Low Tidal Range Research Articles

Morphodynamics of two Mediterranean microtidal beaches presenting permanent megacusps under the influence of waves and strong offshore winds

This study focuses on four years of survey of two low-microtidal emerged beaches (average tidal range ≈ 0.3 m), presenting permanent megacusps on the French Mediterranean coast. These beaches are representative of the southern part of the Gulf of Lion (45 km of coast): the Leucate beach backed by a small dune and the La Franqui beach backed by a small lagoon. An analysis of the hydrodynamic and meteorological forcing along with morphological changes allows to define the key parameters controlling the system. These results are used to develop a conceptual model composed of five main situations and then compare it to the microtidal literature. Dominant offshore winds can reach speeds of up to 20 m s−1 (Gusts up to 30 m s−1) and have an erosive action on the backshore and produce advance of the shoreline of a few metres. This shoreline advance is mainly concentrated on the horns when it is concomitant with small fair-weather waves. Waves of moderate to high intensity (storms) lead to strong erosion and steepening of the beach face, as well as the migration or construction of a new higher berm located landward and associated with sediment deposition on the upper beach. The low tidal range may also allow the high run-up level to stabilise for a longer period of time in a high elevation on the backshore. The alternation of storm episodes and offshore wind periods could control the relative stability of the emerged beach.

Vibrio vulnificus and Vibrio parahaemolyticus in Oysters under Low Tidal Range Conditions: Is Seawater Analysis Useful for Risk Assessment?

Human-pathogenic Vibrio bacteria are acquired by oysters through filtering seawater, however, the relationships between levels of these bacteria in measured in oysters and overlying waters are inconsistent across regions. The reasons for these discrepancies are unclear hindering our ability to assess if -or when- seawater samples can be used as a proxy for oysters to assess risk. We investigated whether concentrations of total and human pathogenic Vibrio vulnificus (vvhA and pilF genes) and Vibrio parahaemolyticus (tlh, tdh and trh genes) measured in seawater reflect concentrations of these bacteria in oysters (Crassostrea virginica) cultured within the US lower Chesapeake Bay region. We measured Vibrio spp. concentrations using an MPN-qPCR approach and analyzed the data using structural equation modeling (SEM). We found seawater concentrations of these bacteria to predictably respond to temperature and salinity over chlorophyll a, pheophytin or turbidity. We also inferred from the SEM results that Vibrio concentrations in seawater strongly predict their respective concentrations in oysters. We hypothesize that such seawater-oyster coupling can be observed in regions of low tidal range. Due to the ease of sampling and processing of seawater samples compared to oyster samples, we suggest that under low tidal range conditions, seawater samples can foster increased spatial and temporal coverage and complement data associated with oyster samples.

Regional wave model climate projections for coastal impact assessments under a high greenhouse gas emission scenario

In the future, shifts in wind storms across the North and Baltic Seas are highly unpredictable, challenging the projection of wave conditions for managing coastal hazards. Moreover, regional sea level rise (SLR), with very large uncertainty, complicates the situation for stakeholders seeking recommendations for climate adaptation plans. The purpose of this study is to examine the change of the storm surge and wind wave components of the water level due to climate change in a low tidal range Køge Bay near the entrance of the Baltic Sea. Under a high greenhouse gas emission scenario RCP8.5, we employed a regional climate model (HIRHAM) forced wave model (WAM) and focused on the wave model results during the “storm surge conditions” (exceeding 20 years storm surge events) and “stormy conditions” (exceeding 90th percentile of wave heights). We find that the change in both wave height and period in the future is negligible under “stormy conditions”. Nevertheless, under “storm surge conditions” when considering SLR, the simulated wave height is projected to double in the near future (mid-century) under RCP 8.5, and the wave period may also increase by about 1.5 seconds. This is because some high significant wave height events in the future are associated with the storm surge events when considering SLR. The findings suggest that the combined effects of mean sea level rise, storm surge and waves are likely to increase the risk to a bay with geography and exposure comparable to Køge Bay. As a result, the future plan for climate engineering protection should place a premium on the additional wave energy protection associated with storm surges.

Multi-criteria analysis of selected coastal protection measures in areas with a low tidal range

Multi-criteria analysis of selected coastal protection measures in areas with a low tidal range

On the Intermittent Formation of an Ice Bridge (Nunniq) across Roes Welcome Sound, Northwestern Hudson Bay, and Its Use to Local Inuit Hunters

Ice bridges are unique features that form when sea ice consolidates and remains immobilized within channels. They form in many locations throughout the Arctic and are typically noted for the polynyas that form on their lee side. However, ice bridges also provide a temporary platform that may be used by both humans and wildlife to cross otherwise impassable channels. For generations, Inuit in Coral Harbour, Nunavut, have used an ice bridge to cross Roes Welcome Sound and expand their hunting territory, though they report that the bridge only forms approximately every four years. Of interest both to Inuit and the scientific community is why the bridge forms so intermittently, by what mechanisms, and whether the frequency will change with ongoing warming and sea ice loss. Using satellite imagery, we determined that the bridge formed during 14 of the past 50 years (1971 – 2020). Generally, the bridge forms between January and March, during a cold period that coincides with neap tide, and after surface winds have rotated from the prevailing northerly (along-channel) winds to west-northwesterly (across-channel) winds. This rotation compresses the existing ice pack against Southampton Island, where it remains stationary because of the calm along-channel winds and low tidal range, and coalesces under cold air temperatures. Breakup occurs between mid-June and early July after the onset of melt. Overall, the bridge forms when a specific set of conditions occur simultaneously; however, a warming climate, specifically a reduction in very cold days, and shorter ice season may affect the frequency of bridge formation, thereby limiting Inuit travel.

Estuarine tidal range dynamics under rising sea levels.

How an estuary responds to sea level rise (SLR) is complex and depends on energy drivers (e.g., tides and river inflows), estuarine geometry (e.g., length and depth), intrinsic fluid properties (e.g., density), and bed/bank roughness. While changes to the tidal range under SLR can impact estuarine sediment transport, water quality, and vegetation communities, studies on the altered tidal range under SLR are often based on case studies with outcomes applicable to a specific site. As such, this study produced a large ensemble of estuarine hydrodynamic models (>1800) to provide a systematic understanding of how tidal range dynamics within different estuary types may change under various SLR and river inflow scenarios. The results indicated that SLR often amplifies the tidal range of different estuary types, except for short estuaries with a low tidal range at the mouth where SLR attenuates the tides. SLR alters the location of the points with minimum tidal range and overall tidal range patterns in an estuary. Variations in tidal range were more evident in converging estuaries, shallower systems, or in estuaries with strong river inflows. These findings provide an indication of how different estuary types may respond to estuaries and may assist estuarine managers and decision makers.

Rip current hazard at coastal recreational beaches in China

Rip current has become the primary coastal hazard globally. This work presents the operational investigation of nation-wide rip current hazard and its implications for the beach recreational safety in China. Accumulated domestic surfzone fatalities were reported more than the marine disaster casualties over recent ten years. The surfzone accident has high occurrence frequency in the southern regions and reaches its peak from July to August. The spatial distribution of comprehensive hazard levels at 101 major coastal beaches is evaluated based on the proposed risk index system. The methodology involves multiple approaches of statistical analysis and field survey. Southern provinces feature higher rip current hazard than the north due to larger wave, lower tidal range, and more dynamic littoral morphology. The rip current prominently contributes to the demographic variations of beach drowning statistics. The occurrence probability of rip currents could be high in either hotter or cooler weather while the seasonal shift depends on both wave climate and the local shoreline profile. Enhancing public awareness of the rip current hazard has been proved to be a very effective way decreasing surfzone accidents.

Multi hazards risk assessment of Indian Sundarbans using GIS based Analytic Hierarchy Process (AHP)

The people of Sundarbans are well experienced with multiple hazards affected their life and livelihood since the incitation of 1st civilization over here. Low lying delta plain and massive population pressure increases the exposure limit of this area. For saving this valuable ecosystem and millions of people living here coastal planners and decision makers require a comprehensive risk assessment of this area. Present study applied a GIS based analytic hierarchy process (AHP) for assessing risk of Indian Sundarbans at a micro regional scale (1 km2). Total 4989 grids have been generated and all calculations were made at a grid level scale. Fourteen factors representing forcing (4), vulnerability (8) and exposure (2) of this area were used for the calculation. All factors were categorized into 5 point risk classes based on their relative contribution to the risk. Risk has been represented at grid level and consequently at mouza (lowest revenue unit) level scale for representing the area and populations under certain risk categories. The results showed that around 26% (11.3 lakh) and 23% (9.9 lakh) populations of Indian Sundarbans are under high to very high risk categories. Major parts of Basanti, Gosaba, Hingalganj, Canning-I, Canning-II, Jaynagar-I, Jaynagar-II, Sandeshkhali-I, Sandeshkhali-II are belongs to the high-very high risk classes. Higher effective sea level rise, lower tidal range, high population densities are associated with higher risk of these areas. The risk map provides essential information for identifying relative risk of an area which can be used for future management and planning.

The importance of weather and tides on the resuspension and deposition of microphytobenthos (MPB) on intertidal mudflats

Abiotic variables, such as weather and tidal forces, are potentially as important as biotic factors (growth, predation, competition) in driving the variability of microphytobenthic (MPB) biomass on intertidal flats. Patterns of spatial distribution and temporal variability in MPB Chl. a, sediment Extracellular Polymeric Substances (EPS) and benthic diatom species composition were investigated during daily sampling spanning neap to spring tide periods on intertidal mudflats in the Colne Estuary, U.K., in three different seasons, with a particular focus on the influence of wind, rainfall, sun hours in the days prior to sampling, and tidal range. Spatial distribution (at < 1 m and <5 m scales) made the greatest contribution to biomass variability, followed by temporal (inter-monthly) variability. MPB Chl. a and EPS concentrations were positively correlated with sun-hours and tidal range, and negatively with rainfall and wind speed. Higher benthic MPB biomass was associated with lower suspended solid and Chl a loads, indicating biostabilisation of surface sediment. Suspended sediment loads and suspended Chl. a concentrations were positively correlated, and were significantly higher during neap rather than spring tides. Sediment settlement rates were higher during neap tides and related to suspended sediment load. The percent similarity in the benthic and suspended diatom assemblages (species relative abundance, RA) increased linearly with suspended solid load, with highest similarity during neap tides, with pennate benthic diatom taxa (Gyrosigma balticum, G. scalproides and Pleurosigma angulatum) dominant, indicating local sediment resuspension. During Spring tides, species similarity was lower, with a higher RA of planktonic centric diatoms (Actinoptychus, Coscinodiscus and Odontella) and lower sediment loads. Despite greater volumes of water movement during high tidal range periods, the highest levels of localised resuspension and remobilisation of MPB biomass across the mudflats occurred during low tidal range neap tide periods, when wind-induced waves were a key factor, particularly with shallower water depths over the intertidal mudflats.

Exploring the potential of solar, tidal, and wind energy resources in Oman using an integrated climatic-socioeconomic approach

This study presents - for the first time-a comprehensive assessment of the potential renewable energy resources in Oman, with a particular focus on solar, wind, and tidal energy resources. This study adopts a novel approach to assess the potential of these energy resources, in which information from multiple climatic indicators is coupled with socioeconomic drivers of energy development. Specifically, based on a daily dataset of the National Centers for Environmental Prediction (NCEP) Climate Forecast System Reanalysis (CFSR), three climate indicators were employed to characterize the frequency, intensity and duration of solar radiation and wind speed. Then, we introduced a new overall assessment index (OAI) based on these three climatic indicators to explore the best localities – from a climatic perspective-for generating solar and wind energies. The validity of the recommended sites was discussed in the context of important physiographic, environmental, and socioeconomic constraints (e.g. population density, urban settlements, distance to water bodies, transportation network, etc.). Results demonstrate that both solar radiation and wind can be seen as promising and substantial alternative sources of fossil fuel resources in Oman, with almost 3.2% and 4.4% of the Omani territory being valid for a sustainable use of wind and solar radiation, respectively. The most recommended sites for wind generation are located mainly along Al-Jazir and Duqum coasts of southeastern Oman, where a promising wind energy center can be constructed. The best localities for the development of hybrid solar radiation generation centers are likely to be placed in Sohar and Thumrayt, where solar intensity approaches 8.1 kWh/m2, with a high frequency of occurrence throughout the year. In contrast, Oman showed low potential to generate tidal power, mainly due to a low tidal range (<2 m) along the majority of the Omani coastline. This study provides a solid base for national and local decision makers in Oman for a reliable assessment, monitoring, and sustainable exploitation of clean and renewable energy resources, especially with high population growth, accelerated urbanization, and rapid economic growth over the past few decades, which can pose more challenges to future energy demand in this country.

Vulnerability of mangrove ecosystems to climate change effects: The case of the Yucatan Peninsula

Climate change adds an additional pressure on mangrove health, and the present study evaluated mangroves' vulnerability to sea level rises at four sites (Los Petenes, Celestun, Cancun, and Mahahual) on the Yucatan Peninsula, Mexico. Exposure, sensitivity, and adaptive capacity were evaluated on a scale from 1 to 5 to identify characteristics that cause the mangrove vulnerability. Mangroves in sites with different characteristics had different vulnerabilities, despite having similar exposure. The best-conserved mangroves had low vulnerability and were in good health because of their sensitivity, whereas mangroves affected by human activity were more vulnerable in terms of sensitivity and adaptive capacity. Overall, Mahahual had the highest vulnerability (3.0) because of its low tidal range (~5 cm), changes in precipitation (−25 mm year−1), poor ecological conditions (low basal area without positive changes), low resilience of adjacent ecosystems (poor condition of coral reefs and seagrass meadows), and poor mangrove protection. This vulnerability assessment method identifies factors that affect vulnerability and can be used to develop management strategies that decrease mangrove vulnerability to climate change by reducing sensitivity and increasing the adaptive capacity of the ecosystem and the surrounding communities.

Multi proxy analysis for reconstructing the late Holocene evolution of a Mediterranean Coastal Lagoon: Environmental variables within foraminiferal assemblages

This study reconstructs the evolution of foraminiferal assemblages and the environmental variables (type of substrate, content in calcium carbonate and content in organic matter) in the Valencia lagoon (western Mediterranean) in response to changes in the late Holocene. In this area of low tidal range, several multiproxy analyses were carried out to determine which environmental variables influence the distribution of the fossil assemblage, and its association with global, regional or local climatic phenomena. The statistical results show that in environments with higher exposure to marine conditions, the calcium carbonate content is the dominant factor, whereas in more restricted environments the type of substrate (grain size) is determinant. The micropaleontological content reveals the evolution from a saline paleoenvironment with a clear marine influence towards the hyposaline or freshwater conditions, recorded at the top.Three phases were identified in the evolution of this area from 2800 cal yr BP to the present. A brackish lagoon with marine connection at the base, followed by a deposit of brackish lagoon (1232 ± 74 cal yr BP − 791 ± 104 cal yr BP), culminating in a brackish marsh (791 ± 104 cal yr BP to present), interpreted as the definitive closure process of the lagoon, favored by the coastal progradation processes related with an extraordinary input of sediments. These findings reflect the climatic variability of the Medieval Climate Optimum (MCO) (1.05 and 0.65 kcal BP) and the migration of the river Turia mouth, which favored the coastal progradation processes. The flood events registered at this phase, may have coincided with changes in the landscape and greater anthropic influence at the end of the LIA, 150 cal yr BP. Coastal processes are mainly responsible for the evolution of this area during phase I, while the influence of fluvial processes is significant towards the top, especially in phase III.

Archaeological, geomorphological and cartographical evidence of the sea level rise in the southern Levantine Basin in the 19th and 20th centuries

Sea level variability affected by sea water mass is strongly associated with global, regional and local climate. In this context, the eastern Mediterranean Sea has been intensively investigated in recent decades because of its sensitivity to climatic and environmental variables, due to the influence of the Eastern Mediterranean Transient (EMT). The sea level in Israel during the Crusader period (12th-13th centuries CE) was found to be −0.5 ± 0.20 m relative to the present mean sea level (MSL). The difference between the Crusader sea level and the present-day MSL raises some questions which bring us to the aim of this study: estimating the timeline of the changes in sea level elevation in the eastern Mediterranean over the last two centuries. Archaeological evidence from areas of low tidal range, such as the Mediterranean Sea, can provide significant information on sea level changes for times when instrumental measurements where not yet available (e.g., before 1955 in Israel). The method employed in this study integrates two dimensions: The vertical—estimating the changes in sea levels relative to the present MSL, based on archaeological evidence; and the horizontal—determining the coastline changes, based on coastal architectural and geomorphological structures appearing in historical maps. Both the structural and the cartographic evidence for sea level changes date to the 19th Century, and indicate a rise of 0.36 m over the last two centuries.Findings attesting to horizontal changes, indicate a gradual migration of the coastline landward, to the east since 1863 and a rapid change in the coastal geomorphology at the beginning of the 20th century. The sea level increase from the 19th century might be, in part, a consequence of regional trends and, in part, a result of a gap between method accuracy (archaeology and modern measurements). Nevertheless, the drastic change in the geomorphology of the coastline may indicate an extreme meteorological event, such as a storm at sea, accompanied by a local rise of sea level, but further research is required to verify this.

Impact of upstream runoff and tidal level on the chlorinity of an estuary in a river network: a case study of Modaomen estuary in the Pearl River Delta, China

Abstract Saltwater intrusion exerts great impact on water supply and water withdrawal from estuarine areas. A chlorinity prediction model based on backpropagation neural network was constructed, calibrated, and validated, considering phase lags, with the Modaomen estuary in the Pearl River Delta (PRD), China as case study. This study aimed to investigate impacts of upstream runoff and tidal level on the changing properties of estuarine chlorinity. Nine boundary conditions – low tide and tidal range both with three different frequencies – were designed to explore the changing process of estuarine chlorinity and obtain the critical upstream runoff for saltwater suppression. Results indicated the model performed efficiently; Nash–Sutcliffe efficiency coefficient and R2 were both 0.91 in training period, 0.76 and 0.82 in testing period, and 0.64 and 0.77 in validation period, respectively, and estuarine chlorinity shows slightly different changing processes of decline rate under the nine boundary conditions when the upstream runoff increases. The higher the designed tidal range and lower daily tides together with the smaller the amount of upstream runoff, the higher the estuarine chlorinity. The critical upstream runoff of the Pinggang pumping station is 2,500 m3/s. These findings provide a foundation for water supply security and upstream reservoir dispatching in estuarine areas in dry periods.

Tidal range and recovery from the impacts of mechanical beach grooming

Mechanical grooming to remove litter and wrack from sandy beaches reduces strandline biodiversity. The impact of tidal range on recovery rates of strandline ecosystems after grooming has not been examined to date, even though tidal range is known to affect the spatial and temporal patterns of seaweed. We compared taxon richness of macroinvertebrates that occur all year round at 104 sites on two coastlines at similar latitudes in Northern Europe that have pronounced differences in tidal range. Macroinvertebrate taxon richness was positively correlated with algae depth on both groomed and ungroomed beaches but was lower on groomed beaches. This was the case even in the off season despite wrack depths returning to similar levels found on ungroomed beaches. These impacts of grooming which extend into the winter offseason where found to be higher on beaches with a lower tidal range. We suggest this is likely to be because in areas with little tidal variation, irregular and unpredictable storm events are likely to be the predominant source of new wrack deposits. Our results suggest it is particularly important that management strategies to mitigate the impacts of grooming are adopted in areas with low tidal range.

Optimal submergence of horizontal plates for maximum wave energy dissipation

Rubble-mound breakwaters are widely used for beach protection and generate shelter zones in the water, although their feasibility diminishes as water depth increases, due mainly to construction costs. In this paper an alternative structure, a fixed submerged horizontal plate, is tested in the hope that such a design may be a practical engineering option for the protection of small ports and marinas, and/or providing a sheltered zone for recreational purposes. The interaction of irregular unidirectional-waves with the plates was studied using CADMAS-SURF software and validated experimentally. Several non-dimensional parameters were tested in order to evaluate their contribution in dissipating the incoming waves. Results suggest that energy loss depends to a large degree on the combination of the relative depth, wave steepness, relative thickness, relative length and relative submergence, with the last being the most important, as it significantly affects the wave-plate interaction. The plate produces greatest dissipation when placed at a depth of 3% of the water column. It should therefore be deployed near the surface and in regions with low tidal range conditions. Plate lengths of 20% of the incoming wavelength and a relative thickness of 0.08 are recommended to produce greater energy dissipation with lower transmission and reflection.

Rekonstruiranje promjena morske razine na istočnoj obali Jadrana (Hrvatska) – pregled

Rocky karstified coast, low tidal range, indented shoreline with numerous islands, diverse coastal biocenoses, abundant palaeontological, archaeological and historical evidence, relatively dense tide-gauge stations and developing GPS network – all these facts offer optimal prerequisite for the sea-level changes studies on the Croatian coast. Through various methodological approaches (geomorphological, biostratigraphical, archaeological/historical, mareographic, geodetic, radiometric), most of these issues have been used in order to reconstruct relative sea and land motions, yielding scattered and sometimes erroneous results. Unfortunately, some of them have been often uncritically used as the basis for the subsequent research. Only recently, with multidisciplinary approach, sequences of relative sea-level variations have been successfully revealed, but opportunities that eastern Adriatic coast offers will, undoubtedly, ensure relatively rapid research progress.

Did Vessels Beach in the Ancient Mediterranean? An assessment of the textual and visual evidence

The practice of beaching seafaring ships in the ancient Mediterranean is a widely accepted phenomenon. This paper examines the evidence for beaching and outlines the various methods, tools and technology employed. While habitual beaching for seafaring vessels is testified for the Geometric Period Aegean, for later periods the evidence is primarily negative. With the increasing robustness of the structure and weight of ships, the addition of the ram for naval vessels, and developing economic circumstances leading to the necessity of round merchant vessels, habitual beaching became impractical also in this region. In the Mediterranean, where the low tidal range practically precludes the technique of tide beaching, both galleys and merchantmen were largely restricted to anchoring and mooring.

Integração da gestão de recursos hídricos e da zona costeira em Santa Catarina: a zona de influência costeira nas bacias dos rios Mampituba, Araranguá, Tubarão e Tijucas, SC

The land use in the basin directly affects the coastal zone as both are connected and must be managed in an integrated manner. However, in Brazil the management policies of both environments are fragmented and there is no effective consideration that the coastal zone is part of the basin. This study aims to test whether the use of a zone of coastal influence (ZCI) based on physical criteria is useful for integrated coastal management. The physical criterion used is the propagation of tidal wave in the estuary, which is simulated by the non-permanent flow module of HEC-RAS model. The case study is the basins of Mampituba, Ararangua, Tubarao and Tijucas rivers, Santa Catarina state, Brazil. The ZCI was set using the minimum affluent flow, which leads to: up to 29 km upstream in the Mampituba River, 34.4 km in Itoupava River and 28.8 km in Mae Luzia River (both Ararangua River affluents), 20.7 km in Tubarao River and 21,25 km in Tijucas river. The model showed good results for the penetration of the astronomical tide, although the ZCI was small due to low tidal range in the analyzed estuaries. The ZCI based on physical criteria proves to be a useful tool, but the criteria used need adaptations, such as the inclusion of 50 km line from the coast or the propagation of meteorological tide. The ZCI is important to include the cause and effect relationships between land and water use and coastal zone management, especially for the grant of water rights and environmental licensing.

Geomorphic knowledge for mangrove restoration: a pan‐tropical categorization

AbstractExtreme events such as storm surges and tsunamis in combination with subsidence of densely populated coastal areas pose an increasing threat to millions of people in the tropics. Intertidal mangrove forests may form a natural protection against some extreme events, but have also widely been destroyed by coastal development. The establishment of mangroves and the maintenance of their stability over the short‐ to long‐term requires an understanding of sedimentary processes and landforms in the coastal zone, making geomorphology a crucial, but sometimes neglected discipline when attempting restoration for disaster risk reduction. Mangrove geomorphic setting varies markedly across the tropics, depending on abiotic parameters such as suspended sediment supply and tidal range, with different restoration strategies suitable for each. In this study we provide a global categorization of mangrove geomorphic settings, based on the literature and global remote sensing data. The world's mangroves can be broadly defined as: (1) minerogenic and high tidal range; (2) minerogenic and low tidal range; and (3) organogenic and low tidal range. We further discuss restoration and management approaches most suitable for each geomorphic setting. Overall, this study can be used to inform managers about the relevance of geomorphic knowledge for successful mangrove restoration, how an understanding of geomorphology can influence site selection and restoration success, and how to match specific restoration methods to the prevailing geomorphic context. The stronger incorporation of geomorphic knowledge into site planning and design will improve the success rates of restoration for this important and globally threatened ecosystem. Copyright © 2015 John Wiley &amp; Sons, Ltd.