Nearshore Currents Research Articles

Wave-driven current and vortex patterns at an open beach: Insights from phase-resolving numerical computations and Lagrangian measurements

Wave-driven currents have a substantial impact on local circulation patterns in and across the surf zone, and are responsible for cross-shore and longshore exchange of mass and momentum over a broad range of spatial and temporal scales. Nearshore currents may drive sediment transport, lead to beach erosion, and also affect the spread of bacteria and other marine microorganisms, as well as the distribution of pollutants such as chemicals and microplastics. In addition, surf zone currents can cause hazardous conditions for beach-goers in the form of rip currents.It is known from previous work (Chen et al., 2003; Feddersen et al., 2011; Hally-Rosendahl and Feddersen, 2016) that Boussinesq-type models in combination with appropriate boundary conditions and wave breaking capabilities can function as powerful tools for the analysis of circulation patterns in the surf zone. In the present work, data from a recent field campaign reported on in Bjørnestad et al. (2021) are used to further validate the capability of Boussinesq systems to simulate nearshore dynamics.The numerical model is then used to study the influence of tidal elevation, peak direction and directional spread of the incoming wavefield on the quantity, extent, and circulatory magnitude of the nearshore circulation. In addition, fundamental features such as horizontal eddies are investigated, and comparisons are made to solid-body rotation and irrotational vortices.Overall, it is observed that local variations in the bathymetry across the surf zone are the controlling factor regarding the size of these circulations, and an increasing tidal level, which can be seen as a uniform offset to the bathymetry, favors the generation of larger vortex patterns. For a given tidal stage, the directional spread of the incoming wavefield has the most pronounced influence on the size and strength of the nearshore eddies while the peak direction has the strongest effect on the total number of circulations.

Integrated Modeling of Coastal Processes Driven by an Advanced Mild Slope Wave Model

Numerical modeling of wave transformation, hydrodynamics, and morphodynamics in coastal regions holds paramount significance for combating coastal erosion by evaluating and optimizing various coastal protection structures. This study aims to present an integration of numerical models to accurately simulate the coastal processes with the presence of coastal and harbor structures. Specifically, integrated modeling employs an advanced mild slope model as the main driver, which is capable of describing all the wave transformation phenomena, including wave reflection. This model provides radiation stresses as inputs to a hydrodynamic model based on Reynolds-averaged Navier–Stokes equations to simulate nearshore currents. Ultimately, these models feed an additional model that can simulate longshore sediment transport and bed level changes. The models are validated against experimental measurements, including energy dissipation due to bottom friction and wave breaking; combined refraction, diffraction, and breaking over a submerged shoal; wave transformation and wave-generated currents over submerged breakwaters; and wave, currents, and sediment transport fields over a varying bathymetry. The models exhibit satisfactory performance in simulating all considered cases, establishing them as efficient and reliable integrated tools for engineering applications in real coastal areas. Moreover, leveraging the validated models, a numerical investigation is undertaken to assess the effects of wave reflection on a seawall on coastal processes for two ideal beach configurations—one with a steeper slope of 1:10 and another with a milder slope of 1:50. The numerical investigation reveals that the presence of reflected waves, particularly in milder bed slopes, significantly influences sediment transport, emphasizing the importance of employing a wave model that takes into account wave reflection as the primary driver for integrated modeling of coastal processes.

The Lake Effect: Lake Michigan, Landscape Evolution, and the Archaeological Record of the Chicago Region

Abstract Lake Michigan continues to have a major impact on the environment in the Chicago region, and changes in lake levels were a major driver of landscape evolution throughout the late Pleistocene and Holocene. Fluctuating lake levels reduced or increased the extent and character of terrestrial resources. The landscape has also been altered by erosional and aggradational processes from near-shore currents and wave action. Interpretation of archaeological site and settlement patterns in this region requires an understanding of the factors that have shaped and continue to shape this landscape. In the PaleoIndigenous and Archaic periods, foraging groups adapted to rapidly changing vegetation patterns and episodes of lake transgression and recession that opened or closed new habitats. In the Woodland and Upper Mississippian periods, lake levels stabilized, but the landscape continued to evolve, with erosion and deposition of sediments along Lake Michigan shorelines. Evidence for lake-level fluctuations over the last 12,000 years is available from a variety of data sets, including those for deep lacustrine sediments, ostracods, abandoned shorelines, and sand dunes. By synthesizing these data and utilizing GIS to reconstruct past lakeshores, we seek to better understand how people interacted with and adjusted to this dynamic landscape.

Impacts of Climate Change on Coastal Hydrodynamics Around a Headland and Potential Headland Sediment Bypassing

AbstractShorelines face growing threats due to climate change and diminishing sand supply. Coastal headlands, common rocky features along coastlines, are crucial in shaping hydrodynamics and sediment transport. Yet, the influence of future climate conditions, including sea‐level rise (SLR) and intensified storm energy on complex shorelines with headlands has remained relatively unexplored. In this study, we model changes in hydrodynamics and headland bypassing under different SLR and higher storm wave scenarios. Our findings reveal the formation of circulation cells on both sides of a headland, where wave energy converges around the headland zone. Future climate conditions result in larger storm waves on the beach. However, SLR enhances nearshore currents through a landward shifting of the circulation cells, while higher storm waves intensify offshore flow currents due to the seaward movement of the cells. This effect, in turn, increases the potential for headland sediment bypassing.

Multi-Timescale Characteristics of Southwestern Australia Nearshore Surface Current and Its Response to ENSO Revealed by High-Frequency Radar

The surface currents in coastal areas are closely related to the ecological environment and human activities, and are influenced by both local and remote factors of different timescales, resulting in complex genesis and multi-timescale characteristics. In this research, 9-year-long, hourly high-frequency radar (HFR) surface current observations are utilized together with satellite remote sensing reanalysis products and mooring data, and based on the Empirical Orthogonal Function (EOF) and correlation analysis, we revealed the multi-timescale characteristics of the surface currents in Fremantle Sea (32°S), Southwestern Australia, and explored the corresponding driving factors as well as the impact of El Niño-Southern Oscillation (ENSO) on the nearshore currents. Results show that the currents on the slope are dominated by the southward Leeuwin Current (LC), and the currents within the shelf are dominated by winds, which are subject to obvious diurnal and seasonal variations. The strong bathymetry variation there, from a wide shelf in the north to a narrow shelf in this study region, also plays an important role, resulting in the frequent occurrence of nearshore eddies. In addition, the near-zonal winds south of 30°S in winter contribute to the interannual variability of the Leeuwin Current at Fremantle, especially in 2011, when the onshore shelf circulation is particularly strong because of the climatic factors, together with the wind-driven offshore circulation, which results in significant and long-lasting eddies. The southward Leeuwin Current along Southwestern Australia shows a strong response to interannual climatic variability. During La Niña years, the equatorial thermal anomalies generate the westward anomalies in winds and equatorial currents, which in turn strengthen the Leeuwin Current and trigger the cross-shelf current as well as downwelling within the shelf at Fremantle, whereas during El Niño years, the climate anomalies and the response of coastal currents are opposite. This paper provides insights into the multi-timescale nature of coastal surface currents and the relative importance of different driving mechanisms. It also demonstrates the potential of HFR to reveal the response of nearshore currents to climate anomalies when combined with other multivariate data. Meanwhile, the methodology adopted in this research is applicable to other coastal regions with long-term available HFR observations.

Assessing Empirical Components in Wave Breaking and Rollers Through Model Comparison of Radiation Stress and Vortex Force

AbstractAs incoming waves approach shallow water, they break and result in nearshore currents. The assessment of the wave‐induced nearshore currents often relies on the application of radiation stress (RS) and vortex force (VF) in circulation models, both of which incorporate empirical components to describe wave breaking and wave rollers. In this study, we compared a recent 3D RS formulation and a VF formulation by assessing the modeled cross‐shore velocities against the measured counterparts from the LIP11D and Duck’94 experiments. The comparison results indicate that the RS model performs better in LIP11D, whereas the VF model exhibits better with respect to Duck’94. Using momentum balance analysis, we found that the cross‐shore velocities were dominated by the breaking term (representing the RS terms and non‐conservative breaking term in the RS and VF models, respectively) and the roller term. The breaking term generates undertow currents across the entire surf zone. The roller term cooperates with the breaking term in the inner surf zone, but counteracts the breaking term and tends to trigger unrealistic offshore currents at the water surface in the outer surf zone. Further analysis reveals that the RS and VF formulations can simulate almost identical velocity results by adjusting the vertical distribution of the breaking and roller terms. Overall, this study indicates that both the RS and VF formulations are effective in evaluating wave effects on the cross‐shore currents, and empirical components in the breaking and roller terms are important for modeling cross‐shore velocities.

Monitoring the nearshore currents pattern along the anthropogenically influenced coast of Puducherry

Monitoring the nearshore currents pattern along the anthropogenically influenced coast of Puducherry

APPLICATION OF EQUILIBRIUM-BASED SHORELINE EVOLUTION MODELING TO DIVERSE COASTAL ENVIRONMENTS

Coastal zones are highly complex and dynamic environments shaped by diverse forcing agents such as waves, nearshore currents, sea levels, storm surges, winds, human interventions, and other oceanographic and sediment supply factors that occur on different spatio-temporal scales. Hence, coastal managers and stakeholders need simplified and practical models in order to estimate future beach morphodynamic changes to face decision-making. The shoreline hindcast under the influence of changing marine conditions has been mostly considered by means of existing robust shoreline evolution models, such as one-line shoreline models, multi-line shoreline models, combined models, and 3D models. All of them require long data series, many calibration parameters and are computationally intensive. This study presents the potential performance of some newly equilibrium-based shoreline evolution models used for daily to multiannual shoreline prediction, in diverse coastal environments (e.g. Jaramillo et al. 2020, 2021a, 2021b).

РАДИОЭКОЛОГИЧЕСКОЕ СОСТОЯНИЕ ПРИБРЕЖНОЙ ЗОНЫ КОЛЬСКОГО ПОЛУОСТРОВА (ПО ДАННЫМ НАБЛЮДЕНИЙ В 2013-2020 ГОДАХ)

The current radionuclide pollution of the marine environment (water and bottom sediments) in the coastal zone of the Kola Peninsula have been analyzed. The background pollution of the coast is formed by the Barents Sea water inflow, nuclear fleet infrastructure facilities, and radioactive waste management operations. The main factors determining radiation background and spatial dynamics of pollution in the largest bays and open coastal areas have been considered. As a result, it is stated that the main factor determining the radiation background of the open coastal zone is the transfer of 137Cs and 90Sr radioisotopes from the Norwegian Sea and the North Atlantic by the Murmansk nearshore current. The emission of radionuclides from nuclear infrastructure facilities in the Andreev, Zapadnaya Litsa, and Kola bays is insignificant and has a local nature in terms of the scale of impact.

Modulation of the Marine Environment in the Natal Bight

Modulation of the marine environment in the Natal Bight (~29.1°S, 31.6°E) was studied using daily high-resolution climate reanalysis products and monthly satellite green- and red-band reflectance in the period 2002–2022. The KwaZulu-Natal shelf edge is characterized by a narrow band of upwelling next to the warm Agulhas Current. Strong, reversing longshore winds ~7 m/s and meandering poleward flow ~1 m/s pulse the system, but along the leeward coast that forms the Natal Bight, environmental conditions are buffered by a weak cyclonic gyre. Wind and current shear create a shadow zone that aggregates plankton, recycles nutrients, and sustains marine resources. The seasonal cycle is of high amplitude: the surface heat balance reaches +70 W/m2 in December, followed by river discharges ~3 M m3/yr of fresh nutrient-rich water that peak in February. This induces a buoyant surface layer that inhibits wind wave turbulence during summer. By contrast, winter (June–August) cooling −95 W/m2 and frequent cyclonic storminess deepen the mixed layer from 25 to 65 m, enabling wind wave turbulence to reach the seafloor (Tugela Bank). Red-band reflectance increases 3-fold from summer to winter and is significantly correlated with net heat balance −0.54, daily wave heights > 2.5 m +0.51, mixed layer depth +0.47, sea surface temp −0.41, and wind vorticity −0.39. Daily longshore winds from the northeast and southwest were, unexpectedly, most amplified in spring (August–October). The seasonality exhibits sequential effects that supports year-round marine nutrification in the Natal Bight. Intra-seasonal fluctuations were related to meandering of the Agulhas Current and changes in longshore winds and shelf waves that impart significant pulsing of near-shore currents at 4–9-day periods. Although the cyclonic gyre in the Natal Bight spins up and down, SST variance was found to be relatively low in its center, where external influences are buffered. Considering linear trends for winds and runoff and surface temperature over the period 1950–2021, we found that northeasterlies increased, runoff decreased, and inshore sea surface temperatures have warmed slowly relative to the adjacent land surface temperature. New insights derive from the use of monthly satellite red-band reflectance and daily 10 km climate reanalysis fields to understand how air–land–sea fluxes modulate the marine environment in the Natal Bight.

The importance of resolving nearshore currents in coastal dispersal models

Biophysical models often require shelf-scale domains to map larval dispersal over several weeks, presenting a computational challenge. This can be overcome by decreasing model spatial resolution; however, nearshore processes, which potentially play a significant role in larval dispersal, will inevitably be unresolved. Here, we evaluate how simulated larval dispersal in the nearshore is sensitive to model spatial resolution. We use an unstructured, finite element, hydrodynamic model of a topographically-complex coastline in North Wales, UK (which includes headlands, bays and channels) at four different spatial scales (50, 100, 250, 500 m) to compare the influence of spatial resolution on transport and dispersal patterns of particles released within the nearshore region (within 1 km of the shore). In the higher resolution (50 and 100 m) simulations, particles generally travelled offshore more quickly and further (∼18%) than in the coarser (250 and 500 m) simulations. This had important implications for potential connectivity along the coast: for the lower resolution simulations, retention of particles near source sites was increased by ∼50% and, whilst the magnitude of connectivity among discrete regions along the coast was also increased (by ∼27%), the number of connected regions was reduced (by ∼9%), compared with the higher resolution simulations. Our results, based on a case study in a highly energetic and topographically complex region, suggest that model spatial resolution of ≤100 m should be used for dispersal studies in the nearshore zone. These findings add to growing evidence of the importance of using appropriately scaled models when simulating the transport of material within – and out of – the coastal zone, with many applications, such as marine ecology, marine biosecurity, marine spatial planning and marine pollution.

Interactions Between Internal Tidal Bores and Submesoscale Currents on the Continental Shelf

AbstractA realistic simulation of Central California reveals interactions between shoaling internal tidal bores and submesoscale currents on the inner‐shelf (approximately 30–60 m depth). These interactions comprise collisions between internal tidal upwelling, “forward” bores (FBs) with submesoscale currents (SMCs) in the form of surface layer density fronts or filaments with downwelling secondary circulation. Along‐shore oriented FBs collide with both cross‐shore (perpendicular interaction) or along‐shore (parallel interaction) oriented SMCs. In perpendicular interaction, FBs colliding into cross‐shore oriented SMCs refract around the offshore tip of the downwelling front or filament. SMCs generally survive perpendicular interaction, despite partial disruption of downwelling secondary circulation by FBs. An example of parallel interaction demonstrates regional wind regulating the competition between FBs and SMCs to set cross‐shore stratification structure. This example comprises (a) blocking of FB propagation by elevated mixing (strong wind) and dense filament formation on the inner‐shelf and (b) the subsequent destruction of the dense filament that is initiated by a decrease in vertical mixing (weakening wind) and completed by renewed FB propagation underneath it. For both perpendicular and parallel interaction, FB propagation is modulated by a varying medium introduced by SMC density and current structure. The computational evidence of these interactions corroborates recent observations of interactions between small‐scale, nearshore currents in the real ocean. This study motivates further exploration of interactions between fronts, filaments, internal tidal bores, and vortices in the nearshore.

Genetic Structure of the Endemic Fiddler Crab Uca (Xeruca) formosensis on the West Coast of Taiwan.

Xeruca formosensis is the only endemic species of fiddler crab on the west coast of Taiwan. However, its natural habitats and populations have been compromised by excessive anthropogenic activities and improper land use over the past four decades. In light of these changes, we sought to evaluate the genetic diversity and gene flow of the species by examining the genetic variation of X. formosensis at different sampling locations. To this end, we performed molecular analyses of three endonuclease-amplified fragment length polymorphisms (TE-AFLP) and the cytochrome oxidase subunit I (COI) marker from leg muscle samples. We found that the genetic variation within sampling locations was higher than that among sampling locations, and the expected heterozygosity of genetic diversity (Hj) was 0.152 for TE-AFLP data. Meanwhile, the COI marker showed high haplotype diversity (h = 0.976 ± 0.008) and a low genetic differentiation level (FST = 0.021) in X. formosensis populations. Importantly, the genetic connectivity of X. formosensis may be influenced by larval-stage crabs drifting between coastal and marine habitats. As such, crab gene flow is promoted among populations by larval exchange via nearshore currents. Although X. formosensis has high gene flow, the species could undergo an extinction crisis if the population sizes continue to decline, as with most endangered species. In order to maintain the natural habitats and population size of X. formosensis, long-term monitoring and investigation will be necessary.

Periodicity in Chthamalus fissus reproduction does not guarantee periodicity in settlement

The timing of life history events can have profound implications for populations and communities, especially those events that influence species dispersal and recruitment. In benthic invertebrates, the majority of dispersal occurs during the larval phase of life. Yet the extent to which timing of reproduction (the beginning of the larval phase) directly influences timing of settlement (the end of the larval phase) is unclear, because biological and hydrodynamic processes can act to decouple these 2 events, and because reproduction and settlement are seldom studied together. Here, we used long-term (2014-2019) daily and weekly data from Bird Rock, La Jolla, California, USA, to look for lunar and seasonal cycles in reproduction and settlement timing of the acorn barnacle Chthamalus fissus, and we incorporated measurements of nearshore currents to examine the implications of reproduction timing on alongshore larval transport distances. We found evidence of lunar and seasonal cycles in reproduction but only limited cyclicality in settlement, possibly due to plasticity in larval development coupled with variable larval transport and dispersal. Our results demonstrate the complex nature of relationships between reproduction, larval transport, and settlement, which must be disentangled before accurate predictions can be made regarding the impacts of climate change on the population dynamics of marine species.

Spatial Variability of Surface Waves and Nearshore Currents Induced by Hurricane Harvey along the Southern Texas Coast

Extreme weather events such as hurricanes are expected to become more severe with the human-induced increase in average global temperatures, exacerbating the risk of major damage. Efforts to predict these events typically require detailed hydrodynamic data that are difficult to collect in the field. Here, nearshore data collected with three ADCP moorings were used to describe the hydrodynamics induced by Hurricane Harvey along the southern Texas coast. Wave spectra and nearshore current variations were analyzed along the hurricane’s trajectory and compared to other offshore locations. The results indicate that winds intensified along the coast as Harvey approached the Port Aransas coastline. Southerly wind stresses of ~−0.9 Nm−2 generated ~2 ms−1 depth-averaged flows towards the southwest close to landfall in the north, while flows of ~1 ms−1 and <1 ms−1 were measured in the center and the south of the study site, respectively. The hydrodynamics induced by the hurricane were compared to those induced by an intense synoptic-scale cold front (CF). Both events generated southward-directed alongshore wind stresses of similar magnitudes (τy ~−0.4 Nm−2) that caused similar depth-averaged flows (0.5 to 0.7 ms−1) and wave energy conditions (Hs of ~4 m) in the south. Harvey caused extremely energetic conditions close to landfall in the north compared to the CF; depth-averaged flows and Hs of 2 ms−1 and 10 m were induced by Harvey, as opposed to 0.6 ms−1 and 4 m by the CF, respectively. While intense currents (>1 ms−1) and waves (Hs > 4 m) lasted for less than a day during Harvey, these persisted a few days longer during the CF. This study highlights the relevant role of synoptic-scale cold fronts in modulating the nearshore hydrodynamics, which occur more frequently than tropical cyclones in the northwestern Gulf of Mexico.

Influence of Kelp Forest Biomass on Nearshore Currents

AbstractAs part of a project focused on the coastal fisheries of Isla Natividad, an island on the Pacific coast of Baja California, Mexico, we conducted a 2‐1/2 year study of flows at two sites within the island's kelp forests. At one site (Punta Prieta), currents are tidal, whereas at the other site (Morro Prieto), currents are weaker and may be more strongly influenced by wind forcing. Satellite estimates of the biomass of the giant kelp (Macrocystis pyrifera) for this period varied between 0 (no kelp) and 3 kg/m2 (dense kelp forest), including a period in which kelp entirely was absent as a result of the 2014–2015 “Warm Blob” in the Eastern Pacific. During this natural “deforestation experiment”, alongshore velocities at both sites when kelp was present were substantially weaker than when kelp was absent, with low‐frequency alongshore currents attenuated more than higher frequency ones, behavior that was the same at both sites despite differences in forcing. The attenuation of cross‐shore flows by kelp was less than alongshore flows; thus, residence times for water inside the kelp forest, which are primarily determined by cross‐shore velocities, were only weakly affected by the presence or absence of kelp. The flow changes we observed in response to changes in kelp density are important to the biogeochemical functioning of the kelp forest in that slower flows imply longer residence times, and, are also ecologically relevant in that reduced tidal excursions may lead to more localized recruitment of planktonic larvae.

Numerical modelling of sediment transport in southwest coast of Nigeria: Implications for sustainable management of coastal erosion in the Bight of Benin

Coastal erosion is widespread across the Bight of Benin owing to the perturbation of the sediment transport by the installation of the major ports of Lomé (Togo), Cotonou (Benin), and Lagos (Nigeria), among other factors. While different coastal management measures have been put in place to mitigate the effects of this hazard, they have seldom lessened the damage caused by it. To this end, this study examined the coastal processes in Southwest Nigeria (Barrier-Lagoon and Mud coast sections) through the numerical modelling of the hydrodynamic, spectral-wave, and sediment transport for three months to apprehend the poor performance of the management measures. Model results reveal that the nearshore current is mainly directed eastward with the persistent exposure of the area to wave-action. Two major sediment transports; the eastward/south-eastward and westward/north-westward sediment transports, were also identified. The predominance of these sediment transport patterns implies that the continuous adoption of reactive, site-specific hard-engineering coastal management approaches will give counter-productive results. Thus, to sustainably manage the coastal erosion problem across the Bight of Benin, there is the need to adopt a long-term, regional perspective with a cascade of coastal management measures covering all areas under the influence of the predominant sediment transports.

Development of a Numerical Model to Analyze the Formation and Development Process of River Mouth Bars

An integrated sediment management approach that includes the recovery of the amount of declined sediment supply is effective as a fundamental solution to coastal erosion. During planning, it is essential to analyze the transfer mechanism of the sediments generated from estuaries (the junction between a river and sea) to assess the amount and rate of sediment discharge (from the river to sea) supplied back to the coast. Although numerical models that interpret the tidal sand bar flushing process during flooding have been studied, thus far, there has been no study focusing on the formation and development processes of tidal sand bars. Therefore, this study aims to construct wave deformation, flow regime calculation, and topographic change analysis models to assess the amount of recovered sediment discharge and reproduce the tidal sand bar formation process through numerical analysis for integrated littoral drift management. The tidal sand bar formation process was simulated, and the wave energy and duration of action concepts were implemented to predict the long-term littoral movement. The river flux and wave conditions during winter when tidal sand bars dominantly develop were considered as the external force conditions required for calculation. The initial condition of the topographic data directly after the Maeupcheon tidal sand bar flushing during flooding was set as the initial topography. Consequently, the tidal sand bar formation and development due to nearshore currents dependent on the incident wave direction were reproduced. Approximately 66 h after the initial topography, a sand bar formation was observed at the Maengbang estuary.

Numerical Investigation of Hydrodynamics and Cohesive Sediment Transport in Cua Lo and Cua Hoi Estuaries, Vietnam

Two-dimensional models of large spatial domain including Cua Lo and Cua Hoi estuaries in Nghe An province, Vietnam, were established, calibrated, and verified with the observed data of tidal level, wave height, wave period, wave direction, and suspended sediment concentration. The model was then applied to investigate the hydrodynamics, cohesive sediment transport, and the morphodynamics feedbacks between two estuaries. Results reveal opposite patterns of nearshore currents affected by monsoons, which flow from the north to the south during the northeast (NE) monsoon and from the south to the north during the southeast (SE) monsoon. The spectral wave model results indicate that wave climate is the main control of the sediment transport in the study area. In the NE monsoon, sediment from Cua Lo port transported to the south generates the sand bar in the northern bank of the Cua Hoi estuary, while sediment from Cua Hoi cannot be carried to the Cua Lo estuary due to the presence of Hon Ngu Island and Lan Chau headland. As a result, the longshore sediment transport from the Cua Hoi estuary to the Cua Lo estuary is reduced and interrupted. The growth and degradation of the sand bars at the Cua Hoi estuary have a great influence on the stability of the navigation channel to Ben Thuy port as well as flood drainage of Lam River.

A case study of coastal currents in relation with tides and winds in a tropical coastal waters of Vengurla, West Coast of India

Coastal currents consist of wind-driven, tidal, surface wave and geostrophic flows. These currents have a major role for nearshore sediment transport, but the measured data availability on coastal currents for the Indian coast is relatively less. This study analyze the variability of coastal currents along with the tides at nearshore and offshore waters during two different seasons (fag end of summer monsoon and initial stage of pre-monsoon) at Vengurla, west coast of India. Results of this study exhibited that the tides at Vengurla are mixed semi-diurnal dominated by solar constituent during summer monsoon (September to October); whereas the lunar constituents dominates during pre-monsoon (February to March). The nearshore current was dominated by the westward flow (sluggish current) during monsoon and south eastward flow during pre-monsoon, whereas the offshore flow (strong current) showed seasonality. At offshore, southerly current dominated during summer monsoon, whereas the northerly current played a major role during pre-monsoon. The current profile analysis at offshore revealed that the gradation of strong current at the surface to the sluggish nature of currents at the bottom and were comparatively higher during summer monsoon than pre-monsoon periods. This study revealed a complex pattern among winds, tides and currents at offshore.