Beach Morphology Research Articles

Morphological variability of sandy beaches due to variable oceanographic conditions: a study case of oceanic beaches of Rio de Janeiro city (Brazil)

Due to their overall east-west orientation, the Rio de Janeiro oceanic urban beaches are exposed to high energy meteoceanographic events, exhibiting large spatial and temporal morphodynamic variability that affect their use and functionality. The main goals of this study are to describe the morphology of these sandy beaches and to evaluate their response to different oceanographic conditions. Between 2016 and 2018 quasi-monthly monitoring surveys, comprising topographic and sedimentological sampling, were carried out at 21 sites distributed along Macumba, Recreio-Barra da Tijuca, Sao Conrado, Leblon-Ipanema-Arpoador and Copacabana-Leme beaches. During this period, 29 storm events were recorded by an oceanographic buoy near the study area (~20 m depth). The most energetic event occurred between 11 and 14 August 2017 and caused widespread morphological changes, as the 45 m retreat at the Recreio-Barra beach eastern sector. Overall, mean grain size decreases from west to east varying from coarse to medium sand. The topographic record shows decreasing slope and increasing width from west to east, except in the Leblon-Ipanema-Arpoador beaches, where beach rotation was documented. The main findings were the interannual variability trends to beach morphometric records, the period each beach needs to recover its mean width after erosional events and how severe are storm impacts. Besides contributing to the morphodynamic understanding of the studied beaches, new understandings of the impacts of storm events and the subsequent recovery of sandy beaches are presented.

STOK KARBON DI ATAS PERMUKAAN TANAH PADA HUTAN MANGROVE SUNGAI AWAN KIRI KABUPATEN KETAPANG

Mangrove forests, often referred to as mangrove forests, brackish forests or tidal forests, is a transitional ecosystem between land and sea which are tropical or sub-tropical areas along the sheltered coast and river mouth. Mangrove forest is a coastal plant community dominated by several species of mangrove trees that are able to grow and develop during the tides in accordance with their tolerance to salinity, duration of inundation, substrate and beach morphology. Awan Kiri Mangrove Forest has a total area of 114 hectares including the area of Other Management Areas (APL) then seen from the density of the Mangrove Forest only has 92 hectares. This study uses a non-destructive survey method. Vegetation carbon stock calculation is carried out using vegetation biomass calculation approach. Vegetation biomass calculation based on the calculation of allometric equations. Calculation the value of stored carbon using the formula according to (SNI 7724:2011) the value of parent carbon content,amounting to 0,47. Bassed on the research that has been done, it is found that there are 185 individuals, Rhizophora spp., Bruguiera gymnorhiza, Rhizpphora apiculata, Xylocarpus gerantum and Excoecaria agallocha. The biomassa content can be known in the 3 pathways to store 242,16 tons biomassa and the total biomassa content in 1210,8 tons/ha with an everage of 403,6 tons/ha. The carbon content is 569,06 tons/ha so that it gets an average total of 186,68 tons C/ha.Keywords: Carbon Stock, Ketapang Regency, Sungai Awan Kiri in Mangrove Forests.

How changes in beach morphology affect hawksbill turtle (Eretmochelys imbricata) nesting distribution at Celestun, Yucatan, Mexico

The Yucatan Peninsula harbors important nesting beaches for the largest hawksbill turtle (Eretmochelys imbricata) populations in the Western Atlantic. Over the last decade, erosion has substantially modified segments of the nesting beach along the coastal zone of Celestun town, Mexico. The recent rise in sea level makes this area among the most vulnerable of the Yucatan coastal zone, potentially jeopardizing its suitability as a nesting site for hawksbill turtles. The objectives of this study were to: (1) identify spatiotemporal patterns of the hawksbill nesting season over 11 years (1997–2007); (2) characterize spatiotemporal dynamics in the morphology of the nesting beach; and (3) assess the relationship between beach morphology changes and hawksbill nesting activity. We observed a well-defined spatial pattern of hawksbill nesting activity along the beach, occupying steep and narrow beach zones where human presence and activity was low. The beach was under a strong erosional process, causing a retreat displacement that varied in magnitude along the littoral zone. Principal component analysis showed a strong correlation between beach morphology variables, separating segments of beach according to the effect of morphology. Variation in hawksbill nest densities was inversely correlated to the distance to town and to artificial light intensity. It is suggested that the influence of human activities and infrastructure on nesting females forces the use of beach segments where flooding and nest erosion from high tides and storm surges jeopardize their reproductive success and makes more relevant the identification of spatial priority zones for targeted management strategies that aim to preserve hawksbill nesting.

Uncertainty in runup predictions on natural beaches using XBeach nonhydrostatic

The wave time series that forces phase-resolving models is a source of model uncertainty that can propagate into wave runup predictions when the wave phase information is unknown. The effect of beach morphology on the propagation of this intrinsic uncertainty related to wave randomness (Ui) is largely unexplored. Here, we quantify the importance of uncertainty in wave runup at a dissipative (TS), intermediate (DU) and reflective (DE) beach using the phase-resolving model XBeach nonhydrostatic. Intrinsic uncertainty is evaluated with respect to the effect of free model parameters and of an evolving bed. Uncertainty contributions due to model equations and numerical methods are not assessed. The model is forced at each beach with 100 different wave time series corresponding to the same storm condition. Computed uncertainty metrics reveal that Ui is most important at TS, where extreme runup (R2%) of a single simulation can deviate up to 31% from the 100-simulation ensemble average. Intrasite differences in R2% can be attributed to the predominance of low-frequency swash (SLF), which is more sensitive to Ui than high-frequency swash and setup. Additional simulations using the suggested range of breaking and bed friction coefficients demonstrate that Ui produces more variability in SLF than the two most important model parameters, whereas the parametric range is more important for high-frequency wave height. Furthermore, morphodynamic simulations show that Ui produces a larger variability in R2% and SLF than an evolving bed under a 7-hr storm. Not surprisingly, Ui causes larger variability in morphologic than hydrodynamic predictions due to morphologic feedback. Trends can reverse from swash zone accretion to erosion (TS) by using a wave time series with differently distributed phase. Ensemble simulations are recommended for forecasts based on wave time series with randomly distributed phase.

Molecular Traits of Dissolved Organic Matter in the Subterranean Estuary of a High-Energy Beach: Indications of Sources and Sinks

Advective flows of seawater and fresh groundwater through coastal aquifers form a unique ecohydrological interface, the subterranean estuary (STE). Here, freshly produced marine organic matter and oxygen mix with groundwater, which is low in oxygen and contains aged organic carbon (OC) from terrestrial sources. Along the groundwater flow paths, dissolved organic matter (DOM) is degraded and inorganic electron acceptors are successively used up. Because of the different DOM sources and ages, exact degradation pathways are often difficult to disentangle, especially in high-energy environments with dynamic changes in beach morphology, source composition, and hydraulic gradients. From a case study site on a barrier island in the German North Sea, we present detailed biogeochemical data from freshwater lens groundwater, seawater, and beach porewater samples collected over different seasons. The samples were analyzed for physico-chemistry (e.g., salinity, temperature, dissolved silicate), (reduced) electron acceptors (e.g., oxygen, nitrate, and iron), and dissolved organic carbon (DOC). DOM was isolated and molecularly characterized via soft-ionization ultra-high-resolution mass spectrometry, and molecular formulae were identified in each sample. We found that the islands’ freshwater lens harbors a surprisingly high DOM molecular diversity and heterogeneity, possibly due to patchy distributions of buried peat lenses. Furthermore, a comparison of DOM composition of the endmembers indicated that the Spiekeroog high-energy beach STE conveys chemically modified, terrestrial DOM from the inland freshwater lens to the coastal ocean. In the beach intertidal zone, porewater DOC concentrations, lability of DOM and oxygen concentrations, decreased while dissolved (reduced) iron and dissolved silicate concentrations increased. This observation is consistent with the assumption of a continuous degradation of labile DOM along a cross-shore gradient, even in this dynamic environment. Accordingly, molecular properties of DOM indicated enhanced degradation, and “humic-like” fluorescent DOM fraction increased along the flow paths, likely through accumulation of compounds less susceptible to microbial consumption. Our data indicate that the high-energy beach STE is likely a net sink of OC from the terrestrial and marine realm, and that barrier islands such as Spiekeroog may act as efficient “digestors” of organic matter.

Spatial analysis of accretion, abrasion and shoreline change in banda aceh costal area

The coast of Banda Aceh City has a gentle sloping beach morphology, making it prone to changes in coastlines due to hydro-oceanographic dynamics. Areas that are particularly vulnerable are the mangrove areas and around the Krueng Aceh estuary and coastal area of Lampulo. Therefore, to determine the extent of shoreline changes, a spatial analysis of coastal vulnerability was carried out with the aim of knowing how much change had occurred at Lampulo beach in Banda Aceh City of Aceh Province. The research was conducted using Google Earth data technology and the use of Geographic Information System (GIS) software. The analysis was carried out over a period of 14 years starting from 2004 to 2017. Field data verification and georeferencing were also carried out to check the accuracy of mapping and calculations. The results showed that in 2004-2005 there was a large erosion that changed the shape of the coastal profile where the mangrove coastline turned into water without mangroves as a result of the tsunami on December 26, 2004. In 2008-2009, after the construction of the breakwater and the Port of Lampulo there was a large accretion occurred having the impact on the morphology of the coast. The results also concluded that the annual average accretion value was 20.48 ha and the annual abrasion was 19.28 ha. The value of shoreline reduction due to abrasion is around 217.25 ha and accretion of 166.56 ha over a period of 14 years.

Coastal erosion in Vietnam: Case studies and implication for integrated coastal zone management in the Vietnamese south-central coastline

Vietnam is a country that is heavily affected by global climate change, with the coastal zone and low-lying river deltas being especially vulnerable. The coastal zone has rapidly evolved over the past few decades, as coastal tourism and other social-economic developments and industries all seek fortune and exploit resources in this area. Along with this rapid economic growth, the coastal zone has suffered severe impacts of both human activities and global climate change, resulting in an increasing number of coastal hazards, such as typhoons, floods, saline intrusion, and coastal erosion. The purpose of this paper is to identify natural and human factors that affect coastal erosion through case studies in the south-central coastline. Measures for minimizing threats to both socio-economic activities and the surrounding natural environments are brought forward, in which integrated coastal zone management approach plays a key role. In addition to addressing the issues and potential management strategies, selected coastal areas in Vietnam characterized by severe coastal erosion are studied in terms of coastline dynamics, changing beach morphologies and coastal engineering structures through on-site measurements and aerial images. Seasonal variations and changing beach morphologies after the construction of coastal engineering works are clearly visible.

LiDAR Observations of Multi-Modal Swash Probability Distributions on a Dissipative Beach

Understanding swash zone dynamics is of crucial importance for coastal management as the swash motion, consisting of the uprush of the wave on the beach face and the subsequent downrush, is responsible for driving changes in the beach morphology through sediment exchanges between the sub-aerial and sub-aqueous beach. Improved understanding of the probabilistic characteristics of these motions has the potential to allow coastal engineers to develop improved sediment transport models which, in turn, can be further developed into coastal management tools. In this paper, novel descriptors of swash motions are obtained by combining field data and statistical modelling. Our results indicate that the probability distribution function (PDF) of shoreline height timeseries (p(ζ)) and trough-to-peak swash heights (p(ρ)) measured at a high energy, sandy beach were both inherently multimodal. Based on the observed multimodality of these PDFs, Gaussian mixtures are shown to be the best method to statistically model them. Further, our results show that both offshore and surf zone dynamics are responsible for driving swash zone dynamics, which indicates unsaturated swash. The novel methods and results developed in this paper, both data collection and analysis, could aid coastal managers to develop improved swash zone models in the future.

Assessment of the Performance of an Artificial Reef Made of Modular Elements through Small Scale Experiments

Artificial reefs have proven to be an optimal and effective solution in stabilizing coastlines around the world. They are submerged structures that imitate the protection service provided by natural reefs accomplishing the functions of dissipating wave energy and protecting beach morphology, but also being an ecological solution. In this paper, 2D small-scale experiments were performed to analyze the hydrodynamic, morphological, and ecological behavior of an artificial reef constructed of modular elements. Two typical beach-dune profiles were constructed in a wave flume over which two locations of an artificial reef were tested. From these tests, transmission coefficients were obtained as well as the beach profile response to the presence of the artificial reef. These results are used to discuss about the hydrodynamic, morphological, and ecological performance of the artificial reef. The proposed artificial reef showed good morphological performance while its hydrodynamic function had limited success. In turn, the ecologic performance was theoretically addressed.

Analysis of long- and short-term shoreline change dynamics: A study case of João Pessoa city in Brazil

The coastal area of João Pessoa city, Paraíba, Brazil, is densely populated and has a large flow of trade and services. More recently, this region has been suffering from the advance of the sea, which has caused changes in the shoreline and caused a decrease in the beach area and damage to various urban facilities. Thus, the spatiotemporal changes of the short- and long-term characteristics of the shoreline of João Pessoa city over the past 34 years (1985–2019) were calculated and the forcing mechanisms responsible for the shoreline changes were analyzed. Remote sensing data (Landsat 5-TM and 8-OLI) and statistical techniques, such as endpoint rate (EPR), linear regression rate (LRR) and weighted linear regression (WLR), using Digital Shoreline Analysis System (DSAS), were used. In this study, 351 transects ranging from ~1.1 km to ~6 km were analyzed within four zones (Zones I to IV), and the main controlling factors that influence the shoreline changes in these zones, such as sea level, tidal range, wave height, beach morphology and ocean currents, were discussed. The long-term change from 1985 to 2019 showed primarily accretion on the shoreline of João Pessoa city, with the rate of 0.55 m/year (WLR method); 282 transects showed accretion. The results showed that Zone-I, which was located in the south of the study area, was the only zone that primarily recorded erosion from 1985 to 2019, with a mean rate of −0.23 m/year according to the WLR method. According to the short-term shoreline change analysis, a cyclical pattern of erosion was observed in the 1985–1990, 1993–1999, 2005–2011 and 2014–2019 periods, and accretion was observed in the 1990–1993, 1999–2005 and 2011–2014 periods. It was inferred that the patterns of all analyzed zones were similar, i.e., when majority accretion was detected within a zone, the other zones also recorded accretion, except for during the period from 2014 to 2019, when Zone-I showed different behavior. Finally, the long- and short-term analyses showed that the coastal area of João Pessoa city is influenced by various forcing mechanism responsible for the shoreline changes.

Beach Sustainability Assessment: The Development and Utility of an Interdisciplinary Approach to Sandy Beach Monitoring

Patsch, K.; King, P.; Reineman, D.R.; Jenkins, S.; Steele, C.; Gaston, E., and Anderson, S., 2021. Beach sustainability assessment: The development and utility of an interdisciplinary approach to sandy beach monitoring. Journal of Coastal Research, 37(6), 1130–1157. Coconut Creek (Florida), ISSN 0749-0208. Sandy beaches are valued for various ecosystem services but are increasingly imperiled by anthropogenic stressors. Sea-level rise (SLR), reductions to sand supply, hardening the position of the coastline, and the prevalence of human development along California's coast combine to reduce the fundamental dynamism critical to the resilience of California's beaches. If California continues with business as usual, many of its beaches will erode and eventually disappear. Coastal jurisdictions in California are planning for SLR. However, these coastal managers lack a standardized regional assessment tool that compiles information on the current and likely future condition of sandy beaches. Without such a tool, these managers have limited ability to analyze the integrated impacts of historic decisions or future alternative management scenarios upon beach morphology, ecological functioning, economics, and social utility. This paper presents a study of the Beach Sustainability Assessment (BSA) decision support tool applied to 17 beaches spanning Santa Barbara, Ventura, and Los Angeles counties. In addition to scoring and grading geomorphological, ecological functioning, and social utility components, the BSA provides a single, overall grade for each beach. To demonstrate the utility of the BSA, a scenario with 1 m of SLR and a 100-year storm was simulated to assess the changes to the overall grade and component grades. The BSA offers a cost-effective, standardized protocol to monitor the condition of California's sandy beach ecosystems. The metrics support spatial and temporal comparisons on a regional scale, giving coastal managers and stakeholders the ability to assess real trade-offs among management solutions. Current BSA indices indicate that beaches in the Southern California Bight study area are already struggling, with most urban beaches receiving Cs and Ds for ecological functioning. The SLR stressor test indicates that ecological functioning and social utility will continue to decline with increasing sea levels.

ENHANCE DUNE-BUILDING PROCESSES WITH NATURE-BASED NOURISHMENT DESIGN

Vast coastal stretches around the world rely on dunes for flood protection. At the same time, the protection level of many dune systems can be undermined due to coastal erosion, sea-level rise, and greater population densities. To enhance dune building processes and the growth of coastal dunes, nature-based solutions, such as multi-purpose sand nourishments, are increasingly being implemented. However, the performance of the nourishment projects in terms of dune growth do not always match the expectations due to unforeseen supply-limiting factors (Hoonhout and de Vries, 2019). Sediment on a beach should be within a site-specific range of grain sizes to be available for pick up by the wind and deposition in the dunes. However, the grain-size characteristics do also influence several other supply-limiting factors, e.g., surface moisture, crust development, and beach slope, making nourishment design complicated. The process-based model Aeolis has been developed to predict aeolian transport rates considering several supply limiting factors. In this study, we introduce a new surface moisture functionality in Aeolis and demonstrate how the model can be used to optimize nourishment designs with respect to dune build-up. A number of test cases are presented to illustrate how grain size, sorting, and beach morphology are influencing aeolian transport rates.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/K_eiZ5kPk2g

FUTURE CHANGES IN SPECTRAL WAVE CLIMATE AROUND JAPAN UNDER GLOBAL WARMING

Future projections of ocean wave climate related with global warming has been conducted for the assessment of climate change impacts on coastal disaster, beach morphology, and coastal structure design. In this study, we conduct the high-resolution future wave climate projection in the East Asia region and detail analysis on wave climate based on two-dimensional wave spectra in addition to conventional wave statistics (significant wave height). Future changes in wave height, period and direction can be discussed consistently owing to analysis on the mean wave spectra.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/FEYPZFRr5SQ

NUMERICAL SIMULATION OF WAVE-DRIVEN FLOWS ON A MORPHOLOGICALLY EVOLVING BEACH

Wave-driven flows in the nearshore zone are responsible for the erosion and transport of beach sediments, causing a continuous cycle of bathymetric change that is linked with changes to wave transformation and nearshore hydrodynamics. Numerical models have been used to investigate the evolving nearshore wave field corresponding to beach morphology change in field studies (e.g., Ruiz de Alegria-Arzaburu et al., 2013). In the present study, the non-hydrostatic wave-flow SWASH model (Zijlema et al., 2011) is applied to five laboratory cases to investigate the change in wave and flow fields corresponding to evolving beach morphology during a simulated storm event.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/LZQQuuiqsPY

MACHINE LEARNING CLASSIFICATION OF BEACH STATE FROM ARGUS IMAGERY

Nearshore beach morphology is of interest to coastal managers due to the strong influence it exerts on subaerial beach erosion, pollutant dispersal, and recreational safety. In particular, wave breaking conditions and nearshore hydrodynamics are highly dependent on sandbar configuration. The term 'beach state' describes specific planform configurations of nearshore morphology that are in dynamic equilibrium with the time-varying forcing conditions. Beach state categories were first introduced by Wright and Short (1984), who observed sandbar systems in Narrabeen-Collaroy, Australia and extended by Lippman and Holman (1990), based on observations of time-exposure Argus imagery of sandbar systems in at Duck, NC, USA. In this study, we use machine learning algorithms to identify beach states from Argus imagery at two distinct sites: Narrabeen-Collaroy (hereafter Narrabeen), SE Australia, and Duck, NC. We assess the ability of the algorithm to classify beach states at each site and its transferability from one beach to another. Additionally, we investigate the extent to which the spatial and temporal evolution of beach states influences the ability of the algorithm to classify images into discrete beach states.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/38OM8CseIww

The Grounding of Floating Objects in a Marginal Sea

AbstractBeaches, especially at or above the high tide line, are often covered in debris. An obvious approach to understanding the source of this debris elsewhere in the ocean is to use Lagrangian methods (observationally or in numerical simulations). However, the actual grounding of these floating objects, that is, the transition between freely floating near the coast and motionless on land, is poorly understood. Here, 800 groundings from a recent circulation project using expendable tracked drifters in the Salish Sea are statistically analyzed. Although the grounding process for individual drifters can be complex and highly variable, suitable analyses show that the complications of coastlines can be statistically summarized in meaningful ways. The velocity structure approaching the coastline suggests a quasi-steady “log-layer” associated with coastline friction. Although groundings are marginally more likely to occur at higher tides, there are many counterexamples and the preference is not overwhelming. The actual grounding process is then well modeled as a stationary process using a classical eddy-diffusivity formulation, and the eddy diffusivity that best matches observations is similar to that appearing in open waters away from the coast. A new parameter in this formulation is equivalent to a mean shoreward velocity for floating objects, which could vary with beach morphology and also (in theory) be measured offshore. Finally, it appears that currently used ad hoc beaching parameterizations should be reasonably successful in qualitative terms, but are unlikely to be quantitatively accurate enough for predictions of grounding mass budgets and fluxes.

Sandy beaches in low-energy, non-tidal environments: Linking morphological development to hydrodynamic forcing

The morphodynamic behaviour of low-energy beaches is poorly understood, compared to that of exposed coasts. This study analyses the morphological development of sandy, low-energy beaches and the steering hydrodynamic processes. Four densely-monitored study sites in the non-tidal lake Markermeer in the Netherlands offered a unique opportunity to examine the relation between their hydraulic boundary conditions and morphodynamics. Regular bathymetric surveys were executed at all locations. Furthermore, the wave climate was monitored at one of these four sites. All four sites exhibit a commonly found low-energy beach morphology, with a narrow beach face and a low-gradient, subaqueous platform. This platform reaches an equilibrium depth quickly and then stays relatively stable. The stable elevation of the platform is located near Hallermeier's depth of closure. A sediment budget analysis over time demonstrates that the beach faces at all study sites have eroded during more energetic periods, and sediment accumulated offshore. During the monitoring periods of 2 to 4 years, the elevation of the platforms reached an equilibrium, but other morphological dimensions are still developing. The new insights gained from this study enable the prediction of platform elevations along sandy beaches in low-energy, non-tidal environments, and have contributed to our insight in the underlying processes driving the morphological evolution.

Supermoon Drives Beach Morphological Changes in the Swash Zone

AbstractThe effect of the supermoon, which appears much larger than a normal full moon, on the morphological changes of a sandy beach was investigated by analyzing a 25‐year daily observation data set of beach morphology in the swash zone. The beach morphology fluctuated in two cycles related to the supermoon: the semisynodic month cycle (from full moon to new moon, and vice versa) and the anomalistic month cycle (from perigee to perigee). The supermoon makes the erosion of the upper swash zone more likely by generating a larger tidal range. The high‐water‐level contour positions observed during supermoons retreated significantly, although there were no trends in the change for all the observations. Erosion due to high waves coincident with a supermoon can be expected to be more severe in the upper swash zone; including the supermoon effect in beach morphodynamic models can improve coastal management.

Spatial Variation in Coastal Dune Evolution in a High Tidal Range Environment

Coastal dunes have global importance as ecological habitats, recreational areas, and vital natural coastal protection. Dunes evolve due to variations in the supply and removal of sediment via both wind and waves, and on stabilization through vegetation colonization and growth. One aspect of dune evolution that is poorly understood is the longshore variation in dune response to morphodynamic forcing, which can occur over small spatial scales. In this paper, a fixed wing unmanned aerial vehicle (UAV), is used to measure the longshore variation in evolution of a dune system in a megatidal environment. Dune sections to the east and west of the study site are prograding whereas the central portion is static or eroding. The measured variation in dune response is compared to mesoscale intertidal bar migration and short-term measurements of longshore variation in wave characteristics during two storms. Intertidal sand bar migration is measured using satellite imagery: crescentic intertidal bars are present in front of the accreting portion of the beach to the west and migrate onshore at a rate of 0.1–0.2 m/day; episodically the eastern end of the bar detaches from the main bar and migrates eastward to attach near the eastern end of the study area; bypassing the central eroding section. Statistically significant longshore variation in intertidal wave heights were measured using beachface mounted pressure transducers: the largest significant wave heights are found in front of the dune section suffering erosion. Spectral differences were noted with more narrow-banded spectra in this area but differences are not statistically significant. These observations demonstrate the importance of three-dimensionality in intertidal beach morphology on longshore variation in dune evolution; both through longshore variation in onshore sediment supply and through causing longshore variation in near-dune significant wave heights.

Cusp and Mega Cusp Observations on a Mixed Sediment Beach

AbstractFrequent surveys using modern remote sensing technology enable observations of subaerial beach morphology and surface sediment type (sand vs. gravel/cobble) with unprecedented spatial and temporal resolution. Here we show weekly terrestrial mobile light detection and ranging (LiDAR) observations of cusps on a mixed sediment beach, consisting of sand and gravel/cobble, spanning ∼2 km alongshore. Surface gravel/cobble coverage varied from almost complete to none (e.g., all sand), over times ranging from weekly to seasonal, and with location. Cusp morphologies also varied in space and time. Cusps with 11–20 m alongshore wavelengths (L) primarily developed in winter and were composite with gravel‐cobble horns and sandy bays. Cusps with L between 21 and 40 m developed throughout the year and were either composite or entirely sandy. Previously not reported, composite mega cusps (L between 200 and 400 m) occurred in winter. Composite cusps, with L between 11 and 40 m, were clustered in gravel/cobble‐rich mega cusp bays and absent on the sandier mega cusp horns.