Sediment Transport Dynamics in Ports, Estuaries and Other Coastal Environments

Given ever expanding global trade, the international economy is linked to the well-being of major coastal infrastructures such as waterways and ports. Coastal areas comprise about 69% of the major cities of the world; therefore the understanding of how coastal aquatic environments are evolving due to sediment transport is important. This manuscript discusses topics from both modelling and observation of sediment transport, erosion and siltation in estuarine environments, coastal zones, ports, and harbour areas. It emphasises particular cases of water and sediment dynamics in the high energy system of the Po River Estuary (Italy), the Adriatic Sea, the Mokpo Coastal Zone (South Korea), the Yangtze Estuary and the Shanghai Port, the Yellow Sea (near China), and Darwin Harbour (Northern Australia). These systems are under the influence of strong sediment resuspension/deposition and transport that are driven by different mechanisms such as surface waves, tides, winds, and density driven currents. The development of cities around ports is often associated with the expansion of port activities such as oil, coal, and gas exportation. Such development results in multiple environmental pressures, such as dredging to facilitate the navigation of larger ships, land reclamation, and changes in the sediment and nutrient run-off to catchment areas caused by human activities [1]. The increase in mud concentrations in coastal waters is a worldwide ecological issue. In addition, marine sediment may carry nutrients and pollutants from land sources. An understanding of sediment transport leads to a better comprehension of pollution control, and thus helps to preserve the marine ecosystem and further establish an integrated coastal management system [e.g., 2-3]. [4] observed that many historical sandy coasts have been replaced by muddy coasts, and is considered permanent degradation. Additionally, [5] reported that recreational and maritime activities may be adversely impacted by processes of sediment resuspension and deposition. It was shown by [6] that increased sediment concentration in the Adriatic Sea has affected the growth of phytoplankton at the subsurface, because sunlight penetration is considerably reduced.Full Tex

Numerical simulation of the hydrodynamic in the Curimataú estuary, RN Brazil

The Curimataú River estuary is a shallow partially mixed (type 2) tropical estuary, located in the Rio Grande do Norte (RN) state, northeast Brazilian coast (lat. 06o18’S); the main system is composed by three rivers: Curimataú, Cunhaú and Guaratuba. The numerical model Delft3D-Flow was used to study hydrodynamic features of the estuary. The model predictions were evaluated using the Skill parameter based in the comparison of the theoretical solutions with observations of hourly values of tidal heights, currents and salinity at an anchor station located at the cell (M=279; N=323). The applied computational grid is curvilinear with around 6,000 horizontal wet points, including the inner shelf. Open boundary conditions was obtained from the analysis of 2.7 years of hourly tidal heights, recorded at Natal harbor, and the inner boundaries conditions were controlled by freshwater input into the three main rivers. Initial conditions of hydrographic properties were uniform in the previous simulations and, only the temperature was set to a constant value in whole simulation. The steady-state of the fields of velocity and thermohaline properties was reached after almost four weeks of simulation of the baroclinic mode. The best fit between the model and the observations was for the semidiurnal spring tide oscillation with a Skill=0.98; for the velocities and salinities simulations during this tidal condition the best mean Skills values were 0.82 and 0.94, respectively

Connectivity and systemic resilience of the Great Barrier Reef

Australia’s iconic Great Barrier Reef (GBR) continues to suffer from repeated impacts of cyclones, coral bleaching, and outbreaks of the coral-eating crown-of-thorns starfish (COTS), losing much of its coral cover in the process. This raises the question of the ecosystem’s systemic resilience and its ability to rebound after large-scale population loss. Here, we reveal that around 100 reefs of the GBR, or around 3%, have the ideal properties to facilitate recovery of disturbed areas, thereby imparting a level of systemic resilience and aiding its continued recovery. These reefs (1) are highly connected by ocean currents to the wider reef network, (2) have a relatively low risk of exposure to disturbances so that they are likely to provide replenishment when other reefs are depleted, and (3) have an ability to promote recovery of desirable species but are unlikely to either experience or spread COTS outbreaks. The great replenishment potential of these ‘robust source reefs’, which may supply 47% of the ecosystem in a single dispersal event, emerges from the interaction between oceanographic conditions and geographic location, a process that is likely to be repeated in other reef systems. Such natural resilience of reef systems will become increasingly important as the frequency of disturbances accelerates under climate change

Robustness and uncertainties in global multivariate wind-wave climate projections

Understanding climate-driven impacts on the multivariate global wind-wave climate is paramount to effective offshore/coastal climate adaptation planning. However, the use of single-method ensembles and variations arising from different methodologies has resulted in unquantified uncertainty amongst existing global wave climate projections. Here, assessing the first coherent, community-driven, multi-method ensemble of global wave climate projections, we demonstrate widespread ocean regions with robust changes in annual mean significant wave height and mean wave period of 5–15% and shifts in mean wave direction of 5–15°, under a high-emission scenario. Approximately 50% of the world’s coastline is at risk from wave climate change, with ~40% revealing robust changes in at least two variables. Furthermore, we find that uncertainty in current projections is dominated by climate model-driven uncertainty, and that single-method modelling studies are unable to capture up to ~50% of the total associated uncertainty

The estuarine system of the Caravelas and Peruíbe rivers (Bahia): Observations, simulations, residence time, and advective and diffusive processess

O modelo numérico Delft3D-Flow foi utilizado nos estudos da distribuição e variabilidade de propriedades termohalinas, e da circulação tridimensional do sistema estuarino dos rios Caravelas e Peruípe-SERCP. Os resultados do modelo foram validados quantitativamente usando dados experimentais de marés de quadratura e de sizígia de correntes e salinidades em quatro estações fixas (duas em cada um dos estuários de Caravelas e Nova Viçosa). No processamento foram aplicadas inicialmente condições iniciais homogêneas da salinidade, densidade e dos coeficientes cinemáticos de viscosidade e difusividade vertical, e após quatro semanas de simulação foram extraídos resultados de diferentes condições. Esses resultados foram utilizados como condições iniciais mais realistas, tendo o campo espacial variado das propriedades termohalinas, e dos parâmetros físicos. Essas novas condições iniciais permitiram pular o tempo transiente otimizando assim as simulações subsequentes. A validação das simulações foi feita com base nas medições da campanha de verão, por causa do atraso do período chuvoso a vazão do rio Peruípe foi bem representativa para condições de inverno e, portanto, seria redundante usar as forçantes dos rios com valores tão próximos na validação, além da necessidade da demanda de um tempo muito maior nas analise comparativas dos resultados. Durante o verão (janeiro de 2008), os dados de vazão do rio Peruípe obtidos na Agência Nacional de Águas (ANA) levaram a estimativa da descarga fluvial de ~ 20 m3.s-1, com a extrapolação de ~ 4 m3.s-1 para vazão conjunta dos dois principais afluentes do canal estuarino do rio Caravelas (rios Cúpido e Jaburuna). As oscilações da maré foram simuladas satisfatoriamente para as quatro estações de controle utilizadas na validação, com valores médios do parâmetro Skill superiores a 0,97. As amplitudes da maré calculadas numericamente foram de aproximadamente 1,3 m e 2,5 m na quadratura e sizígia, respectivamente. Os resultados numéricos das simulações das velocidades foram melhores em condições de sizígia com valores médios do parâmetro Skill entre 0,77 e 0,93, enquanto que na quadratura esse parâmetro variou entre 0,38 a 0,65. Para a estrutura de salinidade durante as condições de maré de sizígia, melhores resultados no SERCP do skill e, portanto abrangendo as quatro estações de controle, foram confirmados pelos parâmetros Skill médios superiores a 0,83. Na maré de quadratura os correspondentes valores médios também foram relativamente altos, variando entre 0,73-0,85. Entretanto, houve dificuldades em simular adequadamente a alta estratificação (vertical e longitudinal) do estuário de Nova Vicosa, podendo-se atribuir esse fato à maior vazão do rio Peruípe, que é muito maior do que a do rio de Caravelas. Com os resultados da estrutura de salinidade a intrusão da massa de Água Tropical (AT) foi adequadamente representada nos quilômetros iniciais do canal estuarino do rio Caravelas, e na parte interna da desembocadura na região de Nova Viçosa. Movimentos bidirecionais foram observados nos resultados das simulações na preamar e baixamar, na região de desembocadura dos estuários da Caravelas e Nova Viçosa, movimentos estes forçados pela componente baroclínica da força de gradiente de pressão. Vale ressaltar que o efeito baroclínico ficou mais visível nos instantes da baixamar. Na preamar para a maior parte destas duas regiões verificou-se apenas um pequeno desvio no sentido das correntes entre superfície (Z = -0,1) e fundo (Z = -0,9) e em geral inferior a 30 graus. Usando os traçadores lagrangeanos virtuais lançados ao longo dos canais estuarinos das entradas norte (Caravelas) e sul (Nova Viçosa) do SERCP foi obtido como resultado um tempo de residência relativamente pequeno e comparável ao estuário tropical do rio Curimataú. No trecho analisado no canal estuarino do rio Caravelas, a ~ 3 km e ~ 12 km distantes da Boca do Tomba o tempo de residência médio foi ~ 4,2 dias e ~10,3 dias, respectivamente. Já no estuário de Nova Viçosa, ou canal estuarino do rio Peruípe, apenas o trecho inicial de 5 km foi considerado para o lançamento dos traçadores, e os tempos de residência de ~ 1,5 dias e 2,5 dias foram estimados para as posições de ~2,5 km e 5,0 km distantes da desembocadura. O modelo analítico proposto e usado no cálculo de tempo de residência teve resultados comparáveis aos obtidos pelas simulações pelo método lagrangeano do Delft-3D Flow. Diferentemente, o modelo LOICZ apresentou valores bem diferentes do tempo de residência para os seis estuários analisados (Caravelas, Nova Viçosa, Curimataú, Hudson, Conwy and Mersey), em geral bem inferiores aos do modelo proposto, indicando assim uma possível estimativa maior do fluxo difusivo na formulação do modelo LOICZ.The numerical model Delft-Flow was used to study the spatial distribution and variability of the termohaline properties, and the tridimensional circulation in the estuarine system of the rivers Caravelas and Peruípe. The model results were validated quantitatively using field data of tidal oscilation and currents, and salinity measurements during neap and spring tides at four mooring stations, two in each estuary. In the data processing homogeneous conditions were used initially for the fields of salinity, density and the vertical kinematic coeficients of viscosity and diffusivity, then after four weeks of running simulation those fields were saved with spatially varied conditions. Those results were used for a more realistic initial condition, thus having a varied field of the termohaline properties, and of the physical parameters. The new initial conditions allowed avoiding the transient time and thus optimizing the following simulations. The model evaluation was done based on measurements undertaken during the summer season, because of the delay in the raining season, the Peruípe river discharge was low and more representative of dry season condition, for those reasons we just used the measurement taken in the January 2008. In the summer the measurements of the Peruíbe river discharge taken from the Agência Nacional de Águas (ANA), and the river flow of was estimated at ~ 20 m3.s-1, with the extrapolation of ~ 4 m3.s-1 for the unified flow from the rivers Cúpido and Jaburuna, with contribute to the flow in the Caravelas estuary. Tidal oscillation at neap and spring tides were well simulated for the 4 controling sites used to the validation, and with the mean skill values over 0.97. The tidal amplitudes were numerical calculated and nearly between 1.3 and 2.5 meters at neap and spring tides, respectively. The numerical results of the velocities were better simulated in spring tides with the mean skill values in the range of 0.77 and 0.93, while at neap tides this parameter varied between 0.38 and 0.65. For the salinity structure at spring tides good results in the estuarine system were achieved, hence comprising all the controling station for validation, with all mean skill values over 0.83. At neap tides the corresponding mean skill values were relatively high, varing in the range of 0.73-0.85. In addition, there were difficulties in simulation adequately the highly vertical and longitudinal stratification of the Nova Vicosa estuary. That was caused by the stronger river inflow of the Peruípe River, which is much higher than the inflow by Caravelas River. The intrusion of the Tropical Water mass (TW) was properly simulated given the right distribution of the salinity along the first quilometers of the estuarine channel of Caravelas, and the internal part of the Nova Viçosa estuarine mouth. Bidirectional movements were observed from the model outputs at the high and low tides, at the region near the mouth of both, Caravelas and Nova Viçosa estuary. Those moviments are forced by the baroclinic component of the pressure gradient. Is worth to mention the the baroclinic effect was better observed at the low tides of these regions. At high tide most of areas showed only a small change in the current direction between surface (Z = -0.1) and bottom (Z = -0.9) and usually smaller than 30 degrees. The virtual lagrangian drifters released along the estuarine channels of Caravelas (north) and Nova Viçosa (south) have shown a residence time relatively short, and comparable to the Curimataú tropical estuary. In the released location between 3 and 12 km of distance from the Caravelas mouth, the residence time was in the range of 4.2 and 10.3 days. Differently, at the Nova Viçosa estuary, only the first 5 km were studied and the residence time of 1.5 and 2.5 days was estimated for the respectives positions of 2.5 and 5.0 km away from the mouth. The analytical model proposed and used to calculate the residence time leaded to results comparable to the results from the numerical simulation using the Lagrangian method of the Delft-3D Flow. Differently, the LOICZ model has shown results really different of the residence time for all the six estuaries (Caravelas, Nova Viçosa, Curimataú, Hudson, Conwy and Mersey), and in general much smaller then the results from the proposed formula, thus indicating a possible overestimation of the diffusive flux assumed in the LOICZ formulation

Water dynamics and transport timescales of coastal waters and estuaries

The transport time scales of water have been of considerable interest to marine biologists and biological oceanographers, as they are important parameters to determine aquatic ecosystem health and sensitivity to pollution threats (Lucas et al., 2009; McLusky and Elliott, 2004; Wolanski, 2007; Wolanski, et al., 2012). This thesis has two major components, (a) application of a numerical model to determine transport timescales of the GBR (Great Barrier Reef), and (b) the development and application of a new analytical model to determine timescales for river estuaries.\ud \ud The SLIM model was used for the numerical simulations in the GBR (SLIM: Second-generation Louvain-la-Neuve Ice-ocean Model). The simulations were run with the Eulerian and Lagrangian schemes depending upon the application. This is the first model of the GBR that has been calibrated to accurately model mixing processes, which was done by comparison of model results with measurements of the hypersaline conditions of the dry season. The model properly simulated the rise of the salinity concentration, and the time to achieve steady state conditions in the dry season.\ud \ud Model results of the hypersaline coastal waters in the central Great Barrier Reef have shown that the hypersaline waters formed near the coast and inside the bays are exported along the coast from bay to bay during the dry season. The bays supply hypersaline waters to coastal areas. The cross-shelf gradient of the hypersaline waters is mainly controlled by turbulent diffusion, whereas along the coast the salinity gradient is controlled by the residual currents due to the North Caledonia Jet inflow (NCJ) and the wind driven currents.\ud \ud Results of the flushing time and the age of waters from the North Caledonia Jet inflow into the GBR were estimated under realistic boundary forces. The wind decreases the flushing time in the bays. In contrast, in coastal waters the wind may increase this timescale because the normal southerly flow due to the ocean inflow is opposed by the northward directed wind stress. A typical flushing time for the GBR under real wind conditions was about 70 days.\ud \ud The sticky water effect in the Great Barrier Reef was estimated quantitatively using the SLIM model. It was demonstrated that some reef configurations result in high exposure time, which depends on the reef density (i.e. degree of aggregation by reefs). Two empirical formulations to estimate larvae retention within the reef matrix were provided. One formula required measurement of tidal and mean currents, and the other formula, that was less accurate, requires only information of the bathymetry and reef density.\ud \ud The transport time scales, namely water renewal, residence time and exposure time were calculated using analytical solutions for a range of estuaries worldwide, and the results were compared with residence time results from numerical models where estimates were available. A new modified LOICZ model has been developed that quantifies the relative contribution of advection and diffusion to water renewal in estuaries using simple measurements of river discharge, salinity and the estuarine geometry. The modified LOICZ model resulted in the best fit against numerical results. A graphic conceptual model, the advection/diffusion timescale diagram, was also developed, which was used to visualize where different estuaries lie in the advective/diffusive timescale space diagram. Estuaries can now be divided into those which are dominated by diffusion, those which are dominated by advection and those where diffusion and advection are of similar magnitude

Experiments and numerical model with application to the tropical estuary of the Catimataú river, RN

A distribuição e a variabilidade de propriedades termohalinas e a circulação tridimensional do estuário do rio Curimataú foram estudadas com a aplicação do modelo numérico de simulações Delft3D-Flow, validado com dados experimentais medidos durante dois ciclos consecutivos de maré de quadratura e de sizígia. Duas grades numéricas foram aplicadas com o intuito de observar as diferenças entre as simulações nos modos barotrópico e baroclínico. As condições iniciais de simulações tais como: salinidade, velocidade, densidade e coeficientes cinemáticos de viscosidade, difusividade horizontal e vertical foram obtidas mediante resultados de simulações sob condições iniciais homogêneas. A seguir, o modelo numérico foi utilizado em condições mais realistas que foram comparadas aos dados experimentais. As simulações para a estrutura de salinidade, no modo barotrópico na maré de sizígia, apresentaram os melhores resultados, em comparação com os resultados experimentais, confirmado pelo índice de validação Skill igual 0,96; no modo baroclínico as simulações também foram de boa qualidade e o Skill foi muito próximo ao anterior (0,94). As simulações teóricas do campo de velocidade também foram de boa qualidade, comparativamente aos dados experimentais; os índices de validação médios foram muito próximos para os modos barotrópico e baroclínico (0,80 e 0,79). Esses valores do índice de validação confirmam que a dinâmica e os processos de mistura de natureza advectiva e difusiva foram bem representados matematicamete. Durante a maré de quadratura os resultados teóricos dos modos barotrópico e baroclínico não foram de boa qualidade (índice skill próximo a 0,60), devido às dificuldades de imposição de condições de contorno adequadas para a alta descarga fluvial que ocorreu durante os experimentos. Além das simulações por intervalos de tempo de 25 h, que foram utilizadas para validação com os dados experimentais, também foram feitas simulações inéditas horárias das características termohalinas, da circulação e do transporte advectivo de sal em séries temporais de 16 e 90 dias nos modos baroclínico e barotrópico, respectivamente. Aos resultados simulados das estruturas de salinidade e de velocidade, no modo baroclínico e maré de sizígia, foram aplicadas as metodologias rotineiramente utilizadas no processamento e análise de dados experimentais, com a finalidade de interpretar o comportamento dinâmico e os processos de mistura e transporte. No modo baroclínico, durante ambas as marés de sizígia e quadratura, a região inferior do estuário foi classificada como parcialmente misturado (tipo 2a), com valores baixos para os parâmetros de estratificação O(10-2)<pe< O(10-3) e com o parâmetro de circulação variando consideravelmente entre valores altos (pc&#61627;50) e baixos (pc&#61627;2). A análise da variabilidade dos coeficientes cinemáticos de viscosidade e difusividade no canal estuarino do rio Curimataú indicou que esses coeficientes variaram no seguinte intervalo: 10-3 m2 s-1 a 1,2x10-2 m2 s-1. A energia cinética turbulenta e as taxas de energia dissipada por unidade de massa, nas proximidades da boca do estuário, apresentou os maiores valores com ordens de grandeza de 6,5x10-3 m2 s-2 e 2,4 m2 s-3, respectivamente.The distribution and variability of the termohaline properties and the three-dimensional circulation of the Curimataú river estuary had been studied with the application of the numerical model of simulations Delft3D-Flow, validated with experimental data measured during two consecutive cycles of neap and spring tide. Two numerical grids were applied with the intention of observing the differences between the barotropic and baroclinic simulations. The initial conditions such as: salinity, velocity, density and the horizontal and vertical kinematic coefficients of viscosity and difusivity had been undertaken through the results under homogeneous initial conditions. After that, the numerical model had been used in more realistic conditions which were compared with the experimental data. The simulations of the structure of salinity, in the barotropic model during the spring tide, showed better results when compared with the experimental data, validated by the Skill equal to 0.96; in the baroclinic model the simulations also had presented a good quality and the Skill was very close to those one (0.94). The theoretical simulations of the field of velocity were also of a good quality, comparatively the experimental to the experimental data; the mean Skill had been very close the barotropic and baroclinic models (0.80 e 0.79). Those values of the Skill confirm that the dynamic and the mixing process of advective and diffusive nature had been well presented mathematically. During the neap tide the theoretical results of the barotropic and baroclinic models had not been of a good quality (Skill 0.60), due to the difficulties of imposition of suitable boundary conditions to the high river discharge during the experiments. Besides the simulations with time intervals of 25 h, which were used to the validation with the experimental data, also had been realized hourly simulations of the termohaline features, of the circulation and the advective salt transport into temporal series of 16 and 90 days in the barotropic and baroclinic models respectively. To the simulated results of the salinity and velocity structures, in the baroclinic model and under spring conditions, had been applied the aim methodology used in process and analyzes of experimental data, with the finality of interpretation of the dynamic behavior and the mixing process and the transport. In the barolinic model, during both tides, neap and spring, in the lower reaches of the estuary was classified as partially mixed (tipe 2a), with low values to the stratification parameters O(10-2)<pe< O(10-3) and with the circulation parameter varying considerably between high values (pc&#61627;50) and low values (pc&#61627;2). The analyses of the variability of the Kinematic and diffusivity coefficients in the Curimataú river channel indicated that those coefficients had been in the interval of: 10-3 m2.s-1 a 1.2x10-2 m2.s-1. The kinetic turbulent energy and the rate of energy dissipation had indicated that in the vicinity mediations of the estuary mouth are concentrated the highest values: 6,5x10-3 m2 s-2 and 2,4 m2 s-3, respectively

Estuarine Hydrology

[Extract] The word estuary is of sixteenth century origin and originated from the Latin aestuarium, which means marsh or channel, and this is derived from the Latin aestus, meaning tide or billowing movement. Estuaries are transitioning environments between the land and the ocean, where fresh water coming from the rivers mixes with saline oceanic water. This river inflow need not be perennial. There are several definitions of estuaries. For freshwater scientists the main thing is to define the head of an estuary; in one definition, this is the salinity limit; in another definition, this is the tidal limit; and in still another definition, it is the source of the fluvial sediment. For coastal scientists and oceanographers, the mouth of an estuary, i.e., the point where an estuary ends, is also ill-defined. It can be a geographic feature or the seaward edge of a tidal plume in the open ocean

'Sticky water' enables the retention of larvae in a reef mosaic

To study retention of waterborn larvae in a reef matrix we used a finite-element unstructured numerical model with a minimum horizontal resolution of 150 m that can capture variability of currents on a spatial scale relevant to coral reefs in the Great Barrier Reef (GBR). Areas of high reef density (i.e. closely aggregated reefs) are poorly flushed because the prevailing currents are directed around and away from these regions, which is an oceanographic process called the 'sticky water' effect. The model showed that the sticky water effect leads to decreased flushing and a high exposure time in high reef density areas in the southern and central regions of the GBR matrix. In turn this generated hot spots of high self-seeding, and these hot spots existed under both calm weather conditions and wind conditions typical of those during the coral spawning season. Away from these areas, self-seeding was less likely to occur and larval replenishment would result mainly from connectivity between reefs located kilometres to tens of kilometres apart. The location of sticky water areas varied spatially within the reef matrix according to tidal and mean currents, local bathymetry and reef density (defined as the degree of aggregation by reefs). A simple analytical formula is presented that explains ~70% of the variation in larval retention in both calm weather and windy conditions. Complex reef mosaics and the related sticky water effect may have significant implications on the fate of larvae, and thus on connectivity for coral reefs worldwide