Tidal Water Level Research Articles

Is marine sediment the source of microbes associated with accelerated low water corrosion?

Accelerated low water corrosion (ALWC) is a form of microbiologically influenced corrosion (MIC) associated with the degradation of marine structures around the low tide water level. A better understanding of the role of microbes in this degradation and the source of these microbes is required to improve the prediction and mitigation of the costly failures occurring due to ALWC. The microbial communities present in a sediment sample and on an ALWC tubercle on adjacent steel sheet piling from a tidal estuary were studied using culture-based isolation and metabarcoding. A total of 43 pure cultures were isolated from the sediment using a variety of culture conditions. Phylogenetic analysis of their 16S rRNA genes placed them in the Actinobacteria, Bacteroidetes, Firmicutes, and Proteobacteria (Alphaproteobacteria and Gammaproteobacteria). 16S rRNA gene metabarcoding of the sediment and tubercle revealed similar microbial groups at varying relative abundances. No Deltaproteobacteria were isolated from the sediment but they were present in both samples according to metabarcoding and their high abundance (49.3%) in the tubercle could indicate an important functional role. Although some sediment isolates and operational taxonomic units from the metabarcoding have previously been associated with surface colonisation or biofilm formation in MIC, there was no strong evidence for the notion that the sediment adjacent to ALWC was the source of tubercle microbes. Further isolation strategies and functional investigations of representative bacteria at different stages of corrosion are being carried out for additional laboratory-based corrosion studies.

Topography of the intertidal zone along the shoreline of Chittagong (Bangladesh) using PROBA-V imagery

ABSTRACTAcross the oceans shorelines, monitoring the topography of the intertidal zone is generally challenging. The present study is motivated by the recognized role of the intertidal topography in the near-shore hydrodynamics. We consider the region of Chittagong (northern Bay of Bengal) because of its propensity to powerful cyclone surges and associated inundation hazard. So as to curb the lack of in situ knowledge of intertidal topography, we present an original procedure relying on spaceborne optical imagery. Our method essentially amounts to a water line detection performed at various tidal levels. We apply our procedure to the recent PROBA-V (Project for On-Board Autonomy-Vegetation) multi-spectral imagery mission. The first step of our procedure concerns the shoreline extraction. PROBA-V imagery consists of four bands (Red, Blue, near-infrared – NIR, short-wave infrared – SWIR), which are then combined to generate an artificial red-green-blue (RGB) image. This RGB image is then converted into the hue-saturation-value (HSV) colour space. A simple thresholding is applied to hue and value channels to separate water masses from land masses. This process is applied to several images taken at different water levels (i.e. different parts of the tidal cycle) and the corresponding water lines are inferred. To estimate the altitude level of the water lines, we rely on tidal observations from two gauges located at Chittagong and Cox’s Bazar. We operate an ad-hoc extrapolation of the point-wise gauge data to generate a synthetic tidal water level record all along the shoreline. These synthetic tidal heights are then combined with the shorelines to generate the final digital elevation model (DEM). The DEM we generated covers a 40-km long stretch of shoreline around Chittagong city. We assessed this DEM by comparison with two independent data sets based on in situ surveys as well as on Pléiades spaceborne stereoscopy. We conclude that our DEM is accurate within 1 m to 2 m, which is within the error bar of these validation data sets. Our procedure being essentially objective, it is easy to automate, for processing of other imagery satellite, including at high resolution and/or in real time.

A simple approach to estimating freshwater discharge in branched estuarine systems

AbstractIn tidal estuaries, quantifying freshwater discharge is still a difficult problem that has not yet been overcome due to the inherent difficulty in measuring and analysing the tidal discharge, especially during periods of low river flow. Because observations are often made in the stations further upstream, where the ratio of river to tidal discharge is large, it remains difficult to determine the discharge rate in the saline region. Freshwater discharge estimation is even more difficult in a branched estuary system having multiple diversion channels that connect with each other at a junction. To date, several methods have been developed for estimating freshwater discharge in estuaries. The most widely used are analytical and conceptual models that employ salinity as the principal trace and numerical simulations. However, these methods are very time consuming and costly as they require large sets of observations before the computations can take place. This paper presents a simple approach to investigating the discharge distribution over branched channels by considering the energy loss due to friction. We develop an analytical model that can obtain the discharge rate quantitatively at a junction where the main flow bifurcates into two branches. The model uses the bed roughness, tidal water level, and cross‐sectional profile under tidally averaged conditions as input data. Two selected estuarine systems in the Hiroshima delta in Japan and the Mekong delta in Vietnam have been investigated. Computations of the newly developed model show good agreement with earlier published results computed by sophisticated analytical and numerical models.

Prediction of nontidal sea level variations in the Persian Gulf using data assimilation techniques

ABSTRACTThe regular pattern of tidal water level fluctuation in the open seas is often deviated by the effect of weather systems. The stochastic behavior of these systems makes it difficult to predict the nontidal residuals (NTR) precisely. The hydrodynamic models as efficient tools for the simulation of NTR may suffer from lack of accuracy due to approximate boundary conditions and forcings. Data Assimilation (DA) techniques combine hydrodynamic model predictions with available field observations to improve the predictions. In this study, a number of DA methods were employed to improve the NTR predictions in a semienclosed basin. The results have shown the studied DA techniques, which are originally developed for weather prediction problems, can be improved by considering the physical mechanisms of NTR generation. A new formula was introduced for the calculation of weight factors of the existing methods. Application of the proposed method increased the accuracy of NTR predictions significantly so that the correlation coefficient of the NTR predictions increased from 0.660 to 0.896 and the root mean square error decreased from 5.22 cm to 2.51 cm. In addition, so it is concluded among the studied DA schemes, Barnes method has better efficiency for prediction of NTR in the region.

Yanliao Beach Nourishment Methods

Yanliao Beach, part of Taiwan’s Northeast Coast National Scenic Area, is a major sightseeing and recreation spot. In recent years, the number of tourists has increased, and maintaining the beach’s recreation function has become crucial. In 2007, Typhoon Krosa caused substantial beach erosion at Yanliao Beach; sand dunes collapsed, resulting in a beach scarp and endangering facilities toward the back of the beach. To protect the sand dunes and beach scarp of the post-typhoon topography, based on long-term Yanliao Beach topographic survey information and long-term tidal water level records, this study conducted an integrated artificial beach nourishment method that comprised replenishing the coastal beach and dunes. The planned areas for sand replenishment were those above the mean high water line. This beach nourishment measure protected the dunes from collapsing further and mitigated the risk of beach nourishment polluting the water in front of the beach. Topographic survey results revealed that the large amount of sand deposited in the intertidal zone resulted in the 0 m shoreline advancing toward the seaside. The width of the beach increased, indicating the success of this integrated beach nourishment method.

Temporal variations and temperature sensitivity of ecosystem respiration in three brackish marsh communities in the Min River Estuary, southeast China

Ecosystem respiration (Reco) is an important pathway for gaseous carbon loss in coastal wetland environments. However, little is known regarding the dynamics of Reco and its temperature sensitivity (Q10) under different tidal stages, and vegetation types. In this study, Reco was measured with dark chambers for nearly 2 years in three different brackish marsh stands dominated by Cyperus malaccensis, Phragmites australis, and Spartina alterniflora, respectively, in the Min River estuary of southeast China. The mean Reco across tidal stages and vegetation types exhibited strong temporal variations, and the Q10 value for Reco was higher in the warm months than in the cold months. The mean annual Reco was negatively correlated with electrical conductivity and soil water content, but positively correlated with both tidal water level and soil pH (P < 0.05). On the other hand, the seasonal variation in Reco and Q10 was largely driven by the thermal regimes and soil salinity. Also, we found that the mean Reco and Qs10 value were both relatively higher when the site was exposed before tidal inundation, as compared to that after tidal inundation for all the vegetation types studied (P > 0.05). Overall, the C. malacensis and S. alterniflora stands had the highest and lowest average rates of Reco, respectively, while the mean Qs10 values were lower in the Phragmites australis stand than the other two vegetation types. Our findings point to the need of strengthening the in situ measurements of gas fluxes at multiple time scales in order to develop a better understanding of the response of Reco to changing environmental conditions in the subtropical coastal wetlands. Our results also reiterate the importance of considering the influence of vegetation types in characterizing the magnitude and temperature sensitivity of Reco in estuarine tidal marshes for predicting ecosystem responses to future global change.

Building digital topography model of the intertidal zone between Caofeidian Nanpu town and Tanggu district using multi-period remote sensing data

The intertidal zone, a change zone of land and sea interaction, has abundant land reserves, tourism and other resources, which has a location advantage of great engineering construction in China’s coastal areas and thus is very important to investigate and monitor the topography of the tidal zone and also keep track of its topographic changes. In this study, the new section of the Bohai sea coastal zone from Nanpu to Tianjin Bohai sea area has been chosen as an example. Based on the terrain feature of the information expressed by the multi-period remote sensing image information and the tidal water level information as well as the tidal data acquisition time in the remote sensing image data, we have been calculated the water line (or edge point) digital elevation topography inversion analysis, and also constructed the digital terrain elevation model, and most importantly have provided a kind of quantitative method to get tidal zone (tide beach) terrain information.

A study on the influence of tides on the water table conditions of the shallow coastal aquifers

Tidal variation and water level in aquifer is an important function in the coastal environment, this study attempts to find the relationship between water table fluctuation and tides in the shallow coastal aquifers. The study was conducted by selecting three coastal sites and by monitoring the water level for every 2-h interval in 24 h of observation. The study was done during two periods of full moon and new moon along the Cuddalore coastal region of southern part of Tamil Nadu, India. The study shows the relationship between tidal variation, water table fluctuations, dissolved oxygen, and electrical conductivity. An attempt has also been made in this study to approximate the rate of flow of water. Anyhow, the differences are site specific and the angle of inclination of the water table shows a significant relation to the mean sea level, with respect to the distance of the point of observation from the sea and elevation above mean sea level.

Seepage Flow Model and Deformation Properties of Coastal Deep Foundation Pit under Tidal Influence

As the coastal region is the most developed region in China, an increasing number of engineering projects are under construction in it in recent years. However, the quality of these projects is significantly affected by groundwater, which is influenced by tidal variations. Therefore, the regional groundwater dynamic characteristics under tidal impact and the spatiotemporal evolution of the seepage field must be considered in the construction of the projects. Then, Boussinesq function was introduced into the research to deduce the seepage equation under tidal influence for the coastal area. To determine the spatiotemporal evolution of the deep foundation pit seepage field and the coastal seepage field evolution model, numerical calculations based on changes in the tidal water level and seepage equation were performed using MATLAB. According to the developed model, the influence of the seepage field on the foundation pit supporting structure in the excavation process was analyzed through numerical simulations. The results of this research could be considered in design and engineering practice.

Renewable Energy Potentials along the Bay of Bengal due to Tidal Water Level Variation

The projected increase in energy demand coupled with concerns regarding present reliance on fossil fuel and associated environmental concerns had led to increased interest in exploiting renewable energy sources. Among different renewable energy sources, tidal energy is unique and most suitable because of its predictable nature and capability to ensure supply security. Tide consists of both kinetic and potential energy which can be converted to electricity using well-proven technology. The potential energy of tides - the principal focus of the study, is stored due to rise and fall of the sea level. Head difference created due to tidal variation between basin side and sea side of a barrage stores potential energy which is converted into fast-moving water that rotates turbine and generates electricity. Bangladesh with its long coastline has promising prospects of tidal energy resource development. The study focuses on tidal energy resource exploration and exploitation along several competent locations of the Bengal coastline. Tidal records of flood and ebb tide of these locations are analyzed to calculate the potential energy. Finally, available potential techniques of energy extraction are evaluated for annually generated energy estimation. This study investigates the prospect and utilization of tidal energy concept and reviews the possibilities and opportunities of employment of the technology for sustainable development and climate change mitigation in context of Bangladesh.

Do wave heights and water levels increase ocean lifeguard rescues?

ObjectiveTo investigate the association of wave height and tidal water level changes with the frequency of ocean lifeguard rescues. MethodsAll ocean lifeguard rescues recorded by Newport Beach Lifeguards in 2015 and 2016 were linked by time and location to weather and ocean variables contained in other historical databases. We performed separate multivariable analyses using mixed effects negative binomial regression to evaluate the total effects of wave height, mean water level (primarily set by tidal elevation), and rising vs. falling water level, on the frequency of ocean rescue in the study location, controlling for confounding variables. ResultsNewport Beach Lifeguards made 8046 rescues during the study period. In all areas of the beach, rescue frequency increased as waves got larger (IRR: 3.25; 95%CI: 2.91–3.79) but then decreased in large surf (IRR: 0.52; 95%CI: 0.37–0.73). In two sections of beach, lifeguards made more rescues during lower water levels, but in the third section of beach, made more rescues during higher water levels. Rescue frequency increased in two sections of beach with rising water levels, but did not in the other section. ConclusionsWave height, water level, and water level direction were associated with rescue frequency, but the environmental factors included in the analysis did not fully account for most variation in rescue frequency. Other factors need to be evaluated to identify major determinants of rescue frequency.

A Kalman Filter Approach to Realize the Lowest Astronomical Tide Surface

ABSTRACTIn this paper , we present a novel Kalman filter approach to combine a hydrodynamic model-derived lowest astronomical tide (LAT) surface with tide gauge record-derived LAT values. In the approach, tidal water levels are assimilated into the model. As such, the combination is guided by the model physics. When validating the obtained “Kalman-filtered LAT realization” at all tide gauges, we obtained an overall root-mean-square (RMS) difference of 15.1 cm. At the tide gauges not used in the data assimilation, the RMS is 17.9 cm. We found that the assimilation reduces the overall RMS difference by ∼ 31% and ∼ 22%, respectively. In the Dutch North Sea and Wadden Sea, the RMS differences are 6.6 and 14.8 cm (all tide gauges), respectively. Furthermore, we address the problem of LAT realization in intertidal waters where LAT is not defined. We propose to replace LAT by pseudo-LAT, which we suggest to realize similarly as LAT except that all water level boundary conditions and assimilated tidal water levels have to be enlarged by a constant value that is removed afterward. Using this approach, we obtained a smooth reference surface for the Dutch Wadden Sea that fits LAT at the North Sea boundary within a few centimeters.

Beachrock morphology and genesis on a paraglacial beach

Beachrock is present in deep, stable sections of a mixed sand and gravel beach at Whitepark Bay (55o14′N) on the paraglacial coast of Northern Ireland. The beachrock was revealed following progressive and extreme beach erosion during two particularly stormy winters (2013/14 and 2014/15). It occurs as large (up to 1m diameter, 0.2m thick), rounded, disc-shaped concretions in which original beach bedding structures are preserved. Both sand and gravel beach facies are cemented. The cements are similar to those of tropical beachrocks and comprise an initial thin micrite rim, and subsequent grain rims of aragonitic needles. The cementation is attributed to saturation of beach groundwater with calcium carbonate sourced from adjacent Cretaceous chalk outcrop in cliffs behind the beach and dunes. The micrite rims suggest microbial activity in the initial cementation, possibly by scavenging from chalk and skeletal carbonate grains. Subsequent aragonite rims were formed through degassing of CO2 aided by tidal water level fluctuations. Despite similar cementation processes to low latitude beachrocks, only isolated concretions occur rather than extensive shore-parallel outcrops. Conditions necessary for cementation (and ultimately preservation) in this cold temperate and paraglacial setting include long-term beach stability, a carbonate source (in this case, adjacent chalk cliffs and stream sapping) and tidal water level fluctuations. Bacterial activity may initiate calcite precipitation. Following extreme storms and with progressive shoreline retreat prompted by rising sea levels, increased reporting of cold-water beachrocks is to be expected as formerly stable sections of beaches are exposed to wave action.

A simple approach to adjust tidal forcing in fjord models

To model currents in a fjord accurate tidal forcing is of extreme importance. Due to complex topography with narrow and shallow straits, the tides in the innermost parts of a fjord are both shifted in phase and altered in amplitude compared to the tides in the open water outside the fjord. Commonly, coastal tide information extracted from global or regional models is used on the boundary of the fjord model. Since tides vary over short distances in shallower waters close to the coast, the global and regional tidal forcings are usually too coarse to achieve sufficiently accurate tides in fjords. We present a straightforward method to remedy this problem by simply adjusting the tides to fit the observed tides at the entrance of the fjord. To evaluate the method, we present results from the Oslofjord, Norway. A model for the fjord is first run using raw tidal forcing on its open boundary. By comparing modelled and observed time series of water level at a tidal gauge station close to the open boundary of the model, a factor for the amplitude and a shift in phase are computed. The amplitude factor and the phase shift are then applied to produce adjusted tidal forcing at the open boundary. Next, we rerun the fjord model using the adjusted tidal forcing. The results from the two runs are then compared to independent observations inside the fjord in terms of amplitude and phases of the various tidal components, the total tidal water level, and the depth integrated tidal currents. The results show improvements in the modelled tides in both the outer, and more importantly, the inner parts of the fjord.

Evaluation of tidal stream energy and its impacts on surrounding dynamics in the Eastern Region of Pingtan Island, China

Using an improved FVCOM numerical model, combined with the momentum-sinking scheme based on the structural characteristics of specific turbines, this study analyzed the temporal and spatial distributions of tidal energy resources before and after the deployment of tidal turbines near Pingtan Island, China. Considering factors such as the distribution of tidal stream energy, bathymetry, topography, and the design parameters of the turbines, an appropriate location for a demonstration tidal turbine was selected and the corresponding energy resource was evaluated. Several sites with strong tidal streams were considered: south of the northern cape, east of the southern cape, and the southern end of Haitan Bay. The former was thought most suitable for the deployment of a tidal energy turbine, with projected power generation for approximately 470 h per month. The average power of this demonstration was about 2.4 kW, and the annual electricity output was approximately 17.47 MWh. The intervention of the turbine device had little influence on the near-field tidal stream or water level. The tidal stream was reduced slightly in the area south of the northern cape, although the effect weakened further from the turbine. Conversely, the velocity increased slightly on both sides of the demonstration site. The difference in current speed with and without the turbine was greater at slack tide than still tide. The influence of turbine operation on water level was minor. The method adopted in this study can be considered a reference for the selection of sites for the demonstration of tidal stream energy. However, the method is unable describe the dynamic characteristics of the turbulent flow surrounding the deployed turbines, which has an important role regarding the optimal designs of the turbine blade and pile foundations. Therefore, we will continue to work to improve this model in future research.

Ecotone formation induced by the effects of tidal flooding: A conceptual model of the mud flat-coastal wetland ecosystem

The boundary between mud flat and coastal wetland ecosystems is highly productive and a haven of considerable biodiversity. It is also embedded in a highly dynamic environment and can be easily destabilised by environmental changes, invasive species, and human activity. Thus, understanding the processes which govern the formation of this ecotone is important both for conservation and economic reasons. In this study we introduce a simple conceptual model for this joint ecosystem, which demonstrates that the interaction between tidal flooding and habitat elevation is able to produce an ecotone with similar characteristics to that observed in empirical studies. In particular, the transition from mud flat to vegetated state is locally abrupt, occurring at a critical threshold elevation, but, on broader spatial scales can occur over a range of elevations determined by the variability in high tide water levels. Additionally, the model shows the potential for regime shifts, resulting from periods of unusual weather or the invasion of a fast growing, or flood resistant, species.

Design Concept of an Automated Irrigation System for Simulating Saltwater Intrusion in a Mesocosm Experiment

Coastal wetlands make up about one third of the overall wetland area in the conterminous United Stated based on the Environmental Protection Agency 2016 [1]. Sea-level rise is expected to elevate water salinity and effect carbon sequestration, nitrogen removal, further alter plant communities and shift ecosystem function. To promote understanding of the influence of seawater intrusion into tidal freshwater wetlands, we designed a mesocosm experiment with automated irrigation system at Spring Hill, Storrs, CT, USA (41.8°N, 72.3°W). To simulate marine water intrusion, we designed an automated irrigation to work for an on-going mesocosm experiment, which is composed of 64 tanks with 4 wetland species: Carexstricta, Spartinapectinata, Typhalatifolia, Phragmitesaustralis. During low tide, solenoid valves quantify water based on the instruction of system core controller (Arduino) and water is distributed to assigned tank [2] [3]. During high tide, water is pumped up into assigned tank, salinity is varied with plant species, Carexstricta and Spartinapectinata are fresh water species, Typhalatifolia, Phragmitesaustralis are brackish water species. The manipulation core of system is an open-source microcontroller platform. The irrigation system was designed daily twice change from low tide water level to high tide water level, and same water tank should keep at constant salinity within 30 days. Staff just needs monthly visit to add sea salts, the raw material of artificial seawater. Ecosystem CO2 and CH4 gas exchanges were measured monthly from May to September 2015 using large transparent chambers that enclosed emergent plants and the soil surface; field sampling and analysis procedures followed [4]. The simulated saltwater intrusion results are expected to alter plant growth, emission of carbon dioxide, methane and other greenhouse gases, and effect interaction with coastal marsh ecosystem.

海州湾及毗邻海域潮不对称性研究

外海潮波传播到近海河口海湾过程中，由于地形作用而发生变形，表现为潮汐潮流涨落潮的不对称。本文利用海州湾附近18天连续高频观测资料，分析了潮汐和潮流的不对称性，潮波向海州湾传播过程中，潮波变形较小，潮流变形较大，4个站位均为涨潮占优，本研究可为海州湾的泥沙输运、污染物迁移等研究提供参考。 Tidal current and water level are distorted from their sinusoidal forms during propagation into coastal waters and entry into bays, which gives rise to tidal asymmetry. On the base of continuous observation data for 18 days, the characters of the tidal asymmetry are analyzed. The results show that the duration of falling tide is longer than the rising tide, which means that the flood flow is dominated. The study results can provide reference for the sediment transport and the pollutant transport in Haizhou bay.

Numerical investigation of surge–tide interactions in the Bay of Bengal along the Bangladesh coast

The tidal amplitude at the Bay of Bengal along the Bangladesh coast varies from 2 to 7 m, whereas the tidal phase differs by more than 3 h from the outer part toward the inner part of the Meghna Estuary. At the time of cyclone landfall, the tidal phase has a significant impact on surge height, arrival time and duration. In this paper, the nature of surge–tide interactions at the Bay of Bengal along the Bangladesh coast has been investigated using a two-dimensional nonlinear shallow water model coupled with a storm surge model. Two previous major storm surge events along the Bangladesh coast have been analyzed for surge–tide interaction: Cyclone 1991 and Cyclone Sidr in 2007. To investigate the impact of the tidal phase on surge characteristics, in addition to the base cases, storm surges have been calculated at different phases of an entire tidal cycle at 1-h intervals. The results indicate that during the ebb tides the calculated total surge height of the surge–tide interaction model was higher compared to the total surge height obtained by superimposing surge height that is separately calculated with mean water level over the local tidal water level; the opposite occurs during high tide. The surge propagation time toward the inner part of the bay significantly varied depending on the tidal phases. When the tidal water level along the coast was low, the speed of surge propagation was much slower compared with when the tidal water level was high. The surge duration increases when the falling surge profile encounters an opposing strong tidal current at the landfall location.

A comprehensive hydro-geomorphic study of cliff-top storm deposits on Banneg Island during winter 2013–2014

Large clastic cliff-top storm deposits (called CTSDs) are one of the most remarkable signatures that characterizes extreme storm wave events on coastal cliffs. Hence, the study of CTSDs is of key importance for understanding and predicting the impacts of extreme storm wave events on rocky coasts or establishing proxies for storm intensity. The present study uses new data including hydrodynamic measurements in both deep and intertidal waters, and records of CTSDs displacement and deposition across Banneg Island during the stormy winter 2013–2014. Two drone-based surveys were carried out in January 2013 (pre-storms) and in April 2014 (post-storms). In addition, complementary field observations were carried out during the winter, providing a comprehensive and detailed dataset. Concerning the hydrodynamic measurements, nine pressure sensors deployed along four cross-shore profiles on the western coast of the island, recorded wave and water level conditions between December 2013 and April 2014. Aerial orthorectified photographs and digital elevation model of differences provide a detailed spatial description of cliff erosion and the reworking of cliff-top storm deposits. After the storms, 172 fresh scars corresponding to quarrying in the bed rock were localized above high spring tide water level, 507 blocks were transported up to 40m inland, at altitudes of 8 to 14m above mean sea level, and the tracks of 170 of them were identified. The water levels and wave parameters estimated from the pressure sensor measurements provided accurate information on the maximum water elevation reached during the largest storms at the sensor locations and were extrapolated to provide run-up elevation along the four survey profiles for the whole winter 2013–2014. The results demonstrate that a large number of overwash episodes occurred, at times of high tides and energetic waves. These episodes generally correspond to morphological changes. This study confirms the major role played by extreme storm wave events on CTSDs quarrying, transport, and deposition on Banneg Island, and clearly identify the events of major evolutions.