Search

The morphological responses of two mesotidal beaches located in different coastal settings (embayed and open sandy beaches) on the northwestern Iberian coast were monitored during the winter of 2018/19. The offshore wave time series analysis is related to high-resolution topo-bathymetric measurements to explore spatial-temporal morphological variability at monthly to seasonal scales. Both locations are subjected to the North Atlantic wave climate which exhibits a pronounced seasonality. Throughout the last decade (2010–2020), significant wave heights reached values of up to Hs~9 m during winters and up to Hs~6 m during summers. On average, approximately 12 storms occurred annually in this region. The results clearly reveal divergent morphological responses and sediment transport behaviors at the upper beach and the intertidal zone during the winter for each location. In the embayed beach (Patos), sediment transport in the nearshore is governed by cross-shore processes between the beach berm and a submerged sandbar. In contrast, the open beach (Mira) showed dynamic sediment exchanges and three-dimensional morphologies alternating between accumulation and erosion zones. Overall, both beaches exhibited an erosional trend after the winter, particularly concerning berm erosion and the subaerial beach volume/shoreline retreat. This study highlights the contrasting morphodynamic response on open and embayed beaches to winter conditions, integrating both the subaerial and submerged zones. Local geological and environmental factors, as well as the coastal management strategies applied, will influence how the beach responds to winter wave events. Monitoring and understanding these responses are essential for effective coastal management and adaptation to changing climate. [ABSTRACT FROM AUTHOR]

Simple Summary: Coastal sharks are especially susceptible to anthropogenic pressures due to their use of nearshore habitats. It is therefore necessary to distinguish species-specific variation in occurrence among ocean beaches and identify key environmental drivers that may influence shark distribution patterns. For swell-influenced coastal beaches, however, information on shark abundance and occurrence is still limited. The relative abundance and occurrence of sharks off 42 ocean beaches of New South Wales (NSW), Australia, was investigated using a long-term drone-based monitoring program from 2017–2021. Overall, there were 36,384 drone flights conducted, sighting a total of 281 sharks. Shark observations occurred in <1% of drone flights, indicating that potentially dangerous sharks, and sharks in general, are rare off NSW beaches. Key environmental predictors, such as the distance to the nearest estuary, headland, and island, as well as ocean temperature and wave height, were identified for species-specific shark distribution. This study demonstrated that existing drone-based monitoring programs used to reduce shark bite incidents can also provide valuable information about the distribution of potentially dangerous, vulnerable, and endangered coastal sharks. This information will be beneficial for implementing evidence-based conservation strategies and may also assist in minimising negative human-shark interactions. There is still limited information about the diversity, distribution, and abundance of sharks in and around the surf zones of ocean beaches. We used long-term and large-scale drone surveying techniques to test hypotheses about the relative abundance and occurrence of sharks off ocean beaches of New South Wales, Australia. We quantified sharks in 36,384 drone flights across 42 ocean beaches from 2017 to 2021. Overall, there were 347 chondrichthyans recorded, comprising 281 (81.0%) sharks, with observations occurring in <1% of flights. Whaler sharks (Carcharhinus spp.) had the highest number of observations (n = 158) recorded. There were 34 individuals observed for both white sharks (Carcharodon carcharias) and critically endangered greynurse sharks (Carcharias taurus). Bull sharks (Carcharhinus leucas), leopard sharks (Stegostoma tigrinum) and hammerhead species (Sphyrna spp.) recorded 29, eight and three individuals, respectively. Generalised additive models were used to identify environmental drivers for detection probability of white, bull, greynurse, and whaler sharks. Distances to the nearest estuary, headland, and island, as well as water temperature and wave height, were significant predictors of shark occurrence; however, this varied among species. Overall, we provide valuable information for evidence-based species-specific conservation and management strategies for coastal sharks. [ABSTRACT FROM AUTHOR]

Keywords: bivalve; fisheries; nearshore; semi-quantitative; thermal stress EN bivalve fisheries nearshore semi-quantitative thermal stress 1 7 7 10/06/22 20221001 NES 221001 From 26 to 28 June 2021, an unprecedented atmospheric heatwave coincided with the lowest low tides of the year in the Pacific Northwest (i.e., the region consisting of the northwestern corner of the contiguous United States and southwestern Canada). Butter clams, which often burrow >15 cm deep in sediment and live at lower tidal elevations than other clam species (Dethier, 2006), were less affected by the heatwave than surface-dwelling cockles. Given that all of the bivalve species discussed here were likely reproductive during the heatwave (Anderson et al., 1982), it is possible that high mortality in certain species (e.g., cockles) may manifest itself in reduced adult populations in ~4 years. However, we did observe a range in butter clam condition among sites separated by ~30 km, indicating that local scale factors may also contribute to postheatwave clam condition. [Extracted from the article]

Coastal zones are important components of marine ecosystems that link upland and marine areas, and are often maintained by landslides, though these habitat forming processes are poorly understood. They are also often sites of commercial development, including mining, and restoration. In this ecosystem restoration project, we rapidly removed a large volume of shoreline armoring from the perimeter of an intertidal earthen filled mine structure. The remaining feature mimicked the toe of a large land slide characteristic of the region. Physical and ecological monitoring allowed us to understand how coastal ecosystems respond to large scale coastal sediment processes, including landslide function that forms them, and restoration actions to restore them. As a course of restoration, over 22,936 m3 of non-native armor totaling 0.47 hectares was rapidly removed from the perimeter of a 2.8 hectare earthen pier. Three years after removal, the feature is less than half its original configuration (area). Beach composition and ecological community of the restoration area responded positively relative to pre-project conditions and to the control site. Applying these results to historic deep seated landslides that define coastal zones of the region, we conclude that nearshore ecosystems are resilient and respond similarly to episodic natural and restored large-scale hydrodynamic processes. [ABSTRACT FROM AUTHOR]

Cross‐shore transport of larvae, pollutants, and sediment between the surf zone and the inner shelf is important for coastal water quality and ecosystems. Rip currents are known to be a dominant pathway for exchange, but the effects of horizontal temperature and salinity gradients are not well understood. Airborne visible and infrared imaging performed on the California coast shows warm and cool plumes driven by rip currents in the surf zone and extending onto the shelf, with temperature differences of approximately 1°C. The airborne imagery and modeled temperatures and tracers indicate that warm plumes exhibit more lateral spreading and transport material in a buoyant near‐surface layer, whereas cool plumes move offshore in a subsurface layer. The average cross‐shore extent of warm plumes at the surface is approximately one surfzone width larger than for cool plumes. Future work may explore the sensitivity of nearshore plumes to density patterns, wave forcing, and bathymetry. Plain Language Summary: Waves and currents in the coastal ocean move plankton, pollutants, nutrients, and sediment between the beach and deeper waters, impacting ecosystems and water quality. Rip currents, strong narrow seaward currents caused by breaking waves, provide a conduit for larvae to move offshore and also carry pollutants away from the beach. One common type of rip current formed in channels interrupting sandbars can sometimes be observed as a plume of brown sediment‐laden water moving offshore. Previous studies of this rip‐current type have assumed that the movement of material by these currents is not affected by differences in the water density (temperature and salinity) between shallower and deeper water. However, thermal (infrared) images taken from an aircraft on the coast of California show that the wave‐breaking region near the beach is often significantly cooler or warmer than the ocean immediately offshore. Rip currents in these images and in numerical simulations appear either as warm plumes, which carry material further offshore and are concentrated at the water surface, or cool plumes, which move material offshore under the surface. The results show that differences in water temperature from the beach to deeper water impact how rip currents move material in the coastal ocean. Key Points: Airborne infrared imagery on the CA coast shows cool and warm plumes driven by rip currents that connect the surf zone to the inner shelfThe surface cross‐shore extent of warm plumes is about one surfzone width larger than that of cool plumes in observations and simulationsModeled cool nearshore plumes entering a stratified shelf subduct, whereas warm plumes extend offshore in a near‐surface layer [ABSTRACT FROM AUTHOR]

The intertidal beach profile provides coastal engineers and managers with a good indication of the current state of a sandy coastline, however regular beach profile measurements are time consuming and expensive to obtain using conventional surveying methods. The potential to reconstruct the intertidal beach profile from measurements of reflected waves is tested here using three field datasets covering a different range of hydro-morphological conditions from dissipative, to reflective. The swash is found to behave as a low-pass filter on reflected waves, with a cut-off frequency that primarily depends on the swash slope. An agreement is found between video-derived swash spectrum saturation tail and the shortest reflected waves, computed from deep water directional wave measurements. By integrating this swash slope over a tidal cycle, the shape of the intertidal beach profile can be reconstructed. Our results clearly show the potential of such method to estimate complex intertidal beach profile, such as double-slope beaches. • The intertidal beach profile can be reconstructed by integrating the swash slope over a tidal cycle. • The swash behaves as a low-pass filter, with a cut-off frequency that primarily depends on the swash slope. • A good agreement is found between video-derived swash spectrum saturation tail and the shortest reflected waves. [ABSTRACT FROM AUTHOR]

The installation of wave energy converter (WEC) arrays near the coast can have significant impacts on sediment dynamics and coastal morphodynamics. However, methodologies for quantifying these impacts and strategies to minimize them are still in need of development. In this study, we assessed the coastal response to a WEC array on the La Guajira coast in the Colombian Caribbean using a two-step numerical strategy. We used the Delft-3D model to estimate the wave field, which was then transferred to the XBeach model to compute morphological changes. This modelling strategy was applied to three WEC array layouts and compared the morphological responses in terms of the distance and relative orientation of the WEC array to the coast. The results showed that the impact of the simulated WEC array on the beach response varied significantly depending on its distance from the coast, the configuration of the array, and its orientation. These findings highlight the need for further research to develop effective strategies for minimizing coastal erosion impacts on coastal ecosystems through innovative alternatives. Developing such strategies will be crucial to ensure the sustainable implementation of WEC arrays and other renewable energy technologies near the coast. • WECs have the capability to convert wave energy into useable electricity efficiently. • Coastal communities can benefit from renewable energy and coastal protection. • Delft 3 d and XBeach models are useful for estimating energy potential and beach erosion. • WECs array configuration is a key element in energy efficiency and wave reduction. [ABSTRACT FROM AUTHOR]

With high anthropogenic pressure and the effects of climate change (e.g., sea level rise) on coastal regions, there is a greater need for accurate and up-to-date information about the topography of these systems. Reliable topography and bathymetry information are fundamental parameters for modelling the morpho-hydrodynamics of coastal areas, for flood forecasting, and for coastal management. Traditional methods such as ground, ship-borne, and airborne surveys suffer from limited spatial coverage and temporal sampling due to logistical constraints and high costs which limit their ability to provide the needed information. The recent advancements of spaceborne remote sensing techniques, along with their ability to acquire data over large spatial areas and to provide high frequency temporal monitoring, has made them very attractive for topography and bathymetry mapping. In this review, we present an overview of the current state of spaceborne-based remote sensing techniques used to estimate the topography and bathymetry of beaches, intertidal, and nearshore areas. We also provide some insights about the potential of these techniques when using data provided by new and future satellite missions.

The understanding of cross-shore sediment sorting is of primary importance for the design of sand nourishments and for assessing the suitability of the seabed to different ecological species. In this paper, sediment sorting processes were investigated by using a combination of physical and detailed numerical modelling. Data from large-scale wave flume experiments were used to validate a 2DV cross-shore Delft3D model. The model solves coupled short-wave averaged equations for flow, sediment transport, bed composition and bed level change. The infra-gravity wave motions were explicitly resolved. In order to investigate sorting processes, eight sediment fractions were used as well as a layered bed stratigraphy. The effects of different wave conditions (high energetic and more moderate energetic waves) on the morphodynamic profile development and sorting processes were investigated. The Delft3D model reproduced the profile development and bar position very accurately. Additionally, model predictions of sediment sorting across the profile fitted very well with the available observations. The numerical model simulations showed the importance of including short-wave grouping and infragravity wave effects in order to reproduce the cross-shore profile development, especially the breaker bar dynamics and sediment sorting processes. Infragravity waves contribute to larger sediment entrainment and more offshore bar development. Besides leading to a better prediction of the bed profile, infragravity waves also lead to a better prediction of the bed composition. Model results are in agreement with experimental data, showing its capabilities in functioning as a tool to predict sorting processes. [ABSTRACT FROM AUTHOR]

The Chavara coast of southwest India is well known for its rich beach placer deposits which are being commercially exploited by the industries. Replenishment of these resources, which consist of heavy minerals of varying densities, by the hydrodynamic processes is essential for maintaining the stability of the coast as well as sustenance of mining. Rich concentrations of heavy minerals were reported consistently in the beach sediments of this coast in the past, but a systematic reduction in the concentration of the heavies has been reported during the past one-and-a-half decades. This paper, the first in a series of three, emanates from a programme of study launched to understand the mechanisms that manifest the reported changes in the morphology and mineralogy along this coast. In this study the longshore and cross-shore sediment transport rates along this coast have been estimated adopting numerical model studies. The validated LITDRIFT and LITPROF modules of the LITPACK modelling system have been used for computing the longshore and cross-shore sediment fluxes in the surf zone and innershelf region. The net annual longshore sediment transport is northerly in the surf zone where as it is southerly in the innershelf. Detailed analysis of the computed results shows domination of onshore transport over offshore transport. The beach volume change estimated from the measured beach profile on the other hand shows a reduction in the annual replenishment. The domination of the onshore flux as seen in the computations is actually not reflected in the field observations, and this can be attributed to the influence of excessive sand mining by the industries. [ABSTRACT FROM AUTHOR]

The Chavara coast of south-west India is well known for its rich beach placer deposits which are being commercially mined by two public sector firms. The erosion of the beach and innershelf and the depletion of heavy mineral content of this coast have attracted a lot of attention of late, and an investigation of the mechanisms that drive these changes was taken up recently. The results of the investigation are presented in three parts. This paper, which is the last in the series, presents a study of the morphological changes of the beach and innershelf and integrates the results from the other two papers with an analysis of multi-dated shoreline and bathymetry data. The analysis of the multi-dated data showed an overall retreat of the shoreline and a relative deepening of the innershelf. The shoreline retreat has been quite alarming at the mining sites with one of the mining sites showing a retreat of nearly 400 m. The sediment deposition adjacent to the breakwater (built during 2000-2007) at the northern inlet has defused to some extent the high erosion observed earlier in the northernmost sector, and the presence of well-maintained seawalls has nearly maintained the shoreline south of the mining site. The erosion of the beach is accompanied by a deepening of the innershelf which is more pronounced in the shallower portions up to 10 m depth. The observed changes in the beach-innershelf morphology are analysed with respect to the nearshore sediment transport regime and heavy mineral distribution of the coast. It is observed that the combined intake of sediments by the two firms during the past one and a half decade is much above the sustainable mining level. Another contributing factor is the 2004 tsunami which drained off a sizable quantity of innershelf sediments rich in heavy minerals to the hinterland regions. The breakwaters at the two inlets bordering this coast have virtually compartmentalized this coast from the rest of the south-west coast making it a sediment sub-cell. In addition, the breakwaters act as groins causing imbalances in the erosion/accretion pattern. The recent spate in construction of shore protection structures like groins and seawalls is another contributing factor to the morphological changes. The study points to the urgent need for regulating the mining volumes to the sustainable levels as well as controlling the introduction of hard structures without proper impact analysis. [ABSTRACT FROM AUTHOR]

Laudier et al. (2011) suggested that there may be a systematic bias error in runup predictions using a model developed by Stockdon et al. (2006). Laudier et al. tested cases that sampled beach and wave conditions that differed from those used to develop the Stockdon et al. model. Based on our re-analysis, we found that in two of the three Laudier et al. cases observed overtopping was actually consistent with the Stockdon et al. predictions. In these cases, the revised predictions indicated substantial overtopping with, in one case, a freeboard deficit of 1 m. In the third case, the revised prediction had a low likelihood of overtopping, which reflected a large uncertainty due to wave conditions that included a broad and bi-modal frequency distribution. The discrepancy between Laudier et al. results and our re-analysis appear to be due, in part, to simplifications made by Laudier et al. when they implemented a reduced version of the Stockdon et al. model. [ABSTRACT FROM AUTHOR]

Nearshore hydrodynamics and sediment transport patterns induced by waves and tide adjacent to a structured tidal inlet with complex bathymetry are investigated to determine the potential causes of downdrift beach erosion. A coupled wave and hydrodynamic model is used to simulate the nearshore hydrodynamics and morphodynamics. Near the inlet, the tidal-induced pressure gradient dominates the wave radiation stress gradient only in the first half of the flood duration. The nearshore hydrodynamic pattern for the rest of the tidal cycle is driven mainly by the wave-driven pressure gradient. The wave-driven pressure gradient results from alongshore variation of water surface elevation induced by nearshore wave focal points caused by wave refraction over irregular bathymetry (with ebb tidal shoals and nonparallel shoreline depth contours). The resulting alongshore sediment transport patterns suggest that the direction of the time-averaged alongshore sediment transport rate near the inlet and at the downdrift beach is against that of the larger-scale net sediment transport along the coast. The inlet-adjacent time-averaged alongshore sediment transport rate increases for waves with larger wave height and an incident angle closer to shore normal in contrast to expectations under the assumption of straight and parallel depth contours. [ABSTRACT FROM AUTHOR]

The response of physical models of beach profiles to random breaking waves was studied to investigate size-selective sediment transport and cross-shore profile evolution. Three types of beach profiles with different sediment mixtures were considered and subjected to waves until profiles reached equilibrium. Size-selective sediment transport was evident in the experiments, with the mean sediment size varying up to 20% along the beach profiles. Consistent coarsening and fining of the surface sediment in the experiments revealed size-selective sediment transport governed by cross-shore variations in energy dissipation, affecting important beach profile features such as sandbar structures and offshore and foreshore slopes. The theoretical basis of the transport phenomenon was described by analyzing the relationship between the transport processes and essential wave and hydrodynamic parameters obtained using a new set of numerical models. The results showed that beach profile changes and associated sediment grain sorting are most sensitive to instantaneous total water velocity and local energy flux under propagating waves. [ABSTRACT FROM AUTHOR]

Abstract: A sequence of daily beach surveys acquired over one month covering an area larger than 100,000m2, was analyzed to study morphological changes resulting from a cluster of storms. The beach response was highly variable in both the cross- and alongshore. A cumulative storm effect was not observed, despite one storm being characterized by a 10-year return period that had significant wave height (Hs) of 8.1m and a peak wave period (Tp) of 17s. Instead, storms that can potentially cause significant erosion in terms of Hs had a limited effect on the morphology because the large wave height was coupled to either neap tides, normally-incident short-waves (f >0.04Hz), or low levels of infragravity (0.004< f <0.04Hz) energy. Multiple linear regression analysis shows that volumetric changes in the upper part of the beachface are explained by offshore wave characteristics (period, height and direction), tidal range or by infragravity energy in the inner surf zone (assessed using pressure and velocity measurements). The results indicate that it is not possible to scale-up single-storm erosion studies into predictions of cluster-storm erosion. [Copyright &y& Elsevier]

A Lagrangian numerical method called smoothed particle hydrodynamics (SPH) is used to analyze a simplified bar/rip channel system on a beach. Prior studies have shown that SPH models propagate water waves well, including breaking waves; here, it is shown that SPH also models the mean wave-induced nearshore circulation created by breaking waves. The model predictions are compared with the previous laboratory measurements and show good agreement, including the mean velocity profiles, mean surface elevation, and cross-shore velocity components over the rip channel. The alongshore variation of various components of radiation stress and the resulting alongshore force that acts as a feeder for the rip current are obtained from the numerical results. [ABSTRACT FROM AUTHOR]

This study contributes to the understanding of the extent at which antecedent hydrodynamic and morphological conditions affect post-storm morphology in response to individual storms and storm clusters. Nearshore wave measurements and concurrent fortnightly to monthly topographies from 2012 to 2020 were used to determine the morphological response of a swell-dominated beach in the Pacific coast of NW Baja California to different storm types. The beach attained an almost nil volumetric balance over the eight-year period, but significant variations existed related to storm incidence. Higher storminess occurred during El Niño years and lower or absence of storminess during years of La Niña phase. The integral wave characteristics of the analyzed swell-dominated storms did not conclusively explain subaerial volume variations. Dissipative morphodynamic conditions prevailed during the analyzed storm events (Ω of 6 to 8) and the wave steepness presented relatively small variations (0.006 to 0.015). The beach quickly reached a storm equilibrium state, preventing subsequent adjustment when further storms in the sequence acted. Moreover, consecutive storms to highly-erosive events caused subaerial beach accretion when low pre-storm volumes (< 50 m3m−1 than average) and mild lower intertidal slopes (tanβ > 0.03) existed. It is concluded that the erosive potential of the swell-driven storms primarily depended on the antecedent sediment availability and near-shoreline slope. • Higher and lower storminess occurred during El Niño and La Niña phases of ENSO, respectively. • Storm equilibrium state is quickly reached, preventing relevant morphological adjustments by subsequent storms. • Antecedent sand volume and beach slope are key controls of the erosion induced by swell-storms of similar wave-steepeness. [ABSTRACT FROM AUTHOR]

Abstract: Grain size is an important variable when predicting beach morphodynamics. Beaches, to the eye, seem relatively uniform in grain size and morphodynamic modeling efforts usually assume a single mean grain size for an entire beach environment. Therefore, estimating grain size is traditionally done by collecting only a few samples and averaging to characterize the mean grain size of the whole beach. However, some studies have shown that even small variations in grain size can have a significant effect on model results when predicting beach morphology changes. Here, a mobile digital imaging system (DIS) has been developed for surveying spatial and temporal variation in grain size across a beach following the ideas of Rubin (2004). Using an off-the-shelf camera and underwater housing, macro photographs are taken of sand across a beach, which produce estimates of mean grain size that are highly correlated with estimates from sieves (R2 =0.92). High resolution maps of mean surface grain size are produced using the DIS (with ~1000 images over a 300×500m area), which suggest that large variations in grain size exist (0.2–0.7mm over tens of meters with accuracies of ~±0.03mm) and that there is a correlation between spatial grain size variations and morphological variability. [Copyright &y& Elsevier]

Abstract: Record flooding on the Santa Clara River of California (USA) during January 2005 injected ∼5millionm3 of littoral-grade sediment into the Santa Barbara Littoral Cell, approximately an order of magnitude more than both the average annual river loads and the average annual alongshore littoral transport in this portion of the cell. This event appears to be the largest sediment transport event on record for a Southern California river. Over 170m of local shoreline (mean high water (MHW)) progradation was observed as a result of the flood, followed by 3years of rapid local shoreline recession. During this post-flood stage, linear regression-determined shoreline change rates are up to −45ma−1 on the subaerial beach (MHW) and −114ma−1 on the submarine delta (6m isobath). Starting approximately 1km downdrift of the river mouth, shoreline progradation persisted throughout the 3-year post-flood monitoring period, with rates up to +19ma−1. Post-flood bathymetric surveys show nearshore (0 to 12m depth) erosion on the delta exceeding 400m3/ma−1, more than an order of magnitude higher than mean seasonal cross-shore sediment transport rates in the region. Changes were not constant with depth, however; sediment accumulation and subsequent erosion on the delta were greatest at −5 to −8m, and accretion in downdrift areas was greatest above –2m. Thus, this research shows that the topographic bulge (or “wave”) of sediment exhibited both advective and diffusive changes with time, although there were significant variations in the rates of change with depth. The advection and diffusion of the shoreline position was adequately reproduced with a simple “one line” model, although these modeling techniques miss the important cross-shore variations observed in this area. This study illustrates the importance of understanding low-frequency, high volume coastal discharge events for understanding short- and long-term sediment supply, littoral transport, and beach and nearshore evolution in coastal systems adjacent to river mouths. [Copyright &y& Elsevier]

Study of beach morphological changes during monsoon and development of capabilities towards its prediction is of vital importance in coastal zone management. A study of the beach erosion/accretion processes during south-west monsoon and its numerical modelling is attempted in this communication for a micro-tidal and high-energy beach. Comprehensive hydrodynamic and beach profile data measured in the field were used for the study. The beach morphological changes as a result of the high intensity monsoon waves are found to be characterized by erosion of beach coupled with deposition in the offshore leading to formation and migration offshore longshore bar. The model LITPROF of the LITPACK software of DHI is found to simulate well the beach morphological changes by adjustment of the calibration parameters. The integrated cross-shore transport computed across the profile, using the model shows high erosion in the beach face coupled with an equivalent accretion in the offshore. The model performance computed using different statistical methods is found to be good. [ABSTRACT FROM AUTHOR]

Abstract: This work aims to demonstrate an advancement towards the integrated modelling of surf zone hydrodynamics by means of a VOF-type numerical model (COBRAS-UC) based on the Reynolds-Averaged Navier–Stokes equations. In this paper, the numerical model is adapted and validated for the study of nearshore processes on a mildly-sloping beach. The model prediction of wave energy transformation and higher order statistics (skewness and asymmetry) are in good agreement with detailed laboratory observations from a barred beach [Boers, M. (1996). “Simulation of a surf zone with a barred beach; Report 1: Wave heights and wave breaking”. Tech. Rep.96-5, Comm. on Hydrol. and Geol. Eng., Dept. of Civil Engineering, Delft University of Technology]. Moreover, the numerical model allows us to study the low-frequency motions inside the surf zone. It is found that in order to achieve a satisfactory simulation of both short- and long-wave transformation, the numerical model must achieve: (i) the simultaneous second-order wave generation and absorption, (ii) the energy transfer between triad of components, (iii) the short- and long-wave energy dissipation inside the surf zone, and (iv) the wave reflection at the shoreline. Comparisons between numerical and experimental results demonstrate the model capability to satisfactorily simulate all the aforementioned processes. [Copyright &y& Elsevier]

Abstract: Beach cusps are a common feature of steep reflective and intermediate beaches. Although many observations of beach cusp spacing exist, there are few observations quantifying the incipient formation, evolution and eventual destruction of these features. Beach cusp morphodynamics were analyzed using a 3-year dataset of video images collected at Tairua Beach (New Zealand). Twenty-four beach cusp episodes were selected to monitor the cycle of beach face changes, from planar to the appearance of the cusp patterns and back to planar again. Observations show that beach cusp disappearance can be ascribed not only to the erosive influence of storms but also to the persistence of accretionary conditions leading to the infilling of beach cusp bays and the development of an alongshore continuous berm. We also report observations of changes in beach cusp spacing over time which can be attributed to the merging of adjacent cusps within the cusp field, with the overall cusp spacing re-adjusting to accommodate the disappearance of a horn. Although the self-organization theory provides a better fit to the data and theory, we were unable to conclusively refute any of the mechanisms causing beach cusp formation since both existing theories, subharmonic standing edge wave and self-organization, can predict the trend in the observed beach cusp spacing. These observations show that initial beach cusp formation primarily occurs (around 70% of the episodes analyzed) under mildly accretionary conditions and, when accretion persists, the pattern disappearance is likely to occur as a result of bay infilling to form a featureless berm. [Copyright &y& Elsevier]

The temporal growth of the envelope of bed motion owing to the migration of bedforms, which can be considered a proxy for maximum object burial depth, is examined using five different data sets. These data sets support the hypothesis that the envelope of bed motion will grow as an exponential taper, quickly at first, tapering off and approaching an asymptotic value. This growth is largest and fastest in the surf zone where wave and current flows are strong. Within the surf zone, envelopes owing solely to the migration of megaripples (bedforms with heights from 20 to 40 cm and lengths from 1 to 5 m) grow fur about 8 d and reach an asymptote of about 40 cm. When wave energy becomes larger (Hsig greater than 1 m), bed envelopes are dominated by migrating sand bars and approach an asymptote of 3-4 m, but only after 2-12 years (depending on the beach). In addition, the frequency of object burial (the percentage of time that an object would be buried by the crests of migrating bedforms) is highest in the surf zone and grows rapidly with time. [ABSTRACT FROM AUTHOR]

Remote sensing using terrestrial optical charge-coupled device cameras is a useful data collection method for geophysical measurement in the nearshore zone, where in situ measurement is difficult and time consuming. In particular, optical video sensing of the variability in human-visible surface refraction due to the nearshore incident wave field is becoming an established method for distal measurement of nearshore subtidal morphology. We report on the use of a low-mounted shore-normal camera for gathering data on cross-shore dissipative characteristics of a dynamic open beach. Data are analyzed for the purposes of classifying three of Wright and Shorts' intermediate classes of morphological beach state as determined by expert raters. Although these beach states are usually thought of as being distinctive in terms of their longshore bar variability, theory predicts that differences should also be observed in cross-shore dissipative characteristics. Three methods of generating features from statistical features from the archived optical data are described and compared in terms of their ability to discriminate between the beach states. Principal component scores of the percentile distributions were found to provide slightly better classification performance (i.e., 85%, while approximating the data using relatively fewer features), whereas classification using intensity distributions alone resulted in the worst performance, classifying 78% of beach states correctly. Class center moment profiles for each beach state were constructed, and results indicate that cross-shore wave dissipation becomes more disorganized as linear bars devolve into more complex transverse structures. [ABSTRACT FROM AUTHOR]

This paper presents a theoretical model for the prediction of near-shore hydrodynamics in the surf zone along long straight beaches. The waves may be periodic or narrow-banded random waves, and the beach profile may be plane or barred. The theoretical model consists of three components: wave model, surface roller model, and near-shore mean current model. Both wave and surface roller models are based on simple energy balance equations and all the variables applied for the current model are determined in terms of wave energies. The near-shore mean current model consists of two-layer 2DH momentum equations, integrated above the wave trough level and over the entire depth, which determine mean shear stresses at the trough level and on the bottom, respectively. Coupled with a simple turbulent eddy viscosity model, analytical solutions are obtained for the vertical mean shear current profiles. The bottom boundary condition is specified by a wave–current bottom boundary layer model requiring knowledge of the equivalent bottom roughness. Model predictions of undertow velocity profiles compare favorably with experimental observations which were not used in the model’s development. [ABSTRACT FROM AUTHOR]

Abstract: Rip current kinematics and beach morphodynamics were measured for 44 days at Sand City, Monterey Bay, CA using 15 instruments composed of co-located velocity and pressure sensors, acoustic Doppler current profilers, and kinematic GPS surveys. The morphology consisted of a low-tide terrace with incised quasi-periodic rip channels, representative of transverse bars. Offshore (17 m depth) significant wave height and peak period ranged 0.20–3.0 m and 5–20 s. The mean wave direction was consistently near 0° resulting in rip channel morphology, which evolved in response to the changing wave characteristics. An inverse relationship between sediment accreting on the transverse bar and eroding in the rip channel was found. The spatial distribution of sediment is reflected in the background rip current flow field. The mean velocity magnitudes within the rip channel (transverse bars) increased offshore (onshore) with decreasing tidal elevations and increased with increasing sea-swell energy. Eulerian averaged flows were predominantly shoreward on the transverse bars and seaward within the rip channel throughout the experiment, resulting in a persistent cellular circulation, except during low wave energy. The rip current spacing to the rip channel width was less than or equal to two, which suggests that the rip currents are influenced by each other and that no two-dimensional bar return flow should be present. The vertical velocity profile on the bar indicated that the flow was predominantly shoreward. The flow field within the surf zone was depth uniform, except for significant shear occurring near the surface, owing to Stokes drift. The wave-induced transport hypothesis is evaluated. [Copyright &y& Elsevier]

The Argus network is a series of video cameras with aerial views of beaches around the world. Intensity contrasts in time exposure images reveal areas of preferential breaking, which are closely tied to underlying bed morphology. This relationship was further investigated, including the effect of tidal elevation and wave height on the presence of wave breaking and its cross-shore position over sand bars. Computerized methods of objectively extracting shoreline and sand bar locations were developed, allowing the vast quantity of data generated by Argus to be more effectively examined. Once features were identified in the images, daily alongshore mean values were taken to create time series of shoreline and sand bar location, which were analyzed for annual cycles and cross-correlated with wave data to investigate environmental forcing and response.These data extraction techniques were applied to images from four of the Argus camera sites. A relationship between wave height and shoreline location was found in which increased wave heights resulted in more landward shoreline positions; given the short lag times over which this correlation was significant, and that the strong annual signal in wave height was not replicated in the shoreline time series, it is likely that this relationship is a result of set-up during periods of large waves. Wave height was also found to have an effect on sand bar location, whereby an increase in wave height resulted in offshore bar migration. This correlation was significant over much longer time lags than the relationship between wave height and shoreline location, and a strong annual signal was found in the location of almost all observed bars, indicating that the sand bars are migrating with changes in wave height. In the case of the site with multiple sand bars, the offshore bars responded more significantly to changes in wave height, whereas the innermost bar seemed to be shielded from incident wave energy by breaking over the other bars. A relationship was also found between a site''s mean wave height and inner sand bar location; sites with the highest wave heights tended to have sand bars farther from shore than those with relatively low wave heights. [Copyright &y& Elsevier]

The importance of wave reflection on nearshore hydrodynamics has recently been acknowledged by an increasing number of studies, yet it is difficult to simulate by the conventional parametric wave transformation models widely used in coastal engineering practice. Here, we propose a simple and efficient semi-empirical method to deal with this issue. The proposed method considers wave reflections resulted from both the underwater sloping bottom and the shoreline. The former is represented by a local underwater reflection-induced energy transfer term, based on a similarity analysis of the bulk wave reflection from equivalent sloping steps. The latter is calculated as the shoreline boundary condition by utilizing a simple empirical formula of wave reflection coefficient for an emerged coastal structure. Model verifications against the previous theoretical/empirical formulas, experimental data and numerical results suggest a promising predictability of the proposed method for the cross-shore reflected wave height transformation with various bathymetry configurations. Three different formulas of the bulk reflection coefficient for an underwater sloping step are tested and compared, indicating the importance of considering slope effects in these formulas. Model results also suggest that wave reflection along a steep beach profile can be quantitatively comparable to the shoreline reflection, and it is important to include reflections of both sources in numerical modelling. The simple method can be extended and incorporated into the existing operational parametric wave models. It serves as a possible approach to simulate wave reflection with low computational demand and reasonable accuracy, and to include wave reflection influences in studying coastal processes on a broad range of time and spatial scales. • A simple and efficient method to simulate nearshore wave reflection with the phase-averaged parametric wave models. • The proposed method considers wave reflections resulted from both the underwater sloping bottom and the shoreline. • A promising predictability of the cross-shore reflected wave height transformation with various bathymetry configurations. • Wave reflection along a steep beach profile can be quantitatively comparable to the shoreline reflection. [ABSTRACT FROM AUTHOR]

Eroded sediment can return to the subaerial beach through onshore sandbar migration, thus understanding this process is key for rebuilding coastal morphology. While offshore sandbar migrations are fairly predictable based on wave conditions alone, landward migrations are less predictable and more dependent on sandbar morphometrics. In this study, monthly collected topographic and bathymetric data from August 2014 to September 2018 were analyzed and related to the incoming wave conditions to investigate the control of sandbar location and morphometry on the landward migration process. Four distinct onshore sandbar migration modes were identified, primarily governed by the sandbar crest location and size (volume and height), and the preceding cumulative wave energy. A cross-shore distance of 150 m equivalent to ~3 m depth was defined as a boundary for the fate of the sandbar during the landward migration process. Sandbar welding (SW; Mode I) occurred during low-energy conditions after a moderately energetic winter (cum Pt ≤ 50 kWm−1) when the sandbar (of up to 1 m height and ~ 100 m3m−1) was located shoreward from the cross-shore boundary. A large sandbar (> 100 m3m−1; > 1 m height) that formed offshore from the boundary during a highly-energetic winter (cum Pt >50 kWm−1) turned into a terrace-bar (STT; Mode II) in a subsequent very low-energy period. A terrace-bar of ~100 m3m−1 located near the boundary (~ 3 m depth) became a sandbar (TST; Mode III) during moderately energetic conditions at the beginning of the winter. Sandbar splitting (SS; mode IV) occurred during low-energy conditions when a sandbar of ~100 m3m−1 situated offshore from the boundary; the outer section flattened and followed a net offshore migration cycle while the inner section migrated shoreward. This study highlights the need for considering sandbar morphometric properties in addition to the preceding wave conditions to adequately predict the shoreward migration process of the sandbar. • A sandbar of ≤1 m located at < 3 m depth welds to the shoreline during low energy conditions (Pt max < P ¯ t anual) after a mild winter (Pt max < 10 x P ¯ t anual). • After an energetic winter (Pt max > 10 x P ¯ t anual) a >1 m sandbar at > 3 m depth becomes a terrace-bar during very-low conditions (Pt max < 0.5 x P ¯ t anual). • A ~100 m3m-1 sandbar at > 3 m depth splits into two parts (outer terrace-bar and inner sandbar) during low-energy conditions (Pt max < 2 x P ¯ t anual). [ABSTRACT FROM AUTHOR]

Beach nourishment is a soft engineering intervention that supplies sand to the shore, to increase the beach recreational area and to decrease coastal vulnerability to erosion. This study presents the preliminary evaluation of nourishment works performed at the high-energy wave-dominated Portuguese coast. The shoreline was adopted as a proxy to study beach evolution in response to nourishment and to wave forcing. To achieve this aim, images collected by a video monitoring system were used. A nourishment calendar was drawn up based on video screening, highlighting the different zones and phases where the works took place. Over the six-month monitoring period, a total amount of 25 video-derived shorelines were detected by both manual and automated procedures on video imagery. Nourishment works, realized in summer, enlarged the emerged beach extension by about 90 m on average. During winter, the shoreline retreated about 50 m due to wave forcing. Spatial analysis showed that the northern beach sector was more vulnerable and subject to erosion, as it is the downdrift side of the groin. [ABSTRACT FROM AUTHOR]

With high anthropogenic pressure and the effects of climate change (e.g., sea level rise) on coastal regions, there is a greater need for accurate and up-to-date information about the topography of these systems. Reliable topography and bathymetry information are fundamental parameters for modelling the morpho-hydrodynamics of coastal areas, for flood forecasting, and for coastal management. Traditional methods such as ground, ship-borne, and airborne surveys suffer from limited spatial coverage and temporal sampling due to logistical constraints and high costs which limit their ability to provide the needed information. The recent advancements of spaceborne remote sensing techniques, along with their ability to acquire data over large spatial areas and to provide high frequency temporal monitoring, has made them very attractive for topography and bathymetry mapping. In this review, we present an overview of the current state of spaceborne-based remote sensing techniques used to estimate the topography and bathymetry of beaches, intertidal, and nearshore areas. We also provide some insights about the potential of these techniques when using data provided by new and future satellite missions. [ABSTRACT FROM AUTHOR]

Shand, R.D., 2007. Bar splitting: system attributes and sediment budget implications for a net offshore migrating bar system. Journal of Coastal Research, SI 50 (Proceedings of the 9th International Coastal Symposium), 721 – 730. Gold Coast, Australia, ISSN 0749.0208 Net offshore bar migration or NOM, refers to the systematic seaward migration of longshore (primary) sand-bars across the surf zone. NOM appears to be the product of storm-induced seaward bar migration (sediment transport) exceeding landward bar migration (sediment transport) during intervening fair weather periods. NOM also appears to involve the cross-shore redistribution of sediment rather than the continual loss of sediment to the shoreface. While 'grain by grain' return processes appear to predominate within the outer surf zone, alternative return mechanisms may exist within the inner surf zone. The aim of this paper is to assess whether sediment travelling landward within inner bifurcates formed during the process of bar splitting can offset a NOM-induced cross-shore sediment imbalance. Bar splitting has been observed on several NOM coasts and involves a longshore bar bifurcating, with the inner bifurcate detaching, moving landward, and in some cases welding to the foreshore. Analysis of several years of morphological data from Wanganui, on the west coast of New Zealand's North Island, found that the sediment gained by the foreshore from inner bifurcate welding amounted to approximately half the sediment lost from the foreshore by newly generated sand-bars which subsequently underwent NOM. In addition, during the study, several other types of 3D morphological behaviour were identified which are also capable transporting sediment shoreward across the inner surf zone as a coherent sand body. Landward migrating secondary bars therefore appear to play a significant role in returning sediment to the inter-tidal beach. Finally, a conceptual morphodynamic model of the NOM system at Wanganui is presented which incorporates 3D morphological behaviour in contrast with existing models which are entirely 2D. [ABSTRACT FROM AUTHOR]