Reflective Beaches Research Articles

The swash zone selects functionally specialized assemblages of beach interstitial meiofauna (Platyhelminthes, Proseriata)

Life is not a beach for those animals that survive in the rough ecological conditions found in marine sandy beaches – and yet, microscopic animals thrive on them. We explore the drivers for meiofaunal diversity in beaches by analysing taxonomic and functional patterns of 348 flatworm communities across 116 reflective beaches in the western Mediterranean, totalling 152 species (61.2% new to science). First, we confirm that species richness does not differ between beach hydrodynamic levels (swash, shoaling and surf) but rather depends on the characteristics of each beach. Second, we demonstrate that species composition across those levels depends on the species traits, in addition to geographical and abiotic factors. Third, we highlight that the species functional space has a lower richness than expected and a lower redundancy in the wave‐exposed swash level compared to the shoaling and subtidal levels, suggesting a trait‐based ecological filtering. Finally, we show that those differences depend on the higher frequency of hydrodynamics‐related traits in the species of the swash level. Our results suggest that the rough hydrodynamic conditions in the swash level favour a unique combination of species traits, which might be linked to ecological speciation in flatworms but also in other interstitial animals.

Drivers of variability in surf zone habitat use by sandy beach fish: Unwitting citizen scientists reveal detailed spatiotemporal patterns

Surf zones of sandy beaches are among the most heavily impacted aquatic ecosystems, yet are of critical ecological importance for inshore fish and fisheries. Knowledge of the drivers of fish habitat use in surf zones is needed across broad scales to advise conservation and fisheries management, but sampling capabilities can be limited in spatio-temporal extent and resolution. The lesser weever Echiichthys vipera is a small, benthic, venomous fish that dominates surf zone fish assemblages in Northwest Europe and inflicts painful stings on beachgoers. This study capitalises on an extensive record of E. vipera sting incidents to characterise variations in surf zone habitat use in relation to key physical environmental factors. Sting incidents, standardised by water user numbers, are used as a proxy for E. vipera abundance across 77 beaches throughout Southwest England, with 2 h resolution, from April–November 2018. General Additive Models indicated a clear peak in E. vipera abundance at spring low tides, in the afternoons of summer months, under calmer wave conditions and at higher levels of solar irradiance. Although the order of significance differed, human water users were also driven by the same variables, compounding sting interactions over time. Key physical variables did not explain spatial variation in E. vipera abundance, although there was a weak relationship with sea surface temperature, and some evidence that reflective beaches are unsuitable. Physical factors explained more spatial variation in human water users, who gathered at more dissipative beaches with greater wave heights. This detailed study of an important surf zone fish reveals clear drivers of temporal variation in habitat use, yet infers wide suitability of beaches varying in the key physical drivers of sandy shore ecology.

Bar and berm dynamics during transition from dissipative to reflective beach profile

Bar and berm morphology characterize the seasonal beach evolution, and determine the protection against storm erosion as well as the touristic use of beaches. Thus, they are of particular interest for coastal management and engineering in the nearshore zone. This study used large-scale wave flume experiments to observe the transition from fully dissipative to fully reflective beach profile at a high level of detail. Starting from a post-storm profile generated under energetic waves, a very low energy wave condition caused dissipation of the outer and the inner bar, shoreline recovery, and berm accretion. Measurements revealed feedback between hydrodynamics and beach profile evolution with an onshore shift of the wave breaking location. As a result, the magnitude and cross-shore evolution of wave asymmetry-related bedload net onshore and suspended net offshore transport changed. The relative magnitudes of the two transport components and the way they shifted relative to each other caused the observed beach recovery. Additionally, a link between bar and berm morphology (surf-swash sand exchange) was observed. The shifting breakpoint enabled sustained, wave asymmetry-related onshore transport in the inner surf zone, feeding the berm accretion which occurred through advective swash zone processes including berm overwash.

Analysis of Beach Cusp Formation and Evolution Using High‐Frequency 3D Lidar Scans

AbstractIn this study, beach cusp characteristics were explored using 15 months of 3D lidar scans collected hourly at the Field Research Facility in Duck, NC. Fourier analyses were performed on lidar‐derived beach elevation contours to generate spatial cusp spectra. Active cusp events were identified on the basis of the location and magnitude of each spectrum's peak and used to evaluate conditions during cusp formation and evolution. Cusps primarily developed during times with normally‐incident, long period, low energy wave conditions with low frequency spread, and reflective beach conditions. The upper and lower beaches often exhibited different behavior and morphologies, with persistent upper‐beach cusps lasting days to months and dynamic lower‐beach cusps evolving over individual tidal cycles. At times, beaches exhibiting multiple cusp systems reverted to a single cusp system extending over the entire beach when the high‐tide waterline reached the upper‐beach cusps, with the location and spacing of the resulting lower‐beach cusps controlled by the upper‐beach cusps. These observations are consistent with a “morphological coupling” hypothesis proposing that hydrodynamic‐morphodynamic feedbacks between the swash and upper‐beach cusps can result in the formation of lower‐beach cusps with a related wavelength as the tide falls. However, there were also times when the high‐tide waterline reached the upper‐beach cusps that did not result in a unified beach state. These results suggest that while morphological coupling is often an important factor in controlling the development of new lower‐beach cusps, this coupling cannot initiate cusp formation in hydrodynamic conditions outside those favorable for cusp activity.

Benthic fauna along sandy beaches enriched by metals after mining disaster

In 2015, 60 million tons of ore tailings from the Fundão dam failure entered the Doce River basin, Brazil, and reached surrounding sandy beaches. This study evaluated the influence of sedimentology and morphology of beaches that received mining tailings on chemical element concentrations and consequent benthic community responses. We collected sediments for physical (granulometry, heavy mineral, and calcium carbonate content) and geochemical (chemical elements) analyses and biological diversity parameters (benthic macro- and meiofauna density, richness, and composition) on 8 beaches with different morphodynamic types. Beaches with more dissipative characteristics retained the highest contents of mud, As, Fe, Mn, V, and heavy minerals, present in the tailings. We also recorded the lowest density and richness of macrofauna on these beaches, compared to more reflective beaches. These results contradict the global trend, suggesting that anthropic disturbances outweigh the effects of morphodynamics in structuring the benthic fauna community, mainly in dissipative sandy beaches.

Global patterns in sandy beach erosion: unraveling the roles of anthropogenic, climatic and morphodynamic factors

Beach erosion is a complex process influenced by multiple factors operating at different spatial scales. Local (e.g., waves, tides, grain size, beach width and coastal development) and regional (e.g., sea level rise and mean sea level pressure) factors both shape erosion processes. A comprehensive understanding of how these drivers collectively impact sandy beach erosion is needed. To address this on a global-scale we assembled a database with in-situ information on key physical variables from 315 sandy beaches covering a wide morphodynamic range and complemented by satellite data on regional variables. Our results revealed the combined influence of local and regional factors on beach erosion rates. Primary drivers were regional anomalies in mean sea level pressure and variations in mean sea level, and local factors such as tide range, beach slope and width, and Dean’s parameter. By analyzing morphodynamic characteristics, we identified five distinct clusters of sandy beaches ranging from wave-dominated microtidal reflective beaches to tide-modified ultradissipative beaches. This energy dissipation gradient emerged as a critical factor, with erosion rates increasing with beach width and dissipativeness. Our study also highlighted the tangible impact of climate change on beach erosion patterns. Hotspots were identified, where intensification of regional anomalies in mean sea level pressure, increasing onshore winds and warming rates, and rising sea levels synergistically accelerated erosion rates. However, local variables were found to either amplify the effects of regional factors on erosion or enhance a beach’s resistance, mitigating erosive trends initiated by regional drivers. Our analysis showed that more than one-fifth of the analyzed beaches are experiencing intense, extreme, or severe erosion rates, and highlighted the significant role of human activities in explaining erosion trends, particularly in microtidal reflective and intermediate beaches. This underscores the long-term threat of coastal squeeze faced by sandy beaches worldwide and emphasizes the need to consider both local and regional drivers in order to understand erosion processes. Integrating localized measurements with broader satellite observations is required for a comprehensive understanding of the main drivers behind coastal evolution, which in turn is needed to manage and preserve these fragile ecosystems that are at risk.

Beach morphodynamics modulate the effects of multidirectional habitat loss on population density and size structure of the Atlantic ghost crab Ocypode quadrata

Sandy beaches are land-sea transitional habitats experiencing ‘multidirectional’ habitat loss due to coastal developments (e.g. armoring and/or conversion of natural vegetation into manmade structures) and beach erosion. This ‘coastal squeeze’ is a chronic and progressive process; however, its impacts on beach biodiversity across morphodynamic gradients are still to be unveiled. We hypothesized that the effects of multidirectional habitat loss would be more severe on dissipative than on reflective beaches, due to the higher elevation, amount of built up sediment, and width of the backshore compartment of the latter. We, thus, examined the effects of coastal developments and erosion on density and size structure of the Atlantic ghost crab, Ocypode quadrata, on beaches with different morphodynamics. Given that the living area of ghost crabs spans all cross-shore compartments and the whole dissipative-to-reflective morphodynamic gradient, they are appropriate organisms to access the synergic effects of coastal developments and beach erosion under different morphodynamic regimes. On dissipative beaches, density and mean crab size increased with moderate erosion, attributed to the effects of space loss, which might increase territorial competition, favoring the remaining larger individuals. However, mean size and density decreased with high erosion given the more intense reduction in the abundance of large-sized crabs living in up-shore habitats. Mean crab size also decreased in the presence of coastal development while crab density did not vary with loss of backshore habitats occupied by larger individuals. On reflective beaches, both density and crab size decreased with coastal development; the crab size decrease recorded under moderate erosion was more evident in the presence of coastal development. Under high erosion, mean crab sizes declined, reflecting those under low erosion conditions. Overall, populations on reflective beaches appeared more resilient to extreme erosion. Notwithstanding, coastal developments affected population structure across all beach types, and especially in areas subjected to high erosion, exhibiting a synergic effect. We predict that, in combination, these stressors may lead to functionally extinct populations where conditions necessary for individuals to reach sexual maturity (i.e. occurrence of only small-sized and immature individuals) are not met. Thus, the connectivity between water, beach compartments and dunes/coastal plain, on both local and regional scales, may be essential to maintain viable and connected populations of ghost crabs. Further, our results strongly suggest that both size and density (complemented with crab abundance) must be considered equally important and in combination in future efforts to assess anthropogenic stressors on ghost crab populations and when guiding conservation strategies and policies to prevent their local and regional extinctions.

Geomorphological and hydro-oceanographic analysis related to the characteristics of marine debris on the south coast of Yogyakarta, Indonesia

Bantul Regency in Yogyakarta has a shoreline of 16.85 km and is famous for its beach attractions, including Baru and Samas beaches. In Bantul, the Progo river is also recorded in the top 20 rivers globally, contributing to plastic waste pollution in coastal areas. Therefore, the problem of marine debris in Bantul is a serious matter because it can impact the environment and the tourism sector. However, marine debris characteristics in Bantul are still poorly understood. This research aims to determine the characteristics of meso- and macro-sized marine debris, its source and transportation, and the geomorphic and hydro-oceanographic processes that may affect it. A combination of geospatial analysis of high-resolution aerial photographs, field surveys with the transect method, and GIS approaches are used to achieve those objectives. Research shows that the marine debris found at Baru and Samas beaches in Yogyakarta is 149 pieces and 95 pieces, respectively. Macro-sized marine debris was dominantly found in Samas (80%), and meso-sized marine debris was dominantly found in Baru (67%). The total mass of marine debris in Baru and Samas beaches is 129 g and 1722 g, respectively. The vast amount of marine debris and smaller size in Baru is thought to have originated from land and was carried away by fluvial processes in the wider (2462.08 km2) and more elongated (Rb: 0.355) Progo watershed. Meanwhile, the larger mass of marine debris at Samas may be caused by the reflective beach typology (ε: 52.86), which can carry a higher abundance of marine debris.

Facies model, cementation and sedimentary evolution of a 20th-century beach and beachrock: The Gorrondatxe wave and tidal coastal system (NE Spain)

Lithology, bedding, and sedimentary structures of the Gorrondatxe coastal and beach system show an upper shoreface around the low-water level and containing the coarsest grain sizes; a foreshore in the main intertidal zone, which is mainly composed of sands with minor gravels and a distinctive low-angle, seaward-dipping, planar-parallel lamination; and a backshore zone with a mixture of marine-derived sands (washover) and non-marine sands and muds (aeolian, subaerial ponds) above the high-tide water level. The facies model shows a wave-dominated, mesotidal, composite beach with a fining-upwards and aggradational trend. Over the 20th century, a beachrock developed in this area as a result of heavy-industry waste dumping (steel industry) off the coast, which later became attached to the coast. There are a variety of cements and degrees of lithification in the beachrock, suggesting that the beachrock-related processes, although coetaneous, were not similar in all these zones and that different cements developed at the same time. Sand cementation can be used to recognize such facies in the stratigraphic record or in well cores, when other kinds of data are not available. The upper shoreface sandstones are hard and well-cemented, with a whitish circumgranular aragonite cement and good intergranular porosity; the foreshore sands are medium-hard, with a brown, irregular, aragonite needle cement, which shows higher intergranular porosity; finally, the backshore sands are only lightly cemented, with a brown aragonite and rhombohedral calcite cement, with the highest intergranular porosity. SEM images show the presence of Coccus-type bacteria in all the different facies and zones; these are the best proof of metabolic activity, probably of ureolytic bacteria, in the origin of all these cements. Over the course of the 20th century, Gorrondatxe evolved from a formerly dissipative, ridge and runnel beach to an active, aggrading and prograding, reflective beach, and finally to an inactive beach prone to erosion. The change to a reflective profile and the cementation of the beachrock indicate that anthropic offshore inputs were rapidly recycled into the beachface. Another major change occurred when waste discharges ended, and the former sediments and beachrock started to be eroded to their current state.

The efficacy of benthic indices to evaluate the ecological quality and urbanization effects on sandy beach ecosystems

Benthic indices have been widely used across different coastal ecosystems to assess ecological quality and detect anthropic impacts, but very few studies investigated their effectiveness on sandy beaches. Here, we evaluated and compared the efficacy of 12 assemblage-based benthic indices in assessing ecological quality in beaches, across a gradient of anthropic pressure and natural variability in 90 sandy beach sites. Overall, when sandy beaches were considered collectively, benthic indices had a poor performance in identifying decreases in ecological quality with increasing urbanization. However, when each morphodynamic type was evaluated separately, a few indices, especially those that were calibrated by reference conditions (i.e., M-AMBI, BAT, and BEQI-2), showed promising results for dissipative, and to a lesser extent, intermediate beaches. For reflective beaches, indices performed poorly, likely a reflection of the stronger natural disturbance these beaches are subjected to. Among functional indices, richness was found to be lower in urbanized beaches, but only in dissipative ones. Overall, our results show that benthic indices have the potential to be incorporated in sandy beach management and monitoring programs, especially for dissipative and intermediate beaches. For reflective beaches, given the early stage of studies with benthic indices in beaches, more research is needed to corroborate the observed patterns.

Rip current and channel detection using surfcams and optical flow

Rip currents are a common, naturally occurring surf-zone hazard that pose a risk to beach patrons. This study presents a remote-sensing-based algorithm to detect rip currents and rip channels. Optical flow-based computer vision methods are implemented to analyze large data sets and the automatic detection of these features. Surfcam video was collected from dissipative (La Jolla, CA), intermediate (Long Beach, NY), and reflective beaches (Pensacola Beach, FL) to demonstrate the efficacy of the methods. A clustering technique using the dominant wave period was implemented to transition from detected offshore movements to rip currents. The methods presented in this paper were used to detect 20,327 rip currents and 1,100 rip channels. The average accuracy for rip current and rip channel detection was 67.3% and 96.2%, respectively. The remote-sensing-based detection methods can be adapted for use on other video-based equipment and, with additional modifications, can be implemented in an operational capacity.

Relationship between beach morphodynamics and body traits in a sand-dwelling wolf spider

Sandy beach macrofaunal communities are mainly structured by the independent response of species to the harsh physical environment. The theoretical framework for sandy beach ecology has been mainly developed on the basis of the outstanding role of morphodynamic factors on resident fauna in this narrow land-sea interface. In the case of supralittoral species, the habitat safety hypothesis (HSH) predicts an increase in body size and weight (among several individual and population attributes) from dissipative beaches (fine sand, gentle slope) to reflective beaches (coarse sand, steep slope). Spiders are relevant components of coastal ecosystems due to their strict dependence on prey availability and their carnivore condition; however, the HSH has never before been tested in this taxonomic group. We studied the relationship between beach morphodynamics and body size, weight and body condition of the wolf spider Allocosa marindia. We performed simultaneous collections of adults of A. marindia in two contiguous estuarine beaches with contrasting morphodynamics. As males were scarce, we measured and weighed only females. In agreement with predictions of the HSH, individuals were larger and heavier at the reflective beach. Individual size, weight and body condition were higher at the beginning of the reproductive period. Reflective beaches would act as more benign environments, providing secure microhabitats for the individuals and their potential prey, while affecting positively body traits during development. Our results provide the first formal testing of the HSH in a sand-dwelling spider on beaches with contrasting morphodynamics.

Unravelling the role of local and large-scale factors in structuring sandy beach populations: the wedge clam Donax hanleyanus

Changes in the structure and dynamics of sandy beach macrofaunal populations result from the simultaneous action of local and regional factors acting synergistically. This is particularly noticeable in transitional interfaces between freshwater and marine ecosystems, where large-scale gradients affect local beach morphodynamics and resident fauna. The wedge clam Donax hanleyanus occurs on beaches with contrasting morphodynamics along the salinity gradient generated by the Rio de la Plata estuary. We conducted sampling surveys to determine a fine-grained comprehensive coverage of the species’ distribution in Uruguay to assess the concurrent effects of large-scale variations in salinity and local beach morphodynamics on wedge clam populations along 400 km (16 sandy beaches) over 2 yr. The main factor controlling wedge clam occurrence was salinity, overriding the effects of local habitat features. On beaches where the species was present, total abundance was higher on oceanic dissipative shores, which also harbored a higher abundance and relative representation of recruits. Recruitment was almost lacking in reflective beaches. However, biomass of adults with larger body sizes prevailed on reflective beaches, suggesting a scaling of abundance to body size and potential density-dependent effects. In this metapopulation, estuarine beaches are sinks, whereas oceanic beaches act as source habitats. We concluded that large-scale gradients generated by salinity variations translated into local population patterns (distribution, abundance and population structure) and processes (recruitment), which were secondarily driven by local morphodynamics. The relative importance of pre- and post-settlement processes across the morphodynamic spectrum from reflective to dissipative beaches has yet to be elucidated.

Granulometric dynamics of the coastal sediments of the Central West coast of India: Insight into morpho-tectonic influences on the beach processes

Beach morphologies, primarily include shape, surface changes/variation, and beach volume along with slope, are very dynamic and believed to be largely controlled by waves and currents (Komar, 1998). Contrary to this general notion, results presented in this paper suggest a strong control of the local morpho-tectonic frame-work on foreshore sedimentation. In the 20 km long study area between Bhatkal on the north and Uppunda in the south, foreshore morphology range from reflective and dissipative to intermediate types, but nearshore hydrodynamic regime is similar. The inland morpho-tectonic frame-work reveals graben and horst-like structures. The foreshores bordering these grabens and horsts are dissipative and reflective respectively, have distinctly different granulometric dynamics and sedimentation processes, whereas an intermediate type between the dissipative and the reflective show a large seasonal variability in terms of beach width and slope. The foreshore profile modification indicated that the reflective beaches remained reflective and the dissipative beaches remained dissipative throughout the year, despite the large variation in the wave energy condition from monsoon through post-monsoon to pre-monsoon. Spit growth is observed only in the dissipative beach. Granulometric dynamics in all the three types of beaches show distinct differences. The reflective beaches show significant fluvial characteristics of sediments in all the seasons, dissipative beaches show minor fluvial characteristics and the intermediate beaches show significant fluvial characteristics only during the monsoon seasons. Sediment transport process in the reflective beaches is dominantly by rolling process, in the dissipative beaches suspension is the dominant mechanism, and in the intermediate type beaches a large range from suspension to rolling is observed. Sediments in the beaches are negatively skewed through symmetrical to positively skewed in reflective beaches, while in dissipative beach negative skewness is dominant. Integration of the tectonic framework, beach morphology and granulometric dynamics suggest that temporal and spatial variations in textural characteristics are related to a strong morpho-tectonic control rather than seasonal variations in wave energy condition.

Arthropodofauna richness and abundance across beach–dune systems with contrasting morphodynamics

The across-shore distribution of arthropods in two Uruguayan sandy beach–dune​ systems with contrasting morphodynamics was investigated. A deconstructive analysis was performed to describe faunal changes from the dunes to the shoreline. The Habitat Safety Hypothesis (HSH), which states that sandy beach supralittoral species are more abundant in the backshore of reflective beaches than in dissipative ones, was assessed. A hypothesis that predicts more diverse and abundant supralittoral and dune insects and arachnids in dissipative beaches was also tested. Sampling was performed simultaneously in both beaches with pitfall traps that were kept active for 24 h at three transects that included 17 sampling levels. The reflective beach presented significantly higher elevation, sand temperature, grain size and sorting, and lower sediment compaction and moisture than the dissipative one. Total abundance of arthropods was significantly higher in the reflective beach, supporting the HSH. However, the deconstructive analysis revealed different patterns in the across-shore distribution, diversity and abundance among taxa. Crustaceans, coleopterans and dipterans exhibited higher abundance in the backshore of the reflective beach, whereas acarines were more abundant in the dunes of the dissipative beach. Ants were similarly abundant in the dunes of both beach types. Species diversity did not differ between beaches and was higher in the dunes than in the backshore. The higher abundance observed in the backshore of the reflective beach supports the HSH, reinforcing the idea that the backshore of reflective beaches can be a safer zone not only for beach crustaceans inhabiting this beach fringe, but also for some insects (coleopterans and dipterans). Other arthropods (acarines) inhabiting the dunes were more abundant in the dissipative beach. The similar abundance of ants found in both beaches suggests that dunes offer suitable microhabitats for them, overriding the effects of beach morphodynamic factors.

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.

Simulating Destructive and Constructive Morphodynamic Processes in Steep Beaches

Short-term beach morphodynamics are typically modelled solely through storm-induced erosion, disregarding post-storm recovery. Yet, the full cycle of beach profile response is critical to simulating and understanding morphodynamics over longer temporal scales. The XBeach model is calibrated using topographic profiles from a reflective beach (Faro Beach, in S. Portugal) during and after the incidence of a fierce storm (Emma) that impacted the area in early 2018. Recovery in all three profiles showed rapid steepening of the beachface and significant recovery of eroded volumes (68–92%) within 45 days after the storm, while berm heights reached 4.5–5 m. Two calibration parameters were used (facua and bermslope), considering two sets of values, one for erosive (Hm0 ≥ 3 m) and one for accretive (Hm0 < 3 m) conditions. A correction of the runup height underestimation by the model in surfbeat mode was necessary to reproduce the measured berm elevation and morphology during recovery. Simulated profiles effectively capture storm erosion, but also berm growth and gradual recovery of the profiles, showing good skill in all three profiles and recovery phases. These experiments will be the basis to formulate event-scale simulations using schematized wave forcing that will allow to calibrate the model for longer-term changes.

Estimation of Irregular Wave Runup on Intermediate and Reflective Beaches Using a Phase-Resolving Numerical Model

Accurate wave runup estimations are of great interest for coastal risk assessment and engineering design. Phase-resolving depth-integrated numerical models offer a promising alternative to commonly used empirical formulae at relatively low computational cost. Several operational models are currently freely available and have been extensively used in recent years for the computation of nearshore wave transformations and runup. However, recommendations for best practices on how to correctly utilize these models in computations of runup processes are still sparse. In this work, the Boussinesq-type model BOSZ is applied to calculate runup from irregular waves on intermediate and reflective beaches. The results are compared to an extensive laboratory data set of LiDAR measurements from wave transformation and shoreline elevation oscillations. The physical processes within the surf and swash zones such as the transfer from gravity to infragravity energy and dissipation are accurately accounted for. In addition, time series of the shoreline oscillations are well captured by the model. Comparisons of statistical values such as R2% show relative errors of less than 6%. The sensitivity of the results to various model parameters is investigated to allow for recommendations of best practices for modeling runup with phase-resolving depth-integrated models. While the breaking index is not found to be a key parameter for the examined cases, the grid size and the threshold depth, at which the runup is computed, are found to have significant influence on the results. The use of a time series, which includes both amplitude and phase information, is required for an accurate modeling of swash processes, as shown by computations with different sets of random waves, displaying a high variability and decreasing the agreement between the experiment and the model results substantially. The infragravity swash SIG is found to be sensitive to the initial phase distribution, likely because it is related to the short wave envelope.

Simulating wave runup on an intermediate–reflective beach using a wave-resolving and a wave-averaged version of XBeach

The prediction of wave runup, as well as its components, time-averaged setup and the time-varying swash, is a key element of coastal storm hazard assessments, as wave runup controls the transitions between morphodynamic response types such as dune erosion and overwash, and the potential for flooding by wave overtopping. While theoretically able to simulate the dominant low-frequency swash, previous studies using the infragravity-wave–resolving model XBeach (XBSB) have shown an underestimation of the observed swash variance and wave runup, which was in part related to the absence of incident-band swash motions in the model. Here, we use an incident-band wave-resolving, non-hydrostatic version of the XBeach model (XBNH) to simulate wave runup observed during the SandyDuck '97 experiment on an intermediate–reflective sandy beach. The results show that the XBNH model describes wave runup and the individual setup and swash components well. We subsequently examine differences in wave runup prediction between the XBSB and XBNH models and find that the XBNH model is a better predictor of wave runup than XBSB for this beach, which is due to better predictions of both the incident-band and infragravity-band swash. For a range of beach states from reflective to dissipative it is shown that incident-band swash is underestimated by XBSB relative to XBNH, in particular for reflective conditions. Infragravity-band swash is shown to be lower in XBSB than XBNH for most conditions, including dissipative conditions for which the mean difference is 16% of the deep water wave height. The difference in infragravity-band swash in XBNH relative to XBSB is shown to mainly be the result of processes occurring outside the swash zone, but approximately 15% of the difference is caused by explicitly resolving incident-band wave motions within the swash zone, such as swash-swash interactions, which inherently cannot be simulated by wave-averaged models.

Patterns in diversity and composition of the microbenthos of subarctic intertidal beaches with different morphodynamics

Diversity and composition of benthic diatom algae and ciliates were studied at several beaches along the White and Barents seas: from highly exposed, reflective beaches with coarse-grained sands to sheltered, dissipative silty-sandy flats. For diatoms, the epipelic to epipsammic species abundance ratio was significantly correlated with the beach index and mean particle size, while neither α-diversity measures nor mean cell length were related to beach properties. In contrast, most of the characteristics of ciliate assemblages (diversity, total abundance and biomass, mean individual weight and percentage of karyorelictids) demonstrated a strong correlation to beach properties, remaining low at exposed beaches but increasing sharply in more sheltered conditions. β-diversity did not correlate with beach properties for either diatoms or ciliates. We suggest that wave action and sediment properties are the main drivers controlling the diversity and composition of the intertidal microbenthos. Diatoms and ciliates, however, demonstrated divergent response to these factors. Epipelic and epipsammic diatoms exhibited 2 different strategies to adapt to their environments and therefore were complementarily distributed along the environmental gradient and compensated for each other in diversity. Most ciliates demonstrated a similar mode of habitat selection but differed in their degree of tolerance. Euryporal (including mesoporal) species were relatively tolerant to wave action and therefore occurred under a wide range of beach conditions, though their abundance and diversity were highest in fine, relatively stable sediments on sheltered beaches, whereas the specific interstitial (i.e. genuine microporal) species were mostly restricted to only these habitats.