Flood Tide Research Articles

The Structure and Dynamics of an Estuarine Tidal Intrusion Front

AbstractTidal intrusion fronts are surface convergences that occur at constrictions in estuaries during the flood tide, separating incoming higher‐salinity water from lower‐salinity, stratified estuarine water. Previous observations of tidal intrusion fronts describe a V‐shaped planform, with the apex of the V pointing into the estuary, however the significance of this structure has not been previously explained. Observations near the mouth of the James River estuary during the flood tide reveal the development of a quasi‐steady, V‐shaped front. Considering a reference frame oriented normal to the front, the velocity and density structure are consistent with gravity‐current dynamics, but the oblique orientation of the front relative to the impinging flow indicates strong, along‐front shear, which results from vorticity produced by flow separation at the lateral boundaries as well as topographic torque from upstream. The combination of convergence and along‐front shear leads to enhanced mixing, as revealed by acoustic backscatter images of shear instability and persistent subcritical gradient Richardson number in the frontal zone. Oblique fronts such as this tidal intrusion front are common features of estuaries, and they play an important role in vertical exchange due to subduction and mixing of surface water.

Surface Current Measurement Using Large Scale Particle Image Velocimetry (LSPIV) in Ender Estuary, Cirebon

The Large-Scale Particle Image Velocimetry (LSPIV) method is an image- based technique that uses a non-intrusive approach or avoids direct physical contact with the water being studied to measure the velocity of water flow. The present study aims to identify surface velocity using LSPIV captured by Unmanned Aerial Vehicle (UAV) in Ender estuary, Cirebon. Field observation for surface velocity was conducted at three locations during flood and ebb tides. The surface current results of LSPIV compared with in situ velocity measurement by a current meter. The results of the LSPIV method are strongly influenced by the data acquisition process such as lighting, interrogation area, and video recording angle. Based on comparing the surface flow between results of LSPIV and observation data, the coefficient correlation (R) is 0.84 for velocity magnitude and R = 0.92 for flow direction. The Root Mean Square Error (RMSE) of 0.024 m/s for velocity magnitude and 4.81 degree for flow direction, and the Mean Absolute Error (MAE) range from 0.002 to 0.059 m/s (1 to 12 degree) for the velocity magnitude and the flow direction, respectively. Furthermore, the Mean Absolute Percentage Error (MAPE) value of 10.41% (8.84%) for magnitude and direction, respectively. Therefore, LSPIV was applied successfully to obtain surface velocity measurements.

Generation and Evolution of Internal Solitary Waves in a Coastal Plain Estuary

Abstract Large-amplitude internal solitary waves were recently observed in a coastal plain estuary and were hypothesized to evolve from an internal lee wave generated at the channel–shoal interface. To test this mechanism, a 3D nonhydrostatic model with nested domains and adaptive grids was used to investigate the generation of the internal solitary waves and their subsequent nonlinear evolution. A complex sequence of wave propagation and transformation was documented and interpreted using the nonlinear wave theory based on the Korteweg–de Vries equation. During the ebb tide a mode-2 internal lee wave is generated by the interaction between lateral flows and channel–shoal topography. This mode-2 lee wave subsequently propagates onto the shallow shoal and transforms into a mode-1 wave of elevation as strong mixing on the flood tide erases stratification in the bottom boundary layer and the lower branch of the mode-2 wave. The mode-1 wave of elevation evolves into an internal solitary wave due to nonlinear steepening and spatial changes in the wave phase speed. As the solitary wave of elevation continues to propagate over the shoaling bottom, the leading edge moves ahead as a rarefaction wave while the trailing edge steepens and disintegrates into a train of rank-ordered internal solitary waves, due to the combined effects of shoaling and dispersion. Strong turbulence in the bottom boundary layer dissipates wave energy and causes the eventual destruction of the solitary waves. In the meantime, the internal solitary waves can generate elevated shear and dissipation rate in local regions. Significance Statement In the coastal ocean nonlinear internal solitary waves are widely recognized to play an important role in generating turbulent mixing, modulating short-term variability of nearshore ecosystem, and transporting sediment and biochemical materials. However, their effects on shallow and stratified estuaries are poorly known and have been rarely studied. The nonhydrostatic model simulations presented in this paper shed new light into the generation, propagation, and transformation of the internal solitary waves in a coastal plain estuary.

Strategi masyarakat pesisir Margolinduk dalam penanganan banjir rob serta implikasi terhadap sikap peduli lingkungan

Margolinduk Village is one of the coastal villages on the north coast of Central Java which is worst affected by the tidal floods in Demak Regency. The various losses felt by the people of Margolinduk Village due to tidal floods have not reduced the resilience of the people to stay put. So that various handling efforts are deployed by the community in order to survive. However, so far there has been no research that examines the strategies of the Margolinduk Village community in dealing with tidal floods. Therefore, this research aims to find out the strategies used by the Margolinduk Village community in dealing with tidal floods and the implications for attitudes toward caring for the environment. Community efforts to deal with tidal floods should lead to concern for the environment. However, this attitude of caring for the environment must be proven by measuring indicators of caring for the environment. The method in this research is descriptive qualitative. Data collection was carried out through questionnaires, interviews, and observations. The number of samples used in this research was 30 people taken by purposive sampling. The Margolinduk Village community's strategy for dealing with tidal floods is by raising house buildings and looking for other alternative jobs. Even though the education level of the people of Margolinduk Village is still relatively low, the attitude of caring for the environment of the people of Margolinduk Village is in the very good category. Thus, what is found in this research is that attitudes that care about the environment do not always arise because of the knowledge taught at school. Direct experiences or individual impacts due to tidal floods have deep emotional and practical dimensions, thus playing a crucial role in shaping changes in attitudes and behavior towards greater environmental awareness.

Forecast of Land Cover Change as a Sustainable Flood Prevention Strategy using Cellular Automata Model in Lampoko Watershed, South Sulawesi, Indonesia

The Lampoko watershed is the biggest watershed in South Sulawesi's Barru Regency. Flooding is a common occurrence in this area, particularly tidal flooding. To get around this, this research uses a geographic information system to estimate land cover and reveal how an organization will grow in the future. This forecast is meant to help plan preventive measures in organizational regions where flooding is anticipated. The CA-Markov model was used to analyze satellite imagery data (Landsat 8 OLI TIRS Year 2015-2021). The findings revealed an increasing pattern of land cover change in several land cover classes that were hubs of communal activity including villages, fisheries (ponds) and agricultural (rice fields). Balusu, Lampoko and Ajakkang are areas that need to be prepared for since they are part of regions with a high likelihood of flooding in the future.

Analisis Pengaruh Banjir Rob Terhadap Kualitas Air Tanah Di Kawasan Pesisir Selatan Puger Kabupaten Jember

The potential benefits of a beach for the surrounding community are numerous, including increasing the tourism sector and supporting the economy of local residents. Apart from this potential, there is also the potential for disasters, one of which is ROB flooding. Recently there was a tidal flood that hit the southern coast, causing seawater to enter residential areas and damage various public facilities in the Puger coastal area. The aim of this research is to identify the influence of tidal floods that occurred in the southern coastal area of ​​Puger, on groundwater quality, in terms of water quality in accordance with the quality standards of Minister of Health Regulation No. 2 of 2023 concerning Implementing Regulations of Government Regulation Number 66 of 2014 concerning Environmental Health. The method used is descriptive qualitative conservation data and sampling at three locations by conducting laboratory tests. From this research, it can be concluded that there is a decline in the quality of groundwater in the affected area which includes three observation locations. Where the TDS parameter is still below the quality standard of <300 mg/L, while for salinity and e-coli each has a value greater than the established quality standard. In this study, both parameters had <0% with values ​​for sampling 1 (2 per cent) sampling 2 (0.9 per cent) and sampling 3 (0.5 per cent ), for salinity and <0 CFU/100ml for e-coli content with values ​​for sampling 1 (50 CFU/100ml), sampling 2 (70 CFU/100ml) and sampling 3 (100 CFU/100ml). The ROB floods that occur in coastal areas result in the quality of groundwater becoming polluted and it must be treated first before it can be used by local communities.

Kebertahanan Bangunan dengan Adaptif terhadap Lingkungan

Title: The Resilience of Buildings with Adaptability to the Environment (Case Study: Tomb of Syekh Mudzakir in Bedono, Sayung, Demak) Coastal areas have the potential to be affected by abrasion and tidal floods. Syekh Mudzakir's grave is in Tambaksari Subvillage, Bedono Village, Sayung Subdistrict, Demak District, and in the coastal area of the North Coast (Pantura) of Java Island. However, the existence of the tomb and its buildings to this day still survives amidst the marine environment that surrounds it. This tomb has become a religious tourism destination in Demak Regency, with the number of tourists increasing. This research aims to determine and explore the resilience of tomb buildings that are adaptive to abrasion and tidal flood environments. This research is field research. Research data uses primary data and secondary data through the results of observations, interviews, and documentation. The research analysis uses qualitative descriptive analysis. This research shows that Syekh Mudzakir's tomb does not float in the middle of the sea. However, the tomb survives adaptively to the environment by adapting the area, building development, building structural systems, and expanding the site to be robust against abrasion and tidal floods. This research concludes that the family and community survive the grave by adapting to the environment and mitigating disasters that befall the grave area.

Impact of tidal shear fronts on terrigenous sediment transport in the Yellow River Mouth: Observations and a synthesis

A tidal shear front (TSF) can be defined as an obvious horizontal gradient of flow velocity formed by opposing tidal currents (reversed TSF) or same-direction tidal currents (homogenous TSF) on both sides of the front with limited impact by river runoff. Observational and modeling studies have been conducted to investigate the impact of a reversed TSF on the transport of freshwater and sediment in the Yellow River Mouth (YRM). The reversed TSF existence period is only about 40% of a tidal cycle (around slack of flood and ebb); however, when this front disappears (around maximum flood and ebb), sediment transport across the frontal zone is still rare. This suggests that the dynamic mechanism of cross-frontal sediment transport in a tidal cycle remains unclear. In this study, synchronous observations of sea current and suspended sediment concentrations along the river mouth profiles at the YRM in 1995, 2003, and 2019 were used to investigate the long-term variation characteristics, mechanisms, and impacts of the TSF on cross-frontal sediment transport. The results indicate that in addition to the reversed TSF, there are also homogenous TSF during flood and ebb tides, with the ebb homogenous TSF being more significant due to tidal asymmetry in the YRM. The ebb homogenous TSF is located between shallow shoals and the slopes of the subaqueous delta front and lasts for about 3 h around the maximum ebb. Its maximum shear strength is similar to that of the reversed TSF, and the formation mechanism is also similar. The presence of the ebb homogenous TSF reduces the efficiency of cross-frontal sediment transport during the ebb. The reversed and homogenous TSFs alternately block sediment moving towards the sea. Thus, terrigenous sediment is difficult to cross the frontal zone to the central Bohai Sea by tidal currents solely. Over the past two decades of low discharge, with the Yellow River implementing artificial water and sediment regulation, the homogenous TSF during the ebb tide has become more and more important and cannot be neglected for cross-frontal sediment transport under normal conditions. Furthermore, from a long-term perspective, the shear strength of the TSF is positively correlated with the distance of river mouth siltation into the sea. Additionally, salinity and turbidity gradients are also positively correlated with the shear strength in the estuary. This indicates that the blocking of cross-frontal sediment transport by the TSF is a key process in river-sea interaction in the YRM.

Coastal Compound Flood Simulation through Coupled Multidimensional Modeling Framework

Coastal watersheds are prone to compound flooding caused by heavy rainfall, storm surge, and high tide. Accurate prediction and modeling of coastal compound floods (CCF) require precise physical representation in numerical models with appropriate numerical approximation associated with multi-driver physical processes for simulating the flood dynamics. To address this, an integrated and tightly coupled modeling approach is implemented to capture the nonlinear and complex processes involved in CCF and interconnectivity among Multidimensional Hydraulics (pipe and channel), Hydrodynamics (2D overland flow), and distributed Hydrologic (MH3) models are developed. The coupled modeling framework focuses on the development of interconnected meshes of the node-link-basin using the Interconnected Channel and Pond Routing (ICPR) model. This framework effectively incorporates the complex drainage network system of tidal creeks, tidal channels, underground sewer networks, and detention ponds of the Charleston Peninsula of South Carolina (SC). The dynamics of the urbanized floodplain in the peninsula are represented using high-resolution LiDAR-derived Digital Elevation Model (DEM) and Digital Surface Model (DSM). The overland flow is simulated using energy balance, momentum balance, and diffusive wave methods. The performance of the CCF model is tested for the 2015 SC historical flood and a high tide flood event. The momentum balance-based CCF model shows 98.35% accuracy in identifying street-level flooding locations. Furthermore, the model shows that incorporating DSM processing in the current study improves the accuracy of urban flood simulation by approximately 15% to 33% compared to LiDAR DEM. It is revealed that the momentum balance method outperforms to simulate the flood dynamics. Consequently, this study contributes to the modeling of CCF by developing an integrated MH3 system that enhances the physical representation of coastal hydrology at a fine scale.

Intra-tidal upwelling variability off Zhoushan Islands, East China Sea

The coastal upwelling that takes place off the Zhoushan Islands is of great importance in the transport of nutrients, nourishing local fisheries and exerting a substantial environmental influence. While it is known that tides play a central role in triggering and controlling the Zhoushan upwelling, its short-term variability within the tidal cycle remains uncertain, thereby constituting the primary focus of this study, which relies on the analysis of high-resolution Sea Surface Temperature (SST) satellite images and in-situ data. In a tidal cycle, cold upwelling patches exhibit a westward shift during the flood tide and an eastward shift during the ebb tide. The extent of cold upwelling patches is greatest during maximum flood and ebb periods. At maximum ebb, the core temperature within the cold patches notably decreases, which indicates intensified upwelling. At the same time, a similar pattern of sudden increases is also observed throughout the entire water column in the upwelling region. The strong ebb current swiftly transports the upper water mass during maximum ebb, facilitating the compensation of lower water and augmenting the intensity of the upwelling. The calculated vertical velocity within the study area ranged from −9.04 × 10−4 m/s to 12.66 × 10−4 m/s during the observational period, when upwelling showed a significant congruence with low-temperature phenomena. Alternating upwelling and downwelling phases were discernible within a tidal cycle, with upwelling being prevalent. The influence of surface heat flux on seawater below the thermocline and night-time SST was negligible. Furthermore, compared to the vertical velocity, the calculated wind-induced upwelling velocity was much lower, reaching just 3.38 × 10−6 m/s during the observed tidal cycle, which suggests that wind does not exert a primary influence on upwelling within the tidal cycle. This study contributes to an enhanced understanding of upwelling variability under the influence of tides, a topic of paramount importance in the marine environment.

Stochastic properties of coastal flooding events – Part 2: Probabilistic analysis

Abstract. Low-intensity but high-frequency coastal flooding, also known as nuisance flooding, can negatively affect low-lying coastal communities with potentially large socioeconomic effects. Partially driven by wave runup, this type of flooding is difficult to predict due to the complexity of the processes involved. Here, we present the results of a probabilistic analysis of flooding events measured on an eroded beach at the Texas coast. A high-resolution time series of the flooded area was obtained from pictures using convolutional neural network (CNN)-based semantic segmentation methods, as described in the first part of this contribution. After defining flooding events using a peak-over-threshold method, we found that their size follows an exponential distribution. Furthermore, consecutive flooding events were uncorrelated at daily timescales but correlated at hourly timescales, as expected from tidal and day–night cycles. Our measurements confirm the broader findings of a recent multi-site investigation of the probabilistic structure of high-water events that used a semi-empirical formulation for wave runup. Indeed, we found a relatively good statistical agreement between our CNN-based empirical flooding data and predictions using total-water-level estimations. As a consequence, our work supports the validity of a relatively simple probabilistic model of high-frequency coastal flooding driven by wave runup that can be used in coastal risk management and landscape evolution models.

Tidal asymmetry and mud transport in Oualidia Lagoon: Actual conditions in 2012 and rehabilitation scenarios

Oyster aquaculture in Oualidia Lagoon, Morocco, has suffered from poor water quality and water confinement in its upstream region. Tidal asymmetry (TA) has been suggested as a possible cause, and a sediment trap was dredged in 2011 to mitigate this condition. This study addresses TA in the lagoon using field measurements and numerical modeling in the presence of the sediment trap. Results indicate that the lagoon is flood-dominated mostly in its upstream end, where frictional forces exceed inertia accelerations during the tidal cycle and fine sediments settle on the tidal flats and inside the sediment trap. However, this study shows that a large mass of suspended sediments is exported to the ocean, which is contrary to expectations in flood-dominated lagoons. Defining the sediment trap as the rehabilitation scenario S1, the impacts of three additional scenarios on TA are examined. These are scenario S2 (dredging the upstream section of the main channel), scenario S3 (dredging the channels surrounding the flood delta near the inlets), and scenario S4 (raising the ocean level by 0.5 m following climate change predictions). Results show that none of these scenarios modify the tidal flood dominance in the lagoon, although scenarios S2 and S4 decrease its intensity in the upstream region. Nevertheless, all scenarios still contribute to a significant export of sediments to the ocean. This suggests that lagoon management activities should not rely on tidal asymmetry analyses that normally predict upstream sediment transport in flood-dominated lagoons.

Impact of sea level rise on tidal energy budget in a macro-tidal coastal bay with archipelago

With sea level rise (SLR), tidal nuisance flooding has become a growing threat, especially around estuaries with large tidal amplitudes. This study investigated how sea level change affects tides in Hangzhou Bay, a macro-tidal estuary with high SLR rate. By downscaling climate projections to a regional hydrodynamic model, the amplitude of primary tidal constituent (M2) was predicted to increase by 0.25 m in the upper bay, where the amplitude of major diurnal tide (K1) was also predicted to increase by 15%. In addition, the sensitivity of tidal amplitude to mean sea level was examined by a set of numerical simulations with different SLR. It was found that the increase of tidal amplitude is nonlinear to SLR, and the tidal amplitudes almost cease to increase when SLR is over 1.5 m. Although predictions show less amplitude changes in the lower bay, Zhoushan Archipelago around the bay mouth strongly modulates the incoming tidal energy, thus affecting the tidal amplitude in the upper bay. Energy budget analysis revealed that the complex topography, such as narrow channels, in the archipelago area leads to strong horizontal shear, which dissipates approximately 25% of total tidal energy in the bay. On the other hand, around 60% of the energy is dissipated in the bottom boundary layer. However, the bottom dissipation decreases by 4% due to reduced friction, while horizontal dissipation increases by 10% due to enhanced horizontal shear with SLR. This suggests that the strong horizontal shear in the Zhoushan archipelago region can play a more important role in the tidal energy budget in the future.

Influencing Mechanism of Tidal Disasters on Locust Breeding Area Evolution in the Eastern Coastal Area of China during the Ming and Qing Dynasties

Locust plagues and tidal disasters are primary natural hazards in China’s eastern coastal regions, yet their interrelationship remains unclear. This study, drawing on historical documents from the Ming and Qing dynasties (1368–1911 AD), focuses on Zhejiang Province and its Hangzhou Bay coastline, areas typically affected by tidal disasters. Employing advanced quantitative analysis and spatiotemporal models, the research aims to reveal the mechanisms behind tidal disasters and their impact on locust population dynamics. The findings indicate a limited spatiotemporal correlation between locust plagues and tidal or drought disasters but a significant association with flooding. The relationship between locust infestations and floods is notably strong in the unique geographical context of Hangzhou Bay’s northern shore. The ‘hydromarginal’ nature of the north coast creates an ideal habitat for locusts. This study pioneers in identifying flooding as a crucial mediator between tidal disasters and locust plagues, shedding light on the ‘typhoon-tidal-flood-locust’ disaster sequence and offering new insights into understanding and mitigating natural disasters in the region. In this study, we primarily employ a quantitative methodology, utilizing advanced data analysis and sophisticated spatiotemporal modeling to investigate the interplay between locust plagues and tidal disasters. Although some progress has been made in the study of historical natural disasters, systematic studies of the relationship between tidal floods and locust breeding sites along the east coast of China during the Ming and Qing dynasties are still scarce. This study fills this gap by employing advanced GIS and time series analysis techniques, combining traditional historical documentary studies with modern scientific methods and providing a new methodological approach to the analysis of historical disaster patterns.

Study of Shoreline Changes Due to Tidal Flood at the Coastal City of Meulaboh

The coastline is constantly changing over time. The process of change that occurs continuously makes the coastline dynamic. Shorelines are vulnerable to changes caused by natural and human factors. One of the causes of shoreline changes due to natural factors is tidal flooding. Tidal floods cause abrasion of the coastline and create inundation on land. The coast of Meulaboh City has experienced tidal floods in 2020. The tidal floods that occur make the coastline abrasion and residential areas inundated. This study aims to determine the shoreline changes and the shoreline recovery process due to abrasion and accretion after tidal floods from 2020 to 2021. The shoreline in July 2019, 2020 and 2021 were analysed using DSAS tools to see horizontal shoreline changes. Measurement of the transverse profile of the beach was carried out 17 times in 12 transverse profiles. This measurement aims to map the profile condition after the tidal flood in July 2020. Measurement data for each profile was analysed using the EOF method to see vertical shoreline changes one year after the July 2020 tidal flood. Based on DSAS analysis, the shoreline conditions after tidal flooding (2019-2020) regressed with an average regression of 25.48 m and showed an accretion process after a year (2020-2021) with an average accretion of 14.38 m. Shoreline recovery due to tidal flooding can be seen well based on measurements for 1 (one) year and the results of Empirical Orthogonal Function (EOF) analysis. The recovery pattern is visible after 4 months of tidal flooding in July 2020. The beach profile tends to experience an accretion process in the 8th to 13th measurements and tends to experience abrasion in the 16th to 17th measurements. This shows that the accretion process on the transverse coastal profile is influenced by the east wind season, and the abrasion process generally occurs in the west wind season.

Analysis of Tidal Flood Management in the Coastal Region, West Aceh Regency

Tidal flooding in Gampong Pasir Village, West Aceh Regency, reached 100 cm in July 2020, submerging 42 houses. Efforts like buis concrete, sandbags, and tetrapods have been used to address the issue. This study aims to determine the public’s perception of the efforts to overcome tidal floods that have been carried out in Gampong Pasir. This study uses primary data to assess the response efforts and secondary data, including population, research location, and building data. The first questionnaire processes public perception using a Likert scale, while the second processes expert opinions using Analytical Hierarchy Process (AHP). This study interviewed 81 respondents from a total of 418 residents in the community with three expert opinions. The study results indicate that the efforts made have had a positive impact on mitigating tidal flooding in Gampong Pasir, but they are still not optimal. Using the AHP method, the study prioritizes resilience as the highest criterion with a value of 0.75 and identifies Tetrapod as the top-performing alternative with a value of 0.76. Therefore, Tetrapod has been built as a priority structure to address tidal flooding in Indonesia.

Spatial Distribution of Tidal Floods Using Geographic Information System (GIS) in Medan Belawan District

Tidal floods are one of the threats that occur in coastal areas. The impact is felt for the community, as well as other impacts felt for the surrounding ecosystem, namely the mangrove population, where tidal floods that continue to occur can have a serious impact on the community and mangrove vegetation because they can threaten the sustainability of the mangroves. This research uses GIS to map tidal flood inundation areas and determine their relationship with biophysical factors. Spearman correlation is used to determine the relationship between points in tidal flood areas and biophysical factors such as elevation, slope, distance from rivers and distance from the beach. The research results show that the four variable factors are related to the point of tidal flood inundation. Distance from the river greatly influences the tidal flood point in Medan Belawan District, with a correlation coefficient value of -0.100. This is because rivers act as a medium for the entry of water from the sea without any obstacles to entering the land, so when the river flow reaches its carrying capacity, sea water immediately overflows into residential areas.

Acidification and hypoxia in seawater, and pollutant enrichment in the sediments of Qi’ao Island mangrove wetlands, Pearl River Estuary, China

Mangrove forests are crucial in absorbing, storing, and purifying pollutants while maintaining ecological balance. A study was conducted in 2020 to investigate the biogeochemical processes of seawater and sedimentary environmental factors in the Qi'ao Island mangrove wetland. The study comprised two survey sections and ten survey stations within the mangrove forest and 16 large-scale survey stations in the adjacent sea area. During ebb tides, the mean concentrations of inorganic nitrogen and phosphate in Section D1 of the mangrove forest were 0.63 mg/L and 0.003 mg/L, respectively. These levels were significantly lower than the results observed in the adjacent sea area and Section D2 of the mangrove forest during flood tides. The mangrove forest efficiently absorbed and consumed nutrients, with the nitrogen-to-phosphorus ratio of consumed nutrients being notably higher than that typically utilized by plants during growth. We identified various biogeochemical processes, including nitrogen fixation, mineralization, nitrification, and denitrification, occurring within the mangrove forest. Seawater measurements in Section D1 during ebb tides showed the mean pH of 7.58 and dissolved oxygen levels of 4.52 mg/L, resulting in a dissolved oxygen saturation level of only 57.0 %. The low dissolved oxygen levels were attributed to organic matter degradation in the forest. Consequently, the longer the water retention time, the more obvious the trend of hypoxia and acidification was observed. In the adjacent sea area, the sedimentary environment was deemed healthy, with pollutants primarily originating from runoff and ship discharge from waterways and ports. However, within the mangrove forest, the sediments exhibited higher enrichment factors for organic carbon and sulfide, indicating significant pollution compared to the adjacent sea area. The sediments were conducive to the accumulation and burial of total Hg, Zn, and Cu, while other heavy metals did not show prominent deposition and enrichment. Notably, the enrichment factor of oils was as high as 4.37, leading to the formation of an oil pollution zone at the forest edge, and the enrichment of pollutants in sediment may inhibit the growth and expansion of mangroves. Overall, this study shed light on the occurrence of seawater acidification, hypoxia, and the behavior of sediment pollutants within the mangrove forest. The findings provide valuable insights to support efforts aimed at promoting and maintaining the ecosystem health of mangrove forests.

Discussion on low-carbon energy supply and scour protection technology for cross-sea bridges combined with tidal current energy

In the context of achieving carbon peak and carbon neutrality, the construction and maintenance of transportation infrastructure should also comply with the requirements of green and low-carbon development. There are many long-span cross-sea bridges in Zhejiang Province, which consume large amounts of electricity for lighting, dehumidification, and anticorrosion, etc., and the energy required usually relies on external energy transfer, which is costly and intermediate losses are high. Tidal current energy, which is the kinetic energy generated during ebb and flood tides, is abundant along the coast of Zhejiang Province, mainly concentrated in Hangzhou Bay and Zhoushan Islands, which is also a dense area of sea-spanning bridges, and the foundation of sea-spanning bridges often suffers from severe scouring to the strong tidal current action. This paper discusses two forms of joint development of tidal current power generators and cross-sea bridges, analyses the advantages and disadvantages as well as the feasibility of each scheme, and gives suggestions for subsequent development.

Structures of Lateral Flow and Turbulence in a Breaking Tidal Bore Rushing through a Curved Channel of the Qiantang Estuary

Abstract Tidal bores form in distinct funnel-shaped estuaries and bays initially and cause unique flow and turbulence dynamics when passing through meandering channels, such as in the Qiantang Estuary, Amazon River Estuary, and Seine River Estuary. To understand the lateral currents and turbulence processes of tidal bores in curved channels, velocity profiles and free-surface elevations are sampled for four semidiurnal tidal cycles in a curved channel located upstream of the Qiantang Estuary. During flood tides, the evolution of lateral currents experiences three distinct phases: first, there are inner-bank-toward lateral currents at the front of tidal bores, followed by two-layer helical currents in the middle of the flood tides, and finally, outer-bank-pointing lateral currents at the end of flood tides. Tidal bore breaking creates outbursts of turbulent kinetic energy. The enhanced turbulence emerges above the middle layers and persists for more than 10 minutes after the breaking front. The lateral momentum balance indicates that the decreasing lateral barotropic pressure gradient (LBTPG) and the increasing summation of centrifugal and Coriolis acceleration give rise to the variation in lateral currents. The phase lead of bores near the outer bank induced by shoal-channel topography generates an inner-bank-pointing LBTPG at the bore front and then gradually weakens it. Significant turbulence following bore breaking may be induced via the wave-induced turbulence mechanism by violent secondary waves. This research shows that complicated lateral currents are an important component of tidal bores flowing through meandering channels and that secondary waves after bore breaking can continually feed turbulence. Significance Statement The purpose of this study is to discern and explain the variation in lateral flows and turbulence when tidal bores rush through a curved estuarine channel. Lateral currents and turbulence play important roles in momentum exchange, scalar dispersion, and transverse topography evolution. Moreover, the discussion on lateral flows is necessary to extend the understanding of tidal bore hydrodynamics from the x–z dimension to the x–y–z dimension. In situ observations reveal that a complicated but regular pattern of lateral currents occurred in every tidal cycle and that there was significant turbulence at the tidal bore front. Our findings show that the lateral difference in tidal bore propagation speed caused by shoal-channel topography in the curved bend is an essential reason for the generation of lateral currents and that the secondary waves simulated by bore breaking can continuously feed tidal bore turbulence.