High Tide Research Articles

A Study of the Drainage Capacity, Flood Risks and Mitigation Measures for Selected Areas in Guyana’s Coastal and Riverine Regions: Williamsburg- Hampshire, Kilcoy-Chesney and Mabaruma-Kumaka-Barabina

This research investigates the drainage challenges and flood risks in three areas of Guyana: Williamsburg-Hampshire, Kilcoy-Chesney, and Mabaruma-Kumaka-Barabina. These drainage areas are characterised by low-lying terrain, proximity to waterways, and inadequate drainage infrastructure. The study identifies how these factors lead to frequent and sometimes costly flooding, especially during periods of peak rainfall and high tides that prevent the opening of drainage sluices. Using rainfall and runoff data, with the analysis of drainage coefficients and discharge capacities, the study examines the existing drainage systems in these regions. It highlights the inefficiencies of undersized drainage structures, inadequate maintenance, and the growing pressure from urbanisation, which has led to the expansion of impervious surfaces, thus increasing runoff. In the case of Mabaruma-Kumaka-Barabina, under- maintained sluices, narrow bridge culverts, and low earthen dams exacerbate the area’s flood vulnerabilities. To address these issues, the study recommends several key interventions. These include upgrading drainage infrastructure by widening internal drains, replacing narrow culverts, installing additional sluices, and using modern technologies like automated pumps and self-actuated sluices. The construction of higher, vegetated embankments and raising the earthen river dams are also recommended to prevent erosion and overtopping during high tides. Monitoring water levels and rainfall data regularly is proposed to inform drainage maintenance and flood prevention efforts. The findings underscore the need for public-private partnerships to maintain drainage systems while engaging the community in flood risk mitigation. By implementing these recommendations, these regions can better manage water flow, reduce the impact of flooding, and improve the quality of life for residents, particularly as climate change continues to pose greater challenges for water management in Guyana.

Measuring nearshore waves at break point in 4D with Stereo-GoPro photogrammetry: A field comparison with multi-beam LiDAR and pressure sensors

Measuring nearshore waves remains technically challenging despite wave properties are being used in a variety of applications. With the promise of high-resolution and remotely-sensed measurements of water surfaces in four dimensions (spatially and temporally), stereo-photogrammetry applied to video imagery has grown as a viable solution over the last ten years. However, past deployments have essentially used costly cameras and optics, requiring fixed deployment platforms and hindering the applicability of the method in the field.Focusing on close-range measurements of nearshore waves at break point, this paper presents a detailed evaluation of a field-oriented and cost-effective stereo-video system composed of two GoProTM(Hero 7) cameras capable of collecting 12-megapixel imagery at 24 frames per second. The so-called ‘Stereo-GoPro’ system was deployed in the surf zone during energetic conditions at a macrotidal field site using a custom-assembled mobile tower. Deployed concurrently with stereo-video, a 16-beam LiDAR (Light Detection and Ranging) and two pressure sensors provided independent data to assess stereo-GoPro performance. All three methods were compared with respect to the evolution of the free-surface elevation over 25 min of recording at high tide and the wave parameters derived from spectral analysis. We show that stereo-GoPro allows producing digital elevation models (DEMs) of the water surface over large areas (250 m2) at high spatial resolution (0.2 m grid size), which was unsurpassed by the LiDAR. From instrument inter-comparisons at the location of the pressure transducers, free-surface elevation root-mean square errors of 0.11 m and 0.18 m were obtained respectively for LiDAR and stereo-GoPro. This translated into a maximum relative error of 3.9% and 12.5% on spectral wave parameters for LiDAR and stereo-GoPro, respectively. Optical distortion in imagery, which could not be completely corrected with calibration, was the main source of error. Whilst stereo-video processing workflow remains complex, cost-effective stereo-photogrammetry already opens new opportunities for deriving wave parameters in coastal regions, as well as for various other practical applications. Further tests should try to address specifically challenges associated to variable ambient conditions and acquisition configurations, affecting measurement performance, to guarantee a larger uptake of the technique.

Spatial and temporal variation of water reflectance in an Amazonian estuary: a case study around Tatuoca Island

Abstract. Studies of water color are related to its optically active components, including suspended sediments. The correlation of this parameter with reflectance data is well documented in the literature, to understand its concentrations and transport in the water body. The spatio-temporal variations of water color in an estuary are affected by various physical and hydrological components, which makes it complex to understand. In this study, we sought to understand the spatio-temporal variation of water color, for sampling purposes, in an estuary on the Amazon coast. To achieve our objectives, we applied geostatistical and statistical tools to test the spatio-temporal variability of water color, based on multisensor reflectance data, Landsat-8/9 and Sentinel-2 in the red band. The spatial variation showed distances of more than 48 m ±4.26 at high tide and 44 m ±7.62 at low tide. For the temporal variation, we found that the monthly variations are significant according to seasonality and have the same variation at different stages of the tide. Therefore, the color of the water in the Tatuoca Island region shows geostatistically and statistically significant spatio-temporal variation. The distances and temporal frequency of sampling should be adjusted according to the tides and seasonality to ensure that data is sampled in accordance with the variations in the environment.

Distinct molecular responses of mangrove plants to hypoxia and reoxygenation stresses contribute to their resilience in coastal wetland environment

Mangroves adapt to periodical submergence and constitute resilient ecosystems in coastal environments. The question is whether they can sustain long submergence stress when sea level rises as a consequence of climate change. To address this, seedlings of two representative mangrove species that acclimate to low to mid tide (Avicennia marina) and mid to high tide (Kandelia obovata) conditions were treated with continual submergence for 7 days as extended hypoxia, or semi-diurnal cyclic submergence and reoxygenation for 7 days. At specific time points, leaves were collected to construct RNA-Sequencing libraries for gene expression analysis. Through the lens of transcriptome, the initial response of A. marina to submergence was mild but more dramatic after prolong immersion. However, the initial response of K. obovata was drastic and reduced in latitude later, suggesting distinct species-specific responses. After adapting to diurnal cycles, both species minimized transcriptome fluctuations similarly. Metabolically, during initial response, sucrose and starch were converted into glucose for fermentation to increase glycolytic flux, coupled with regeneration of NAD+. The energy amelioration was accompanied by longer term phytohormone regulations where ethylene signal transduction pathway was enhanced, but abscisic acid biosynthesis was reduced. Notably, gibberellic acids biosynthesis increased in A. marina but decreased in K. obovata as a unique feature. Genomic level analysis indicated that only about 30 % of the conserved plant submergence responsive genes were expressed during submergence in these mangroves. The function of an ethylene responsive gene was validated in transgenic Arabidopsis. This research elucidates distinct molecular mechanisms and metabolic pathways that empower A. marina and K. obovata to endure prolonged submergence and hypoxia. By highlighting their unique adaptive strategies in response to rising sea levels, these findings enhance our understanding of mangrove resilience and provide insights for the conservation and management of these essential coastal ecosystems in the face of climate change.

High Water Level Forecast Under the Effect of the Northeast Monsoon During Spring Tides

One of the manifests of air-sea interactions is the change in sea level due to meteorological forcing through wind stress and atmospheric pressure. When meteorological conditions conducive to water level increase coincide with high tides during spring tides, the sea level may rise higher than expected and pose a flood risk to coastal low-lying areas. In Hong Kong, specifically when the northeast monsoon coincides with the higher spring tides in late autumn and winter, and sometimes even compounded by the storm surge brought by late-season tropical cyclones (TCs), the result may be coastal flooding or sea inundation. Aiming at forecasting such sea level anomalies on the scale of hours and days with local tide gauges using a flexible and computationally efficient method, this study adapts a data-driven method based on empirical orthogonal functions (EOF) regression of non-uniformly lagged regional wind field from ECMWF Reanalysis v5 (ERA5) to capture the effects from synoptic weather evolution patterns, excluding the effect of TCs. Local atmospheric pressure and winds are also included in the predictors of the regression model. Verification results show good performance in general. Hindcast using ECMWF forecasts as input reveals that the reduction of mean absolute error (MAE) by adding the anomaly forecast to the existing predicted astronomical tide was as high as 30% in February on average over the whole range of water levels, as well as that compared against the Delft3D forecast in a strong northeast monsoon case. The EOF method generally outperformed the persistence method in forecasting water level anomaly for a lead time of more than 6 h. The performance was even better particularly for high water levels, making it suitable to serve as a forecast reference tool for providing high water level alerts to relevant emergency response agencies to tackle the risk of coastal inundation in non-TC situations and an estimate of the anomaly contribution from the northeast monsoon under its combined effect with TC. The model is capable of improving water level forecasts up to a week ahead, despite the general decreasing model performance with increasing lead time due to less accurate input from model forecasts at a longer range. Some cases show that the model successfully predicted both positive and negative anomalies with a magnitude similar to observations up to 5 to 7 days in advance.

Biogeographic Patterns in Density, Recruitment, Body Size and Zonation of Rocky Intertidal Predators Suggest Increased Population Vulnerability Near Southern Range Limits

ABSTRACTAimSurveying the demography of populations near species range edges may indicate their vulnerability to range contractions or local extinction as the climate changes. In the rocky intertidal, not only are latitudinal ranges constricted by thermal stress, but tides also create zonation or a ‘vertical range’ driven by sharp environmental gradients. By investigating demographics along the latitudinal and vertical ranges simultaneously, we can investigate whether populations may be vulnerable to a changing climate.LocationRocky intertidal habitats along west coast of the United States.TaxaOchre sea star Pisaster ochraceus, six‐armed sea star Leptasterias spp., emarginate whelks (Nucella ostrina and N. emarginata) and channeled whelk N. canaliculata.MethodsIn 2018, we surveyed the demographics of the taxa above at 33 sites spanning > 11° latitude from central Oregon to southern California, near the southern range limits of each taxon. We counted and sized individuals from the high to low intertidal zone. To understand how environmental stress changed with latitude, we evaluated intertidal temperatures in situ, as well as tidal extremes, tidal amplitude and wave exposure using offshore buoys.ResultsFor all taxa, population density, the relative proportion of smaller individuals (except for emarginate whelks) and the upper vertical limits on the shore declined from north to south as temperatures increased and high tide height, tidal amplitude and wave heights decreased. In addition, smaller individual Leptasterias spp. generally inhabited lower shore levels while smaller individual emarginate whelks inhabited higher shore levels coastwide. For N. canaliculata, smaller animals were higher on shore northward, but lower on shore southward.Main ConclusionsWhile this study is a snapshot in time and cannot assess impacts of climate change, our surveys suggest environmentally‐related demographic limitation toward southern range limits and demographically vulnerable southern populations. Therefore, a warming climate may cause local extinctions or range contractions near southern limits.

Submarine Groundwater Discharge at a Mega‐Tidal Beach

ABSTRACTTidally influenced groundwater systems in coastal environments represent important mixing zones of fresh groundwater and circulating seawater, manifesting as submarine groundwater discharge (SGD). Water circulation induced by tidal pumping enhances the exchange of chemicals between aquifers and coastal waters and thereby influences the biogeochemistry of coastal zones. Here, we report the results of an SGD field study conducted at a steep, mega‐tidal sand and gravel beach along the Canadian coast of the Bay of Fundy, a region with the world's highest tides (semi‐diurnal tidal ranges exceeding 10 m). Several physical and geochemical measurement techniques were employed to document the spatiotemporal SGD variability. SGD was directly sampled from seepage meters installed over multiple tidal cycles and two summer campaigns. SGD rates were estimated from tracer mass balances for radon (August 2020) and radium isotopes (July 2021) over multiple tidal cycles. Tidally averaged SGD estimates from seepage meters ranged from 12 to 87 cm d−1, with an average of 42 cm d−1, while radon tracing yielded a tidally averaged rate of 86 cm d−1. SGD estimates from radium tracing ranged from 23 to 43 cm d−1 along the shoreline and 6 to 71 cm d−1 offshore, depending on the estimated residence times. Radionuclide analyses of seepage meter waters suggest that the residence time of seawater circulation through the aquifer is less than 1 day. SGD measurements in mega‐tidal settings are rare, and the results suggest that the combination of the steep slopes, highly permeable sediments and high tidal range drive very high seepage rates for diffusive SGD. Salinity gradients in the intertidal zone demonstrate that SGD is primarily comprised of circulated seawater with negligible fresh groundwater. Although the freshwater proportion of SGD is relatively low, the large volumetric rates of total SGD can still contribute large amounts of terrestrially derived and remineralized nutrients to coastal waters.

Assessing the health risks from flooding and chemical contamination: a scoping review

Abstract Flooding can increase the mobilization of hazardous chemicals in the environment. This scoping review provides an overview of the evidence on how flood events effect our health through chemical contamination and describes the exposure pathways to guide prevention and response measures. Flooding includes surface water flooding, coastal flooding, river flooding, storm surge, monsoon rainfall and high tide. We found 110 papers that looked at the association between flooding and chemicals in the environment, with most studies looking at heavy metals, polyhydroxyalkanoates (PAHs), and arsenic. There was a lack of information on rural populations and studies on mobilisation of pesticides. Very few studies mapped or modelled human exposures, including for high-risk populations (e.g., children), and this remains an important evidence gap. Studies considering climate change highlighted the likelihood of chemical contamination and health risks to be exacerbated. Our results highlighted new pathways by which flood events mobilise chemicals and pose risks to human health (i.e., urban runoff, industrial sources). Although found extensively in the environment, gaps were identified in the evidence for pesticides, microplastics and heavy metals. Limited studies reported response measures to address the chemical contamination linked to flooding despite the health risks likely to increase due to poor infrastructure and management measures despite the extent of contaminated land and landfill sites. A dual risk management strategy (i.e., the coordinated management of both flood-related and chemical release risks is required to address flooding events, chemical releases, and health impacts.

Comparison of Phytoplankton Composition and Abundance (River, Estuary dan Coast) as Potential Water Contamination Bio-Indicators in Tallo Watershed Area

This study aims to compare phytoplankton composition and abundance in the Tallo watershed area, evaluate its ecological factors and water quality, and their correlation to particular types of water contamination. The study was performed from June to August 2021 at three stations in the Tallo watershed, including the river (1), estuary (2), and coast (3). The results suggested that the ecological parameters were still within the tolerable limit for the organisms to live. 4 classes of phytoplankton found in the Tallo watershed included Bacillariophyceae, Cyanophyceae, Dinophyceae, and Chlorophyceae, with a total of 15 genera. No Dinophyceae was found in the river during the high and low tides and there were 9 genera found during the high tide and 10 genera found during the low tide. As many as 3 classes with 12 genera were found in the estuary during the high tide, and 4 classes with 12 genera were found during the low tide. No Chlorophyceae was found on the coast during both the low and high tides. A total of 10 genera were found during the high tide and 9 genera were found during the low tide. Analysis of variance indicated that Phytoplankton Composition there is a difference in phytoplankton abundance in 3 habitats. Phytoplankton abundance on the coast was the highest, followed by the estuary and the river (coast > estuary > river). From the abundance and the composition of phytoplankton in 3 habitats, there was a strong indication of inorganic nitrogen, heavy metal, and microplastic contamination that occurred in the Tallo watershed.

A preliminary study of carbon dioxide and methane emissions from patchy tropical seagrass meadows in Thailand.

Seagrass meadows are a significant blue carbon sink due to their ability to store large amounts of carbon within sediment. However, the knowledge of global greenhouse gas (GHG) emissions from seagrass meadows is limited, especially from meadows in the tropical region. Therefore, in this study, CO2 and CH4 emissions and carbon metabolism were studied at a tropical seagrass meadow under various conditions. CO2 and CH4 emissions and carbon metabolism were measured using benthic chambers deployed for 18 h at Koh Mook, off the southwest coast of Thailand. The samples were collected from areas of patchy Enhalus acoroides, Thalassia hemprichii, and bare sand three times within 18 h periods of incubation: at low tide at 6 pm (t0), at low tide at 6 am (t1), and at high tide at noon (t2). Seagrass meadows at Koh Mook exhibited varying CO2 and CH4 emissions across different sampling areas. CO2 emissions were higher in patchy E. acoroides compared to patchy T. hemprichii and bare sand areas. CH4 emissions were only detected in vegetated areas (patchy E. acoroides and T. hemprichii) and were absent in bare sand. Furthermore, there were no significant differences in net community production across sampling areas, although seagrass meadows were generally considered autotrophic. Koh Mook seagrass meadows contribute only slightly to GHG emissions. The results suggested that the low GHG emissions from Koh Mook seagrass meadows do not outweigh their role as significant carbon sinks, with a value 320 t CO2 -eq. This study provided baseline information for estimating GHG emissions in seagrass meadows in Thailand.

SPECIFIC FEATURES OF TIDAL EXCHANGE IN THE KURIL STRAITS ACCORDING TO MODELING DATA

Specific features of tidal fluctuations of sea level and tidal currents in the straits of the Kuril Islands are studied using numerical modeling. Two-time intervals, i. e. 02.06.1977-03.06.1977 and 11.10.1977-12.10.1977, were taken to compare the parameters of tropical and equatorial tides. The simulation results were verified with the field data. It was found that the straits of the northeastern part of the Kuril Ridge have a mixed type of tides with a predominance of the diurnal course, and in the southwestern part a semi-diurnal course prevails. The highest tides (up to 2,5-3 m) in the study period were observed on 02.06.1977 near the Kamchatka Peninsula and the Hokkaido Island, as well as large islands of the Kuril Ridge. Four main oscillation periods of 12, 12,4, 24 and 25,8 hours were identified, which corresponds to the S2, M2, K1 and O1 harmonics. Analysis of the data obtained showed that the maximum velocities of the depthaveraged currents reach 4,5 m/s. The highest speeds were recorded in the Kruzenshtern, Frieze and Sredny Straits. Estimates of the tidal flow have shown that semi-daily fluctuations are more pronounced in the straits with lower average depths during a tropical tide. In deeper straits, semi-daily fluctuations at tropical tides are very weak or absent at all, an example is the Boussol Strait. It is calculated that when using a two-dimensional model, the maximum values of the tidal flow are observed in the Boussol Strait, reaching ~40 Sverdrups (Sv).

Assessment of tangible coastal inundation damage related to critical infrastructure and buildings: The case of Mauritius Island

Storm tides, which combine sea level rise (SLR), astronomical tides, and storm surges generated by tropical cyclones, pose significant threats to coastal zones, leading to flooding and substantial damage to property and infrastructure.There is a clear upward trend in the frequency of storms reaching tropical cyclone strength. A notable example is Cyclone Belal, which struck Mauritius on January 2024, during high tide, causing extensive infrastructure damage. This underscores the importance of conducting risk assessments to identify vulnerable areas and develop risk reduction strategies. However, quantitative risk assessments of storm tides are often challenging due to the lack of long-term projections. To address this, we developed a GIS-based flood model for Mauritius to simulate inundation areas and quantify the assets exposed to flooding. Under current conditions, the estimated damage exposure from extreme coastal flood events with return periods of 50 to 500 years is significant, with 6.2% and 27.1% of the area inundated, respectively. By 2100, damage exposure associated with these events is projected to increase by a factor of 1.1, with minimal variation between sea-level rise scenarios (0.3m). However, by 2200 and 2300, damage exposure is expected to rise by factors of 3.1 and 6.6, respectively. In the worst-case scenario for 2500, Mauritius could experience maximum inundation of 66.3 km2, with buildings covering 5.02 km2 submerged. Additionally, this study presents a detemporalized inundation scenario to assess impacts from any coastal flood event. This approach enables the identification of critical thresholds ( 1.5 m and 4.5 m) and , beyond which significant increases in damage exposure are likely, and allows for evaluating adaptation strategies against user-defined levels of change, rather than relying solely on predefined scenarios. These findings highlight the urgent need for strategic sectoral interventions to address the widespread consequences of coastal inundation, especially in light of critical thresholds for remedial action.

Satellite-derived bathymetry using Sentinel-2 in mesotidal coasts

Coastal zones are strategic environments of high socioeconomic, political, and ecological value, with over half of the world’s population residing within 200 km of the coast. This proximity highlights their vulnerability to extreme events, which are exacerbated by global changes, leading to significant coastal impacts such as erosion, flooding, and ecosystem services deterioration. Consequently, efficient and operational methodologies for continuous monitoring are urgently needed to face these challenges. Bathymetric data are essential for understanding coastal dynamics, yet traditional data collection methods are often constrained by logistical challenges and high costs. Spaceborne remote sensing techniques offer significant advantages over traditional ground-based methods, particularly in terms of cost-effectiveness and operational efficiency. Over the last half-century, different Satellite-derived bathymetry (SDB) methodologies have been developed; however, challenges still persist. In this research, we applied a robust SDB methodology to three different study sites: Cíes Islands, Baiona Bay, and Vao beach within the Ría de Vigo, Galicia (NW Spain). These areas offer diverse and complex mesotidal environments to test for the very first time the methodology's efficacy. SDB was retrieved with a median absolute error (MedAE) ranging from 0.35 m to 1.55 m for depths up to 14 m. Results with different data source were evaluated, obtaining MedAE for nautical charts ranging from 0.46 m to 1.55 m. The precision between the data sources were quite close. In addition, multi-image composite was generated using images coinciding with both low tide (LT) and high tide (HT) conditions across the three zones. The lowest MedAE values were consistently obtained in images classified as LT (0.46 m) corresponding to Vao area. The results highlight the potential of nautical charts as a reliable source of calibration data for SDB, confirm the effectiveness of multi-image and switching models to correct artifacts and turbidity, considering tidal effects, improving single image approaches, and leverage visible bands for precise depth retrieval under varying conditions.

Assessing sediment CO2 effluxes in the coastal ecosystem of North Sumatra, Indonesia

Coastal wetlands including mangrove play a vital role in regulating the local and global carbon cycle. Coastal areas contribute greatly to the carbon exchange process due to the complex interactions that occur between the atmosphere, land, and oceans. One of the important components in coastal carbon dynamics is CO2 gas exchange between soil, water and the atmosphere. This study aims to assess CO2 efflux across various land covers (namely natural mangrove, restored mangrove, and converted mangroves to oil palm and aquaculture pond) in the coastal areas of North Sumatra Province, and analyze the effect of sea tides and ebbs on the rate of CO2 efflux and their connection with the number and area of macrozoobenthos burrows. We applied direct sampling by using the static closed chamber method attached to portable CO2 analyzer. The mean of CO2 efflux in natural mangrove forest land covers was 866±585 mgCO2/m2/h during low tide conditions and 1137±792 mgCO2/m2/h during high tide conditions, followed by oil palm plantations at 760.71±341 mgCO2/m2/h, restored mangroves during low tide of 575.24±326 mgCO2/m2/h and 597.11±180 mg CO2/m2/h during high tide conditions, and the lowest was recorded in ponds at 588.55±358 mgCO2/m2/h. Further, we observed that tidal conditions affect the magnitudes of CO2 efflux in natural and restored mangrove forests, and we did not observe similar pattern in oil palms and ponds since these land covers were not influenced by regular tidal input. We also observed that no significant relationship between the number and area of macrozoobenthos burrows and CO2 efflux. Our findings suggest that CO2 effluxes in coastal wetlands are highly dynamic and presumably driven by complex factors and therefore, understanding their magnitudes and drivers requires extensive measurement covering large spatial and temporal scales.

The IoT-Based Early Warning System for Detecting High Tide Floods (ROB-EWS) in Tambak Lorok, Semarang Indonesia

Background and Objectives: The Tambaklorok fishing village area, located on the northern coast of Semarang City, Indonesia, is susceptible to sea level fluctuations, which often lead to tidal flooding and seawater encroaching into residential areas. Consequently, a seawater flood detector (rob) is needed for effective disaster mitigation for affected communities. This study aims to implement a disaster mitigation system by installing an IoT-based Seawater Flood (Rob) Early Warning System to reduce disaster risks and their impacts on the community. Methods: The IoT-based Early Warning System is designed to detect floods by monitoring sea level height parameters. Results: IoT-based devices measure sea level using ultrasonic sensors, with the readings processed by a microprocessor. The data is then periodically analyzed and transmitted to an application in real-time. This technology allows for real-time information dissemination through web applications and alerts in the form of sirens. These warnings enable residents to evacuate and move to safer areas. The siren alerts are categorized into two levels: Alert 1 indicates that seawater is approaching the land boundary, while Alert 2 signals that water has begun to enter residential areas. Additionally, designated evacuation zones will guide affected communities to safer areas. Conclusion: The installation of an IoT-based Early Warning System delivers real-time information to help mitigate the impact of rising sea levels (rob) in the Tambak Lorok fishing village community.

Tidal influence on Fish Faunal Distribution and Species Diversity in Kakum Estuary, Ghana

Estuarine and coastal areas are complex and dynamic aquatic environments. In such an area, where river water mixes with seawater, a large number of physical and chemical processes take place, which may influence water quality thereby affecting the distribution and diversity of the biota. The study was conducted in the transition period of dry and wet conditions from February to May 2018. The influence of low and high tides on the hydrographic parameters such as salinity, dissolved oxygen, and water temperature in the three sampling stations was analyzed in relation to fish faunal distribution and species diversity of the estuary. The common fish species in the estuary were juveniles of Sarotherodon melanotheron and Mugil cephalus, Liza falcipinnis and the crab Callinectes amnicola. These species were encountered during both low and high tides in all sampling stations, which indicates their adaptation to a broader range of hydrographic conditions. The majority of species encountered were juveniles. Although most of the fish species were marine in origin, some including Tilapia zillii, Hemichromis fasciatus and Apolochelichthys spilauchen were freshwater in origin whilst, S. melanotheron is a resident fish species in the estuary. Length-frequency distribution and length-weight relationships of S. melanotheron, T. zillii, L. falcipinnis, Mugil cephalus, and Eucinosthomus melanopterus which were the five most dominant fish species during the period of study in Kakum estuary were analyzed. The modal sizes of the dominant fish species were mainly juveniles in the length-frequency distribution. The length-weight relationships of S. melanotheron, L. falcipinnis and M. cephalus showed allometric growth, whereas that of T. zillii and E. melanopterus showed isometric growth. The study, therefore, identified that Kakum estuary is a transitional zone for both marine and freshwater fish species using the estuarine ecosystem as nursery grounds. The presence of marine and freshwater-origin species, and resident species in the estuary further suggest that estuaries are highly dynamic, and slight changes in their environment can cause a great deal of harm to its fish biota.

Tidal pumping and intertidal groundwater springs create pronounced spatiotemporal thermal variability in a coastal lagoon

AbstractIntertidal groundwater springs provide thermally stable, nutrient‐rich freshwater that causes fine‐scale variability in water temperature and salinity and promotes biodiversity in coastal estuaries and lagoons. In this study, we combined three thermal sensing techniques to elucidate summer water temperature patterns at the mouths of intertidal groundwater springs and the ambient coastal lagoon in Prince Edward Island, Canada. Thermal infrared imagery captured the spatiotemporal variability in relative temperatures of the lagoon channel and cold‐water plumes from the springs. Thermal anomalies due to the springs were detected at the surface throughout a tidal cycle, suggesting that the thermal plumes were buoyant. Fiber‐optic distributed temperature sensing paired with temperature loggers near the spring outlets recorded groundwater temperatures at low tide (~ 7°C) but ambient lagoon temperatures (up to 26°C) at high tide due to the vertical thermal gradient in the stratified water column. Calculated estuarine Richardson numbers throughout the study confirm intertidal spring buoyancy due to salinity differences. The fiber‐optic distributed temperature sensing results revealed pronounced variations in temperature as evidenced by spatial (3.7°C) and temporal (5.5°C) standard deviations over the cable length during the study and lower mean lagoon bed water temperatures at high tide (22.5°C) than low tide (24.3°C) due to heat advection from tidal pumping. Lagoon temperatures fluctuate at diurnal (solar) and semi‐diurnal (tidal) frequencies. The findings emphasize the efficacy of a multi‐technology approach to reveal fine‐scale and dynamic thermal processes that drive temperature patterns and habitat distribution in coastal lagoon ecosystems and highlight the thermal influence of intertidal springs.

Tidal Impacts on Zooplankton Dynamics in a Major Ocean-Lagoon Channel: Insights from a 25-Hour Intensive Survey in the Cotonou Channel, Benin

This study investigates the effects of tidal cycles on the zooplankton community within the Cotonou Channel, an important waterway connecting the large Nokoué Lagoon to the Atlantic Ocean in Benin. From the determination of zooplankton composition from 25-hour samples collected in July 2020, alpha diversity indices and abundance were assessed, while relationships between biotic and abiotic parameters were analyzed through Pearson correlation, analysis of variance, and principal component analysis. A total of 66 zooplankton taxa were identified, with rotifers exhibiting the highest species richness (35 taxa), while copepods dominated in abundance (71%). Zooplankton abundance varied significantly, ranging from 2 to 95 ind L−1 depending on the tidal phase. A negative correlation was found between species richness (r = −0.51, p < 0.01) and increasing salinity (3–37), indicating that higher salinity reduced diversity (r = 0.06, p > 0.05). Resilient species like Synchaeta bicornis persisted despite salinity changes. The tidal cycle structurally altered the zooplankton community, with abundance and diversity peaking at different phases, notably higher at high tide (15 ind L−1.) These initial findings underscore the complex interactions between tidal dynamics and estuarine biodiversity, suggesting the need for further research across different tidal and seasonal conditions to inform effective management and conservation efforts.

Impact of the Urbanization Process on the Subsidence Phenomena Using Remote Sensing in the Inner Districts of Ho Chi Minh City, Vietnam

Abstract Subsidence in Ho Chi Minh city (HCM city) occurs in many places, the current reason no longer comes from natural disasters but mainly from human activities (groundwater exploitation, ground improvement,…). Especially in innercity districts, during high tide or heavy rain, many areas are locally flooded, concentrated in places with high construction density. To monitor the subsidence phenomenon in urban areas, the advent of remote sensing technology is an effective tool, helping researchers and managers capture information quickly, accurately and continuously. In this study, the DInSAR method was used to determine the rate of subsidence in urban districts of HCM city. DInSAR is a popular method for estimating land displacement based on the principles of Interferometric Synthetic Aperture Radar (InSAR) using different time series data. We used C-band SAR Sentinel 1 data in the period 2015 - 2023 to analyze subsidence, the results showed that subsidence hot spots were concentrated in District 7, Binh Thanh District and part of Go Vap District at high speeds from 2 - 3 cm/year. Over time, the phenomenon of subsidence with a value of > 2cm/year was distributed in Binh Tan and Tan Phu districts following the trend of new urban expansion to the West of HCM city. Additionally, Sentinel 2 imaging data was also used in this study to demonstrate that areas with high construction density have high subsidence rates. From there, it can be seen that the urbanization process is one of the causes of subsidence in HCM city.

Evaluations of storm tide hazard along the coast of China using synthetic dynamic tropical cyclone events

Concurring with high astronomical tides, storm surges have caused devastating damage in low-lying areas along the Chinese coastal regions. However, accurately calculating tropical cyclone (TC) storm tide hazards, especially those with long return periods, has proven challenging due to limited temporal and spatial information on TCs. In this study, we adopt the Synthetic Dynamic TC Method (SDTM), which enables a more robust estimation of storm tide hazards by generating a large number of synthetic TCs based on historical best track data and ocean-atmosphere environmental data. Within the SDTM framework, synthetic TCs corresponding to 10,000 years are validated using several statistical metrics, and the associated storm tides are simulated. For comparison, we employ the Historical Storm Method (HSM) to simulate storm tides for historical TCs from 1950 to 2019. Storm tide hazard curves are calculated and compared using these two methods. Our results demonstrate that the SDTM can robustly estimate storm tide hazards for both short and long return periods, whereas the HSM performs well for short return periods but struggles to reliably assess storm tide hazards for long return periods. Notably, within the SDTM, storm tide height exhibits nonlinear growth with increasing return periods in the Gumbel plot, a phenomenon not observed in the HSM due to the limited time span of TC records. With sufficient TC data, the spatial storm tide hazard maps obtained from the SDTM can serve as a robust foundation for developing disaster prevention and mitigation policies.