Characteristics Of Tidal Currents Research Articles

Study on the Characteristics of Tidal Current Velocity in Estuarine and Bay Areas

Abstract In estuarine and bay regions, reciprocating tidal currents frequently constitute the predominant hydrodynamic forces. Nonetheless, there exists a paucity of research concerning the hydrodynamic characteristics under intricate tidal conditions. This study employs tidal current data collected from nine sites within the Yellow River Estuary and Hangzhou Bay to examine the periodic characteristics of tidal currents, the vertical velocity distribution, and the attributes of ebb and flood peak velocities. The study revealed that the Yellow River Estuary and Hangzhou Bay predominantly exhibit nearly symmetrical reciprocating tidal currents. Nevertheless, certain regions within Hangzhou Bay also demonstrate asymmetrical tidal currents. The vertical velocity distribution throughout various phases of a single tidal cycle generally adheres to the characteristics described by the SOULSBY distribution. The peak velocities of ebb and flood tides are correlated with the rate of change in water depth (hm/tm), and an equation for calculating these peak velocities has been derived through fitting data.

Assessment of Ocean Circulation Characteristics off the West Coast of Ireland Using HF Radar

Research on coastal ocean circulation patterns over long time periods is significant for various marine endeavors: environmental protection, coastal engineering construction, and marine renewable energy extraction. Based on sea surface current data remotely observed using a shore-based high frequency radar (HFR) system for one year (2016), spatiotemporal characteristics of surface flow fields of sea surface flow fields along the west coast of Ireland are studied using harmonic analysis, rotary spectral analysis and representative flow fields over different seasons and the whole year. Coastal surface currents in the study area are strongly affected by tidal dynamics of the M2 constituent, showing significant characteristics of regular semidiurnal tide, such as M2 and S2. The energy spectrum distribution indicates that the tidal constituents M2 and S2 are the dominant periodic energy constituents in a counterclockwise spectrum, which mainly presents rotating flow; the representative diurnal tidal constituents is the constituent K1, and its energy spectrum distribution is mainly clockwise. A comparison between probable maximum current velocity (PMCV) and measured maximum current velocity (MMCV) is presented. It shows that although tidal current characteristics in the study area are significant, the main driving force of the currents at the time of the maximum currents is wind energy. These results provide new insights into a region of huge societal potential at early stages of sustainable economic exploitation where few data currently exist.

Surface floating objects moving from the Pearl River Estuary to Hainan Island: An observational and model study

A group of self-developed surface drifters were released near the Pearl River Estuary (PRE) from November to December 2021, and it is found that most of the drifters were finally stranded off the coast around Hainan Island after 10–30 days. This result makes us want to find out whether the surface floating objects around the PRE are converging on Hainan Island and what factors dominate this process. The velocity of the drifters not only displays prominent characteristics of tidal currents but is also highly correlated to winds associated with winter monsoon. A particle tracking model is employed to investigate the fate of the drifters and detailed process. Model simulation results show that the most important factor is winds, which affect the movement of floating objects through the direct way (direct wind drag) and indirect ways (wind-driven currents and the wave-induced Stokes drift). The influence of non-wind-driven flows (e.g., geostrophic currents, density-driven currents) is relatively limited. Tidal currents can significantly influence trajectory details within a tidal cycle. Extended model experiments with a large number of surface floaters released in October and January 2021 show that ∼34% of the surface floaters are stranded near the PRE, ∼30% are stranded to the east of Hainan Island, and ∼ 25% move to the west of Hainan Island. Our results indicate that a high proportion of the surface floaters from the PRE would converge around Hainan Island in the autumn and winter, of which the environmental impact warrants further investigation.

The Effect of Storm Surge on Three-dimensional Tidal Current Characteristics: A Case Study of “Lekima”

This study simulated the process of storm surge in the Eastern China Sea (ECS) during typhoon Lekima, based on the MIKE3 wind-surge model driven by the reconstructed typhoon wind field, which was calculated by the Holland empirical formula. The results show that, affected by shoreline and topography, the storm surge in the Hangzhou Bay and the Taizhou Bay can be more than 3.0 m during typhoon Lekima. During the typhoon, the maximum storm surge on the right side of the track was relatively larger than that on the left side, especially along the coast. And the value of maximum current speed was more than 2.5 m/s, which can be obtained in the coast of Zhejiang. The storm current speed at stations presented logarithmic distribution along the depth generally, either the astronomical tide or storm tide. The vertical structure of current velocity responded to typhoon Lekima presented obvious layered distribution. The value of current speed inner the layers was more than that in the side of the layer.

General characteristics of tidal currents in the entrance of Khor Abdullah, northwest of Arabian Gulf

The general characteristics of tidal currents in the entrance of the Khor Abdullah at Iraq marine water, located at the northwest tip of the Arabian Gulf, were studied based on realistic current measurements. The velocity measurements used in this study extended to about one year, which was never previously available in this vital region of the Arabian Gulf. The results illustrated that this area is characterized by strong currents exceeding 1 m/s during both ebb and flood tides, driven by local water level variations. The maximum currents recorded during the study period were 1.65 and 1.36 m/s at the ebb and flood tides, respectively. Additionally, the monthly averages of ebb currents are higher than those of flood currents. The harmonic analysis results revealed that the tidal effect explained approximately 98% of the variation in water currents, with the remaining percentage due to residual currents. Among the 35 tidal components used in harmonic analysis, the M2 component was the main contributor to tidal currents variation in the area, followed by S2, K1, N2, and O1. The residual current seems to have a low effect on the currents variations in the area, with maximum values not exceeding 0.0677 and 0.058 m/s during the ebb and flood tides, respectively. The results obtained give a general view of the tidal current behavior and could be beneficial for several aspects of marine and coastal engineering as well as shipping and navigation activities in this region.

Preliminary application of Air-Wave-Sea coupling model in Bohai sea

In view of the important practical needs of marine forecasting and marine production in the Bohai Sea port, this paper constructs a regional high-resolution coupled forecasting model of sea air waves to carry out 5-day marine forecasting. The resolution of ocean and wave models is higher than 1km, and the resolution of the inner layer grid of the atmospheric model is 3km. Compared with the international advanced model HYCOM, it is found that the simulation results of the high sub regional coupling model are obviously better than those of HYCOM, its results clearly shows the flow field and tidal current characteristics, which are consistent with the observation results; The spatial modes of SST are consistent with HYCOM. The results of current and SST indicate that the prediction results of the coupled model are reliable and better than those of HYCOM.

Observed Tidal Currents in Prydz Bay and Their Contribution to the Amery Ice Shelf Basal Melting

Tides play a key role in regulating the circulation and water properties around Antarctica, yet tidal currents and the corresponding influences in Prydz Bay have not been quantified with observational datasets. This study focuses on the observed characteristics of tidal currents and quantifies the tidal contribution to the basal melting of the Amery Ice Shelf (AIS). Long-term hydrography observations are provided by 10 moorings over the continental shelf and 6 borehole sites drilled through the AIS. Based on the mooring observations, we analyze the observed tidal currents, and evident seasonality in the mixed diurnal–semidiurnal tidal currents is identified. Barotropic tides dominate the tidal currents at the AIS front, except at the western corner where the seabed is abruptly deeper. The spatially and temporally averaged magnitude of tidal currents for all the current meter records is only ~3 cm s −1 . However, an observed maximum tidal velocity of ~11 cm s −1 occurs at the AIS front, and the maximal time-averaged tidal kinetic energy reaches ~31% of the total kinetic energy over the outer continental shelf. Based on the borehole observations, tide-like pulsing is identified in the ocean layer adjacent to the AIS basal surface. The maximal tidal contribution of the AIS basal melting is estimated at 69% based on a simple model. Due to the paucity of long-term velocity observations in the sub-ice-shelf cavity, the uncertainties of the estimated tide-induced melting in this study could be attributed to the simulated velocity.

A comparative study of methods for calculating the exploitable amount of tidal energy

As a kind of clean renewable energy, tidal current energy has a great prospect of development and utilization in China's coastal areas, but there is no unified method for evaluating tidal current energy resources. This paper firstly simulates the tidal field in Zhoushan sea based on a numerical model, analyzes the overall characteristics of tidal currents in the sea, selects the Guimen Channel with high energy density, and compares four tidal energy calculation methods, namely the Farm method, the Flux method, the Garrett method and the Lidan method, which are widely used at present, to evaluate the exploitable amount of tidal energy in the region. The results show that the results of Farm, Flux, and Lidan methods are in good agreement, while the conclusions of the Garrett method are more different from these three methods, and the differences may be related to their assumptions. The annual average current velocity in this area can reach 1.97 m/s, and the highest current velocity exceeds 4.5 m/s. The average water depth is 40 m. The exploitable tidal current energy is above 40 MW, which is suitable for large-scale installation and provides some reference for the local tidal current energy development and utilization.

The shape and residual flow interaction of tidal oscillations

Tidal flows are seldom exactly sinusoidal, leading to a small discrepancy, or residual, over each tidal cycle. Although residuals are generally small in comparison with instantaneous currents, their cumulative effect is important for sediment transport and dispersion of contaminants. The meso-scale characteristics of tidal residual currents are investigated with a computational model of the Irish Sea. The role of the tidal oscillations, or eddies, in forcing the residual flow is considered first through theoretical considerations and secondly by calculating time mean flow quantities directly from the computational model. The tidal eddies contribute to the time mean vorticity balance through the tidal stresses which can be written in the form of a divergence of an eddy vorticity flux. In regions where the tidal flows are approximately horizontally non-divergent the anisotropy of the tidal eddies is strongly linked to their contribution to driving the residual flow. A measure of eddy anisotropy is proposed and this mirrors the shape and orientation of the tidal ellipses of the main tidal constituent. The vorticity balance of the residual flow is dominated by the frictional torque and the eddy vorticity flux divergence, with vorticity advection and vortex stretching by the residual flow generally being of secondary importance.

Influence of Ningbo–Zhoushan Port Main Corridor on the Tidal Current Dynamics in the Zhoushan Sea Area

Ningbo–Zhoushan Port Main Corridor project is important in the development of Zhoushan City, but its impact on the hydrodynamic characteristics of the Zhoushan sea area is still unclear. Finite volume method is used in the present study to solve the shallow water equations and establish a plane two-dimensional tidal current numerical model. The measured tidal current data of the Yangtze River Estuary and Hangzhou Bay is utilized to verify the accuracy of the model in simulating the tidal current process. The results indicate the model can numerically reproduce the tidal current process in the Hangzhou Bay–Yangtze River Estuary–Zhoushan sea area (HYZ). In addition, the dynamic characteristics of tidal currents in the Zhoushan sea area with and without piers are compared. The results show that the construction of the project changes the water level near the bridge piers and causes the water obstruction and deficiency in the front and behind the piers, respectively. Tidal flow velocity increases on sides of the piers with while a low velocity area is formed before and after the piers. The project construction exerts a small impact on the tidal currents but a strong influence on the local area near the bridge piers.

The Properties of the Tide Current and Sediment at a Port of Southern China

Environmental factors of projects in the sea area, such as tidal current characteristics and sediment transport patterns, play a decisive role in the safe operation of the harbor. Based on the observation data of tide level, tidal current, suspended sediment, and surface sediment in the Port of Shenquan, this paper focuses on the study of the characteristics of tidal current and sediment of projects in the sea area. According to the measured tide hydrograph, it can be concluded that the tide in the Port of Shenquan is irregular diurnal, and the flow of rising and falling tides is basically rectilinear. The velocity of the neap tide is higher than that of spring tide, which is mainly related to the strong winds and waves. The sand source is limited, and the sediment concentration in the water is very low. The hourly sediment concentration in each station fluctuates within a narrow range, independent of hourly velocity change. The sediment is coarse and fine, with a distribution pattern of coarse near shore, fine in deep water, coarse in East and West, and fine in the middle, and the sorting coefficient of sediment is medium to well.

Tidal current classification insights for search, rescue and recovery operations in the Yellow and East China Seas and Korea Strait

We investigated spatial relationships between barotropic tidal currents and tides (i.e., tidal elevations) in the tidally predominant Yellow and East China Seas and Korea Strait (YESKS) continental shelf region to understand which tidal current and tide (TCE) characteristics underpin essential insights for maritime search, rescue and recovery operations. As baseline information for such operations, tidal current types were classified using FES2014 model TCE harmonic constant data and phase lag relationships for the predominant M2 constituent, to determine maximum flood currents. In terms of surface current spatial variation, the M2 currents were classified into three types: standing, progressive, and mixed tidal waves. In addition to these horizontal patterns, Acoustic Doppler Current Profiler (ADCP) records from three stations on the west coast of Korea during summertime 2007 and wintertime 2015 were harmonically analyzed to reveal the vertical structure of M2 constituent tidal currents, including ellipse parameter gradients. M2 tidal current types were found to vary through the water column, with the maximum tidal current delayed by up to 40° (∼1.4 h) in near surface waters compared to bottom waters. M2 tidal current types also varied vertically, with changes in its ellipse phase: for example, from a near-surface mixed tidal wave to a standing tidal wave near the seabed. Finally, to explore other TCE conditions relevant to rescue and recovery operations, distributions of the age of the tide and of the tidal current ellipse were compared, with results exhibiting similar distributions for both parameters, including >1.5 days in the Yellow Sea and <1.5 days in Korea Strait. In conclusion, as demonstrated by the spatially and vertically complex tidal current type patterns found in the YESKS, detailed three dimensional understandings of TCE processes are needed to successfully support maritime search, rescue and recovery operations in this and other regions.

Tidal current prediction based on fractal theory and improved least squares support vector machine

An accurate short-term tidal current prediction is essential to optimize the operation mode of offshore microgrids. According to the correlation characteristics of tidal current speed and direction in time series, a tidal current prediction model is proposed by using fractal theory, dragonfly optimization algorithm and least squares support vector machine (DA-LSSVM). First, the Rescaled range analysis (R/S analysis) in fractal theory is used to construct the tidal current analytic model with moving Hurst index of time series characteristics and Von-Mises statistics (V statistic). The model evaluates the stability and autocorrelation of the tidal current and reveals the persistence of tidal current fluctuation. It also shows the orderliness hidden behind the randomness, indicating that the tidal current characteristics can be extended. Second, the least squares support vector machine is used to train the samples in high-dimensional space, and the dragonfly algorithm is used to optimize the parameters of the least squares support vector machine to obtain the best prediction model. Finally, based on the empirical data recorded in the straits in North America, the model was used for the analysis and prediction of tidal current speed and tidal current direction, which verified the validity and accuracy of the proposed method.

Modeling The Hydrodynamic Characteristics of Tidal And Monsoonal Currents In Pondok Dayung Port of Tanjung Priok Harbor, Jakarta

The Pondok Dayung port forms a significant segment of the Tanjung Priok harbor in the Jakarta coastal bay. Studies on the hydrodynamic characteristics of tidal and monsoonal currents appear very important to ship movement and laid/dock operations in port basins/jetties. These flow conditions have been simulated using a two-dimensional shallow water equation, while the tidal and monsoonal wind were coupled to model the ocean current. In general, the simulation results of the ocean current characteristics were dominated by tidal effects, as well as the interactions with the coastlines, jetties, and breakwaters. Also, the geometric replica has been validated satisfactorily, using time series sea elevation from the tidal station in the research area managed by the National Geospatial Agency (BIG). Strong RMSE and linear correlation values ranging from 0.0405-0.0458 m and 0.9648-0.9843 were obtained, respectively. During the flood tides, the ocean current is directed towards the basin area, while an outward flow is observed under ebb conditions. Furthermore, the maximum tidal current speed of ±0.26 m/s was recorded at the port waterways. A similar outcome was also reported during the west and east monsoon, in addition to a minimum ocean current speed of approximately 0.00 m/s. These conditions implied that the Pondok Dayung port and its breakwater system served as protective structures to the surrounding vessels and the harsh ocean current impacts.

Estimation of Effective Range of HFR Data and Analysis of M2 Tidal Current Characteristics in the Jeju Strait

Estimation of Effective Range of HFR Data and Analysis of M2 Tidal Current Characteristics in the Jeju Strait

Validation of a turbulence numerical 3D model for an open channel with strong tidal currents

Abstract Turbulence characteristics of tidal currents, essential to predict the performance of tidal stream energy converters, present a significant spatial and temporal variability. Spatial fluctuations can occur within an area of the order of m2, mainly due to the geomorphologic characteristics of the area. Temporally due to ebb-flood asymmetries and also the effect of meteorological agents such as wind and waves, especially at shallower depths. This paper introduces an FVCOM (Finite Volume Community Ocean Model) numerical model validated with current velocity and turbulent kinetic energy data from three measuring devices installed in the Tanoura and Naru Straits (Goto Islands), one of them covering different vertical layers of the water column, confirming its capacity to estimate turbulence conditions at various depths when these are mostly generated by tidal currents. Correlation coefficients obtained under these conditions at the three locations are higher than 0.84 and 0.8 for current velocity and turbulent kinetic energy, respectively. Results from the validated model show that at deeper layers, TKE is primarily determined by the bathymetry characteristics of the area, while for middle and shallower depths the coastline shape is more important.

Tidal velocities on the Mid-Atlantic Bight continental shelf using high-frequency radar

Surface current velocity from high-frequency radar data are used to study tidal currents in the Mid-Atlantic Bight, which represent an average 32% of the total kinetic energy of the surface circulation. Average annual and seasonal tidal current characteristics and the associated variance of the semi-major axis are computed. The M2 constituent dominates the tide, representing a maximum of 72.26% and an average of 51.63% of the total studied tidal signal. Its semi-major axis reaches a maximum of 10 cm s???1 around mid-shelf and its phase sweeps from north to south. Local maxima of the same order of magnitude are found near the mouths of estuaries (Long Island Sound, Hudson River, Delaware Bay, Chesapeake Bay) and an absolute maximum of 50 cm s???1 is found in Nantucket Shoals. These regions of localized elevated tidal amplitude are associated with high interannual and intra-annual variability due to seasonal stratification, internal waves, and sand waves. Seasonal tidal changes are large in some of these regions; thus, should not be neglected in making tidal predictions. Lastly, the authors position this paper as an updated alternative to the Moody tidal atlas as the source for tidal current values in the Mid-Atlantic Bight.

Role and Impact of Hydrograph Shape on Tidal Current-Induced Scour in Physical-Modelling Environments

For physical model tests, the time-varying characteristics of tidal currents are often simplified by a hydrograph following a shape of a unidirectional current or by resolving the tidal velocity signal into discrete steps of constant flow velocity. The influence of this generalization of the hydrograph’s shape on the scouring process in tidal currents has not yet been investigated systematically, further increasing the uncertainty in the prediction of scour depth and rate. Therefore, hydraulic model tests were carried out to investigate and quantify the influence of the hydrograph shape on the scouring processes under tidal currents. Several different hydrographs including those with continuously changing velocities, constant unidirectional currents, square-tide velocities and stepped velocity time series were analyzed. Results show that the scouring process in tidal currents is characterized by concurrent sediment backfilling and displacement which can only be reproduced by hydrographs that incorporate a varying flow direction. However, if only a correct representation of final scour depths is of interest, similar scour depths as in tidal currents might be achieved by a constant, unidirectional current, provided that a suitable flow velocity is selected. The effective flow work approach was found capable to identify such suitable hydraulic loads with reasonable practical accuracy.

Numerical assessment of the environmental impacts of deep sea cage culture in the Yellow Sea, China

In light of environmental deterioration in coastal areas, deep sea cage aquaculture is becoming an increasingly attractive mode of mariculture. A key factor in determining the potential of deep sea cage aquaculture is to evaluate the environmental impacts of these practices. Here, a numerical model consisting of coupled hydrodynamic-, tracer-tracking- and 3-D Lagrangian particle-tracking models was set up and applied to evaluate the environmental impacts of deep sea cage cultivation of sea bass (Lateolabrax japonicus) in the Yellow Sea, China. The model was verified using water level data on August 1–31, 2018 and nutrient concentration in water and surface sediments in May, August, and November 2018, and January 2019. Results show that the model successfully captures the characteristics of local tidal currents and the total particulate nitrogen and phosphorus concentrations of the underlying sediments. Water quality simulations indicate that deep sea cages account for 26% of the total dissolved inorganic nitrogen and 19% of the active phosphorus content. Residual feed particles are predicted to fall in an ellipse centered on the cage location, with a long axis of 200 m and a short axis of 50 m. Feces are predicted to fall in an ellipse with a long axis of 1400 m and a short axis of 600 m. The Superposition particles are predicted to settle in an ellipse with a long axis of 320 m and a short axis of 150 m. The model results indicate that installation of all deep sea cages will lead to acceptable levels of water quality, but that sediments may become polluted. The coupled model can be used to predict the environmental impacts of deep sea cage farming and provide a useful tool for designing the layout of integrated multi-trophic aquaculture of organic extractive or inorganic extractive species.

Tidal and tidal current characteristics in the Guangxi Gulf of Tonkin, South China Sea

The Guangxi Gulf of Tonkin (GXGT) is rich in mineral, oceanic energy, and biological resources; however, it has not attracted much attention. Based on ECOMSED, a high-resolution three-dimensional numerical model is constructed in this study, and the accuracy is validated using long-term observational data. The results showed that the GXGT is dominated by regular diurnal tide and mixed mainly diurnal tidal currents and some regions to the northwest and south of Weizhou Island are dominant by mixed mainly semi-diurnal tidal currents. Furthermore, the rotation direction of O1 is found to be counter-clockwise and clockwise in the western and eastern domains, respectively, whereas the rotation directions of the other three tidal constituents are clockwise and counter-clockwise in the open sea and coastal bays, respectively. Similarly, the propagation direction of the tidal energy flux of O1 (northwestward) is different from them of the other three tidal constituents (northeastward) in the western GXGT. On the other hand, the propagation directions of the four tidal constituents are all northeastward in the eastern GXGT. A comparison of the reference run with the summed-up effect of six runs, where each of the tidal constituents has been considered separately, revealed that the nonlinear effect due to the interaction of the six tidal constituents cannot be neglected in the GXGT, especially in the western GXGT. Interestingly, energy input from wind to O1 is larger than that to M2 whereas the tidal dissipation of O1 is less than that of M2 at BBL. Additionally, tidally induced residual currents mostly flow westward in the GXGT, with clockwise eddies present outside the Qinzhou Bay and Tieshan Port. Driven by the monsoon wind, the current structure and strength in the GXGT have obvious seasonal variation. And sensitive experiments show that the residual currents in the GXGT are deeply influenced by the monsoon wind and bottom topography.