Nearshore Currents Research Articles

Evaluation of beach nourishment works on Miyazaki coast in Japan

Miyazaki Coast have been suffering from severe erosion problem due to the shortage of sediment supply from rivers and the change of waves and nearshore currents by the construction of an offshore breakwater at Miyazaki Port. In order to reproduce a wide sandy beach, a beach nourishment project has been done since 2008 in combination with the installation of Sand-Packed containers that were placed in front of dune. A certain volume of nourishment sand has been installed for the sand fill works that cover Sand-Packed containers, and the rest has been dumped off the coast. The purpose of this research is to evaluate the effectiveness of beach nourishment works with using long-term bottom sounding data. This study discussed the effect of the beach nourishment on longshore sandbar evolution. The change of the sand volume in research area was also discussed in this study.

FOREWORD: Proceedings of the 36th International Conference

This Proceedings contains 550 papers from the 36th International Conference on Coastal Engineering, which was held in Baltimore, Maryland from July 30 to August 3, 2018. The Proceedings is divided into six parts: Papers; Waves; Swash, Nearshore Currents, and Long Waves; Sediment Transport and Morphology; Coastal Structures; and Coastal Management, Environment, and Risk. The “Papers” sections includes full length Proceedings papers, covering a broad range of topics including theory, numerical and physical modeling, field measurements, case studies, design, and management. The other sections include abstract and presentation files, as presented at the conference. These submissions provide engineers, scientists, and planners state-of-the-art information on coastal engineering and coastal processes.

Nearshore-offshore exchanges in multi-basin coastal waters: Observations and three-dimensional modeling in Lake Erie

Abstract Nearshore-offshore exchanges through upwelling events and subsequent formation of internal Kelvin waves and coastal-jets are expected in the multi-basin coastal waters of Lake Erie; however, these phenomena have yet to be confirmed in the field or numerically modeled. Here, we demonstrate these physical processes in Lake Erie through extensive field data analysis and high-resolution three-dimensional hydrodynamic modeling. The validated model successfully reproduces dominant physical processes in the offshore and nearshore waters including surface seiches (~14 h), near-inertial waves (~17 h) and upwelling events (5–10 days). We show that upwelling events are the predominant nearshore physical processes, and are energized when winds accelerate the epilimnetic waters to the south, causing the thermocline front to move up into the north shore. After the wind subsides, the elevated thermoclines simultaneously form two separate cyclonically propagating internal Kelvin waves in the central and the eastern basins following by two coastal-jets at phase speeds of 0.22 ms−1 and 0.37 ms−1 within 5–15 km off the shoreline, respectively. The predominant south-west winds limit the presence of Kelvin waves only to the northern parts of each basin, where the bathymetry allows, and disappear when shoreline morphology no longer maintain these waves due to nonzero cross-shore transports at the coastal boundary layer. Intrusions of hypolimnetic waters through upwelling events contribute 10–30% to the net cross-shore transport, and are most pronounced in May and June when the offshore thermocline is shallow. The intermittent strong westward nearshore currents by Kelvin waves are in the opposite direction of seasonal eastward currents.

Flash Rip Statistics from Video Images

Floc'h, F.; Mabiala, G.R.; Almar, R.; Castelle, B.; Hall, N.; Du Penhoat, Y., Scott, T., and Delacourt, C., 2018. Flash rip statistics from video images. In: Almar, R.; Almeida, L.P.; Trung Viet, N., and Sall, M. (eds.), Tropical Coastal and Estuarine Dynamics. Journal of Coastal Research, Special Issue No. 81, pp. 100–106. Coconut Creek (Florida), ISSN 0749-0208.The coast of the Gulf of Guinea is exposed to high-energy waves generating strong nearshore currents both driving erosion and posing a threat to recreational beach goers and fishermen. Along this coast, the coexistence of swash and flash rip currents at Grand-Popo beach (Benin) was evidenced in a previous study using a limited number of Lagrangian drifter measurements. In this paper, a method based on color processing of video images from a permanent station has been developed to detect the presence of rip currents via a change of turbidity. Rip current characteristics and their link with tide and wave forcing over a 7-day period are derived. During this experiment, a total of 434 events has been counted during daylight. The majority of rips occurred at low tide and migrates downdrift. Flash rip activity is maximized for shore-normal wave incidence and mild wave conditions showing that flash rips are not driven by shear instabilities of the longshore current at this site. However, the lack of strong variability in wave forcing throughout the experiment prevents a more thorough wave-rip relationship investigation, which motivates the application of the method for a longer period with a wide wave-tide spectrum.

Irregular wave propagation with a 2DH Boussinesq-type model and an unstructured finite volume scheme

The application and validation, with respect to the transformation, breaking and run-up of irregular waves, of an unstructured high-resolution finite volume (FV) numerical solver for the 2D extended Boussinesq-type (BT) equations of Nwogu (1993) is presented. The numerical model is based on the combined FV approximate solution of the BT model and that of the nonlinear shallow water equations (NSWE) when wave breaking emerges. The FV numerical scheme satisfies the desired properties of well-balancing, for flows over complex bathymetries and in presence of wet/dry fronts, and shock-capturing for an intrinsic representation of wave breaking, that is handled as a shock by the NSWE. Several simulations and comparisons with experimental data show that the model is able to simulate wave height variations, mean water level setup, wave run-up, swash zone oscillations and the generation of near-shore currents with satisfactory accuracy.

Numerical Modeling of Coastal Waves and Nearshore Currents on Adaptive Quadtree Grids

Numerical Modeling of Coastal Waves and Nearshore Currents on Adaptive Quadtree Grids

On Strong Nearshore Wind-Induced Currents in Flow-Through Gulfs: Variations on a Theme by Csanady

Csanady’s (1973) model, used to explain the development of strong, wind-induced nearshore currents in long lakes, has been extended to explain the same phenomenon in flow-through semi-enclosed gulfs. As in the original theory, it is predicted that the depth-averaged velocities move with the wind in regions shallower than the characteristic depth and upwind in deeper parts of the basin. The characteristic depth in the modified theory, however, is shown to be larger than the characteristic depth of the original theory, which is the basin mean depth, by a parameter λ, which can be calculated using the wind stress, the cross-section area and the volumetric inflow into the gulf. The theory is further used to examine in detail the scaling of the flow and identify the dimensional parameters underlying the formulation of the Csanady model. By expanding in an appropriately-defined inverse, Rossby number, which can be made arbitrarily large for small times, it is shown that under the influence of the Coriolis force, the free surface assumes a characteristic S-like shape and the shorewise volume flux an M-like shape. It is suggested that the shorewise flux might be of interest in environmental applications. The predictions of both variations of the original model of Csanady have been illustrated by numerical simulations, in pertinent idealized geometries, and have been also used to explain salient features of the wind-induced circulation in the Gulf of Patras in Western Greece.

Numerical Simulation of Parabolic Profile of Longshore Currents

Chun, H. and Suh, K.-D., 2018. Numerical simulation of parabolic profile of longshore currents. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 941–945. Coconut Creek (Florida), ISSN 0749-0208.The three-dimensional nearshore currents model well predicted the typical profile of undertow, i.e. the shoreward near-surface currents and the seaward flow below the wave trough level. Meanwhile, the measurements showed that the longshore currents were logarithmically or parabolically distributed over the depth, but the parabolic profile had not been reproduced by the numerical models (Newberger and Allen, 2007b; Uchiyama et al., 2010). However, Chun and Suh (2017) have shown that the wave-current interaction term in the surface wave stress was attributed to the parabolic profile of longshore currents, and then reproduced the profile of longshore currents in DUCK94. In order to see the parabolic profile of longshore currents in other cases, Chun and Suh's (2017) nearshore current model has been applied to Hamilton et al.'s (2001) laboratory experiment in the present study. Then the numerical results were compared with the measurements including the vertical profiles of longshore currents and undertow.

Variations of Nearshore Currents induced by Seasonal Waves in Haeundae

ABSTRACT Kim, M.; Lim, H.S.; Do, J.-D.; Kim, S.-S.; Lee, H.J., and Shim, J.-S., 2018. Variations of nearshore currents induced by seasonal waves in Haeundae. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 1551–1555. Coconut Creek (Florida), ISSN 0749-0208. Haeundae, located on the southeastern coast of the Korean Peninsula, is a famous sand beach with a 1.6 km long, 70 m wide coastline. It suffers from wave-induced beach erosion in both summer and winter. For beach restoration, the Korean government has conducted beach nourishment (620,000 m3), and installed submerged breakwaters at both ends of the beach. Despite these efforts, the beach is still vulnerable to erosion caused by high waves. To understand beach erosion processes and sediment transport mechanisms, the government initiated an R&D project for the development of coastal erosion control technology ...

Variability of Wave-induced Current Analyzed with Intensive Field Measurements in the Coastal Waters of Anmok

ABSTRACT Lim, H.S.; Kim, M.; Do, J.-D.; Kim, S.-S.; Lee, H.J., and Kim, D.H., 2018. Variation of nearshore currents induced by seasonal waves in Haeundae. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 686–690. Coconut Creek (Florida), ISSN 0749-0208. Wave-induced currents at Anmok, located on the eastern coast of the Korean Peninsula, are one of the main causes of beach erosion related to high waves. Coastline changes induced by beach erosion and deposition are predominantly caused by sediment transport in the surf zone. This sediment transport is generated by wave-induced currents and depends on the wave height and direction. To understand beach erosion processes and the sediment transport mechanisms, field measurements of beach elevation and water depth were conducted for one month in winter 2015–2016. Using AWAC, ADP, VECTOR, and Aquadopp Profiler with OB...

The Açu Reef morphology, distribution, and inter reef sedimentation on the outer shelf of the NE Brazil equatorial margin

Submerged reefs, referred to as the Açu Reefs, have been newly observed on both sides of the Açu Incised Valley on the northeastern equatorial Brazilian outer shelf. This study aims to understand the roles of shelf physiography, its antecedent morphologies, and its inter reef sedimentation on the different development stages of the biogenic reef during last deglacial sea-level rise. The data sets consist of side-scan sonar imagery, one sparker seismic profile, 76 sediment samples, and underwater photography. Seven backscatter patterns (P1 to P7) were identified and associated with eleven sedimentary carbonate and siliciclastic facies. The inherited relief, the mouth of the paleo incised valley, and the interreef sediment distribution play major controls on the deglacial reef evolution. The reefs occur in a depth-limited 25–55 m water depth range and in a 6 km wide narrow zone of the outer shelf. The reefs crop out in a surface area over 100 km2 and occur as a series of NW-SE preferentially orientated ridges composed of three parallel ridge sets at 45, 35, and 25 m of water depth. The reefs form a series of individual, roughly linear ridges, tens of km in length, acting as barriers in addition to scattered reef mounds or knolls, averaging 4 m in height and grouped in small patches and aggregates. The reefs, currently limited at the transition between the photic and mesophotic zones, are thinly covered by red algae and scattered coral heads and sponges. Taking into account the established sea-level curves from the equatorial Brazilian northeastern shelf / Rochas Atoll and Barbados, the shelf physiography, and the shallow bedrock, the optimal conditions for reef development had to occur during a time interval (11–9 kyr BP) characterized by a slowdown of the outer shelf flooding, immediately following Meltwater Pulse-1B. This 2 kyr short interval provided unique conditions for remarkable reef backstepping into distinct parallel ridge sets. Furthermore, the Açu Reefs have trapped relict siliciclastic sediments within the three sets of reefs, west of the Açu Incised Valley and adjacent coasts. Lines evidence of easterly nearshore currents carried sediments from the old Açu Incised Valley and adjacent coasts. These incipiently drowned reefs influence the water circulation patterns of the modern shelf system, its carbonate sedimentation, and sediment transport. This study provides a new example of reef occurrence which might be more commonly observed on similar equatorial continental shelves.

Modeling two-dimensional infragravity motions on a fringing reef

This study investigates infragravity motions on a two-dimensional fringing reef with a concave topography using a wave-resolving nonlinear Boussinesq wave model. The effect of bathymetric nonlinearity on spatial variations of infragravity waves is studied from shore-normal incident random waves. The model is first verified from cross-shore/alongshore significant wave height, wave setup and infragravity wave height measured in laboratory experiments. The modeled velocity is further examined to elucidate the infragravity-wave current field. Wavenumber-frequency velocity spectra show that cross-shore infragravity motions are controlled by the leaky waves, while alongshore infragravity motions exhibit edge waves characteristics. Additionally, high-mode edge waves prevail on the entire infragravity frequency band while low-mode edge waves are dominant at very low frequencies. Furthermore, the model results illustrate the spatial and temporal variability of wave-induced nearshore currents, alongshore and cross-shore flows accompanying with circulation cells and rip currents. The infragavity-wave current field is nearly identical to the mean current field and the circulations develop at the same spatial scale as the reef flat.

Sensitivity of rip current forecasts to errors in remotely-sensed bathymetry

Operational nearshore current forecasts based on numerical model simulations are gaining popularity as a measure to increase the safety of swimmers. Applying remotely-sensed bathymetry in these model simulations is often proposed in order to cope with rapidly changing nearshore bathymetry. Errors in the remotely-sensed bathymetry may negatively affect performance of the hydrodynamic model. Hence, this study aims to determine the sensitivity of modelled nearshore currents (with a strong focus on rip currents) to errors in remotely-sensed bathymetries.The errors in the remotely-sensed bathymetries (depth inversion algorithm applied to video stream) were quantified with a length scale-aware validation technique, providing useful insights in the contribution of pattern and amplitude errors to the total error throughout the analysis domain and over a range of bathymetric length scales. Subsequently, simulations with a nearshore hydrodynamic model were performed, using both in-situ and remotely-sensed bathymetries as an input. A comparison of predicted rip currents on either bathymetry yielded performance statistics for operational current forecasts on remotely-sensed bathymetries, taking the model with in-situ bathymetry as a reference. Linking these performance statistics back to the quantified errors in the remotely-sensed bathymetry finally revealed the relation between errors in flow and bathymetry.Of all rip currents generated on an in-situ bathymetry, 55% were reproduced on the remotely-sensed bathymetry, showing that models predicting nearshore currents on remotely-sensed bathymetry have predictive value. Positive rip current predictions were promoted significantly by accurate reproduction of the pattern and amplitude of nearshore bars at length scales between 200 and 400 m. In contrast to the length-scale aware validation technique applied here, commonly used domain-wide bulk error metrics lack important information about spatial variations in the quality of remotely-sensed bathymetry.

Anthropogenic marine litter composition in coastal areas may be a predictor of potentially invasive rafting fauna.

Anthropogenic plastic pollution is a global problem. In the marine environment, one of its less studied effects is the transport of attached biota, which might lead to introductions of non-native species in new areas or aid in habitat expansions of invasive species. The goal of the present work was to assess if the material composition of beached anthropogenic litter is indicative of the rafting fauna in a coastal area and could thus be used as a simple and cost-efficient tool for risk assessment in the future. Beached anthropogenic litter and attached biota along the 200 km coastline of Asturias, central Bay of Biscay, Spain, were analysed. The macrobiotic community attached to fouled litter items was identified using genetic barcoding combined with visual taxonomic analysis, and compared between hard plastics, foams, other plastics and non-plastic items. On the other hand, the material composition of beached litter was analysed in a standardized area on each beach. From these two datasets, the expected frequency of several rafting taxa was calculated for the coastal area and compared to the actually observed frequencies. The results showed that plastics were the most abundant type of beached litter. Litter accumulation was likely driven by coastal sources (industry, ports) and river/sewage inputs and transported by near-shore currents. Rafting vectors were almost exclusively made up of plastics and could mainly be attributed to fishing activity and leisure/ household. We identified a variety of rafting biota, including species of goose barnacles, acorn barnacles, bivalves, gastropods, polychaetes and bryozoan, and hydrozoan colonies attached to stranded litter. Several of these species were non-native and invasive, such as the giant Pacific oyster (Crassostrea gigas) and the Australian barnacle (Austrominius modestus). The composition of attached fauna varied strongly between litter items of different materials. Plastics, except for foam, had a much more diverse attached community than non-plastic materials. The predicted frequency of several taxa attached to beached litter significantly correlated with the actually observed frequencies. Therefore we suggest that the composition of stranded litter on a beach or an area could allow for predictions about the corresponding attached biotic community, including invasive species.

Wintertime Tidal Hydrodynamics in the Gulf of Patras, Greece

ABSTRACT Horsch, G.M. and Fourniotis, N.Th., 2017. Wintertime tidal hydrodynamics in the Gulf of Patras, Greece. Three-dimensional numerical simulations have been applied to simulate the winter barotropic hydrodynamic response that develops in the Gulf of Patras due to tidal and wind forcing. The simulations were performed using the code MIKE 3 flexible mesh hydrodynamic module. They reproduce already-known features of the tidal flow entering the Gulf of Patras from the Ionian Sea, such as reflection of the tidal wave at the Rio-Antirio Straits and the cove of the Bay of Nafpaktos. Furthermore, details of the flow structure are revealed, such as the gyre that develops during the transition from ebb to flood tide in front of the Messolonghi Lagoon and the gyre in the Bay of Nafpaktos from flood to ebb. The action of prevailing winds on tidal circulation is to create strong nearshore currents, which dictate the sense of rotation of gyres that develop nearshore at both the northern and southern shores of the...

Analysis of Longshore Currents with an Eulerian Nearshore Currents Model

ABSTRACT Chun, H. and Suh, K.-D., 2017. Analysis of longshore currents with an Eulerian nearshore currents model. In the present study, longshore currents are analyzed with the three-dimensional nearshore currents model in the Eulerian framework. It was found that the model was reduced to the classical one-dimensional longshore currents model for a long, straight, uniform coast, which could also be obtained from the Lagrangian nearshore currents model. It indicates that the longshore current velocities calculated by the Eulerian and Lagrangian models are equivalent to each other for a long, straight, uniform coast. In addition, it was shown that longshore currents with a parabolic vertical profile could be reproduced by the wave–current interaction term in the model. The analysis has been confirmed by the numerical experiments on DUCK94. According to the numerical experiment, the depth-averaged velocities from the present numerical model were consistent with those of one-dimensional longshore currents mod...

Depth Dependence of Nearshore Currents and Eddies

AbstractThe three‐dimensional (across‐shore, alongshore, and vertical) structure of hourly mean currents and <0.01 Hz eddies was measured on a natural beach using 12 Acoustic Doppler Profilers. Both eddies and alongshore currents became relatively depth‐uniform inside the surfzone. Eddies showed greater depth dependence than alongshore currents. A two‐layer model, derived by scaling of the wave‐averaged shallow water equations, yielded separate equations for depth‐averaged and depth‐dependent velocity components. Scaling suggests, and observations confirm, only a small role for lateral advection in most surfzone cases, leading to one‐dimensional vertical models for depth dependence. For alongshore currents, depth dependence is generated by opposite forcing on lower and upper layers, respectively by bottom friction (quantified by time scale ) and waves or wind. This generation is balanced by mixing between upper and lower layers (time scale ), so the ratio between depth‐dependent and depth‐averaged alongshore currents equals . Established models for bottom friction and breaker‐induced mixing predicted a surfzone reduction in consistent with the observed reduction in alongshore current depth dependence. Scatter around trends was considerable. Alongshore variability was significant for depth‐dependence of currents and eddies. Inside (but not outside) the surfzone, the mixing time scale was shorter than the eddy period, so a quasi‐steady balance was predicted between forcing and mixing of eddy depth dependence. Observed eddy depth dependence exceeded predictions for barotropic eddies generated by shear production (i.e., shear instabilities), possibly indicating generation of eddies by random breaking waves in the surfzone, or indicating baroclinic effects outside the surfzone.

Observations of the sub-inertial, near-surface East India Coastal Current

We present surface current measurements made using two pairs of HF (high-frequency) radars deployed on the east coast of India. The radar data, used in conjunction with data from acoustic Doppler current profiler (ADCP) measurements on the shelf and slope off the Indian east coast, confirm that the East India Coastal Current (EICC) flows poleward as a deep current during February–March. During the summer monsoon, when the EICC flows poleward, and October–December, when the EICC flows equatorward, the current is shallow (<40m deep), except towards the northern end of the coast. Data from Argo floats confirm a shallow mixed layer that leads to a strong vertical shear off southeast India during October–December. A consequence of the strong stratification is that the upward propagation of phase evident in the ADCP data does not always extend to the surface. Even within the seasons, however, the poleward and equatorward flows show variability at periods of the order of 20–45 days, implying that the EICC direction is the same over the top ∼100m for short durations. The high spatial resolution of the HF radar data brings out features at scales shorter than those resolved by the altimeter and the high temporal resolution captures short bursts that are not captured in satellite-derived estimates of surface currents. The radar data show that the EICC, which is a boundary current, leaves a strong imprint on the current at the coast. Since the EICC is known to be affected significantly by remote forcing, this correlation between the boundary and nearshore current implies the need to use large-domain models even for simulating the nearshore current. Comparison with a simulation by a state-of-the-art Ocean General Circulation Model, run at a resolution of 0.1°×0.1°, shows that the model is able to simulate only the low-frequency variability.

The role of wave‐current interaction in Lake Erie's seasonal and episodic dynamics

AbstractAlthough the significance of surface gravity waves has been consistently emphasized in previous limnetic studies, the roles of wave‐current interactions in lake dynamics are not sufficiently understood due to the lack of high‐resolution wave information. With a two‐way coupled hydrodynamic and wave model system, this study investigated how the Lake Erie dynamics are impacted by the wave‐induced surface and radiation stresses on the seasonal‐mean and episodic scales. The results showed that the surface radiation stress was the same as or an order of magnitude larger than the wave‐induced surface stress in the nearshore area (&lt;5 km offshore), while the latter prevailed in the offshore areas. By enhancing air‐lake momentum and heat transfers, the wave‐enhanced surface stress improved the model's skill in simulating hydrodynamics in the Central and Eastern Basins, and it was of greater importance (at least an order of magnitude larger) in modifying surges, offshore currents, and thermal structures compared to those of the radiation stress. Nevertheless, the radiation stress played key roles in wave‐induced nearshore currents, especially in the shallow Western Basin. Their significances reached O (0.01–0.1 m/s) on the seasonal and episodic scales, respectively, and could have similar importance in other shallow water environments.

Cusp morphodynamics in a micro-tidal exposed beach

Beach cusps have attracted the focus of several studies due to their effect on sediment transport and their rhythmic presence in the midst of complex nearshore interactions among waves, currents and sediment. In this paper, cusp evolution is investigated to determine the factors which influence them within Maracas Bay, Trinidad, in the micro-tidal environment of the southern Caribbean. Data on beach profiles, beach sediment, coastal processes, and cusp dimensions were collected using standard geomorphological techniques across daily, weekly and seasonal time-scales. Results indicate that beach cusp dimensions are predominantly determined by beach volume and beach angle. These two parameters in turn are influenced by wave energy. In both the wet and dry seasons, periods of lower wave energy promote accretion, leading to the formation of smaller beach cusps; conversely, periods of higher wave energy and the associated increase in erosion result in the formation of larger beach cusps. There was agreement with the self-organization theory since cusps were always present along the beach, constantly changing morphologically but never completely being erased and recreated anew. Beach cusps form an integral part of the total sediment deposited and retained on beaches over tidal and seasonal cycles, with implications for nearshore currents and beach safety. As such, a proper understanding of their dynamics will help support planning and management of beaches as they go through cyclic phases annually.