Finite Volume Coastal Ocean Model Research Articles

Numerical Study on the Formation Mechanism of Plume Bulge in the Pearl River Estuary under the Influence of River Discharge

Previous studies have investigated the characteristics and influencing factors of plume bulge in the Pearl River Estuary (PRE) using observations and numerical simulations. However, the understanding of how river discharge affects plume bulge is not consistent, and the response mechanism of plume bulge to changes in river discharge has not been revealed in detail. In this study, a three-dimensional hydrodynamic Finite-Volume Coastal Ocean Model (FVCOM) is constructed, and five experiments were set to characterize the horizontal and vertical distribution of the plume bulge outside the PRE under different river discharge conditions during spring tide. The physical mechanisms of plume bulge generation and its response mechanisms to river discharge were discussed through standardized analysis and momentum diagnostic analysis. The results indicate that the plume bulge is sensitive to changes in river discharge. When the river discharge is relatively low (e.g., less than 11,720 m3/s observed in the dry season), the bulge cannot be formed. Conversely, when the river discharge is relatively high (e.g., exceeding 23,440 m3/s observed in flood season), the bulge is more significant. The plume bulge is formed by the anticyclonic flow resulting from the action of the Coriolis force on the strongly mixed river plume. The bulge remains stable under the combined effects of barotropic force, baroclinic gradient force, and Coriolis force. The reduction of river discharge weakens the mixing of freshwater and seawater, resulting in the reduction of both the volume and momentum of the river plume, and the balance between advective diffusion and Coriolis forces are altered, resulting in the plume, which is originally flushed out from the Lantau Channel, not being able to maintain the anticyclonic structure and instead floating out along the coast of the western side of the PRE, with the disappearance of the plume bulge. Due to the significant influence of plume bulges on the physical and biogeochemical interactions between estuaries and terrestrial environments, studying the physical mechanisms behind the formation of plume bulges is crucial.

Flood risk investigation of pedestrians and vehicles in a mountainous city using a coupled coastal ocean and stormwater management model

AbstractTo examine the attributes, underlying mechanisms, and impacts of rainfall patterns on the vulnerability of pedestrians and vehicles to flood‐induced instability within mountainous urban areas, we introduced an integrated urban flood model that combined the Storm Water Management Model (SWMM) and Finite Volume Coastal Ocean Model (FVCOM). We implemented this model in the Yuelai New Town of Chongqing, China. Our findings indicated that in the case of early peak rainfalls, there was a rapid surge in flood volume during the initial stages of rainfall , while this increase was more gradual when the peak rainfall was delayed. Furthermore, for events with the same return period, flood peaks resulting from later peak rainfalls covered a larger area compared with those from earlier peak rainfalls; however, this effect diminished with increasing return periods. As the return period was extended, the exposed risk area for pedestrians and vehicles expanded. Analysis of instability indices revealed that pedestrians exhibit a lower index compared with vehicles, adults fare better than children, and SUVs outperform sedans. The efficacy of our proposed model framework was demonstrated through its successful application in assessing urban flood risk and evaluating the instability index for pedestrians and vehicles within a mountainous urban setting.

Modelling of fluid mud flow based on a three-dimensional hydrodynamic model : incorporating a 3D rheological model

Modeling fluid mud in estuaries and coastal areas is a complicated task due to its non-Newtonian characteristics. A continuous modeling approach was adopted to investigate the laminar flow of fluid mud, with a three-dimensional (3D) form of the Herschel–Bulkley rheological model introduced into the finite volume coastal ocean model (FVCOM) to calculate the apparent viscosity of fluid mud. The model was validated against two flume experiments for the laminar flow of fluid mud. The results showed that the developed model was capable of accurately reflecting the continuous distribution of velocity and density from the near-bottom to the upper water column. Based on the validated model, the difference between the 3D rheological model and a 1DV rheological model on the simulation results was assessed. The study found the results of the 1DV model and the 3D model show obvious differences. This illustrates the significant effect of apparent viscosity in horizontal direction taken into account by the 3D rheological model.

Studi Laju Sedimentasi di Muara Sungai Perancak Menggunakan Pemodelan Numerik


 
 
 
 Perancak is an estuary area with land use in mangroves and ponds. Land changes that have occurred at the Perancak River estuary and tidal flooding in recent years have increased the potential for sedimentation problems that can cause silting of the riverbed. This study aims to determine the sedimentation rate and identify the potential for siltation in the estuary of the Perancak River. Sediment modeling uses the Finite Volume Coastal Ocean Model (FVCOM) by entering primary and secondary data such as bathymetry, tides, temperature, salinity, river discharge, sediment type, and Total Suspended Solid (TSS) concentration. Modeling for 33 days (January - February 2022). The results showed that the sedimentation rate in the Perancak River estuary ranged from 0.25 to 18.8 kg/m2/day, with an average of 3.83 kg/m2/day. Sedimentation rates are high in the estuary areas and riverbanks bordering the mainland. The potential for siltation shows that it occurs at river mouths with a silting value of about 0.01 m/year to more than 0.05 m/year.
 
 
 

Seasonal dynamics of coastal pollution migration in open waters with intensive marine ranching

Mariculture activities have been recognized as one of the major sources of contamination for marine pollutants, such as the excessive discharging of nitrogen and phosphate. The fully understanding of the pollutants emission and transportation is crucial for coastal environment management. However, the influence of such highly dynamic coastal process on the pollutant migration remain unclear, such as the effects of coastal seasonal hydrodynamics on the dissolved pollutant transportation, especially under intensive marine ranching activities in open waters. This study investigated the seasonal transport mechanisms of pollutants released from three typical mariculture methods (floating raft, cage and bottom pond) in the Wangjia Island (WJ), Yellow Sea, China. We have conducted three field surveys to monitor the coastal dynamics and measure the distribution of dissolved pollutants in the ranching area. Results from these field surveys show that the WJ and adjacent area experienced significant degradation in terms of water quality with the development of regional marine ranching. The average of calculated index for eutrophication Ei increases from 0.12 in the non-farming area to 0.78 in the farming area. In order to delineate the impacts area of pollutant transport associated with these highly dynamics of water exchange, a Eulerian passive tracer-tracking module is applied to simulate the pollutant transport processes based on a field scale three-dimensional Finite Volume Coastal Ocean Model (FVCOM). Then after, the impacts of barotropic and baroclinic coastal dynamics on the migration of dissolved pollutants were evaluated. The transport of pollutants was greatly influenced by the different farming modes. The travel distance of pollutants released from the bottom pond farming mode was limited, whereas pollutants from the surface-farming methods were transported over a longer distance. In this study, there are three folders of finding: 1) The migration direction varies with seasons, with a landward direction in winter and an offshore direction in summer; 2) In winter, strong wind (wind speed over 10 m/s) is the dominant factor for water exchange, which is conducive to the dispersion of pollutants in the study area. However, in summer, the thermal stratification controls pollutant migration; 3) The results of breakthrough time illustrate that the pollutants travelled slower during summer, especially for pollutants discharged from the bottom pond farming method. In summary, this study demonstrates that even in open waters with stronger water exchange capacity, the pollutants from intensive marine ranching can still increase the risk of eutrophication. The finding of this study has important implications for the management and regulation of offshore aquaculture activities, particularly for mitigating pollutants from marine ranching.

Pemodelan Kekuatan Gelombang di Pesisir Barat Kecamatan Kuta, Bali


 
 
 
 The coastal area is an important area with many different functions for both human and marine organisms. Still, coastal regions are vulnerable to changes caused by various things, including waves. Waves can cause shoreline changes and erode coastal regions. Kuta District is one of the coastal areas on the island of Bali that are threatened with constant sediment erosion every year. One way to increase understanding of the wave and its effect on the coastal areas is through numerical modeling. This study aimed to determine the pattern of wave and wave strength distribution on the west coast of the Kuta district. The Finite Volume Coastal Ocean Model and SWAVE (FVCOM-SWAVE) coupling model that was used in this study utilized the Finite Volume method of computation with the unstructured triangular grid. The results showed that in West Season (December-January-February), the range of mean significant wave heights on the west coast of Kuta District is 0.05 - 0.2 m, and the wave power ranged from 1 to 30 W/m with the most considerable value of significant wave heights and wave power were encountered in January. Water areas near land have greater wave heights and wave power than areas far from land, except around Ngurah Rai International Airport. The movement of waves primarily comes from the southwest, the Bali Strait, to the east and is divided by the runway into following the northern and southern parts of the coast. Thus, the most significant wave height ??and wave power values are found in the waters near Kuta beach and Legian beach.
 
 
 

Numerical Investigation on the Influence of Breakwater and the Sediment Transport in Shantou Offshore Area

The coastline of Shantou is tortuous, while the hydrodynamic environment is complicated. In this paper, the hydrodynamic model is established by the FVCOM (Finite Volume Coastal Ocean Model); the open boundary conditions such as water level, river, and wind field are the input; and the model is verified by tidal harmonic function. According to the previous research, the typhoon wind field with a 10-year return period is selected for storm surge simulation. When there is a bank, the accumulated water on the land cannot enter the ocean due to the block of the bank but accumulates on the inner side of the bank, resulting in higher accumulated water, but less than 0.5 m. In the aspect of sediment deposition, a sediment transport model is established to analyze the sediment deposition in Shantou Port and its surrounding waters. Some reasonable suggestions are put forward for the sediment deposition in Shantou. According to the simulation results, the following conclusions can be drawn: (1) In the case of typhoon storm surge in the return period of 10 years, the bank can effectively protect the inland. Still, accumulated water will collect near the bank. (2) The offshore water level will rise by 0.4 m after adding a bank. (3) The sediment in Shantou Bay mainly comes from the ocean sediment caused by tides, and the largest sedimentation occurs in the main channel.

Numerical Study on Tide and Tidal Current along Bali Strait, Indonesia using Finite Volume Coastal Ocean Model (FVCOM)

A numerical study was carried out in Bali Strait, Indonesia. Finite Volume Coastal Ocean Model (FVCOM) was used to simulate the seawater circulation in Bali Strait. The water circulations were forced by the four major tidal components (<i>S</i><sub>2</sub>, <i>M</i><sub>2</sub>, <i>K</i><sub>1</sub>, and <i>O</i><sub>1</sub>). Comparisons of the seawater surface elevation obtained from both modeling and observations show a good result. The tide in Bali Strait is a mixed tide type with two different tidal ranges in one day. The seawater circulation moves from the Indian Ocean to the Bali Sea through narrow strait during the flood tide and then rush back during the ebb tide. In the spring tide, an eddy is also observed on the top of the narrow strait. The simulations show that the flows by tides along the sudden change of the cross-sectional width can be modeled by the finite volume method based model.

Generation of macro-vortices in estuarine compound channels

We report the results of a numerical investigation of the flow structure and mechanism of macro-vortex generation in estuarine compound channels. The Finite-Volume Coastal Ocean Model (FVCOM) was implemented to simulate tidal currents in compound channels, e.g., the Lantau Channel, which lies in the middle of the Pearl River Estuary (PRE). Results showed that the velocity magnitude in channels was significantly larger than that of floodplains during the ebb and flood phases, resulting in a high-velocity gradient at the depth discontinuity. Vorticity and Q-criterion were used to analyze the macro-vortex distribution inside the PRE. Massive macro-vortices were generated along the compound channels where high vorticity was also detected. The across-estuary sections with single and multiple channels were selected as representatives to analyze velocity distribution during ebb and flood tides. To characterize the channel flow, the ratio of the main channel depth of the Lantau Channel to floodplain depth (Rh) was calculated using the topography information and surface elevation of sections. It was found that there existed a channel segment where the flow periodically changed between shallow flow (Rh > 3) and intermediate flow (2< Rh< 3). This dynamic change in Rh greatly influenced the generation of macro-vortices. Transverse dispersive stresses were calculated to evaluate the longitudinal momentum transfer in the lateral direction. We found that the dispersive stresses could play an important role in the redistribution of momentum in addition to barotropic and baroclinic transport. This paper revealed the mechanism of the dynamic generation of macro-vortices in the estuarine compound channel, serving as a valuable example in understanding natural compound channel flows.

Distribution and off–shelf transport of dissolved manganese in the East China Sea

To gain a better understanding of the geochemical behavior of dissolved manganese (Mn) in the marginal seas with respect to distribution and exchange fluxes, more than 200 water samples were collected in the East China Sea (ECS) in May, August, and October of 2013. The concentration of dissolved Mn in the ECS ranged from 1.1 to 81.5 nM, with a gradual decrease with distance from the shore. Seasonal distribution of dissolved Mn varies significantly in the Changjiang estuary, mainly regulated by freshwater input from the Changjiang (Yangtze River) and redox variations. The ECS continental shelf is an important source of Mn for adjacent waters, and the export of Mn–rich coastal waters had an important effect on its re-distribution and internal cycling. The dynamic variation fluxes of water and dissolved Mn across the 100– and 200–m isobaths in the ECS were calculated with an aid of the Finite−Volume Coastal Ocean Model (FVCOM). The ECS continental shelf exported (5.69 ± 1.14) × 108 mol/yr of Mn into the East/Japan Sea from the Tsushima Strait. The Kuroshio surface waters receive an additional (1.02 ± 3.12) × 108 mol/yr of Mn from the ECS continental shelf through a cross–shelf exchange process, which could potentially affect dissolved Mn in the Northwest Pacific. Our data suggest that off-shelf transport from the ECS continental shelf is essential for understanding the biogeochemical cycles of trace metals in the Northwest Pacific Ocean and the East/Japan Sea.

Morphological changes in a macro-tidal estuary during extreme flooding events

River discharge is a controlling factor in estuarine morphological changes; estuarine topography can be significantly altered even by only one flooding event. However, the mechanism of morphological changes in mountain-stream macro-tidal estuaries during wet seasons is not fully understood. Taking the Yalu River Estuary (YRE), China, as an example, this study aims to explore the effects of extreme flooding events on estuarine morphology. An improved Finite Volume Coastal Ocean Model (FVCOM) was applied in the YRE to reproduce the distribution of bed sediment erosion and deposition during dry years, normal years, and wet years. Sensitivity tests were conducted to assess the responses of the estuarine system to river discharge. The influence of the Yalu River on the magnitude of estuarine bed change was examined. With an increase in river discharge, the bed thickness in the main estuarine channel first increased and then decreased after reaching a threshold of 0.4 × 104m3/s. Simultaneously, density stratification became stronger with the increase in runoff. Subsequently, vertical mixing of water was weakened after a certain threshold, which in turn, enhanced the density stratification and changed the location of the Estuarine Turbidity Maxima (ETM). In addition, river effects contributed to nearly half of the bed erosion under 0.6 × 104m3/s (flooding with 50-year return period). The ETM extended and moved approximately 8 km seaward during flooding events. The West River channel experienced strong siltation, which was more significant during flood events. The results of this study demonstrate that estuarine circulation plays a key role in morphology change. The magnitude of bed thickness erosion can reach 22% of the total initial thickness during one flooding event. This rapid change is a threat to the stability of port infrastructures, and actions should be taken to maintain the safety of coastal construction.

Estimation of sea surface pCO2 and air–sea CO2 flux in the East China Sea using in-situ and satellite data over the period 2000–2016

The partial pressure of carbon dioxide (pCO2) is an important variable to characterize the state of the seawater carbonate system. It is required to calculate the air-sea CO2 flux (FCO2) and for understanding ocean acidification. Surface ocean pCO2 is influenced by thermodynamic process, physical mixing, biological activity and air-sea gas exchange. Knowledge of the surface pCO2 in the East China Sea (ECS) is limited due to a lack of observations and well-informed models. This study employed in situ hydrographic (sea surface temperature and salinity) and carbonate system observations combined with satellite observations of chlorophyll a to develop a regional multiple non-linear regression (MNR) model to estimate pCO2 for three different physical-biogeochemical domains of the ECS. Comparison of the pCO2 from in situ observations with the MNR model had a root mean square error (RMSE) of 45.19 μatm and coefficient of determination (R2) of 0.87 in the transitional domain, an RMSE of 11.59 μatm and R2 of 0.92 in the shelf-dominated domain and an RMSE of 3.73 μatm and R2 of 0.97 in the open water domain. The reliability of the MNR model was also validated using an independent dataset with a good accuracy (RMSE of 9.15 μatm for domain II and RMSE of 7.71 μatm for domain III). The MNR model was applied to estimate the surface pCO2 and FCO2 for ten cruises on the period of 2013–2018, and also used to predict monthly surface pCO2 by using Changjiang Biology Finite-Volume Coastal Ocean Model (FVCOM) outputs for the period of 2000–2016 on the ECS inner shelf, and analyzed the seasonal and interannual variability of surface pCO2 and FCO2. The seasonal dynamics of sea surface pCO2 were mainly attributed to temperature changes, biological activities and water mixing process over the seasons. The time series of surface pCO2 and FCO2 on the ECS inner shelf showed an increasing trend of 3.32 ± 0.79 μatm yr−1 and 0.018 ± 0.0125 mol CO2 m−2 yr−2, and the region was a CO2 sink with an CO2 uptake of 0.12 ± 0.48 Tg C yr−1.

Modelling study on the sediment dynamics and the formation of the flood-tide delta near Cullendulla Beach in the Batemans Bay, Australia

The first 3-D current-wave-sediment coupled model of the semi-exposed estuary Batemans Bay, New South Wales, Australia, was developed in our study based on the Finite Volume Coastal Ocean Model (FVCOM). Our study explored the hydrodynamics, sediment dynamics and morphology change inside the Batemans Bay under large wave events. The modeled monthly-averaged residual flow, sediment flux and suspended sediment concentration with a combined tidal and wave forcing in the inner bay were significantly different to those only with tidal forcing, this is because the storm wave events can generate wave-induced currents and large bottom stresses, influencing the sediment transport. In addition, the morphology change of the flood-tide delta (FTD) inside the Batemans Bay under wave effects was also investigated in this study. According to previous studies, the FTD is a sediment deposit located on the landward side of tidal inlets, formed by the incoming tidal currents and ocean waves, which is an important morphology coastal feature influencing the sediment exchange with adjacent beach systems. Yet, the dynamic processes of FTDs have not been fully understood and explored quantitatively in sheltered estuaries. Based on our model results, the FTD near Cullendulla Beach is controlled by wave effects and was in an equilibrium status: when the FTD was eroded deeper to a critical value (about 2 m) by waves, sedimentation occurred. The rocky headland adjacent to the FTD contributed to the formation of the FTD due to sheltering effects, and the FTD actually developed at the ‘wave shadow areas’ behind the headland in Batemans Bay, which were dominantly controlled by sheltering effects. Despite being termed a ‘Flood-Tide Delta’, ‘Tide’ here is misleading, and a new name of ‘Wave Shadow Shoal’ should be given to describe such wave-dominated coastal features. In conclusion, this study demonstrated that waves played the dominant role in the hydrodynamic processes, sediment transport and morphology change in Batemans Bay.

Predictive biophysical models of bivalve larvae dispersal in Scotland

In Scotland, bivalves are widely distributed. However, their larvae dispersion is still largely unknown and difficult to assess in situ. And, while Mytilus spp. dominate shellfish production, it is mostly dependent on natural spat recruitment from wild populations. Understanding the larval distribution pattern would safeguard natural resources while also ensuring sustainable farming practises. The feasibility of a model that simulates biophysical interactions between larval behaviour and ocean motions was investigated. We employed an unstructured tri-dimensional hydrodynamic model (finite volume coastal ocean model) to drive a particle tracking model, where prediction of larval movement and dispersal at defined locations might aid in population monitoring and spat recruitment. Our findings reveal a strong link between larval distribution and meteorological factors such as wind forces and currents velocity. The model, also, depicts a fast and considerable larval movement, resulting in a substantial mix of plankton and bivalve larvae, forming a large connection between the southern and northern regions of Scotland’s West coast. This enables us to forecast the breeding grounds of any area of interest, potentially charting connectivity between cultivated and wild populations. These results have significant implications for the dynamics of ecologically and economically important species, such as population growth and loss, harvesting and agricultural management in the context of climate change, and sustainable shellfish fisheries management. Furthermore, the observations on Scottish water flow suggest that tracking particles with similar behaviour to bivalve larvae, such as other pelagic larval stages of keystone species and potential pathogens such as sea lice, may have policy and farming implications, as well as disease control amid global warming issues.

Thermohaline Dynamics in the Northern Continental Slope of the South China Sea: A Case Study in the Qiongdongnan Slope

Understanding the marine hydro-thermohaline environment is essential for terrestrial meteorology and the coastal ecosystem. Here, we provide insight into the hydro-thermohaline environment at the Qiongdongnan continental slope of the northern South China Sea and the mechanism controlling it, with focus on its short-term characteristics. We employ a well-validated three-dimensional unstructured-grid-based Finite Volume Coastal Ocean Model (FVCOM) to analyze the spatial-temporal behavior of its hydro-thermohaline structures and to quantify the transport fluxes over a full tidal period. The analysis reveals a two-layer flow structure with directionally oppositely moving layers in the along-isobaths direction. Furthermore, transport patterns undergo periodic changes. During the spring tide, the downslope (along-isobaths) transport of water/heat/salt is approximately 119%/70%/120% higher (62%/62%/62% lower) than during the neap tide. From analyzing the different terms in the thermohaline balance equation, we find that the main dynamic factors controlling heat transport over a tidal period are the gravitational convention and the mean flow, while the salt transport is only dominated by the mean flow. The data of the short-term thermohaline evolution of the QDNS provided in this study may be of use for future studies of the northern SCS, including its marine ecology and marine fisheries.

Analisis Spasial dan Temporal Suhu Menggunakan Pemodelan Numerik di Perairan Amed, Karangasem, Bali


 
 
 
 Amed is a marine tourism area in the east of the island of Bali, which has high biodiversity. The high biodiversity is caused by the influence of the Indonesian Throughflow (ITF), which crosses the Lombok Strait and brings cold and rich nutrient that plays a vital role in the marine and fisheries sector. Currents have an essential role in regulating the oceanographic process of waters, so they can be used as parameters in understanding the vertical characteristics of waters, one of which is temperature. Temperature is a critical factor for physiological processes and the distribution of marine organisms. The purpose of this study was to analyze the temperature spatially and temporally in the waters of Amed, Karangasem, and Bali using numerical modeling. Logger recording data was carried out in February - September 2019 at three different locations and depths, namely the depths 30, 60, and 65 m. Finite Volume Coastal Ocean Model (FVCOM) is a numerical modeling method used in this research. Based on the spatial analysis of current movement patterns and the distribution of sea surface temperature (SST) that occurred in January – December 2019 following the seasonal variant of the wind that occurred in Indonesia. The results of the temperature gradient analysis showed that the data at a depth of 30 m did not reveal the presence of a thermocline layer. In contrast, at a depth of 60 and 65, the thermocline layer was found at a depth of 33 and 34 m with a temperature gradient of 0.1 oC/m.
 
 
 

Numerical Study of Hydrodynamics in the waters of Balikpapan Bay using Finite Volume Method

Suci Erniya Rahman. 2021. Numerical Study Hydrodynamic in the waters of Balikpapan Bay using Finite Volume Method. Supervised by Dr. Sc. Mustaid Yusuf, M.Si. and Yuki Novia Nasution, S.Si., M.Sc. Faculty of Mathematics and Natural Sciences, Mulawarman University. The hydrodynamic model FVCOM (Finite Volume Coastal Ocean Model) using the approach method finite volume has been applied to determine the distribution of tidal current patterns in the Balikpapan Bay area. The simulation was carried out for 30 days using river discharge and tides as generating forces. The simulation results has verified by using the Root Mean Square Error (RMSE) method on observation data in the Balikpapan Bay area. The results of the simulation and observation verification have a good agreement, which is 0.09917 meters. The smaller (closer to zero) RMSE value, is the better results of the observation and simulation match. The results of study showed that the pattern and average current velocity in Balikpapan Bay for 15 days (11-26 October 2012) was dominant out of the bay.

Simulated flood forces on a building due to the storm surge by Typhoon Haiyan

ABSTRACT Haiyan in 2013 was one of the most powerful typhoons to have affected the Philippines, devastating in its path a wide portion of Leyte, and causing extensive damage to structures in Tacloban City. To understand the likely impacts that would be exerted by a storm surge on a structure deemed important, the authors used a coupled model that hindcasted the flooding that took place during Haiyan. This coupled model included the use of the Weather Research and Forecasting (WRF) Model (with Bogussing scheme) to simulate the atmospheric conditions during the passage of Haiyan, the Finite Volume Coastal Ocean Model (FVCOM) to simulate the storm surge and obtain the boundary conditions for the wind and flood (hydrostatic, hydrodynamic, and breaking wave), and the Structural Analysis and Designing Program (STAAD.Pro) to calculate the corresponding axial, shear, and bending moment envelopes based on the storm surge simulation. A 4-floor public school building in Tacloban was modeled and the effects that the storm surge would have on a corner column were analyzed. Based on the results, the axial, shear, and moment at the corner column significantly increased when considering flood loads, indicating the importance of including such loads in the design of essential structures.

Numerical Investigation of the Sediment Hyperpycnal Flow in the Yellow River Estuary

Sediment hyperpycnal flow is one of the most important processes for mass transport, which is essential to coastal morphodynamics. Herein, we studied the generation and maintenance of the sediment hyperpycnal flow in the Yellow River Estuary (YRE) using a three-dimensional finite volume coastal ocean model (FVCOM). The model considered the effect of sediment-laden water on density stratification, and was validated by field hydrodynamic and sediment data. Numerical results revealed that the hyperpycnal flow shows periodic characteristics with tidal cycles where the flow is weakened during flood tides and enhanced during ebb tides. A high suspended sediment concentration (SSC) of about 30–40 kg/m3 constitutes an important factor in the formation of hyperpycnal flows. High river discharge with high SSC is essential for maintaining the hyperpycnal flow in the YRE. The Simpson potential energy theory was applied to study the processes of estuarine circulation, tidal straining, and tidal stirring in the YRE. The tidal straining is the main control factor of the periodic stratification-mixing process of hyperpycnal flows in the YRE. Along the axis of the river mouth, the momentum balance is mainly dominated by the pressure gradient and advection.

The coastal macro-vortices dynamics in Hong Kong waters and its impact on water quality

Large-scale macro-vortices could be formed in the lee or around natural obstacles such as islands and headlands during the interaction between geographical features and coastal circulations induced by tides and winds. Tidal and wind-induced vortices play a fundamental role in transport processes of sediments and nutrients and the effects are then reflected on water quality of estuaries and coastal areas. In the present study, the coastal hydrodynamics of the Pearl River Estuary and Hong Kong waters was analyzed in detail using a high-resolution model based on the Finite-Volume Coastal Ocean Model (FVCOM), forced by tides and seasonal winds. The results showed that the local dynamics was strongly affected by the continuous shedding of macro-vortices. A classification of these coherent structures was suggested based on their typical evolution to distinguish between tidal vortices and wake vortices using four non-dimensional parameters. The spatial distribution, the seasonality and the probability density functions of their geometrical characteristics were presented and discussed in detail. The results suggested that tidal currents played a dominant role in most of the Pearl River Estuary and the Hong Kong waters, generating for the entire year a high and constant number of macro-vortices that occupied most of the north channels of Hong Kong. Finally, we linked the vortices distribution and their typical features with several important water quality parameters, suggesting possible explanations of the observed trends.