal zones, and these data will be valuable for coastal ecological restoration and sustainability management.

Mapping mangrove forests in the Red River Delta, Vietnam

Mangrove forests (MFs), which occur along tropical and subtropical coastal zone, are among the most productive and richest carbon-rich ecosystems in the world. However, MFs have experienced great losses worldwide due to the impacts of intensive human activities and relative sea level rise. Here, the recent dynamic changes in the MFs of the Red River Delta (RRD), the second largest delta in Vietnam, were quantified using the random forest algorithm based on 328 remote images obtained by Landsat TM/ETM+/OLI during 1986–2019. The results show obvious increasing trends in the MF area with a change rate of 39 ha/y from 1,655 ha in 1986 to 2,944 ha in 2019. The change rates in the northern RRD (NP) and southern RRD (SP) were 8.44 ha/y and 30.62 ha/y, respectively, even though MFs in the tropics worldwide encountered significant losses. Further, approximately 1,091 ha of MF was converted into aquaculture ponds during 2000–2006 in the interior of the RRD, while the shoreline of MFs in the NP and SP continually expanded seaward to the northeast and southwest at average rates of 38.9 m/y and 17.9 m/y, respectively. Moreover, although the fluvial sediment supply declined dramatically from 199.57 to 16.41 mt/y during 1986–2017, the sediment supply was not responsible for the present seaward expansion of MFs. Wave action drove sediments to overwash barriers, and tidal dynamics carried this sediment into tidal channels, depositing sediments behind the barriers and on both sides of tidal channels with continuing MF growth. In addition, the conversion of MFs into aquaculture ponds by human activities was responsible for the massive losses of MFs in 2000–2006, but these impacts were alleviated as conservation policies were implemented by local governments in subsequent years. This study indicates that the growth, loss and recovery of MFs are affected by various factors, and it is vital to map the variations in MFs to better implement regional ecological restoration programs for coastal MFs.

Modeling investigations of tidal flat reclamation's far-field impact on tidal dynamics in the East China seas

Modeling investigations of tidal flat reclamation's far-field impact on tidal dynamics in the East China seas

IMPACT OF SEA LEVEL RISE ON HYDRODYNAMICS OF ESTUARIES WITH RESTRICTED ENTRANCES

Worldwide, hundreds of millions of people who live on or near estuarine environments are vulnerable to sea level rise (SLR). Using clustering techniques and moving beyond static models and case studies, this study used a large ensemble of idealised estuary models of varying scale, geometry, level of entrance constriction, and SLR scenarios. It was found that tidal forcing, degree of entrance restriction, and estuarine length can primarily control the tidal dynamics of prismatic estuaries under SLR. Further, restricting an entrance can be presented as a potential solution to offset SLR induced tidal amplification if the associated impacts on entrance stability, navigation, and flooding are considered.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/vOptOAbqN3U

Homogenization of a 2D Tidal Dynamics Equation

This work deals with the homogenization of two dimensions’ tidal equations. We study the asymptotic behavior of the sequence of the solutions using the sigma-convergence method. We establish the convergence of the sequence of solutions towards the solution of an equivalent problem of the same type.

Primery mezomasshtabnogo i submezomasshtabnogo chislennogo vikhrerazreshayushchego modelirovaniya okeana

Purpose. The study addresses rotational motion of geophysical fluids in the horizontal and vertical planes. It is aimed mainly at tracing the development of high-resolution numerical modeling of the ocean, as well as at demonstrating new physical processes due to more correct consideration both of the tides in the eddy-resolving numerical models and sub-mesoscale dynamics in the models of the sea straits. Methods and Results. The ocean eddies and their interaction with tides are studied using numerical simulations by four NEMO models for the European North-West shelf with the resolutions ranging from 7 to 1.5 km. The vertical characteristics of motion in the Bosporus Strait were studied using numerical simulations with SCHISM , the unstructured grid model with the ultra-fine model resolution (less than 100 m). The barotropic tidal forcing resulted in substantial flattening of the slopes of the spectral curves. The most important difference between the spectral featurws of four models occurs in the motion rotational component. In the model with the 1.5 km resolution, the magnitude of the vorticity power spectral density at the scales ~70 km is by an order of magnitude higher than in the other three models. Although most of the tidal flattening is associated with the internal tides, beyond a certain horizontal resolution, the eddy dynamics become affected by the barotropic tides. The shelf of the Biscay Bay and the shallows around the Faroe Islands are the most sensitive areas to adding of the barotropic tides to the model forcing. Due to the grid ultra-fine resolution, new elements of physical motion emerged in the Bosporus region. The lateral circulation is dominated by the systems of multiple circulation cells with the scales ~ 1 km. In some areas, the lateral flow magnitude exceeds 0.5 m/s, which is comparable with the magnitude of the axial flow. This reveals importance of the helical elements of the strait circulation for overturning of water masses in the Bosporus. Conclusions. Without proper resolution, the models of tidal oceanic dynamics simulate the ocean general circulation, but do not describe correctly the energy cascades at the eddy scales including interaction between the tides and the mesoscale eddies. Absence of this sub-mesoscale dynamics in the models can largely affect their capability to simulate the two-layer inter-basin exchange.

Tidal sedimentary dynamics of the Early Pleistocene Messina Strait (Calabria, southern Italy) based on its modern analogue

The Messina Strait excursion opens a series of geological field trips associated with the 10th International Congress of Tidal Sedimentology (Tidalites), Matera, Italy, 5-7 October 2021. This guide aims at documenting a number of selected outcrops located along the eastern margin of the modern Messina Strait, in order to illustrate the sedimentary dynamics of the Early Pleistocene tide-dominated Messina Strait. Since the Pliocene, this extensional basin separated Sicily from Calabria, forming a wide non-tidal seaway. Successively, this basin turned into a ca. 10-15 km-wide and 40 km-long, tide-dominated strait during the Early Pleistocene, prior to its definitive closure following a Middle Pleistocene phase of tectonic uplift. As for today in its modern analogue, the ancient strait acted as a major conduit for marine water exchanges between the Ionian and the Tyrrhenian seas. Semi-diurnal, reverse bidirectional tidal currents flowed in phase opposition parallel to the strait margins, being subject to tidal amplification due to bathymetric restriction across the shallower strait-centre zone. This oceanographic setting partitioned the strait into specific environments. Nowadays, their sedimentary record is exposed in a series of outcrops across the western (Sicily) and eastern (Calabria) margins of the modern strait.A series of stops along a south-to-north transect covers a total distance of ca. 20 km. Outcrops of the first day show coarse-grained deposits lying adjacent to a block-faulted central horst and transgressively overlain by cross-stratified, mixed bioclastic-siliciclastic arenites. These strata record bypass and residual sedimentation in the strait-centre zone of the ancient strait. The second day, large- and medium-scale cross-stratification exhibiting a variety of tidal sedimentary indicators are observed, interpreted as the ancient northern tidal dune field. The third day focuses on one major section representing the north-eastern flank of the ancient strait, where subaqueous canyon-fill strata, mass-wasting deposits and tide-influenced delta front-facies are exposed.

Impact of Historical Channel Deepening on Tidal Hydraulics in the Delaware Estuary

AbstractAnthropogenic modifications of estuarine morphology such as navigational channels have changed tidal dynamics in many estuaries. The implications of deepening may include shifts in tidal range, sediment transport, pollutant dispersal, and changes in flood risk, among others. Here, we use a numerical model to study how channel deepening has altered tidal elevation, currents, and energy fluxes in the Delaware, a convergent estuary on the east coast of the United States. Historical (1848) and modern (2014) depth soundings were digitized and gridded for a numerical model of the estuary. Numerical experiments indicate a doubling in tidal range, shifts in the arrival time of high water, and changes in elevation‐velocity phase. A historical increase in the upstream conveyance and transmission of energy is consistent with bigger amplitudes, swifter currents, and more progressive wave dynamics in the navigational channel. Changes in local topography were key in the modulation of tidal energy transmission upstream, especially in the tidal river.

Modern and Holocene microbial mats and associated microbially induced sedimentary structures (MISS) on the southeastern coast of Tunisia (Mediterranean Sea)

AbstractOn the southeastern Tunisian coastline, very diverse living microbial mats colonize the lower supratidal and intertidal zones, and locally may extend into the upper infratidal zone. The interaction between the benthic cyanobacteria and their siliciclastic substratum leads to the development of several types of microbially induced sedimentary structures (MISS). The mapping of the microbial mats has allowed the identification of the types of MISS that characterize the different segments of the coastal environment. The modern microbial mats have been compared with those recorded at the top of the Holocene deposits, which are composed of biodegraded microbial black mats alternating with white laminae made of clastic and evaporitic sediments, indicative of very high frequency cycles of flood and drought. A hypothetic profile showing their occurrences along the different areas bordering the coastline is proposed as a guide for the reconstruction of the ancient depositional environment. The roles of tidal dynamics, storms, and climate in controlling their genesis and spatial distribution, are discussed and highlighted. The modern MISS of southeastern Tunisia are compared with their equivalents that are well documented through the different geological eras.