Estimation of Annual Energy Output from BCM Tidal Barrage and the Corresponding Marine Environmental Impact

Based on the finite-volume coastal ocean model （FVCOM）, a three-dimensional numerical model FVCOM was built to simulate the ocean dynamics in pre-dam and post-dam conditions in Bachimen （BCM）. The domain decomposition method, which is effective in describing the conservation of volume and non-conservation of mechanical energy in the utilization of tidal energy, was employed to estimate the theoretical tidal energy resources and developable energy resources, and to analyze the hydrodynamic effect of the tidal power station. This innovative approach has the advantage of linking physical oceanography with engineering problems. The results indicate that the theoretical annual tidal energy resources is about 2x 108 kwh under the influence of tidal power station; Optimized power installation is confirmed according to power generation curve from numerical analysis; the developable resources is about 38.2% of theoretical tidal energy resources with the employment of one-way electricity generation. The electricity generation time and power are 3479 hours and 2.55~104KW, respectively. The power station has no effect on the tide pattern which is semi-diumal tide in both two conditions, but the amplitudes of main constituents apparently decrease in the area near the dam, with the ME decreasing the most, about 62.92 cm. The tidal prism shrinks to 2.28×107 m3, but can still meet the flow requirement for tidal power generation. The existence of station increases the flow rate along the waterway and enhances the residual current. There are two opposite vortexes formed on the east side beside the dam of the station, which leads to pollutants gathering.

Hydrodynamic Characteristics of Undular Tidal Bores in the Qiantang River Based on Field Observations

Understanding the undular tidal bores in the Qiantang River is essential for effective river management and maintenance.While breaking tidal bores have been studied extensively, reports on undular tidal bores in the Qiantang Riverremain limited. Furthermore, observed data on undular tidal bores fulfilling the requirements of short measurementtime intervals, and spring, medium, and neap tide coverage, and providing detailed data for the global vertical stratificationof flow velocity are quite limited. Based on field observations at Qige in the Qiantang estuary, we analyzedthe characteristics of undular tidal bores. The results showed that the flooding amplitude (a) of the first wave isalways larger than its ebbing amplitude (b). Moreover, the vertical distribution of the maximum flood velocity exhibitesthree shapes, influenced by the tidal range, while that of the maximum ebb velocity exhibites a single shape. Duringthe initial phase of the flood tide in the spring and medium tides, the upper water body experiences multiple oscillatingchanges along the flow direction, corresponding to the alternating process of the crest and trough of the tide levelupon the arrival of the tidal bore. The tidal range is a crucial parameter in tidal bore hydrodynamics. By establishingthe relationship between hydrodynamic parameters and tidal range, other hydrodynamic parameters, such as the tidalbore height, maximum flood depth–averaged velocity, maximum flood stratified velocity at the measurement points,and duration of the flood tide current, can be effectively predicted, thereby providing an important reference for rivermanagement and maintenance.

Contributors to tidal duration asymmetry with varied coastline configurations on western shelf of Yellow Sea

Coastal management in China is confronted with an urgent choice between natural restoration and maintenance of existing seawalls and reclaimed land for economic development.A key criterion for making this decision is the resilience to coastal flooding,which depends on the ability to predict tidal level.Tidal duration asymmetry(TDA)is a key parameter in determination of the arrival and duration of flood tides.This study selected the western inner shelf of the Yellow Sea(WYS)as the study area and investigated the responses of TDA to different shoreline configurations and relative sea level rise.The responses of TDA to shoreline reconstruction yielded spatial variability locally and remotely.In the nearshore area,the responses of TDA to the complex ocean environment mainly originated from the combined functions of reflection,bottom friction,and advection,which controlled the energy transfer from M2 or S2 constituents to their overtides or compound tides.The sensitivity of TDA to coastline typologies was not limited to coastal waters but could stretch over the entire inner shelf.The vulnerability of tidal responses was due to the displacement of the M2 amphidrome of the Kelvin wave on the WYS,which in turn changed tidal energy fluxes over the regime.The relative sea level rise could intensify the feedback of TDA to seawalls and land reclamation.

Analysis of Tidal Current Energy Potential in the Major Channels of the Bohai Strait Based on Delft3D

The utilization and development of tidal current energy can help alleviate the current energy shortage,improve the global ecological environment,and maintain sustainable development.In this study,numerical simulation is carried out on a rectangular grid using Delft3D.The tidal current energy potential of the major channels in the Bohai Strait is further simulated and estimated by comparing the simulated and measured data.Results show that the flow module in Delft3D has good modeling ability for the assessment of tidal current energy potential.The average flow velocity,maximum flow velocity,and energy flow density are consistent.The Laotieshan Channel,located in the northern part of the Bohai Strait,shows a large tidal current energy potential.The maximum flow velocity of this channel can reach 2 m s-1,and the maximum energy flow density can exceed 500 W m-2.The tidal current energy in the Laotieshan Channel is more than 10 times that in other channels.Therefore,this study advocates for the continued exploration and exploitation of the tidal current energy resources in the Laotieshan Channel.

Seasonal response of nitrogen exchange fluxes to crab disturbance at sediment-water interface in coastal tidal wetlands

Coastal wetlands are hotspots for nitrogen(N)cycling,and crab burrowing is known to transform N in intertidal marsh soils.However,the underlying mechanisms remain unclear.This study conducted field experiments and used indoor control test devices to investigate the seasonal response of nitrogen to crab disturbance at the sediment-water interface in coastal tidal flat wetlands.The results showed that crab disturbance exhibited significant seasonality with large seasonal differences in cave density and depth.Due to crab disturbance,nitrogen fuxes at the sediment-water interface were much greater in the box with crabs than in the box without crabs.In summer,NH-N showed a positive flux from the sediment to the overlying water,but NO2-N and NOg-N showed positive fluxes from the sediment to the overlying water only in early stages.In winter,NH-N showed a positive flux from the sediment to the overlying water,but NO-N and NO,-N both exhibited positive and negative fluxes.These results indicated that the presence of crab burrows can cause the aerobic layer to move downward by approximately 8-15 cm in summer and directly promote nitrification at the sediment surface.

Examining the evolution of tidal creeks in the Huanghe River delta using multi-temporal Landsat images

Coastal tidal creeks are important channels for exchanges of material and energy between sea and land,and play an important role in the ecological protection of tidal flats.Although tidal creeks have evolved differently in various regions,the evolutionary process of tidal creeks in the Huanghe(Yellow)River delta of China,one of the most active deltas worldwide,is not entirely clear.Therefore,the evolution of tidal creeks in the delta from 1981 to 2021 was investigated by quantitatively analysing the tidal creeks and developing a standard for dividing their evolution periods.Visual interpretation and supervised classification methods were applied to the Landsat images to extract the tidal creek network,and 17 groups of tidal creek systems were selected.Results indicate that Creek S 1 was the most developed creek for having 113 tidal creeks totaling 65.8 km in length,while Creek E 3 had the fastest growth rate for having average annual increase of 1.9 km.Meanwhile,the level of tidal creeks increased,the average and median lengths of tidal creeks increased,and the number of tidal creeks decreased since 1981.The evolution of the tidal creek system could be divided into four stages,namely,rising,developing,stabilizing,and degrading.Analyses of a representative tidal creek show that there was no degenerated tidal creek during the rising period,with an increase in the number of 50 and a length increase of 57.9 km between 1981 and 1989.The proportion of new tidal creeks in the developing period was more than 50%and the new tidal creeks in the stabilizing period were equal to the degraded tidal creeks.Extinct tidal creeks were greater than 50%during the degrading period.There was no fixed order of tidal creek evolution in each period,and there may be a skip in evolution.Our findings provided a reference for studying the evolution of tidal creeks.

Changes of coastline and tidal flat and its implication for ecological protection under human activities: Take China’s Bohai Bay as an example

The change processes and trends of shoreline and tidal flat forced by human activities are essential issues for the sustainability of coastal area,which is also of great significance for understanding coastal ecological environment changes and even global changes.Based on field measurements,combined with Linear Regression(LR)model and Inverse Distance Weighing(IDW)method,this paper presents detailed analysis on the change history and trend of the shoreline and tidal flat in Bohai Bay.The shoreline faces a high erosion chance under the action of natural factors,while the tidal flat faces a different erosion and deposition patterns in Bohai Bay due to the impact of human activities.The implication of change rule for ecological protection and recovery is also discussed.Measures should be taken to protect the coastal ecological environment.The models used in this paper show a high correlation coefficient between observed and modeling data,which means that this method can be used to predict the changing trend of shoreline and tidal flat.The research results of present study can provide scientific supports for future coastal protection and management.

Prediction of discharge in a tidal river using the LSTM-based sequence-to-sequence models

The complexity of river-tide interaction poses a significant challenge in predicting discharge in tidal rivers.Long short-term memory(LSTM)networks excel in processing and predicting crucial events with extended intervals and time delays in time series data.Additionally,the sequence-to-sequence(Seq2Seq)model,known for handling temporal relationships,adapting to variable-length sequences,effectively capturing historical information,and accommodating various influencing factors,emerges as a robust and flexible tool in discharge forecasting.In this study,we introduce the application of LSTM-based Seq2Seq models for the first time in forecasting the discharge of a tidal reach of the Changjiang River(Yangtze River)Estuary.This study focuses on discharge forecasting using three key input characteristics:flow velocity,water level,and discharge,which means the structure of multiple input and single output is adopted.The experiment used the discharge data of the whole year of 2020,of which the first 80%is used as the training set,and the last 20%is used as the test set.This means that the data covers different tidal cycles,which helps to test the forecasting effect of different models in different tidal cycles and different runoff.The experimental results indicate that the proposed models demonstrate advantages in long-term,mid-term,and short-term discharge forecasting.The Seq2Seq models improved by 6%-60%and 5%-20%of the relative standard deviation compared to the harmonic analysis models and improved back propagation neural network models in discharge prediction,respectively.In addition,the relative accuracy of the Seq2Seq model is 1%to 3%higher than that of the LSTM model.Analytical assessment of the prediction errors shows that the Seq2Seq models are insensitive to the forecast lead time and they can capture characteristic values such as maximum flood tide flow and maximum ebb tide flow in the tidal cycle well.This indicates the significance of the Seq2Seq models.

Interrelationships between Length of the Day, Moon Distance, Phanerozoic Geodynamic Cycles, Tidal Dissipation and Earth’s Core: Review and Analysis

The rotation of the Earth and the related length of the day (LOD) are predominantly affected by tidal dissipation through the Moon and the growth of the Earth’s core. Due to the increased concentration of mass around the rotation axis of the spinning Earth during the growth of the core the rotation should have been accelerated. Controversially the tidal dissipation by the Moon, which is mainly dependent on the availability of open shallow seas and the kind of Moon escape from a nearby position, acts towards a deceleration of the rotating Earth. Measurements of LOD for Phanerozoic and Precambrian times open ways to solve questions concerning the geodynamical history of the Earth. These measurements encompass investigations of growth patterns in fossils and depositional patterns in sediments (Cyclostratigraphy, Tidalites, Stromatolites, Rhythmites). These patterns contain information on the LOD and on the changing distance between Earth and Moon and can be used as well for a discussion about the growth of the Earth’s core. By updating an older paper with its simple approach as well as incorporating newly published results provided by the geoscientific community, a moderate to fast growth of the core in a hot early Earth will be favored controversially to the assumption of a delayed development of the core in an originally cold Earth. Core development with acceleration of Earth’s rotation and the contemporaneous slowing down due to tidal dissipation during the filling of the ocean may significantly interrelate.

Distribution of benthic macrofaunal communities in intertidal flat under hydrodynamic influence:a case study of Jiangsu coast,East China

To identify the distribution pattern of macrofaunal assemblages of the Dafeng intertidal flats in response to hydrodynamic and sediment dynamic processes in the northern Jiangsu coast,East China,macrofauna sampling and hydrodynamic observations were carried out simultaneously across the mud flat,mixed mud-sand flat,and silt-sand flat of the intertidal zone in June 2018.Results show that there was a clear zonal distribution pattern of the macrofaunal communities,as is controlled by local hydrological and sedimentary environments.Principal component analysis(PCA)revealed three types of intertidal area in terms of hydrological and surficial sediment parameters.Similarly,three distinct groups of the macrofaunal communities,i.e.,mud flat,mix mud-sand,and silt-sand groups,were recognized at similarity level of 24%based on the CLUSTER analysis in similarity profile(SIMPROF)test.Correlation analysis upon best variables stepwise search(BVSTEP)indicated the importance of the hydrodynamics(e.g.,water temperature and salinity,tidal duration,flow speed,suspended sediment concentration,and wave height)in the differentiation of macrofaunal communities with different taxonomic classes over the intertidal zone.Therefore,macrofaunal assemblages,similar to hydrology and surficial sediment,have a unique zonation pattern.Small-sized deposit feeders adapt better to low energy environments,thus dominated the upper part of the intertidal flat,whilst the heavy and large-sized filter feeders and deposit feeders were dominant over the middle and lower parts.The hydrodynamic and sediment processes cause biota-niche separation,which affected the biological processes across the intertidal flat.

A review of tidal triggering of global earthquakes

Earthquake prediction remains a challenging and difficult task for scientists all over the world.The tidal triggering of earthquakes is being proven by an increasing number of investigations,most of which have shown that earthquakes are positively correlated with tides,and thus,tides provide a potential tool for earthquake prediction,especially for imminent earthquakes.In this study,publications concerning the tidal triggering of earthquakes were compiled and analyzed with regard to global earthquakes,which were classified into three main types:tectonic,volcanic,and slow earthquakes.The results reveal a high correlation between tectonic earthquakes and tides(mainly for semidiurnal and diurnal tides;14-day tides) before and after the occurrence of significant earthquakes.For volcanic earthquakes,observations of volcanoes on the seafloor and land indicate that volcanic earthquakes in near-shore volcanic areas and mid-ocean ridges have a strong correlation with tidal forces,mostly those with semidiurnal and diurnal periods.For slow earthquakes,the periodicity of the tremor duration is highly correlated with semidiurnal and diurnal tides.In conclusion,the tidal triggering of these three types of earthquakes makes a positive contribution to earthquake preparation and understanding the triggering mechanism,and thus,the prediction of these types of earthquakes should be investigated.However,there are still several inadequacies on this topic that need to be resolved to gain a definitiveanswer regarding the tidal triggering of all earthquakes.The main inadequacies are discussed in this paper from our point of view.

Morphodynamic signatures derived from daily surface elevation dynamics can explain the morphodynamic development of tidal flats

Understanding the sensitivity of tidal flats to environmental changes is challenging.Currently,most studies rely on process-based models to systematically explain the morphodynamic evolution of tidal flats.In this study,we proposed an alternative empirical approach to explore tidal flat dynamics using statistical indices based on long-term time series of daily surface elevation development.Surface elevation dynamic(SED)indices focus on the magnitude and period of surface elevation changes,while morphodynamic signature(MDS)indices relate sediment dynamics to environmental drivers.The statistical analyses were applied to an intervention site in the Netherlands to determine the effect of recently constructed groynes on the tidal flat.Using these analyses,we were able to(1)detect a reduction in the daily SED and(2)determine that the changes in the daily SED were predominantly caused by the reduction in wave impact between the groynes rather than the reduction in tidal currents.Overall,the presented results showed that the combination of novel statistical indices provides new insights into the trajectories of tidal flats,ecosystem functioning,and sensitivity to physical drivers(wind and tides).Finally,we suggested how the SED and MDS indices may help to explore the future trajectories and climate resilience of intertidal habitats.

Modeling effects of a tidal barrage on water quality indicator distribution in the Severn Estuary

In this study, emphasis has focused on assessing the potential hydro-environmental impacts of a barrage across the Severn Estuary, with a numerical model being developed and applied to the estuary to assess the impacts of proposed Severn Barrage on the hydrodynamic, sediment transport and faecal indicator organism distribu- tion within the estuary. The results show that the Severn Barrage has the potential to reduce the tidal currents in a highly dynamic estuary. This leads to the reduction of suspended sediment concentrations, which in turn affects the bacterial transport processes which is highly related to the sediment transport processes.

Contributions of annual and semiannual tidal constituents to chart datum in the China seas and adjacent waters

Global uniform chart datum(CD)surface construction is the basic upon which to realize various vertical datums transformation,and is of great importance for geospatial data expression under the same vertical datum.Generally,the CD level is computed by developing the function between tidal constituents’harmonic constants and time,i.e.,the lowest astronomical tide is taken as the lowest predicted tide level by adopting the major constituents over a 19-a period.The CD surface prescribed in China is the theoretical lowest tide(TLT)and is calculated using 13 tidal constituents,i.e.,short-period(Q_(1),O_(1),P_(1),K_(1),N_(2),M_(2),S_(2),K_(2),M_(4),MS_(4)and M_(6))and long-period(Sa and Ssa)tidal constituents.Although the accuracy in determining short-period tidal constituents has improved gradually,the long-period tide has not been studied thoroughly owing to nonstationary and temporal variations.Previous studies have intended to evaluate the effect of Sa and Ssa tides in the determination of the TLT level for the purpose of determining a more accurate CD surface for the China seas and adjacent waters.Here,the parameters of long-period tidal correction and long-period tidal correction rate were treated as the effect of both Sa and Ssa on the TLT,and the TOPEX/Poseidon and Jason series satellite altimetry data ranged from October 1992 to April 2022 were adopted to analyze the contribution of long-period tidal constituents.Results showed that the average long-period correction value is 10.10 cm(range from 8.57 cm to 14.98 cm),and that the average long-period tidal contribution rate is 14.56%(range from 9.09%to 23.97%)in the China seas and adjacent waters.Finally,data from 82 tide gauge station with at least a 1-a record of hourly observations were compared with satellite-derived result.We concluded that the long-period tidal contribution should not be neglected in TLT construction.Furthermore,to reduce tidal datum uncertainty,accurate extraction of long-period tidal constituents should receive closer attentions.

Relative importance of tidal flats and artificial habitats for two spoonbill species and related interspecific differences

Artificial/seminatural environments,such as aquacultural ponds,saltpans,and croplands,have recently been acknowledged as important habitats for coastal waterbirds.Although coastal waterbirds tend to use artificial habitats around tidal flats as roosting sites during high-tide,it remains unclear whether the importance of surrounding habitats relative to tidal flats varies among landscape types,seasons,species,or tidal conditions.The Black-faced Spoonbill(Platalea minor)and Eurasian Spoonbill(P.leucorodia)are two closely related sympatric species in East Asia with narrow and wide distribution ranges and habitat requirements,respectively.We therefore expect that both species will use surrounding artificial habitats across seasons at high tides,but Blackfaced Spoonbills will use them less frequently than Eurasian Spoonbills.Here,we address these hypotheses in the Imazu tidal flat and its surrounding environments in southern Japan.We investigated the habitat use and behavioral patterns of both species through route and behavioral surveys during the fall migration and wintering seasons in 2021.We found that both species used surrounding habitats including artificial ones more frequently than the tidal flat regardless of the tidal condition or season,but spoonbills used these habitats more frequently in winter than in autumn.We also found that Eurasian Spoonbills foraged in surrounding artificial habitats more frequently than Black-faced Spoonbills.These results not only demonstrate how coastal waterbirds exploit surrounding habitats relative to tidal flats but also suggest that the importance of surrounding habitats varies among species and seasons.Our study thus emphasizes that valuing and managing surrounding habitats in addition to tidal flats are key to conserving globally declining waterbirds.

Coastline changes and tidal current responses due to the large-scale reclamations in the Bohai Bay

China’s Bohai Bay has experienced large-scale land reclamation since 2000.These reclamation projects create a nearshore ecological imbalance and shift sediment transport by changing the tidal current.However,these tidal current changes are not comprehensively understood.In this paper,the coastline changes in Bohai Bay due to reclamation are investigated and the responses of the tidal current are calculated through numerical methods.The results show that the coastline length of the bay increases by more than 500 km from 2000 to 2015 with the largest reclamation rate of 150.9 km^(2)/a.Consequently,the current velocity changes with an uneven distribution near the reclamation due to construction masking and dike protrusion.The tidal symmetry also changes in most nearshore areas,with opposite variations in the current velocity at peak flood and ebb tide.In addition,the tide direction deflects to bypass the reclamation and is usually consistent with the coastline.Harmonic analysis of the dominant M2 tidal constituent shows that the range of the reciprocating current is widely extended.The total influence of the reclamation can reach the-8-m isobaths in Bohai Bay.Changes in the tidal current are the main causes of water environment deterioration.Therefore,the arrangement and structural optimization of reclamation projects should be considered in the future.

Flume Experiment Investigation on Propagation Characteristics of Tidal Bore in A Curved Channel

Tidal bore is a special and intensive form of flow movement induced by tidal effect in estuary areas, which has complex characteristics of profile, propagation and flow velocity. Although it has been widely studied for the generation mechanism, propagation features and influencing factors, the curved channel will complicate the characteristics of tidal bore propagation, which need further investigation compared with straight channel. In this study, the flume experiments for both undular and breaking bores’ propagation in curved channel are performed to measure the freesurface elevation and flow velocity by ultrasonic sensors and ADV respectively. The propagation characteristics,including tidal bore height, cross-section surface gradient, tidal bore propagation celerity, and flow velocity are obtained for both sides of the curved channel. And three bore intensities are set for each type of tidal bores. The freesurface gradients are consistently enlarged in high-curvature section for undular and breaking bores, but have distinct behaviors in low-curvature section. The spatial distributions of tidal bore propagation celerity and flow velocity are compared between concave and convex banks. This work will provide experimental reference for engineering design of beach and seawall protection, erosion reduction and siltation promotion in estuary areas with the existence of tidal bores.

Tidal triggering of seismicity in the region of Palu, Central Sulawesi, Indonesia

This paper investigates the correlation between tidal stress and earthquakes for periods ranging from hours to months in the limited zone of the Palu region(Central Sulawesi,Indonesia).Through Schuster and binomial tests,we examined the relation between the seismicity(time density of seismic events)and tidal potential arising from the Moon and Sun,using all tidal components simultaneously and focusing on the estimation of specific terms.The results show significant correlations between the seismicity and tidal potential for S2(0.5 d)and O1(1.075 d)tidal components in the case of solely isolated earthquake events,particularly for shallow earthquakes.Meanwhile,there is a strong relationship between aftershocks and tidal components larger than the Mf period(13.661 d).Finally,the analysis of the temporal variation of the earthquake-tide relation reveals an optimal correlation for about six years before the 2018 great Palu earthquake.The correlation becomes insignificant afterwards.

Dramatical hydro-sedimentary changes induced by bamboo fences over mangrove tidal flat of the largest delta in Beibu Gulf, southwestern China

Mangrove forest is one of the most important ecological and environmental resources by effectively promoting tidal flat deposition and preventing the coastal region from typhoon.However,there have been mass loss of mangrove forests due to anthropogenic activities.It is an urgent need to explore an effective way for mangrove restoration.Here,three rows of bamboo fences with hydro-sedimentary observation set over Aegiceras corniculatum mangrove tidal flat of the Nanliu Delta,the largest delta of Beibu Gulf,China,were conducted to analyze the hydro-sedimentary variations induced by bamboo fences.Results identified that the mean horizontal velocity Um per burst(20 min)decreased by as much as 71%and 40%in comparison with those without bamboo fences in March and November,respectively,when the tidal current entering the bamboo area during flood.The maximum of mean horizontal flow velocity Um-max at bamboo area was 50%–75%of that without bamboo fences during ebb tide.The suspended sediment concentration of bamboo area suggested a maximum reduction of 57%relative to bare flat during flood,and was 80%lower than bare flat at ebb peak.Moreover,the turbulent kinetic dissipationεat flood tide was significantly higher than that at ebb tide,while the bamboo fences greatly increased the turbulent kinetic dissipationεby 2 to 5 times relative to bare flat,resulting in an increase of the bed elevation by inhibiting the sediment incipient motion and intercepting suspended sediment.The siltation rate at the bamboo area was 140%and 29.3%higher than that at the bare flat and the region covered with A.corniculatum,respectively.These results highlight that bamboo fences can effectively attenuate tidal current and thus promote siltation over mangrove flat,which contribute great benefit to mangrove survival.

Vertical structure of tidal currents in the Xuliujing Section of Changjiang River Estuary

Three long-term fixed acoustic Doppler current profilers were first used for investigating the vertical structure of tidal currents in Xuliujing Section of Changjiang River Estuary.Moreover,three different periods(spring,summer and fall)were also considered for investigating seasonal variations.The semi-diurnal tides were the most energetic,with along-channel speed of up to 80 cm/s for M_(2)constituent,which dominates at all stations with percent energy up to 65%–75%during seasons.The shape of tidal ellipses of the most energetic semi-diurnal constituent M_(2)showed obvious polarization of the flow paralleling to the riverbank,with the minor semi-axis being generally less than 20%of the major one.The maximum velocity of mean current is appeared in top layers at all the three stations,and the velocity decreased with the depth.The seasonal variations of direction are also observed,which is probably caused by complex local topography since the erosion and deposition in riverbed.Observed vertical variation of four parameters of M_(2)ellipses,agreed well with the optimally fit frictional solutions in top and middle layers.However,there was an obvious difference between frictional model and observed data in the lower water column.Discrepancies are probably on account of stratification,which strengthens in summer and fall due to the freshening influence of the Changjiang River Estuary outflow.