Tidal Characteristics Research Articles

The Change of Tidal Characteristics under the Influence of Human Activities in the Yangtze River Estuary

Tan, Y.; Yang, F.; Xie, D, H, 2016. The Change of Tidal Characteristics under the Influence of Human Activities in the Yangtze Estuary. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 163–167. Coconut Creek (Florida), ISSN 0749-0208.The aim of this study is to understand the change of tidal wave characteristics in the Yangtze River Estuary by human activities. The harmonic analysis results based on measurement shows that the semidiurnal tides are dominant in Yangtze River Estuary. The shallow water constituents are significant. Tidal constituent Sa, which is one of main meteorological tides, is gradually increasing with the increase of upper stream river discharge. The amplitude of Sa is highly correlated to the maximum anomaly discharge value (maximum daily discharge differing from the long term mean). Due to human activities, the changes of the river discharge, the water depth and the shape of the costal line in the Yangtze River cause the change of tidal wave propagation. A 2-D numerical model is established to simulate the evolution of main tidal constituents in the Yangtze Estuary under the influence of human activities.

Evaluation of fluvial flow effects on tidal characteristics of tidal rivers by artificial neural networks and genetic algorithm

Interaction of fluvial and tidal flows is a complex phenomenon in tidal rivers study. For determination of tidal characteristics in tidal rivers, an appropriate method is needed. Artificial neural network (ANN) using genetic algorithm (GA) method for determining the parameters is a suitable tool that can determine tide velocity, ebb velocity and variation of water surface elevation by tidal flow. Learning rates and momentum constants are optimised in ANN with GA method. It is observed that results of trained ANN by GA are more accurate than results of ANN. GA increases regression coefficient between output of ANN and desired output from 1% to 8% also decreases MSE extremely (43% to 85%). For case study, the Karun River was selected. The selected reach is between Ahvaz upstream and junction of three branches of Khoramshar downstream.

Tidal characteristics in the Wenzhou offshore waters and changes resulting from the Wenzhou Shoal Reclamation Project

The Wenzhou Shoal Reclamation Project is the core part of Wenzhou Peninsula Engineering which is a big comprehensive development project to expand the city space. The dynamics of the surrounding area was proved to suffer little effect in response to the Lingni north dyke since it was built approximately along the current direction. Therefore, this paper focuses firstly on the tidal characteristics in the Wenzhou and Yueqing bays with the Lingni north dyke being built and then on the changes resulting from the implementation of the on-going Wenzhou Shoal Reclamation Project (WSRP) which will reclaim land from the whole Wenzhou Shoal. To simulate the tidal dynamics, a high-resolution coastal ocean model with unstructured triangular grids was set up for the Wenzhou and Yueqing Bays. The model resolved the complicated tidal dynamics with the simulated tidal elevation and current in good agreement with observations. In the study area, M2 is the predominant tidal component, which means the tide is semidiurnal. The new reclamation project hardly affects the Yueqing Bay and the open ocean, but there are concentrated effects on the mouth of the southern branch of the Oujiang River and the southwest of Wenzhou Shoal. This study provides an indicative reference to the local government and helps to weigh the advantages and disadvantages of the project.

Empirical Orthogonal Function Analysis of Suspended Sediment Concentration in Gulf of Kachchh, India, and Its Tidal Influence

Complexity of the temporal sediment variability within the Gulf of Kachchh is resolved into major modes of variations using empirical orthogonal function (EOF) analysis on sequential OCM derived suspended sediment concentration (SSC) images during spring intermonsoon period of 2011. Variance accounted collectively by the first four modes is around 80% and the principal component (PC) of each mode is correlated with different hydro-meteorological forces influencing the hydrodynamics of the gulf. Hydro-meteorological forces are classified in the order of precedence of influencing the sediment dynamics of the region. PC1 contributing 50% of the total variance is correlated with average of the simulated current velocities between consecutive images, indicating the variation of tides from neap-spring ranges (r2 = 0.86). The ocean state parameters like tidal height, wind speed, and current speed at the time of OCM pass contribute to around 20%, 6%, and 4%, respectively, to the total variability of the temporal dynamics of SSC. The interchange of tides from neap and spring is the major contributor toward the temporal variability of sediment concentration within the gulf, where the sediments are subjected to deposition and resuspension. The gulf being highly tide dominated, the suspended sediment variability also reverberates with the variability of tidal characteristics and subtly with the wind conditions.

Study on hydrography and small-scale process over Zhoushan sea area

This paper mainly analyzes the tidal characteristics and small-scale mixing process near Zhoushan Islands. First, the spectral analysis and wavelet analysis are adopted for the measured tide level data and tidal current data from the Zhoushan sea area, which indicate that the main tidal cycle near Hulu Island and Taohua Island is semi-diurnal cycle, the diurnal cycle is subordinate. Both their intensities are changed periodically, meanwhile, the diurnal tide becomes stronger when semi-diurnal tide becomes weak. The intensity of baroclinic tidal current weakens at first and then strengthens from top to bottom. Then, in this paper, the Gregg-Henyey (G-H) parameterization method is adopted to calculate the turbulent kinetic energy dissipation rate based on the measured temperature and tidal current data. The results of which shown that the turbulent kinetic energy dissipation rate around Hulu Island is higher than that around Taohua Island. In most cases, the turbulent kinetic energy dissipation rate during spring tide is larger than that during the neap tide; the turbulent kinetic energy dissipation rate in the surface layer and the bottom layer are higher than that in the intermediate water; the changes of turbulent kinetic energy dissipation rate and tidal current are basically synchronous. The modeled turbulent kinetic energy dissipation rate gets smaller with the increase of the stratification, however, gets larger with the increase of shearing.

Tidal Analysis and Prediction for the Gangra Location, Hooghly Estuary in the Bay of Bengal

The Hooghly estuary located in the head Bay of Bengal region is a part of the highly dynamic deltaic environment. Tidal variations are pre-dominant in this estuary, and tides propagate considerable distance through a complex network of various riverine systems, inlets, bays and creeks having vital implications on water mass exchange, reworking of deltaic sediments and the mixing process. The Hooghly River houses two major ports of national importance, viz. Kolkata Dock System and Haldia Dock Complex. Tidal forcing is primarily semi-diurnal in nature and with the presence of complex riverine morphology, the tidal characteristics are substantially modified causing various tidal constituents of compound tides. The present study performs location-specific tidal analysis and prediction utilizing one-hourly tide data with SLPR2 harmonic tidal analysis tool for Gangra situated upstream of the Hooghly River. In a geomorphologic perspective, the water-level elevation at Gangra results from natural tidal flow, as well as refracted effects from cross-flow due to the presence of two natural island barriers, namely Sagar Island situated southward off Gangra and Nayachara in the east. The Hooghly channel comprises of complex bathymetric features and tidal analysis at Gangra reveals the presence of Msf (luni-solar synodic fortnightly) tidal constituent. Very few locations in India have reported on the existence of the Msf tides, and Gangra is one among them. This study also performs a comprehensive validation between the computed monthly tidal prediction from SLPR2 and measured water level at Gangra. The skill level of prediction exhibits a good match. This study also investigates the influence of atmospheric effects on sea-level pressure variations and the resultant water-level elevation from extreme weather events such as depressions and severe cyclonic storms that occurred during 2013. The study signifies the importance of tidal analysis and prediction for operational needs.

Corrections for Tidal Residuals Due to Insufficient Representation Using a Single Station in Shallow Water Multibeam Bathymetric Data

Tidal correction is important for shallow water multibeam sonar to ensure vertical accuracy to International Hydrographic Organization Order 1 standards. The number and distribution of tidal control stations have important influences on tidal zoning and reduction. In many cases, tidal residuals will be unavoidable because of tidal representative errors, particularly when using a single tidal station. Tidal residuals cause depth discrepancies in overlapping areas between the two neighboring swaths. They are different from other vertical error sources. For a multibeam survey project, the distance between the tidal control station on the shore and the survey site or the area surveyed in a single day is relatively short. Therefore, the tidal characteristics between them are usually equal. The tidal curve at each bathymetric point in the small area can be recovered by the observed tide at a single station nearby and synchronous multibeam bathymetric data. After other errors have been considered and corrected, the tidal parameters—that is, the time difference of tide, the ratio of tidal ranges, and the direction of tidal wave propagation—can be estimated with the depth discrepancies and the tidal data from a single station using the least squares method. Then, the tidal residuals can be calculated based on the estimated tidal parameters. The quality of final bathymetry can be improved by the corrections as verified by a field test.

Tidal Influence on the Diel Vertical Migration Pattern of Zooplankton in a Tropical Monsoonal Estuary

Monsoonal estuaries, located along the coastline of the Indian subcontinent, differ from other estuaries by their time dependence on the salinity characteristics. Effective sustenance and retention of the mesozooplankton community in the estuarine habitats is often determined by their dominant behavioral patterns: diel vertical migration (DVM) and tidal vertical migration (TVM). The modes of these endogenous rhythms often vary among estuaries based on the river runoff and tidal characteristics. The present study is a pioneering attempt to depict the vertical migration pattern of zooplankton along a diel and tidal scale in a tropical, microtidal, monsoonal estuary. We observed that in spite of the prominent asymmetry in the magnitude of the river runoff between the seasons, most of the zooplankton groups exhibited strong DVM, with a clear increase in biomass and abundance in surface waters during night. The peak increase in biomass and abundance at night always synchronized with the slack periods in the tidal cycles, which differed from the general concepts of downward migration during ebb tide and upward migration during flood tide in estuarine systems. The weak currents during the slack period might have favored the effective vertical migration of the mesozooplankton community in this monsoonal estuarine system.

Analysis of a compounding surge and precipitation event in the Netherlands

Hydrological extremes in coastal areas in the Netherlands often result from a combination of anomalous (but not necessarily extreme) conditions: storm surges preventing the ability to discharge water to the open sea, and local precipitation generating excessive water levels in the inland area. A near-flooding event in January 2012 occurred due to such a combination of (mild) extreme weather conditions, by which free discharge of excessive water was not possible for five consecutive tidal periods. An ensemble of regional climate model simulations (covering 800 years of simulation data for current climate conditions) is used to demonstrate that the combined occurrence of the heavy precipitation and storm surge in this area is physically related. Joint probability distributions of the events are generated from the model ensemble, and compared to distributions of randomized variables, removing the potential correlation. A clear difference is seen. An inland water model is linked to the meteorological simulations, to analyze the statistics of extreme water levels and its relationship to the driving forces. The role of the correlation between storm surge and heavy precipitation increases with inland water level up to a certain value, but its role decreases at the higher water levels when tidal characteristics become increasingly important. The case study illustrates the types of analyzes needed to assess the impact of compounding events, and shows the importance of coupling a realistic impact model (expressing the inland water level) for deriving useful statistics from the model simulations.

Spatial variability in the drag coefficient and its role in tidal dynamics and energetics, a case study: The surface M 2 tide in the subsystem of the Barents and Kara Seas

The QUODDY-4 three-dimensional finite-element hydrostatic model is modified by including a module for the drag coefficient calculated from external determining parameters of the bottom boundary layer (BBL). The modified model is used to evaluate changes in dynamic characteristics (the amplitude and phases of tidal elevations and the maximum barotropic tidal velocity), as well as some components of the barotropic tidal energy budget in the Barents and Kara Seas, induced by the spatial variability in the drag coefficient. It has been shown that the changes in all tidal characteristics, except for the direction of the averaged (over a tidal cycle) horizontal wave transport of barotropic tidal energy, are significant in the sense that they are either greater than the rms absolute vector error or have identical (or near-identical) orders of magnitude when compared to the tidal characteristics themselves. This implies that the concept of a “constant drag coefficient” should be revised.

上海市不同区县中小河道氮磷污染特征

To assess nitrogen and phosphorus pollution in rivers of Shanghai,this study explored 65 water samples from 11 rivers in 19 districts of Shanghai from July 2012 to July 2013. The results showed that Shanghai rivers display incomplete tidal and river network characteristics under the effect of tide and rainfall,which caused temporal distribution differences of nitrogen and phosphorus pollutants. This combination of factors also affected the biodegradation in the rivers. Rainfall and tide had a diluting effect in the rivers during the experiment. There was a significant difference between the rivers of Shanghai in the nitrogen and phosphorus concentrations( P 0. 05). In general,the difference appeared in a ring- like form on the map of the river network,with suburban rivers having lower concentrations of nitrogen and phosphorus than the urban rivers. Rivers located in southern sections of the Huangpu River have better water quality compared to the northern parts,and the concentration of nitrogen and phosphorus in rivers near the Jiangsu Province( northwest of Shanghai,near the estuary of the Yangtze River) were higher than in the sections near the Zhejiang Province( southeast of Shanghai)( P 0. 05). Such distribution of pollutants reflected the close relationship between the concentration of pollutants and urbanization level. Cluster analysis( CA) did not find a significant difference in pollutants between the rivers of Shanghai,whereas multidimensional scaling,opposite to the CA,supported the results of the water quality assessment. Water quality of rivers after ecological restoration improves compared to the state before or to the rivers without ecological restoration( P 0. 05),indicating that ecological restitution has potential in improving the water quality of rivers.

The Along-channel Salinity Distribution and its Response to River Discharge in Tidally-dominated Han River Estuary, South Korea

The Han River Estuary (HRE), located on the west coast of South Korea, is well known for its macro tidal characteristics with a tidal range more than 8.5 m. This estuary has a distinctive salinity distribution because its system consists of 3 main channels and 3 rivers, through which major tidal flow and river discharge meet each other. To determine the effect of change in external forcing (e.g., river discharge and tidal variation) on the salinity, a numerical model is established and verified with observation. Based on previous observation, the main channel of HRE shows well- and/or partially-mixed estuary during spring and neap periods, respectively. The vertical stratification during the neap period is stronger than that during the spring due to decreasing turbulent mixing. The numerical results show that the salinity distribution during high river flow condition can be temporally and spatially characterized by river discharge. The asymmetries of the salinity distribution response to increasing and decreasing river discharge are indicated in this estuary. During high river flow conditions, the front of Incheon Harbor is within the region of the freshwater influence.

Characteristics of Tides in the Red Sea Region, a Numerical Model Study

In this work, a two-dimensional numerical model based on Delft3D modelling system was setup to study the tidal characteristics of the Red Sea. Besides that, analyses of available observed time series of surface elevations were carried out. Sensitivity analyses of the numerical model were carried out by testing different model parameters aiming at selecting optimal settings. The model performance was evaluated against available time series of surface elevation observations. RMS error was found to vary from 0.03 to 0.1 meter, while the ADM values range from 0.02 to 0.05 meter. On the whole, the model is able to reproduce the tidal wave in the Red Sea, reflecting a consistent level of agreement with the observations and previous works. The model results suggest that the semidiurnal tidal waves play a major role in the region except in the central part of the Red Sea where amphidromic system exists. Major semidiurnal and diurnal tidal constituents were computed to generate co-charts and form factor. The results have revealed that the distribution of the co-charts of the major semidiurnal constituents M2, N2, and S2 show the existence of anticlockwise amphidromic system in the central part of the Red Sea at about 19.5°N, north of the Strait of Bab el Mandeb at 13.5°N and in the Gulf of Suez. The chart of the diurnal tidal constituent K1 showed a single counterclockwise system in the southern part of the Red Sea centred around 15.5°N. The form factor chart shows the appearance of diurnal character in the central part of the basin and the northern end of the strait. The hydrodynamics patterns under spring and neap tidal conditions were also analysed (during flood and ebb conditions). Model results showed that currents generally are weak and strongest currents are present in the strait of Bab el Mandeb and Gulf of Suez.

Earth’s Atmospheric Electricity Parameter Response During Venus Transit

Venus transited across the Sun on 06 June 2012, introducing significant contribution to the tidal characteristics of the solar atmosphere. Earth’s atmosphere was perturbed due to an anomalous Coronal Mass Ejection (CME) and γ-radiation influenced by the solar tide due to Venus transit, thereby the Earth-ionosphere waveguide characteristics were changed. In this anomalous situation we measured some atmospheric electricity parameters such as Schumann resonance (SR) amplitude, very low frequency (VLF) sferics, subionospheric transmitted signals and the point discharge current (PDC) along with the vertical electrical potential gradient (PG) at the ground surface on the day of transit. The results showed some remarkable variations during the transit as well as pre- and post-transit periods. The observed anomalies in the recorded data were interpreted in terms of the anomalous solar tidal effects initiated due to Venus transit.

Tidal characteristics of the gulf of Tonkin

The Gulf of Tonkin, situated in the South China Sea, is a zone of strong ecological, touristic and economic interest. Improving our knowledge of its hydro-sedimentary processes is of great importance to the sustainable development of the area. The scientific objective of this study is to revisit the dominant physical processes that characterize tidal dynamics in the Gulf of Tonkin using a high-resolution model and combination of all available data. Particular attention is thus given to model-data cross-examination using tidal gauges and coastal satellite altimetry and to model calibration derived from a set of sensitivity experiments to model parameters. The tidal energy budget of the gulf (energy flux and dissipation) is then analyzed and its resonance properties are evaluated and compared with idealized models and observations. Then, the tidal residual flow in both Eulerian and Lagrangian frameworks is evaluated. Finally, the problem of tidal frontogenesis is addressed to explain the observed summer frontal structures in chlorophyll concentrations.

Accuracy Comparison for the Ocean Tide Models in Estuarine Tidal Prediction, the Pearl River Estuary

Ocean tide models with satellite altimetry can simulate global ocean tides conveniently and accurately. However, it was not sure for them to have a same good performance in estuaties and coastal zones. To assess their accuracy in the Pearl River estuaries, tidal elevations were computed respectively by three models NAO.99b, OTPS and WWT, and compared with the hourly observed data. RMS misfits were calculated and the results suggest that the models are competent to demonstrate the basic time features of tides and the accuracy is not lower than that of traditional methods in some certain periods and areas. The models behave better in the mouth zones, especially in the open area outside, but in the upstreams have differences between dry season and flood season. At the entrances, compared with the river-dominated estuary, the models indicate more accurate estimations for the tide-dominated estuaries. WWT is recommended among these three models.

설계조위와 관련된 약최고고조위의 시·공간적 편차

The approximately highest high water(AHHW), which has been used frequently as a basis of the design sea level, has not only ambiguous return period but also spatio-temporal problems induced by sea level rise and the spatial variability of tidal characteristics. The ratios of 4 major constituents with other constituents were investigated. In addition, tidal data were analyzed by probability density function. The temporal variability may be cured by using the latest tidal data. And the AHHW at summer was examined to lessen the spatial variability. The results show that the design sea levels need to increase by 10 cm or more at the Southern Coast and by 15~25 cm at the East Coast.

Coupling of Sea Level Rise, Tidal Amplification, and Inundation

Abstract With the global sea level rising, it is imperative to quantify how the dynamics of tidal estuaries and embayments will respond to increased depth and newly inundated perimeter regions. With increased depth comes a decrease in frictional effects in the basin interior and altered tidal amplification. Inundation due to higher sea level also causes an increase in planform area, tidal prism, and frictional effects in the newly inundated areas. To investigate the coupling between ocean forcing, tidal dynamics, and inundation, the authors employ a high-resolution hydrodynamic model of San Francisco Bay, California, comprising two basins with distinct tidal characteristics. Multiple shoreline scenarios are simulated, ranging from a leveed scenario, in which tidal flows are limited to present-day shorelines, to a simulation in which all topography is allowed to flood. Simulating increased mean sea level, while preserving original shorelines, produces additional tidal amplification. However, flooding of adjacent low-lying areas introduces frictional, intertidal regions that serve as energy sinks for the incident tidal wave. Net tidal amplification in most areas is predicted to be lower in the sea level rise scenarios. Tidal dynamics show a shift to a more progressive wave, dissipative environment with perimeter sloughs becoming major energy sinks. The standing wave southern reach of the bay couples more strongly back to the central portion of the bay, in contrast to the progressive wave northern reach of the bay. Generation of the M4 overtide is also found to vary between scenarios and is a nonnegligible contributor to net changes in high water elevation.

Development and Use of Tide Models in Alaska Supporting VDatum and Hydrographic Surveying

National Oceanic and Atmospheric Administration’s National Ocean Service uses observations, hydrodynamic models and interpolation techniques to develop many of its products and services. We examine how two projects, computation of tidal datums for vertical datum transformation and the estimation of tidal characteristics for hydrographic surveys, are being developed in Alaska and how they may be more seamlessly integrated. Preliminary VDatum development for Alaska is in progress for the Alaska Panhandle through the setup of a high resolution tide model that will be used to compute spatially varying tidal datums. Tide models such as these can be used for other projects that traditionally rely on estimation of tides in between data locations, such as the planning for hydrographic surveys that need correctors to adjust bathymetry to the chart datum. We therefore also examine how an existing model in western Alaska can be used for better supporting hydrographic survey planning. The results show that integration of tide models with nearshore observations can provide improved information for these correctors and future work will further evaluate this methodology with existing VDatum tide models.

A Numerical Study of Local Variations in Tidal Regime of Tagus Estuary, Portugal

Tidal dynamics of shallow estuaries and lagoons is a complex matter that has attracted the attention of a large number of researchers over the last few decades. The main purpose of the present work is to study the intricate tidal dynamics of the Tagus estuary, which states as the largest estuary of the Iberian Peninsula and one of the most important wetlands in Portugal and Europe. Tagus has large areas of low depth and a remarkable geomorphology, both determining the complex propagation of tidal waves along the estuary of unknown manner. A non-linear two-dimensional vertically integrated hydrodynamic model was considered to be adequate to simulate its hydrodynamics and an application developed from the SIMSYS2D model was applied to study the tidal propagation along the estuary. The implementation and calibration of this model revealed its accuracy to predict tidal properties along the entire system. Several model runs enabled the analysis of the local variations in tidal dynamics, through the interpretation of amplitude and phase patterns of the main tidal constituents, tidal asymmetry, tidal ellipses, form factor and tidal dissipation. Results show that Tagus estuary tidal dynamics is extremely dependent on an estuarine resonance mode for the semi-diurnal constituents that induce important tidal characteristics. Besides, the estuarine coastline features and topography determines the changes in tidal propagation along the estuary, which therefore result essentially from a balance between convergence/divergence and friction and advection effects, besides the resonance effects.