Nested numerical scheme in a polar coordinate shallow water model for the coast of Bangladesh

This study is concerned with the development of storm surge model to predict water level accurately due to surge associated with a cyclone along the coast of Bangladesh. Considering the funnel shape of the Bay of Bengal, coastal bending and the existence of off-shore islands, a vertically integrated model in cylindrical polar coordinate system is developed using nested numerical scheme. A fine mesh scheme capable of incorporating coastal bending and offshore islands properly in the numerical scheme is nested into a coarse mesh scheme covering up to 15° N latitude of the Bay of Bengal. The developed model is used to estimate water levels at different coastal and island stations associated with a few storms that hit the coast of Bangladesh. The computed surge levels compared well with observed ones and predicted surge levels investigated with different approaches.     

A numerical study of hypothetical storm surge and coastal inundation for AILA cyclone in the Bay of Bengal

The head Bay region bordering the Bay of Bengal is highly vulnerable to tropical cyclones. Catastrophic risks from storm surge and associated inundation are quite high due to high population density in coastal areas, socio-economic conditions, and shallow bathymetry. It features the world’s largest deltaic system comprising of ‘Sunderbans’ bordered by West Bengal and Bangladesh. In a geomorphologic sense, the head Bay region is a low-lying belt comprising several barrier islands and river drainage systems, numerous tidal creeks, and mud flats having a high risk for widespread inundation. In addition, the high tidal range together with low-lying topography leads to high risk and vulnerability from storm surge inundation. During May 2009, a severe cyclonic storm Aila struck West Bengal causing enormous destruction to life and property along coastal belts of West Bengal and Bangladesh. It was the strongest pre-monsoon cyclone in the past two decades that had landfall in West Bengal. This work reports on a numerical study for hypothetical storm surge and associated inundation from Aila using the ADCIRC model. The study covers a comprehensive qualitative analysis on water level elevation and onshore inundation for West Bengal and Bangladesh regions. The estimated peak storm surge was about 4 m in the Sunderban region that propagated into all major riverine systems, inundating the river banks as well the inland areas. Numerical simulations indicate an average inland penetration distance of 350 m with a maximum of 600 m at various coastal locations in West Bengal and Bangladesh. The study emphasizes the need and importance of inundation modeling system required for emergency preparedness and disaster management.     

江苏沿海地区海洋灾害类型及其防治探讨

根据江苏沿海地区的地质地貌及气候的特点,综合分析了危害江苏沿海的海洋灾害类型,主要有海洋地质灾害、气候灾害和生物灾害等三种类型。地质灾害主要包括海岸侵蚀、海岸坍塌、和海平面上升;气候灾害主要包括台风风暴潮;生物灾害主要包括赤潮、湿地滩涂面积缩小等。提出相应的防治措施:(1)加强对海岸带地质背景和地质灾害研究,应用GIS和RS等先进技术建立海洋灾害信息系统;(2)加强海防工程建设,加高海堤提高质量,以防御灾害性海浪、风暴潮等侵袭;(3)应用生态学原理,建立沿海生态防护网,增强对风暴潮抵御能力保护沿海湿地资源;(4)加强对海洋灾害及防御知识的教育和对防灾减灾的管理等。     

Coastal inundation in the north-eastern mediterranean coastal zone due to storm surge events

Low-elevation coastal areas and their populations are at risk during and after the appearance of a storm surge event. Coastal flooding as a result of storm surge events is investigated in this paper for a number of areas around the north-eastern (NE) Mediterranean coastal zone (Adriatic, Aegean and north Levantine seas). The sea level rise (SLR) due to storm surge events is examined for the period 2000?C2004. Wind data, atmospheric pressure and wave data for this period as well as in situ sea elevation measurements (from stations around the Mediterranean coasts) were used. Potential inundation zones were then identified using a 90-m horizontal resolution digital elevation model (DEM). At these zones, the sea surface elevations were calculated for the study period, using the collected data and a 2D storm surge simulation model (1/10^o??1/10^o) output, examining the sea level alteration in specific coastal areas, where in situ measurements are absent and are characterised as ??risky?? in inundation areas, due to their topography. In order to determine the level of storm track implication on major SLR incidents, the trajectories of the respective storm events were computed. The aim of this paper is to investigate the major storm surge events that appeared during the study period, identify the major ??risky?? costal regions along the north-eastern Mediterranean coast and determine their hazard level due to inundation caused by storm surge phenomena. The combination of the risk level determination of an area and the calculation of sea level alteration is an important tool in terms of predicting and protecting the coastal area from extreme meteorological incidents.     

Summer zooplankton distribution in a Georgia Estuary

Zooplankton were collected with Van Dorn bottles at two estuarine stations near Savannah, Georgia, USA, during summer, 1974, from the surface, 2 m, 4 m, and at the bottom of the water column at 2-h intervals for 11 days. Acartia tonsa occurred at the surface at night and during high and rising tides in higher concentrations than at the same depth during daylight and other tide stages. The highest bottom concentrations of this calanoid copepod occurred at high tide. A negative phototaxic response was also apparent in this species. While not quantitatively sampled by Van Dorn bottles, harpacticoid copepods and Pseudodiaptomus coronatus Were distributed in a manner similar to that of A. tonsa. Copepod nauplii, on the other hand, were always more abundant at the surface than at the bottom, with the highest concentration occurring during low tide. The distribution pattern of nauplii appears to be a function of dilution and concentration by tidally induced changes in water volume, whereas more advanced copepod stages follow a complexly controlled distribution pattern linked with tidal mixing dynamics as outlined in a previous study by Jacobs (1968).     

Flood tide transport of blue crab, Callinectes sapidus, postlarvae: behavioral responses to salinity and turbulence

Blue crab (Callinectes sapidus) postlarvae (megalopae) use flood tide transport to move upstream in estuaries during nocturnal flood tides. The megalopae have a endogenous diel rhythm in activity that is inconsistent with this tidally timed behavior. Thus, it is hypothesized that this behavior is regulated by behavioral changes in response to exogenous cues associated with tidal currents. In a laboratory flow tank, blue crab megalopae were exposed to simultaneous changes in salinity and turbulence to simulate tides in an estuary. On simulated flood tides, megalopae ascended upon exposure to a salinity increase, remained swimming during times of high turbulence, and descended at times of low turbulence. Turbulence stimulated swimming for several hours, approximating the duration of tidal currents in estuaries. Swimming was inhibited by decreasing salinity on simulated ebb tides. These results support a model for regulation of flood tide transport by blue crab megalopae as follows: (1) blue crab megalopae are stimulated to swim into the water column by increasing salinity associated with flood tide; (2) megalopae remain swimming during flood tide in response to high levels of turbulence; (3) megalopae descend at the end of flood tide, when current speed and turbulence decline to low levels; and (4) megalopae are inhibited from swimming on ebb tides by the associated salinity decrease. This is the first model for regulation of flood tide transport in a species lacking a tidal rhythm in activity.     

A simulation model for projecting changes in salinity concentrations and species dominance in the coastal margin habitats of the Everglades

Sharp boundaries typically separate the salinity tolerant mangroves from the salinity intolerant hardwood hammock species, which occupy the similar geographical areas of southern Florida. Evidence of strong feedback between tree community-type and the salinity of the unsaturated (vadose) zone of the soil suggests that a severe disturbance that significantly tilts the salinity in the vadose zone might cause a shift from one vegetation type to the other. In this study, a model based upon the feedback dynamics between vegetation and salinity of the vadose zone of the soil was used to take account of storm surge events to investigate the mechanisms that by which this large-scale disturbance could affect the spatial pattern of hardwood hammocks and mangroves. Model simulation results indicated that a heavy storm surge that completely saturated the vadose zone at 30 ppt for 1 day could lead to a regime shift in which there is domination by mangroves of areas previously dominated by hardwood hammocks. Lighter storm surges that saturated the vadose zone at less than 7 ppt did not cause vegetation shifts. Investigations of model sensitivity analysis indicated that the thickness of the vadose zone, coupled with precipitation, influenced the residence time of high salinity in the vadose zone and therefore determined the rate of mangrove domination. The model was developed for a southern Florida coastal ecosystem, but its applicability may be much broader.     

上海滨岸带生态环境问题及调控对策

结合长江口上海滨岸带资源与环境现状,重点分析了上海滨岸地区在经济快速发展过程中面临的主要生态环境问题;指出上海滨岸地区面临风暴潮、海平面上升、地面沉降等主要自然灾害;滨岸水环境质量恶化,重金属等污染物的生态风险不容忽视;潮滩过渡围垦导致湿地生态系统破坏严重。探讨了污水排放等人类活动对滨岸带生态环境的影响。此外,从战略环境评价、污染控制、生态恢复、行政法规和管理等方面,提出了相应的调控对策。     

Sediment processes and flow reversal in the undular tidal bore of the Garonne River (France)

A tidal bore is a series of waves propagating upstream as the tidal flow turns to rising, and the bore front corresponds to the leading edge of the tidal wave in a funnel shaped estuarine zone with macro-tidal conditions. Some field observations were conducted in the tidal bore of the Garonne River on 7 June 2012 in the Arcins channel, a few weeks after a major flood. The tidal bore was a flat undular bore with a Froude number close to unity: $\hbox {Fr}_{1} = 1.02$ and 1.19 (morning and afternoon respectively). A key feature of the study was the simultaneous recording of the water elevation, instantaneous velocity components and suspended sediment concentration (SSC) estimates, together with a detailed characterisation of the sediment bed materials. The sediment was some silty material ( $\hbox {d}_{50} \approx 13~\upmu \hbox {m}$ ) which exhibited some non-Newtonion thixotropic behaviour. The velocity and SSC estimate were recorded simultaneously at high frequency, enabling a quantitative estimate of the suspended sediment flux at the end of the ebb tide and during the early flood tide. The net sediment flux per unit area was directed upstream after the bore, and its magnitude was much larger than that at end of ebb tide. The field observations highlighted a number of unusual features on the morning of 7 June 2012. These included (a) a slight rise in water elevation starting about 70 s prior to the front, (b) a delayed flow reversal about 50 s after the bore front, (c) some large fluctuations in suspended sediment concentration (SSC) about 100 s after the bore front and (d) a transient water elevation lowering about 10 min after the bore front passage. The measurements of water temperature and salinity showed nearly identical results before and after the tidal bore, with no evidence of saline and thermal front during the study.     

Habitat expansion among polychaetous annelids repopulating a defaunated marine habitat

Repopulation of the polychaete fauna of a defaunated, marine, intertidal habitat was studied for 2 years.Monthly quantitative samples from 4 stations, from just below mean high water to approximately 10 m below mean low water, were analyzed for species composition, density and distributional relationships. Repopulation occurred most rapidly at the highest tide levels, with slower rates of colonization at lower tide levels. Two species, Apoprionospio pygmaea (Hartman) and Magelona pettiboneae Jones, were density dominants for all but the first month of study. These species partitioned the transect spatially, with M. pettiboneae concentrated at the higher tidal levels, and A. pygmaea concentrated at the lower levels. First-year density dominants, Eteone heteropoda Hartman, Gyptis vittata Webster and Benedict, Nereis succinea Frey and Leuckart, and Paraprionospio pinnata (Ehlers), acted opportunistically by arriving early, quickly increasing their populations, and expanding their habitat distributions.Second-year density dominants, Capitita ambiseta Hartman, Minuspio cirrifera (Wirén), and Travisia sp., arrived much later, took longer to significantly increase their densities, and did not show habitat expansion.     

Habitat use pattern of tidal mud and sand flats by shorebirds (charadriiformes) wintering in southern India

Habitat use pattern and status of shorebirds in southern India were investigated in six tidal flats comprising three mudflats and three sand flats on the east coast of southern India. Totally, 7757 shorebirds belonging to 21 species were recorded during September 2000–March 2002. The birds preferred mudflats over sand flats. Density, diversity and richness of shorebirds were relatively higher in tidal flats, especially in mudflats. The shorebirds preferred mudflats over sand flats as stopover sites and sites for refueling the required energy during migration. Rhythmic changes in tidal pattern also influenced the allochthonous nutrients and prey species, which also attracted the migratory shorebirds. However, the abundance of shorebirds with reference to tidal flats *season*tide and habitats*seasons * tide had strong variations (P < 0.001). During migratory season, bird density, diversity and species richness were observed higher than in other seasons.     

Biological and physical aspects of migration in the estuarine amphipod Gammarus zaddachi

The amphipod Gammarus zaddachi (Sexton) conducts extensive migrations along estuaries from near the limit of tidal influence in winter to more downstream reaches (where reproduction occurs) in spring. A return migration then takes place, primarily by juveniles, until the seaward areas are depopulated in winter. The present study was conducted between 1988 and 1990 in the Conwy Estuary, North Wales. This represents the first investigation on this species in a strongly tidal estuary, where the amphipods appear to migrate vertically into the water column on flood or ebb tides to control horizontal transport and to maintain preferred distributions. The timing of vertical migration seems to be largely controlled by an endogenous circatidal swimming rhythm. Phasing of peak activity relative to the time of expected high tide varies with season; upstream migrants in the autumn showed peak activity at the time of expected high tide, while in the spring at the time of downstream migration the rhythm was phase-delayed, with peak activity during the expected ebb tide. Together with the season, position along the estuary also affected the timing of peak endogenous activity; downstream migrants, originally active on the ebb tide and experimentally displaced seawards, showed a phase-advance of the rhythm relative to the time of high tide. Salinity-preference behaviour also varied between different developmental stages, with ovigerous females (downstream migrants) showing no preference between fresh and saline water, and juveniles (upstream migrants) showing a significant preference for freshwater. The interactions of endogenous rhythmicity and salinity-preference behaviour are discussed as controlling factors of migration in this species.     

Spatial variability of length-specific production in shell,somatic tissue and sexual products of Macoma balthica in the Lower St. Lawrence Estuary

A field study on the spatial variability of production and some demographic parameters was conducted in 1988 in ten populations of Macoma balthica located on the north and south shores along the entire length (230 km) of the Lower St. Lawrence Estuary (LSLE, Canada) at the same intertidal level. Standard-length estimates (10 mm) of shell and somatic tissue production for the period of May to November were highly variable between stations and greater on the north shore than on the south shore. Standard-length estimates of the gamete production for the period of July to November were also highly variable between stations but there was no variation between shores. The inter-population variability of the standard-length estimates of production in shell, somatic tissue and sexual products was as large as the intrapopulation variability between both the upper and lower tidal levels measured in previous studies. There were no significant linear relationships between standard-length estimates of production and biotic (density) or abiotic (temperature, chlorophyll-a in top sediment, mean phi, water salinity) factors, but we observed some significant quadratic relationships between standard-length estimates of production and mean sediment-surface temperature during the growing season. The standard-length estimates of production were lower at the coldest and warmest stations than at the more temperature stations. There was also a significant negative linear relationship between mean sediment-surface temperature during the growing season and the grain size structure of sediment, indicating that the sediment texture, indirectly, largely influenced the inter-station and the inter-shore variability of production in shell, somatic tissue and sexual products of M. balthica in the LSLE.     

Hydrodynamic and ecological assessment of nearshore restoration: A modeling study

Along the Pacific Northwest coast, much of the estuarine habitat has been lost over the last century to agricultural land use, residential and commercial development, and transportation corridors. As a result, many of the ecological processes and functions have been disrupted. To protect and improve these coastal habitats that are vital to aquatic species, many projects are currently underway to restore estuarine and coastal ecosystems through dike breaches, setbacks, and removals. Understanding site-specific information on physical processes is critical for improving the success of such restoration actions. In this study, a three-dimensional hydrodynamic model was developed to simulate estuarine processes in the Stillaguamish River estuary, where restoration of a 160-acre parcel through dike setback has been proposed. The model was calibrated to observed tide, current, and salinity data for existing conditions and applied to simulate the hydrodynamic responses to two restoration alternatives. Model results were then combined with biophysical data to predict habitat responses within the restoration footprint. Results showed that the proposed dike removal would result in desired tidal flushing and conditions that would support four habitat types on the restoration footprint. At the estuary scale, restoration would substantially increase the proportion of area flushed with freshwater (<5 ppt) at flood tide. Potential implications of predicted changes in salinity and flow dynamics are discussed relative to the distribution of tidal marsh habitat.     

Amphipods and isopods in the rocky intertidal: dispersal and movements during high tide

Animals in the intertidal, both mobile and sessile, generally exhibit some zonation pattern, in which each species shows a preference for, or is confined to, some height levels. The study of zonation patterns is, however, almost exclusively based on surveys made during low tide, when many animals are relatively inactive. We studied zonation patterns of amphipods and isopods on rocky shores in southwestern Iceland, both by traditional sampling at low tide as well as by sampling during high tide. The distributional patterns seen at high tide differed significantly from that at low tide. One amphipod, Anonyx sarsi, was common around baits at all levels at high tide but absent from the intertidal at low tide. Several other species were either relatively more common or tended to be recorded higher, or in one instance, lower on the shore when the tide was in than at low tide. There was also evidence of some species changing habitats within the intertidal with the tidal cycle. Many species, however, moved little away from their respective zones occupied at low tide, and for some species, including some capable of rapid swimming, very limited mobility was indicated. We conclude that low-tide surveys of the intertidal give an incomplete picture of the community structure, and even key species may be missed in such surveys.Communicated by L. Hagermann, Helsingør     

Modeling and data assessment of longitudinal salinity in a low-gradient estuarine river

Continuous data of vertical-profile salinity were analyzed for four stations located successively upriver in a macrotidal estuary, the lower St. Johns River (Northeast Florida, USA). The data analysis confirmed well-mixed salinity conditions in the river with at most 1.3 ppt of vertical variability at Dames Point (river km 20), where the main variations of salinity are along the longitudinal axis of the river. Given the well-mixed salinity conditions and dominant horizontal structure of salinity variations in the river, we present and apply a barotropic, two-dimensional modeling approach for hydrodynamic-salinity transport simulation in the lower St. Johns River. When properly forced by offshore surge, high-resolution wind fields and freshwater river inflows, the model replicated the salinity measurements remarkably well, including the separation into tidal and sub-tidal components. The data and model results show that, at times, offshore winds and surge can be more influential on longitudinal salinity variations than local winds over the river. We demonstrate the importance of using proper boundary conditions to force the model relative to the minimal sensitivity of the model to parameter adjustment of horizontal mixing and uncertainty-based perturbation of wind and inflow forcings.     

Occurrence of lysozyme in the common cockle Cerastoderma edule and the effect of the tidal cycle on lysozyme activity

In 1983 a sample of cockles [Cerastoderma edule (L.)] was removed from the mid-tide level at Booterstown Strand, County Dublin, Ireland at 2-h intervals, for a period of 24 h. The gills, mantle and visceral mass tissues contained significant levels of lysozyme, with the gills containing the highest, weight-specific levels. A tidal rhythm of lysozyme activity in the gills, mantle and visceral mass was inversely related to the tidal cycle. The data were best described by a tidal curve shifted-5 hours out of phase, with maximum and minimum levels of activity occurring one hour after low and high tides, respectively. In marine bivalves, lysozyme may be involved in the extracellular digestion and absorption of bacteria during low tide. In this context the present use of bivalves as biological indicators of bacterial pollution is discussed.Constribution No. 6282 from the Woods Hole Oceanographic Institution     

Wind- and tide-induced currents in the Stagnone lagoon (Sicily)

The hydrodynamic circulation is analyzed in the coastal lagoon of Stagnone di Marsala, a natural reserve located in the north-western part of Sicily, using both experimental measurements and numerical simulations. Field measurements of velocities and water levels, carried out using an ultrasound sensor (3D), are used to validate the numerical model. A 3D finite-volume model is used to solve the Reynolds-averaged momentum and mass balance differential equations on a curvilinear structured grid, employing the k–e{\varepsilon} turbulence model for the Reynolds stresses. The numerical analysis allows to identify the relative contribution of the forces affecting the hydrodynamic circulation inside the lagoon. In the simulations only wind and tide forces are considered, neglecting the effects of water density changes. Two different conditions are considered. In the first both the wind stress over the free-surface and the tidal motion are imposed. In the second the wind action is neglected, to separately analyze the tide-induced circulation. The comparison between the two test cases highlights the fundamental role of the wind on the hydrodynamics of the Stagnone lagoon, producing a strong vertical recirculation pattern that is not observed when the flow is driven by tides only.     

Tidal regime dictates the cascading consumptive and nonconsumptive effects of multiple predators on a marsh plant

Prey perception of predators can dictate how prey behaviorally balance the need to avoid being eaten with the need to consume resources, and this perception and consequent behavior can be strongly influenced by physical processes. Physical factors, however, can also alter the density and diversity of predators that pursue prey. Thus, it remains uncertain to what extent variable risk perception and antipredator behavior vs. variation in predator consumption of prey underlie prey-resource dynamics and give rise to large-scale patterns in natural systems. In an experimental food web where tidal inundation of marsh controls which predators access prey, crab and conch (predators) influenced the survivorship and antipredator behavior of snails (prey) irrespective of whether tidal inundation occurred on a diurnal or mixed semidiurnal schedule. Specifically, cues of either predator caused snails to ascend marsh leaves; snail survivorship was reduced more by unrestrained crabs than by unrestrained conchs; and snail survivorship was lowest with multiple predators than with any single predator despite interference. In contrast to these tidally consistent direct consumptive and nonconsumptive effects, indirect predator effects differed with tidal regime: snail grazing of marsh leaves in the presence of predators increased in the diurnal tide but decreased in the mixed semidiurnal tidal schedule, overwhelming the differences in snail density that resulted from direct predation. In addition, results suggest that snails may increase their foraging to compensate for stress-induced metabolic demand in the presence of predator cues. Patterns from natural marshes spanning a tidal inundation gradient (from diurnal to mixed semidiurnal tides) across 400 km of coastline were consistent with experimental results: despite minimal spatial variation in densities of predators, snails, abiotic stressors, and marsh productivity, snail grazing on marsh plants increased and plant biomass decreased on shorelines exposed to a diurnal tide. Because both the field and experimental results can be explained by tidal-induced variation in risk perception and snail behavior rather than by changes in snail density, this study reinforces the importance of nonconsumptive predator effects in complex natural systems and at large spatial scales.