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Estuaries have been shown to be potential hotspots of microplastic accumulation, but the hydrodynamic conditions and particle properties that control this process need further investigation. We have designed a series of numerical particle-tracking experiments to examine the sensitivity of retention in estuaries to particle size, particle density and varying tides and freshwater flow. At the end of the simulation, over 90 % of sinking particles are retained in the estuary, and the retention rate is further increased by high river runoff. In contrast, increased river discharge increases the number of marginally-buoyant (i.e. density close to estuarine water) particles that escape the estuary. Larger particle size tends to limit the downstream transport of sinking particles but can facilitate the transport of marginally-buoyant particles. Tidal asymmetry, vertical turbulent mixing and the vertical structure of the subtidal circulation are proposed as the underlying mechanisms controlling the fate of particles. • Over 90 % of sinking microplastics are likely to be retained in an estuary. • Freshwater input facilitates the sinking and retention of heavy microplastics. • Subtidal current due to the negative buoyancy of freshwater increases retention. • Particles with density close to estuarine water have the greatest chance of escape. • Competition between sinking and mixing a major control on the fate of microplastics [ABSTRACT FROM AUTHOR]

As plastic pollution continues to accumulate at the seafloor, concerns around benthic ecosystem functionality heightens. This research demonstrates the systematic effects of polyester microfibers on seafloor organic matter consumption rates, an important benthic ecosystem function connected to multiple reactions and processes. We used a field-based assay to measure the loss of organic matter, both with and without polyester microfiber contamination. We identified sediment organic matter content, mud content, and mean grain size as the main drivers of organic matter consumption, however, polyester microfiber contamination decoupled ecosystem relationships and altered observed organic matter cycling dynamics. Organic matter consumption rates varied across horizontal and vertical spaces, highlighting that consumption and associated plastic effects are dependent on environmental heterogeneity at both small (within sites) and larger (between sites) scales. Our results emphasize the important role habitat heterogeneity plays in seafloor organic matter consumption and the associated effects of plastic pollution on ecosystem function. • Polyester fiber alters drivers of seafloor organic matter cycling. • Polyester fiber breaks coastal, benthic ecosystem relationships. • In-situ tools of spatial heterogeneity and Rapid Organic Matter Assay (ROMA). • Environmental and ecological context are vital in study design and interpretation. [ABSTRACT FROM AUTHOR]

Estuaries can act as plastic retention hotspots, but the hydrodynamic controls on retention are not well understood. This study investigates the retention of river-sourced buoyant plastics in a well-mixed estuary, the Waitematā Estuary, using validated numerical simulations of floats with different tides, winds, and freshwater discharge. The proportion of floats grounded on the shore in all seven simulations is higher than 60 % and over 90 % in five simulations after ten days. <20 % of the floats leave the estuarine mouth in any of the simulations. An increase of two orders of magnitude in freshwater discharge doubles the likelihood for floats to reach the lower estuary. However, we find increased freshwater discharge doubles the lateral circulation towards the shore and results in similar proportions of grounding (90 %) as the low discharge cases. These findings challenge the conventional view that plastics preferentially enter the open ocean after high river discharge. • <20 % of simulated floats escape the estuarine mouth regardless of the tides, winds and freshwater discharges. • Neap tides lead to a higher proportion of grounded floats while more floats exit the estuarine mouth during spring tides. • Increasing freshwater discharge by two orders of magnitude leads to similar numbers of floats being retained in the estuary. • Clean-ups are effective to prevent plastic transport to the ocean due to the high retention rate in well-mixed estuaries. [ABSTRACT FROM AUTHOR]

We describe the coupled biotic and abiotic dynamics in intertidal environments using a point model that includes suspended sediment deposition, wave- and current-driven erosion, biofilm sediment stabilization, and sediment production and stabilization by vegetation. We explore the effects of two widely different types of vegetation: salt-marsh vegetation and mangroves. These two types of vegetation, which colonize distinct geographical areas, are characterized by different biomass productivities and stabilization mechanisms. We show that changing vegetation and biofilm properties result in differing stable states, both in their type and number. The presence of the biofilm exerts a dominant control on the tidal flat (lower intertidal) equilibrium elevation and stability. Vegetation controls the elevation of the marsh platform (i.e., the upper intertidal equilibrium). The two types of vegetation considered lead to similar effects on the stability of the system despite their distinct biophysical interactions. [ABSTRACT FROM AUTHOR]

We present results from laboratory experiments on flow through submerged arrays of rigid cylinders embedded in a sandy bed. Using rigid, cylindrical elements to mimic vegetation and benthos, we account for only the physical effects resulting from their presence, eliminating biological factors, such as biofilms and root systems. In line with previous findings, rigid arrays modify the flow mean and turbulent velocity statistics. However, even if the flow speed is significantly damped within dense arrays, the amount of sediment that gets lifted into suspension increases as the density of the array increases due to array– and cylinder-scale turbulence. We present a first attempt to provide predictive relationships of suspended sediment concentration using an alternative approach for the Shields parameter with an empirical coefficient to account for turbulence generated by submerged arrays of rigid cylinders. A similar analysis, using a ratio of populated to non-populated Shields parameter, is conducted to predict resuspension as a function of array density. [ABSTRACT FROM AUTHOR]

Buoyant plastics enter estuaries largely from urban streams and an unknown fraction is retained before further transport to the open ocean. Plastic drifters were launched in a well-mixed estuary to simulate the movement of surface buoyant plastics. Two experiments were conducted, one during spring tides and one during neap tides, both with similar river flows and winds. Stronger tidal currents during spring tides resulted in larger dispersion and further downstream transport of the drifters. Half of the drifters were grounded within two tidal cycles. During the neap experiment, even more of the drifters (87%) were retained in the estuary. The grounding of such a high proportion of drifters suggests that much of the plastic pollution in estuaries of this type remains close to the riverine source. These findings imply that local clean-up programs removing grounded litter can reduce over half of the plastic pollution input to these estuaries. • Between 50%–80% of drifters released in the upper estuary grounded within two tidal cycles. • Drifters dispersed more widely and travel further downstream during spring tides. • Drifters were more likely to ground during neap tides with less dispersion. [ABSTRACT FROM AUTHOR]

We extend a numerical model to explore the morphodynamics of intertidal flats, with a specific focus on the sorting dynamics of sand and mud. We investigate the effect of tidal currents, wind waves, sediment properties, external sediment supply, flocculation and initial bed composition on the cross-shore profile shape and sediment sorting of intertidal flats. Consistent with existing analytical theories and benchmark simplified numerical solutions, the equilibrium cross-shore profile of intertidal flats simulated by the extended model is convex-up when tidal currents dominate and it progressively becomes concave-up when the strength of wind waves increases. The equilibrium profile is influenced by the external sediment supply which can lead to the seaward advance of intertidal flats. In line with field observations, mud tends to deposit on the upper intertidal flats when wind waves are relatively weak, while sand is mainly distributed on the middle and lower tidal flats. When wind waves are strong, both sand and mud are more easily resuspended and eroded, resulting in a noticeably concave-up profile near the high water mark. The initial bed composition (e.g., percentage of mud and sand fractions) is also found to play an important role: the intertidal flat is more convex-up in a muddier environment. Numerical modeling demonstrates that sediment properties (e.g., critical shear stress for erosion, settling velocity) and flocculation can pronouncedly influence the sediment sorting dynamics by modifying the initiation threshold and the advection distance of entrained sediments. Application of the extended model to a natural study site indicates a qualitative agreement with field observations. [ABSTRACT FROM AUTHOR]

A three-year dataset (2007–2010) of shoreline and sandbar positions derived from video observations of an open sandy beach (Biscarrosse, France) is analyzed, to explore the impact of storms on the seasonal shoreline dynamics. The results indicate that a clear seasonality is observed in the offshore significant wave height and in the occurrence of ‘winter storm’ events that are defined as periods with significant wave height greater than 4 m lasting at least 12 h. Data indicate that the range of variation of the inner sandbar positions (120 m) is two and a half times larger than the range of variation of the shoreline position. Correlation analyses suggest that the offshore conditions do not conclusively explain the position of the inner bar. Shoreline positions show a clear seasonal pattern, displaying a stable position occurring in February and July, providing evidence of seasonal-recovery although analysis of storm activity indicates that the number and intensity of storms is highly variable over the three years. The Biscarrosse data show that rapid erosion can be observed also under moderate conditions, and that beach recovery after the storm season can be relatively rapid. [ABSTRACT FROM AUTHOR]

Abstract: Applying complex systems perspectives to geomorphic systems leads to the conclusion that cause and effect in landscape systems does not always apply in the ways that common sense and traditional assumptions would suggest. Geomorphologists have long thought that events must have causes and that landscape structures exist where they do for particular reasons. In addition, since the rise of process geomorphology, geomorphologists have often assumed that small-scale processes directly cause large-scale, long-term landscape evolution; that for understanding or predicting the large-scale behaviors, the details of the small-scale processes matter; and that large-scale processes do not directly cause behaviors at much smaller scales. However, in self-organized systems, autogenic events can arise from feedbacks internal to the system, without any variation in the forcing to cause the event. Similarly, structures within self-organized patterns in the landscape can emerge spontaneously, even though there may not be any pre-existing heterogeneity to cause the localization of the structure. In addition, cause and effect can operate from large scales to small ones as well as the reverse, and interactions that emerge at larger scales can determine the characteristics of the landscape, independent of the details of the small-scale processes. To exemplify these points, we will use research on ‘sorted bedforms’, striking shallow seabed grain-sized sorted patterns on scales ranging from tens of meters to kilometers. The stripes of coarse sand or gravel that are segregated from intervening fine-sand domains were originally ascribed to hypothesized, spatially focused currents. However, more recent modeling and field observations point to a self-organization mechanism in which the locations of the features do not correspond with any heterogeneity in the forcing or antecedent conditions. Very recent modeling work shows that regionally the pattern can spontaneously break down and reform, without any corresponding change in the forcing. Experiments with different approaches to modeling these features, and very different ways of representing the small scale processes, tend to cause essentially identical behavior and characteristics at the scale of the pattern—suggesting that emergent interactions at the large scale more directly explain, or cause, the phenomena than do the small scale processes. Finally, as for many systems, behaviors at small scales are strongly influenced by larger scale behaviors. We also use select examples from a range of landscape-evolution studies to contrast predictions made using traditional assumptions about cause and effect from those made using a complex-systems approach. [Copyright &y& Elsevier]

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]

Abstract: Tidal network morphodynamics is an active field of research and advances achieved over the last decade, particularly with respect to laboratory experiments and numerical modelling, have lead to fundamental insight about their functioning. We address how these advances have specifically contributed to the understanding of tidal network functioning, including the interaction between physical and biological processes. We discuss how the prediction of the long-term evolution of tidal networks is still limited and we focus on how it is hampered by three specific challenges. We first discuss the approach to long-term predictions, then focus on the coupling between physical and biological processes, and finally attempt to introduce the role of anthropic drivers in the evolution of these systems. [Copyright &y& Elsevier]

Abstract: We integrate published data sets of field and laboratory experiments of wave ripples and use genetic programming, a machine learning paradigm, in an attempt to develop a universal equilibrium predictor for ripple wavelength, height, and steepness. We train our genetic programming algorithm with data selected using a maximum dissimilarity selection routine. Thanks to this selection algorithm; we use less data to train the genetic programming software, allowing more data to be used as testing (i.e., to compare our predictor vs. common prediction schemes). Our resulting predictor is smooth and physically meaningful, different from other machine learning derived results. Furthermore our predictor incorporates wave orbital ripples that were previously excluded from empirical prediction schemes, notably ripples in coarse sediment and long wavelength, low height ripples (‘hummocks’). This new predictor shows ripple length to be a weakly nonlinear function of both bottom orbital excursion and grain size. Ripple height and steepness are both nonlinear functions of grain size and predicted ripple length (i.e., bottom orbital excursion and grain size). We test this new prediction scheme against common (and recent) predictors and the new predictors yield a lower normalized root mean squared error using the testing data. This study further demonstrates the applicability of machine learning techniques to successfully develop well performing predictors if data sets are large in size, extensive in scope, multidimensional, and nonlinear. [Copyright &y& Elsevier]

Abstract: Tidal embayments are characterized by a wide variety of landscape features, often including either complex tidal channel networks or extensive flood-tidal deltas. The origin of these features and the influence of hydrodynamic drivers and initial geological setting on their long-term characteristics are essentially unexplored. A model was applied to simulate the long-term morphological evolution of tidal embayments, with the purpose of providing insight into the environmental conditions that lead to the differences in tidal embayment morphology. Numerical simulations indicated that the interaction between hydrodynamics, sediment transport, and the evolving topography gives rise to the formation of channel networks. The tidal range and the depth of the initially unchannelized tidal basin controlled the way in which the morphology evolved and determined the timescale over which channels and intertidal areas developed. Channel network formation occurred more rapidly when the tidal range increased and/or when the initial basin depth decreased. Tidal basins with a large initial depth showed the development of a flood-tidal delta and for these deep basins channel incision could remain absent over long timescales. Both tidal range and initial bathymetry affected final basin hypsometry and channel network characteristics, including the channel density and the fraction of the basin occupied by the channels. All the simulated morphologies, with different combinations of the tidal range and depth of the basin, evolved towards a state of less morphodynamic activity for which the relative intertidal area was proportional to the ratio of tidal amplitude to basin depth. [Copyright &y& Elsevier]

Abstract: Using a detailed set of hydrodynamic and suspended-sediment observations, we developed data-driven algorithms based on Boosted Regression Trees and Artificial Neural Networks to predict suspended-sediment reference (near-bed) concentration using water depth, wave-orbital semi-excursion, wave period and bed-sediment grainsize as inputs. With one exception, the response of the data-driven algorithms was physically sound; the exception was the response to water depth. Outside of the range covered by the data, predictor performance could not be assessed and is not necessarily reliable. Boosted Regression Trees provide the best predictor of suspended-sediment reference concentration and have a clear explanatory power. Artificial Neural Networks provide slightly poorer predictions. Although the response of the latter is more difficult to interpret, they can be more easily included in numerical models simulating larger (in space) and longer (in time) morphodynamic behavior. Within the range of variability provided by the measurements, these algorithms outperform conventional process-based predictors. [Copyright &y& Elsevier]

Coastal sediments, where microplastics (MPs) accumulate, support benthic microalgae (BMA) that contribute to ecosystem functions such as primary production, nutrient recycling and sediment biostabilization. The potential interactions between MPs, BMA and associated properties and functions remain poorly understood. To examine these interactions, a survey of 22 intertidal sites was conducted. MP abundance, size and a suite of MP diversity indices (based on color and shape) were determined from surface sediments alongside biochemical and physical properties. MPs were detected at all sites and dominated by polypropylene (34%), polyester (18%) and polyethylene (11%). Fragment and fiber dominance (16–92% and 6–81% respectively) and color-shape category diversity varied significantly by site. Distance-based linear models demonstrated that estuary-wide, mean grain size and mud were the best predictors of MP abundance-diversity matrices, but variance explained was low (9%). Relationships were improved when the data was split into sandy and muddy habitats. In sandy habitats (<8% mud), physical properties of the bed (mean grain size, mud content and distance from the estuary mouth) were still selected as predictors of MP abundance-diversity (14% variance explained); but a number of bivariate relationships were detected with biochemical properties such as BMA associated pigments and organic matter. In muddy habitats (>8% mud), porewater ammonium was lower when fiber abundance and overall MP diversity were higher. The inclusion of porewater ammonium, organic matter content and pheophytins alongside physical properties explained a greater percentage of the variance in MP abundance-diversity for muddy habitats (21%). The results highlight the importance of examining plastic shapes and MP categories in addition to abundance and emphasize that functionally different habitats should be examined separately to increase our understanding of MP-biota-function relationships. [Display omitted] • Grain size was the main predictor for 'whole' estuary and sand habitats. • Including NH 4 + pools and organic matter (OM) improved predictions for muddy sites. • No. fragments increased with mud (up to 8%); No. fibers increased with grain size. • No. fragments higher in OM rich sites; fibers increased at low NH 4 + sites. • Interactions with sediment biochemical properties are an important consideration. Biochemical properties of field sediments influence the abundance and diversity of microplastics across sedimentary ecosystems. [ABSTRACT FROM AUTHOR]

Abstract: The nearshore region exhibits many striking morphological patterns with a variety of spatial and temporal scales. The formation of these rhythmic features has been initially ascribed, depending on the pattern in question, to spatial structures in the flow or geological constrains. These forcing templates have been hypothesized to provide the spatial structure that becomes imprinted on the shoreline or seabed morphology. More recently, new explanations for rhythmic patterns have involved interactions between fluid flow and sediment transport that create morphological feedbacks and lead to pattern self-organization. While forcing-template models do not explicitly treat transport of the sediment that makes up the pattern, self-organization models focus on the strong couplings within flow/sediment systems, and on interactions between emergent structures. We illustrate the sweeping shift from template explanations to self-organization by discussing four nearshore patterns: beach cusps, surfzone crescentic sandbars, inner-shelf sorted bedforms, and large-scale cuspate shorelines. Models involving self-organization show that local interactions between flow and sediment transport can collectively give rise to patterns with large-scale coherence and that the driving feedbacks can be associated with either topographical or grain-size composition instabilities. An approach based on self-organization also allows researchers to establish limitations in the predictability of the occurrence of rhythmic patterns and characteristics as well as to study mechanisms leading to the observed variability of pattern or lack of regularity. [Copyright &y& Elsevier]

Plastic pollution continues to seep into natural and pristine habitats. Emerging laboratory-based research has evoked concern regarding plastic's impact on ecosystem structure and function, the essence of the ecosystem services that supports our life, wellbeing, and economy. These impacts have yet to be observed in nature where complex ecosystem interaction networks are enveloped in environmental physical and chemical dynamics. Specifically, there is concern that environmental impacts of plastics reach beyond toxicity and into ecosystem processes such as primary production, respiration, carbon and nutrient cycling, filtration, bioturbation, and bioirrigation. Plastics are popularly regarded as recalcitrant carbon molecules, although they have not been fully assessed as such. We hypothesize that plastics can take on similar roles as natural recalcitrant carbon (i.e., lignin and humic substances) in carbon cycling and associated biogeochemistry. In this paper, we review the current knowledge of the impacts of plastic pollution on marine, benthic ecosystem function. We argue for research advancement through (1) employing field experiments, (2) evaluating ecological network disturbances by plastic, and (3) assessing the role of plastics (i.e., a carbon-based molecule) in carbon cycling at local and global scales. [ABSTRACT FROM AUTHOR]

Predicting recreational water quality is one of the most difficult tasks in water management with major implications for humans and society. Many data-driven models have been used to predict water quality indicators to allow a real time assessment of public health risk. This assessment is most commonly based on Faecal Indicator Bacteria (FIB), with the value of FIB compared with thresholds published in guidelines. However, FIB values usually tend to be unbalanced within water quality datasets, with small proportions of data exceeding guideline thresholds and far larger numbers that do not. This can be a limiting factor in the uptake of model predictions since, even if the overall accuracy is high, the sensitivity of the predictions can be low. To address this issue, this paper proposes an adaptive synthetic sampling algorithm (ADASYN) to generate synthetic above-threshold FIB instances and test the validity of the approach for the prediction of recreational water quality. The models in this paper are based on four machine learning techniques: k-mean nearest neighbour, boosting decision tree, support vector machine, and multi-layer perceptron artificial neural network and are applied to five different locations in Auckland, New Zealand. Aside from support vector machine, all models provide favourable predictions with relatively high sensitivity (around 75%) and overall accuracy (over 90%), indicating that both the compliant and exceedance conditions can be effectively predicted through the use of more sophisticated model training which involves artificial data. Considering the model accuracy and stability, boosting decision trees (BDT) and multi-layer perceptron artificial neural (MLP-ANN) network are the best two models and the multi-layer perceptron is the most efficient with the shortest computation time. Image 1 • Applied ADASYN to address the problem of unbalanced water quality datasets. • Ssessed the ability of machine learning models when using a balanced dataset. • Compared results at different locations using different machine learning models. [ABSTRACT FROM AUTHOR]

We develop a biomorphodynamic model to investigate sediment and vegetation dynamics on a schematic intertidal flat characterized by an initially well-mixed sand-mud mixture. Major interactions between tides, wind waves, salt marshes, sediment transport and sea level rise (SLR) are taken into account. For a bare flat under only tidal action, the model predicts a convex cross-shore profile with the surficial distribution of mud and sand on the upper and lower part of the intertidal flat, respectively. When wind waves are strong, the intertidal flat is highly eroded resulting in a concave profile near the high water mark. This behavior is pronouncedly altered when the intertidal flat is vegetated with the presence of salt marshes. Numerical results suggest that a considerable amount of mud can still remain in the vegetated region even when wave action is strong. A steeper transition zone forms at the boundary between salt marshes and bare flats because of the differential sediment deposition in the two neighboring regions. The inclusion of wind waves is found to considerably enhance the size of the marsh-edge transition zone. For the numerical experiments designed in this study, the profile shape and sediment sorting behavior of tidal flats are not significantly modified by a gradual rising sea level. However, the impacts of SLR on vegetated tidal flats are still manifold: (a) driving the landward migration of intertidal zone and salt marshes; (b) enhancing sediment erosion on intertidal flats; and (c) drowning salt marshes under limited sediment supply with the constrain of seawalls. Finally, model results suggest that organic carbon accumulation on marshlands may be enhanced with an increasing SLR rate provided that salt marshes are not drowned. [ABSTRACT FROM AUTHOR]

Abstract: We analyse a seven-year dataset (1999–2005) of shoreline and sandbar variations derived from video observations at the embayed Tairua Beach, New Zealand, to explore sandbar–shoreline coupling and to determine how this coupling is related to alongshore-averaged sandbar–shoreline separation and beach rotation. Our results quantify the coupling between the sandbar and the shoreline which is directly related to the reduced separation between the sandbar and the shoreline. Using a simple predictive shoreline model, we show that this behaviour is related to the energy of the incoming waves. Our observations are obtained from a headland-enclosed beach and show aspects of the morphological state that relate to the existence of headlands that are not considered in the Wright and Short beach state classification. Both the sandbar and shoreline at Tairua Beach rotate relatively quickly (<1month) during the winter storm events, when the storms are accompanied by strong alongshore components, gradually returning during the summer months. The sandbar–shoreline coupling length scale is controlled by this rotation, with large wavelengths occurring when the sandbar is strongly rotated. [Copyright &y& Elsevier]

Abstract: Alongshore variability in swash motions – shoreline oscillations about the mean water level on the beach face – were investigated using video images and a high-resolution morphology survey on an intermediate beach. Under mild, swell-dominated offshore wave conditions, alongshore variation of up to 78% in significant runup height Rs (defined as 4 times the standard deviation of the swash time series) was observed. This variation was predominantly driven by energy at the incident (>0.05Hz) frequencies (where most of the swash energy was observed), and, consistent with previous observations, was mainly controlled by changes in the slope of the beach face (measured at the mean swash location). However, alongshore patterning in wave breaking over the sandbar caused variation in the degree of wave dissipation along the beach and also resulted in alongshore changes to swash motions. Although alongshore changes in beach slope and wave breaking patterning over the bar were observed to be typically correlated, both were needed in a regression model to provide the best explaination of alongshore changes in Rs. At infragravity frequencies (<0.05Hz), alongshore variability was not well associated either with changes in beach slope or wave breaking patterning. Low-mode edge waves were observed in the swash measurements and their contribution to the total energy spectrum was greatest near the location where a shoal was observed, suggesting this shoal may play a role in forcing. The edge waves may have contributed to the swash variability observed at infragravity frequencies. However, in these reflective conditions, the infragravity band plays a secondary role in controlling alongshore variations to swash motions. [Copyright &y& Elsevier]

Abstract: Groundwater seepage is known to influence beach erosion and accretion processes. However, field measurements of the variation of the groundwater seepage line (GWSL) and the vertical elevation difference between the GWSL and the shoreline are limited. We developed a methodology to extract the temporal variability of the shoreline and the wet–dry boundary using video imagery, with the overarching aim to examine elevation differences between the wet–dry boundary and the shoreline position in relation to rainfall and wave characteristics, during a tidal cycle. The wet–dry boundary was detected from 10min time-averaged images collected at Ngaranui Beach, Raglan, New Zealand. An algorithm discriminated between the dry and wet cells using a threshold related to the maximum of the red, green, and blue intensities in Hue-Saturation-Value. Field measurements showed this corresponded to the location where the water table was within 2cm of the beachface surface. Time stacks and time series of pixels extracted from cross-shore transects in the video imagery, were used to determine the location of the shoreline by manually digitizing the maximum run-up and minimum run-down location for each swash cycle, and averaging the result. In our test data set of 14 days covering a range of wave and rainfall conditions, we found 6 days when the elevation difference between the wet–dry boundary and the shoreline remained approximately constant during the tidal cycle. For these days, the wet–dry boundary corresponded to the upper limit of the swash zone. On the other 8 days, the wet–dry boundary and the shoreline decoupled with falling tide, leading to elevation differences of up to 2.5m at low tide. Elevation differences between the GWSL and the shoreline at low tide were particularly large when the cumulative rainfall in the preceding month was greater than 200mm. This research shows that the wet–dry boundary (such as often used in video shoreline-finding algorithms) is related to groundwater seepage on low-sloped, medium to fine sand beaches such as Ngaranui Beach (mean grain size ∼0.27mm, beach slope ∼1:70) and may not be a good indicator of the position of the shoreline. [Copyright &y& Elsevier]

Abstract: Morphological observations (terrestrial laser scanning) and sediment analysis are used to study beach cusp morphodynamics at Melbourne Beach (Florida, USA), a moderately sloped beach characterized by fine sand. The study couples rapid high-resolution surveying with surficial sediment sampling over multiple tidal cycles. Surveys were run ~500m alongshore and sediment samples were collected intertidally over a period of 5days. Beach cusp location within larger scale beach morphology is shown to directly influence cusp growth as either gross erosional or gross accretional. Sediment characteristics within the beach cusp morphology are reported coincident with cusp evolution. Variations in particle size distribution kurtosis are exhibited as the cusps evolve, however no significant correlation is seen between grain size and position between horn and embayment. During the end of the study, a storm resulted in beach cusp destruction and increased sediment sorting. [Copyright &y& Elsevier]

Abstract: This paper introduces a semi-automatic computer algorithm designed to detect rip current channels in video imagery. As a case study, this method is applied to 3.3years of video data from an embayed beach to demonstrate the link between antecedent surf zone morphology, wave energy and up/down transitions in beach state. An objective measure of rip channel change was developed to define six significant rip reconfiguration events and relate these events to wave energy. Over the period of study no complete resets of the nearshore morphology occurred. The analysis indicates that direct correlation of rip patterns with the instantaneous wave conditions is not a useful way to demonstrate how rips and waves interact. The average wave energy over a period of ten days, combined with storm duration were good indicators of rip channel change, demonstrating that in general, beach morphology responds with a time lag to changes in forcing. Rip channels with a short cross-shore length and narrow alongshore spacing responded faster to changes in wave conditions than rips with a long cross-shore length and wider alongshore spacing. To force changes in the rip morphology, longer rip channels required wave events of higher energy and/or a longer duration. Offshore islands protect the beach under certain wave approach angles, sometimes resulting in a dual-width surf zone, which was narrow at the sheltered end and wide at the exposed end of the beach. The wider surf zone end was characterised by three dominant and persistent rip channels, whereas the narrow surf zone section contained a number of smaller rips which evolved rapidly under wave forcing. Our observations demonstrate the importance of rip channel size in controlling the response time of nearshore morphology. [Copyright &y& Elsevier]

Highlights • A correction for wave hindcasts based on satellite altimeter data is proposed. • The technique corrects simultaneous sea and swell partitions present in a sea state. • The proposed correction outperforms a similar technique applied for bulk sea states. • The technique helped identifying systematic errors of the wave hindcast. • The method could be applied worldwide to correct any partitioned hindcast. Abstract This paper proposes a buoy independent directional calibration methodology that uses satellite altimeter data to correct the simultaneous wind-sea and all swell partitions available from wave hindcasts. The proposed technique was applied to a 20-year wave hindcast in the New Zealand region and showed promising results. The method could potentially be applied worldwide to fully assess systematic errors in wind-sea and swell partitions. [ABSTRACT FROM AUTHOR]

We develop a consolidation module and merge it into a morphodynamic model to assess the role of consolidation on estuarine morphodynamics. We test the model using two settings: point models without hydrodynamic forcing to validate against two benchmark experimental datasets; and a profile model to simulate a mudflat restoration. The modelled self-weight consolidation influences the simulations by gradually reducing the bed level and decreasing the bed erodibility (i.e., increasing the critical bed shear stress). Both effects modify sediment transport processes on mudflats, leading to long-term morphodynamic effects. Depending on the initial bathymetry, the hydrodynamic forcing and the soil properties, the simulated morphological change of the restored mudflat may differ considerably with and without considering consolidation. The consolidation model developed can be utilised to assess the medium to long term effects related to estuarine development (e.g., wetland restoration) and aims to be a publicly available tool. [ABSTRACT FROM AUTHOR]

Radial sand ridges (RSRs) spread in a fan-shaped pattern over the seabed of the southern Yellow Sea along the Jiangsu Coast (China) with pronounced differences between the northern and southern channel-shoals (indicated as “NCS” and “SCS”, respectively). A depth-averaged nested numerical model is employed to analyze the tidal hydrodynamics and sediment dynamics of the RSRs. Model results show considerable regional differences in terms of tidal current vector ellipses: “eight-shaped” ellipses are typical in the NCS where rotational tidal waves dominate, while the SCS are characterized by “egg-shaped” ellipses because of the dominance of progressive tidal waves. Sand ridges tend to be elongated and straight in the NCS while short and dincontinuous in the SCS. Numerical Lagrange particles released near the ridges in the NCS tend to travel across the crest of the ridges rather than move around them as observed in the SCS. Consistently, the patterns of sediment convergence and divergence indicate that suspended sediments converge over the whole Xiaoyinsha Ridge located in the NCS, while converge to the two sides of the Hetunsha Ridge located in the SCS. Model results also highlight the importance of initial sediment compositions in determining patterns of the net sediment fluxes. The suspended sediment concentration (SSC) time series during one tidal cycle may show single or double peaks depending on the grain size and the related lag effect. Bed load transport is much smaller than suspended load. So sediment compositions should be carefully considered when simulating the SSC field, and the hydrodynamic of the morphological evolution of the RSRs at the regional scale. Overall, this study suggests that the NCS and SCS may be treated as two relatively independent geomorphological systems characterized by different tidal flows and sediment compositions. [ABSTRACT FROM AUTHOR]

The global COVID-19 pandemic has seen extended lockdowns, isolation periods and travel restrictions across many countries around the world since early 2020. Some countries, such as Australia and New Zealand, closed their international borders in early 2020 preventing researchers travelling to other parts of the world. To facilitate the exposure of our students' work, and for them to meet international researchers, as well as foster a sense of coastal community, we started a zoominar series (seminars via Zoom) in April 2020. The Coast2Coast zoominar series had therefore humble origins but we soon discovered that there was an appetite for more widely sharing science across the coastal research disciplines. The Coast2Coast zoominar grew rapidly, attracting researchers from many countries around the world who presented and attended fortnightly online seminars. In just one year and a half we had 38 presentations with roughly 1900 attendees, creating a sense of community and belonging for the researchers involved. In early 2021, two of the co-authors, Giovanni (GC) and Ana (AVC) decided to expand and take this sense of community further creating the Coast2Cast podcast series, where researchers are asked research and non-research questions. In only 7 months, the podcasts have attracted more than 3700 listeners. Importantly, while the main prerequisite was high-quality and impactful research, diversity and inclusion were also a priority in selecting and inviting speakers for the zoominars and guests for the podcast. Importantly, our survey results suggest that there is a place for online events similar to Coast2Coast and Coast2Cast in a pandemic-free future, and that the coastal community involved has greatly benefited from such initiatives. • Two new online initiatives provided unexpected benefits during the COVID-19 pandemic. • Both initiatives contributed to creating a sense of community and belonging for the researchers involved. • The main prerequisite was high-quality and impactful research. • Diversity and inclusion were considered a priority, thus increasing diversity and inclusion. • Our results suggest that there is a place for short online events in a pandemic-free future. [ABSTRACT FROM AUTHOR]

Abstract: The following is a white paper (adapted here for print) for the U.S. National Research Council''s committee on Challenges and Opportunities in Earth Surface Processes, drafted at a National Science Foundation sponsored workshop associated with the 38th Binghamton Geomorphology Symposium, “Complexity in Geomorphology,” held at Duke University in October 2007. [Copyright &y& Elsevier]

A high resolution partitioned wave hindcast of New Zealand waters is presented together with validation results against 9 buoy deployments that are representative of the local wave climate. An analysis of integrated and partitioned mean wave parameters was conducted together with a study of the correlation between wave height anomalies and atmospheric indices. A directional spatial analysis was also performed to identify and quantify wave systems that are not detectable by in situ buoys or hindcast integrated parameters. The presented study outlines a framework of how partitions can be analyzed in order to improve our understanding of the local wave climate in terms of wind-sea and swell waves. • A new hindcast of New Zealand is presented and its partitioned data is explored. • The spatial distribution of wind-sea and swells parameters was extensively analyzed. • Atmospheric indices were found to modulate wind-seas and swells in different ways. • The relationship between wind-seas, swells and spectral partitioning was depicted. • This analysis can help the understanding of other complex wave climates worldwide. [ABSTRACT FROM AUTHOR]

Coastal hazards often result from the combination of different simultaneous oceanographic processes that occur at multiple spatial and temporal scales. To predict coastal flooding and erosion, it is necessary to accurately represent hydrodynamic conditions. For this reason, here we present a stochastic, climate based wave emulator that provides the hydrodynamic conditions needed for these predictions. The emulator can generate an infinitely long data series maintaining its statistical properties at different time scales, from intra-storm to inter-annual variability, and its link to large scale climate patterns. The proposed methodology relies on the use of weather types and an autoregressive logistic regression model forced with different variables to simulate daily scale chronology. Considering the dependencies of wave conditions on the different weather types, the intra-storm chronology is solved by means of shuffling and stretching historical wave sequences. To demonstrate the replicability of this emulator worldwide, we have applied the model to 3 different locations and found good agreement when compared to the historical data. Furthermore, to illustrate and explain the strengths and limitations of the emulator, we present a different application for each of the different locations. • A new stochastic climate-based wave emulator was developed as a tool for probabilistic assessments of coastal hazards. • The emulator generates infinitely long data series maintaining historical properties at different time scales. • The methodology can be reproduced worldwide and can be adapted to generate hydrodynamic conditions under climate change. [ABSTRACT FROM AUTHOR]