Tidal Hydrodynamics Research Articles

Numerical simulation of tidal hydrodynamics in the Arabian Gulf

A vertically 2-D numerical model based on the Delft3D modelling system is set up, calibrated, and validated to simulate the tidal hydrodynamics in the Arabian Gulf. The model is a barotropic solution, controlled by 13 tidal components at open boundaries. The performance of the numerical model was evaluated using the hourly water level observations and the TOPEX/Poseidon altimetry data. Statistical analysis showed a good agreement between the simulated and observed water levels. RMS error was found to be ranged from 0.07 to 0.23 m, with maximum discrepancies observed at Ras Tanura and Mina Sulman stations. However, the IOA between the simulated and observed water levels was significant (0.95–0.99). On average, the errors for the tidal constituents considered in the analysis are in the order of <0.02 m (4%). The M2, S2, K1 and O1 tidal waves represent the largest among other constituents, where the amplitude of S2 represents almost 30% of the M2, and the O1 tidal wave represents about 50% of the K1 tide. The co-tidal charts of the semidiurnal tides show the existence of two anticlockwise amphidromic systems in the north and south ends (centred around 28.25° and 24.5°N respectively) close to the western side, while the diurnal constituents form only a single amphidromic point in the central part, centred around 26.8°N (North Bahrain). On the other hand, the velocity amplitudes of the U and V components of the numerical model were compared with a previous observational study and found to be agreed well.

Numerical investigation of the effects of distributary bathymetry and roughness on tidal hydrodynamics of Wax Lake region under calm conditions

In this paper, we investigate the effects of the bathymetry of the floodplain distributaries using a 2-dimensional hydrodynamic model of the Wax Lake Outlet (WLO), delta and floodplain (Louisiana, USA), using Delft3D. Modelling the tidal-fluvial interaction of this region is challenging because of its complex network of low-lying floodplain distributaries and vegetation coverage. This investigation addresses this interaction by generating the evolution of the flood-map that is used in the calibration and validation phase of the Surface Water and Ocean Topography (SWOT) mission. Accordingly, the model is set up for one week of calm conditions from October 14th to 20th in 2016. Boundary conditions applied at the edges of the 36 × 23 km2 domain include the offshore water level with tidal oscillations, the upstream volumetric river discharge rate and wind time-series (applied spatially uniformly). The topo-bathymetry of the domain is a product of the Pre-Delta-X mission; however, it has considerable uncertainties to represent the small distributaries, especially in the forested section of the region. This paper tackles this uncertainty by parametrically enhancing and calibrating the primary Digital Terrain Model (DTM). The performance of the model is assessed using the water-level time series measured by the stations spread throughout the floodplain, delta and main river. The results show that the morphology of the distributaries play a major role in the hydrodynamic of Wax Lake region under calm conditions. The hydrodynamic of the WLO and floodplain is considerably affected by the discharge capacity of the distributaries (changed by editing their width and depth) due to change of the balance between roughness and topographic convergence. In WLO, higher discharge capacity leads to higher overall roughness friction force, thereby dampening the amplitude of the water-level signal and vice versa. On the other hand, increasing the bottom roughness of the WLO increases the water level in the floodplain, with more considerable effect in the low tides. The calibrated model well matches the measurements along the Wax Lake Outlet. However, the main discrepancies are in the stations further away from the WLO. The tests conducted in this research suggest that the excessive roughness due to uneven bed along the distributaries and vegetation are, respectively, the potentially-responsible parameters for the remaining discrepancies in low- and high-tide periods.

Seasonal Variation and Ecological Risk Assessment of Heavy Metal in an Estuarine Mangrove Wetland

Potential toxic metal pollution in mangroves has attracted extensive attention globally; however, the seasonal variation of potential toxic metals in mangrove wetlands is still poorly understood. Herein, we investigated the variation of content as well as chemical speciation of typical metals (Pb, Cr, Zn and Cu) in the sediments from the Zhangjiang Estuary mangrove wetland, China. The potential risk of metal contamination was also investigated. Compared to the wet season, we found that sediment metal content was higher in the dry season. Mangrove sites show accumulated significant metals than does the mudflat both in wet and dry seasons. Geo-accumulation (Igeo) shows moderate pollution, probably because of the dilution as result of runoff and tidal hydrodynamics in the wet season. Increased concentrations of all metals in the acid-soluble fraction and decreased metal contents in the residue fraction were found in the dry season. Risk assessment indicated that the concentrations of Pb poses a higher environmental risk in the dry season. These results can increase awareness of metal pollution in the dry season and provide information for potential toxic metal management in mangrove wetlands.

Tidal hydrodynamics and flushing characteristics of Gulf of Khambhat, west coast of India – A numerical approach

Tidal hydrodynamics and flushing characteristics of Gulf of Khambhat, west coast of India – A numerical approach

Mapping tidal current and salinity at a shallow tidal channel junction using the fluvial acoustic tomography system

Applying the fluvial acoustic tomography (FAT) system to shallow tidal junctions for studying the flow division and spatiotemporal difference of velocity and salinity is vital to understand the tidal hydrodynamics in multi-channel networks. To the best of our knowledge, this is the first study that monitors continuous 2D current and salinity distributions at a shallow tidal junction using six FATs for ~34.4 days. The horizontal distribution and spatiotemporal variation of the currents and salinity were efficiently estimated by the inverse method. These results demonstrate that FAT is a potential tool for the continuous mapping of variable 2D currents and salinity at shallow tidal junctions. The reciprocating patterns of the current and salinity during the spring tide at the junction responded well to the tide. High salinity occurred around high water, whereas salinity was negligible at low water. During flood tides, significant landward currents flowed with the maximum speed of ~0.4 m/s, and significant seaward currents with the maximum speed of ~0.55 m/s occurred during ebb tides. During neap tides, the salinity pattern began to develop landward from the low water and reached a mature phase around the high water; salinity at the ebb slack remained high. Inverted FAT results indicated a counter-clockwise circulation around the low water during neap tide; some of the currents continuously flowed landward at the downstream of the junction (S4–S5), whereas others continuously flowed to the Tenma River. The behaviors of the currents varied slightly with the tide. The behaviors of the current and salinity during the neap tide mostly resulted from the density-driven current phenomenon. Furthermore, tidal harmonic analyses of the reconstructed currents were performed to clarify the river-tide interactions at the tidal junction. The results reflected the increased tidal wave deformation that occurred with the gradually increasing tidal range and demonstrated the role of the limited river flow on the tidal asymmetry at this tidal junction. This study advances the understanding of river flow dynamics in shallow tidal junction systems.

Tidal and subtidal hydrodynamics over ridge-swale bathymetry

Observations along two inner shelf transects of East-Central Florida provide information on the influence of ridge-swale bathymetry on tidal and subtidal hydrodynamics and the applicability of open channel flow theory in an area of complex bathymetry. Results from vessel-based ADCP measurements were compared to two analytical models that yield tidal and subtidal solutions. Of the two transects investigated, the northern transect, which has a relatively smooth bathymetry and a gentle bottom slope (0.002), exhibited tidal hydrodynamics that were more influenced by local acceleration than by frictional effects. Subtidal hydrodynamics at the northern transect were influenced by Coriolis (geostrophy) or by advection (Bernoulli-type dynamics). The south transect crossed a more prominent swale, with a steeper bottom slope (0.006). Frictional effects dominated the south transect as the flow maximum was located over the deepest part of the transect. Results obtained with both the tidal and subtidal analytical model solutions highlight the influence of ridge-swale bathymetry in inner shelves at those temporal scales. Analyses indicate whether open channel concepts are applicable to inner shelf dynamics.

Stepwise alterations in tidal hydrodynamics in a highly human-modified estuary: The roles of channel deepening and narrowing

With the rapid development of coastal cities, estuarine environments have been drastically changed by human interventions that considerably alter hydrodynamics (e.g., tidal amplitude) and water quality (e.g., salinity intrusion). In this study, we used a well-developed one-dimensional analytical model that accounts for the mutual nonlinear interactions between different tidal constituents to investigate the stepwise alterations in tidal hydrodynamics in Lingdingyang Bay of the Pearl River Estuary during 1965–2016, with a particular focus on the impacts of channel deepening and narrowing. The stepwise alterations in tidal hydrodynamics in Lingdingyang Bay can be divided into three distinct phases: the pre-human period (1965–1989), the transitional period (1990–2007), and the post-human period (2008–2016). It was shown that channel deepening and narrowing exert a dramatic influence on the tidal hydrodynamics in terms of increasing wave celerity, amplifying tidal waves, increasing the velocity amplitude and becoming more standing wave character. Furthermore, analytical results show that the responses of the semi-diurnal constituents (M2 and S2) to morphological changes are much more sensitive than those of the diurnal constituents (K1 and O1). In addition, based on the sensitivity analysis, we show that the effects of channel narrowing on tidal hydrodynamics are stronger than those of channel deepening. These results quantifying the effects of estuarine morphology on tidal hydrodynamics can provide scientific guidelines for sustainable water resources management in Lingdingyang Bay and other tide-dominated estuaries that are subject to intensive human interventions, especially regarding morphological changes.

Assessing the Influence of Shoreline Adaptation on Tidal Hydrodynamics: The Role of Shoreline Typologies

AbstractIn coastal embayments, tidal dynamics are influenced by mean sea level and shoreline configuration. As sea levels rise and coastal communities modify their shorelines to mitigate future flooding, spatial patterns of inundation, tidal amplitude, and tidal phase will change in response. Here we apply a hydrodynamic model to systematically investigate the effect of local‐scale, spatially refined shoreline protection on regional tidal dynamics and peak water levels in San Francisco Bay, California. We find that individual shoreline protection scenarios produce relatively small changes in tidal amplitudes at 50 and 100 cm of sea‐level rise but can result in amplification of the M2 tide by up to 40% at 200 cm of sea‐level rise. Protection of shorelines with gradually sloping topography and space for floodwater accommodation generally has the largest influence on tidal response, both locally and regionally. In the northern part of San Francisco Bay, tides down‐estuary of protected shorelines move closer to a standing wave, while up‐estuary tides become more progressive. In the southern part of the bay, which is already close to a standing wave, effects are more localized and variable. Overall, the tidal response to shoreline protection is a function of both the geographic location within the embayment as well as the geomorphic characteristics of the local landscape that is protected. Understanding the relative influence of local shoreline modifications on tidal dynamics under a range of sea‐level rise scenarios is critical to developing effective shoreline adaptation alternatives that maximize flood mitigation.

Towards enhancing tidally-induced water renewal in coastal lagoons

In order to address the problem of limited water renewal in restricted lagoons of moderate size having at least two tidal inlets, a method is proposed to enhance water exchange between the lagoon and the open sea. The method consists of altering either the amplitude or the phase of the tide in one of the inlets. It is shown in the paper that this will result in an alteration of the function of the lagoon, from a lagoon periodically exchanging water equal to a tidal prism within each tidal cycle with the adjacent water body, towards an effectively flow through system, substantially improving the flushing rate of the lagoon. The method is confirmed by running a series of numerical experiments simulating tidal hydrodynamics in the Papas lagoon. The question of how to alter the tidal amplitude is briefly touched upon, by numerically testing the performance of artificially macro-roughening an inlet and alternatively, designing an inlet to have a meandering shape. It was found that both modifications produce a diminished tidal amplitude, providing positive evidence for the applicability of the proposed method.

Hydrodynamic impacts on tidal-scale dissolved inorganic nitrogen cycling and export across the estuarine turbidity maxima to coast

Estuarine turbidity maxima (ETM) is a transition zone subject to the influence of river flow and tides. Here we showed the distinct impacts of fluvial and tidal hydrodynamics on dissolved inorganic nitrogen (DIN) cycling and export across the ETM to coast. We conducted tidal-scale hourly measurements at the ETM zone of the Jiulong River Estuary in Southeast China in May and December 2015. Generally, ammonium-N (NH4-N) and nitrate-N (NO3-N) increased in ebb tides, primarily controlled by freshwater input. In contrast, nitrite-N (NO2-N) increased in flood tides, largely due to the horizontal advection of NO2-N rich water from the middle estuary (5–10 PSU). During the fresh–saline water mixing period with high suspended particulate matters (SPM), the stronger tides and smaller river discharge in December increased SPM and NO2-N in the ETM, indicating stronger ammonium oxidation in the water column. During the low tide period when freshwater dominated and particles were deposited, the increase of NH4-N in the water column was related to the external source supply (e.g., wetland effluent), while the decline of NO3-N and NO2-N was likely associated with denitrification occurring in anoxic fluid muds and sediments. The larger DIN flux was found in May with larger river discharge, weaker tides and longer duration of the freshwater dominated period than December. This study highlights the combined effects of river and tides on hydrodynamics, which largely determine the major N sources, processes (e.g., nitrification and denitrification) and DIN fluxes across the ETM to coast.

Numerical study of tides in the Malacca Strait with a 3-D model

Malacca Strait (MS) has an important role and potential for many countries. It is a major transportation route for oil and commodities across continents. In addition, various activities such as shipping, fishing, aquaculture, oil drilling, and energy are also carried out in MS. Tides strongly affect the MS environment so that it becomes a major parameter in MS management. This paper is the first study, which presents MS tidal hydrodynamics based on a baroclinic and nonhydrostatic approach. Tidal hydrodynamics in MS and the surrounding waters were assessed using tidal forces, temperature, salinity, and density. This study analyzes the amplitude, phase, current ellipses, and semi-major axis of the tides. These variables are obtained from the simulation results of the three-dimensional numerical models of M2 tides and combined tides (M2, S2, N2, K1, and O1) with nonhydrostatic models. Then the results obtained are verified by observation data. Amplitude and phase of the tidal wave in MS originate from two directions, namely the northern part of MS (Andaman Sea) and the South China Sea (SCS). Tides from the north of MS propagate into the MS, while tides from the SCS travel to Singapore Waters (SW) and the south of MS. This causes a complex residual flow in SW and shoaling in the middle of MS. Shoaling in the middle of MS is characterized by a large amplitude and semi-major, as in B. Siapiapi. The results of this analysis show that tidal waves are dominated by semidiurnal types rather than diurnal types. The M2 current ellipse has dominantly anticlockwise rotation along the west of the MS, while along the east of MS, it has generally a clockwise rotation.

A comparative study for tidal current velocity prediction using simplified and fast algorithms

Interest in marine renewable energies has grown in recent years, especially in northern European shelf seas where several technological devices have been developed. In this context, numerous investigations focused on accurate predictions of tidal currents and their respective kinetic energy. An empirical estimation of the current velocity is explored in this study, where three different methods are presented. The first method is a linear approximation of the tidal vector velocity as a function of the tidal coefficient (ratio of the tidal range over its maximal value). The second and the third methods are a piece-wise linear and an exponential relationships between tidal vector velocity and the tidal coefficient, respectively. These three methods are compared to reference values obtained using a numerical simulation of tidal hydrodynamics. These methods are applied at two prominent tidal stream energy sites along the coast of France, the Fromveur Strait (western Brittany) and the Alderney Race (between the island of Alderney, Channel islands, and the Cap de la Hague, France). Results show that the piece-wise linear and the exponential models are more accurate than the linear approximation, where the mean error decreased by 12.7% and 14.9% respectively at the worst case scenario.

Effects of Tidally Varying River Flow on Entrainment of Juvenile Salmon into Sutter and Steamboat Sloughs

Survival of juvenile salmonids in the Sacramento–San Joaquin Delta (Delta) varies by migration route, and thus the proportion of fish that use each route affects overall survival through the Delta. Understanding factors that drive routing at channel junctions along the Sacramento River is therefore critical to devising management strategies that maximize survival. Here, we examine entrainment of acoustically tagged juvenile Chinook Salmon into Sutter and Steamboat sloughs from the Sacramento River. Because these sloughs divert fish away from the downstream entrances of the Delta Cross Channel and Georgiana Slough (where fish access the low-survival region of the interior Delta), management actions to increase fish entrainment into Sutter and Steamboat sloughs are being investigated to increase through-Delta survival. Previous studies suggest that fish generally “go with the flow”—as net flow into a divergence increases, the proportion of fish that enter that divergence correspondingly increases. However, complex tidal hydrodynamics at sub-daily time-scales may be decoupled from net flow. Therefore, we modeled routing of acoustic tagged juvenile salmon as a function of tidally varying hydrodynamic data, which was collected using temporary gaging stations deployed between March and May of 2014. Our results indicate that discharge, the proportion of flow that entered the slough, and the rate of change of flow were good predictors of an individual’s probability of being entrained. In addition, interactions between discharge and the proportion of flow revealed a non-linear relationship between flow and entrainment probability. We found that the highest proportions of fish are likely to be entrained into Steamboat Slough and Sutter Slough on the ascending and descending limbs of the tidal cycle, when flow changes from positive to negative. Our findings characterize how patterns of entrainment vary with tidal flow fluctuations, providing information critical for understanding the potential effect of management actions (e.g., fish guidance structures) to modify routing probabilities at this location.

Modeling Assessment of Tidal Energy Extraction in the Western Passage

Numerical models have been widely used for the resource characterization and assessment of tidal instream energy. The accurate assessment of tidal stream energy resources at a feasibility or project-design scale requires detailed hydrodynamic model simulations or high-quality field measurements. This study applied a three-dimensional finite-volume community ocean model (FVCOM) to simulate the tidal hydrodynamics in the Passamaquoddy–Cobscook Bay archipelago, with a focus on the Western Passage, to assist tidal energy resource assessment. IEC Technical specifications were considered in the model configurations and simulations. The model was calibrated and validated with field measurements. Energy fluxes and power densities along selected cross sections were calculated to evaluate the feasibility of the tidal energy development at several hotspots that feature strong currents. When taking both the high current speed and water depth into account, the model results showed that the Western Passage has great potential for the deployment of tidal energy farms. The maximum extractable power in the Western Passage was estimated using the Garrett and Cummins method. Different criteria and methods recommended by the IEC for resource characterization were evaluated and discussed using a sensitivity analysis of energy extraction for a hypothetical tidal turbine farm in the Western Passage.

Transport modelling of sediment re-suspended during submarine cable laying operation

A two-dimensional depth-averaged hydrodynamics and suspended sediment transport numerical model is presented, which is discretized with finite volume method based on a triangular mesh. It is applied to investigate the diffusion and transport characteristics of sediment re-suspended during a demonstration staged submarine cable laying across the Jintang Channel, Zhejiang Province, China. The model is validated primarily against the observed data during the spring, middle and neap tidal cycles in July 2015. The model results show well agreements between the predicted and observed processes of tidal level, velocity and suspended sediment concentration (SSC). The validated model is then applied to simulate the distribution of the tidal velocity and additional SSC during the cable laying. The results show a close relationship between the additional SSC distribution and tidal hydrodynamics.

Simulation of Environmental Changes Consdering Sea-level Rise Near a Mega-scale Coastal Dike (Saemangeum [SMG] Dike, Korea)

Yoo, S.-C. and Suh, S.-W., 2020. Simulation of environmental changes considering sea-level rise near a mega-scale coastal dike (Saemangeum [SMG] dike, Korea). In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 309–314. Coconut Creek (Florida), ISSN 0749-0208.The construction of one of the biggest coastal dikes in Korea, the 33-km long Saemangeum (SMG) dike, was completed in 2006. Coastal environmental changes resulted in tidal asymmetry in the near field (i.e., adjacent to the dike) and the far field (i.e., up to opposite part of the Yellow Sea). Coastal hydrodynamic variations and engineering developments for gate operations (to maintain inner reservoir water quality (WQ) standards) rapidly alter coastal environments. The sea level is expected to rise by 80 cm by the end of this century, and an additional 21.4 cm of seasonal local summer sea level jump will serve as a reversing factor of WQ. This study applied the ADCIRC and EFDC models to simulate regional and local hydrodynamic and WQ changes. The far-field impacts of the SMG will occur continuously till year 2100 along the Chinese coast with M2 mordulation. The target water management level was set to elevation with respect to mean sea level (EL) as -1.5 m, which is very limited in terms of free discharge time for gate operation. According to the tidal excursion and residence time simulations, only 14% of gate operations in a month will be possible compared to the existing all-year-round condition, and only 4% will be exchangeable in summer. It is found that SMG yields alteration of tidal hydrodynamics showing overall de-amplification of ∼10 cm in the Yellow Sea (YS), especially along the west coast of Korea (WCK), as well as a slight amplification of ∼10 cm on the eastern coast of China. In addition, reducing the time for inner discharge because of the rising outer sea level directly influences WQ both in the areas near the gates and the inner water due to the increased residence time. Intensive study including long-term variations in tidal asymmetry and associated morphologies is needed to manage the hydrodynamic and/or WQ changes associated with such mega-scale coastal constructions.

Enhanced Lateral Exchange of Carbon and Nitrogen in a Coastal Wetland With Invasive Spartina alterniflora

AbstractLateral movements of materials and energy in coastal wetlands, due mainly to tidal activities, have been recognized as key processes in understanding the biogeochemical cycles of ecosystems. However, our understanding of the roles of lateral movement in shaping ecosystem functions remains limited. Here we quantified the effects of lateral sediment transport on total carbon (C, inorganic + organic) and nitrogen (N) pools in plants and soils in two dominant wetland types: invasive Spartina alterniflora (Spartina) marshes and native Phragmites australis (Phragmites) marshes in coastal Shanghai of the Yangtze Estuary. We found that the accreted sediments across the water‐marsh gradients caused by lateral movement resulted in contrasting C and N contents between the two communities. The sediment load and C and N pools in the plants and soils of the Spartina marshes were significantly higher than those in the adjacent Phragmites marshes. The shifts in species composition and community structure not only altered the C and N balance but also enhanced the ecosystem net primary productivity. Our findings highlight the importance of lateral transport in altering ecosystem structure after Spartina invasion. The ecosystem C and N pools were significantly higher in the invaded ecosystems than in the native community. Our study also reveals that the plant density and structures can alter tidal hydrodynamics and the lateral transportations of sediments, which in turn influence ecosystem C and N cycle. The C accumulation processes of the native and invaded marshes were further complicated by the contrasting productivities of the ecosystems.

Tidal regime shift in Lingdingyang Bay, the Pearl River Delta: An identification and assessment of driving factors

AbstractBoth natural changes (e.g., tidal forcing from the ocean and global sea level rise) and human‐induced changes (e.g., dredging for navigation, sand excavation, and land reclamation) exert considerable influences on the long‐term evolution of tidal regimes in estuaries. Evaluating the impacts of these factors on tidal‐regime shifts is particularly important for the protection and management of estuarine environments. In this study, an analytical approach is developed to investigate the impacts of estuarine morphological alterations (mean water depth and width convergence length) on tidal hydrodynamics in Lingdingyang Bay, Southeast China. Based on the observed tidal levels from two tidal gauging stations along the channel, tidal wave celerity and tidal damping/amplification rate of different tidal constituents are computed using tidal amplitude and phase of tidal constituents extracted from a standard harmonic analysis. We show that the minimum mean water depth for the whole estuary occurred in 2006, whereas a shift in tidal wave celerity for the M2 tide component occurred in 2009. As such, the study period (1990–2016) could be separated into pre‐human (1990–2009) and post‐human (2010–2016) phases. Our results show that the damping/amplification rate and celerity of the M2 tide have increased by 31% (from 7 to 9.2 m−1) and 28% (from 7 to 9 m·s−1) respectively, as a consequence of the substantial impacts of human interventions. The proposed analytical method is subsequently applied to analyse the historical development of tidal hydrodynamics and regime shifts induced by human interventions, thus linking the evolution of estuarine morphology to the dominant tidal hydrodynamics along the channel. The observed tidal regime shift is primarily caused by channel deepening, which substantially enlarged the estuary and reduced effective bottom friction resulting in faster celerity and stronger wave amplification. Our proposed method for quantifying the impacts of human interventions on tidal regime shifts can inform evidence‐based guidelines for evaluating hydraulic responses to future engineering activities.

A novel approach for the assessment of morphological evolution based on observed water levels in tide-dominated estuaries

Abstract. Assessing the impacts of both natural (e.g. tidal forcing from the ocean) and human-induced changes (e.g. dredging for navigation and land reclamation) on estuarine morphology is particularly important for the protection and management of the estuarine environment. In this study, a novel analytical approach is proposed for the assessment of estuarine morphological evolution in terms of tidally averaged depth on the basis of the observed water levels along the estuary. The key lies in deriving a relationship between wave celerity and tidal damping or amplification. For given observed water levels at two gauging stations, it is possible to have a first estimation of both wave celerity (distance divided by tidal travelling time) and tidal damping or amplification rate (tidal range difference divided by distance), which can then be used to predict the morphological changes via an inverse analytical model for tidal hydrodynamics. The proposed method is applied to the Lingdingyang Bay of the Pearl River Estuary, located on the southern coast of China, to analyse the historical development of the tidal hydrodynamics and morphological evolution. The analytical results show surprisingly good correspondence with observed water depth and volume in this system. The merit of the proposed method is that it provides a simple approach for understanding the decadal evolution of the estuarine morphology through the use of observed water levels, which are usually available and can be easily measured.

Impact of 2004 co-seismic coastal uplift on the mangrove cover along the North Andaman Islands

The December 2004 earthquake and the subsequent tsunami have incurred devastating impacts on vital habitats along the Indian coastal region, where few of them are irreversible. The earthquake has uplifted the northern Andaman coast, resulting in a drastic reduction of tidal water influx into the adjoining mangrove-laden mudflats. Satellite images of the period from 2003 to 2019 were used to assess the impact of coastal upliftment on the northern Andaman mangroves. Through satellite data analysis, we report a loss of 6500 ha of northern Andaman mangroves. Tidal hydrodynamics simulation under the post-earthquake scenario showed a vast area of mudflats deprived of tidal influx. This reduction in the tidal inundation has incurred a gradual and permanent mangrove area degradation. The earthquake impact on the mangroves was not spontaneous, but a gradual process, where the mangroves were intact until Mach 2006. The earthquake and the resultant coastal uplift have significantly altered the coastal geomorphology as well as the plant demography of the study area. Field visit revealed the terrestrial vegetation growth along the erstwhile mudflats, and vast areas of mangrove peat are observed, surrounded by successions of marshy and terrestrial plants. As mangroves are preferred habitat for diverse marine and terrestrial organisms and act as a vital food source and juvenile shelters for various fish species, the extensive loss of mangrove area may adversely affect a large scale biological ecosystem.