Tide-dominated Beaches Research Articles

Mapping coastal resilience: a Gis-based Bayesian network approach to coastal hazard identification for Queensland’s dynamic shorelines

Coastal regions worldwide face increasing threats from climate change-induced hazards, necessitating more accurate and comprehensive vulnerability assessment tools. This study introduces an innovative approach to coastal vulnerability assessment by integrating Bayesian Networks (BN) with the modern coastal vulnerability (CV) framework. The resulting BN-CV model was applied to Queensland's coastal regions, with a particular focus on tide-modified and tide-dominated beaches, which constitute over 85% of the studied area. The research methodology involved beach classification based on morphodynamic characteristics, spatial subdivision of Queensland's coast into 78 sections, and the application of the BN-CV model to analyze interactions between geomorphological features and oceanic dynamics. This approach achieved over 90% accuracy in correlating beach types with vulnerability factors, significantly outperforming traditional CVI applications. Key findings include the identification of vulnerability hotspots and the creation of detailed exposure and sensitivity maps for Gold Coast City, Redland City, Brisbane City, and the Sunshine Coast Regional area. The study revealed spatial variability in coastal vulnerability, providing crucial insights for targeted management strategies. The BN-CV model demonstrates superior precision and customization capabilities, offering a more nuanced understanding of coastal vulnerability in regions with diverse beach typologies. This research advocates for the adoption of the BN-CV approach to inform tailored coastal planning and management strategies, emphasizing the need for regular reassessments and sustained stakeholder engagement to build resilience against climate change impacts.Recommendations include prioritizing adaptive infrastructure in high-exposure areas like the Gold Coast, enhancing flood management in Brisbane, improving socio-economic adaptive capacity in Redland, and maintaining natural defences in Moreton Bay. This study contributes significantly to the field of coastal risk management, providing a robust tool for policymakers and coastal managers to develop more effective strategies for building coastal resilience in the face of climate change.

How morphodynamic gradients shape the distribution of meiofauna and nematodes on sandy beaches of the Amazon region?

The present study analyzed how a small-scale morphodynamic gradient, based on the level of exposure to oceanic waves, shapes the spatial distribution patterns of the local meiofauna, with a special focus on the nematodes, of tropical macrotidal beaches on the Amazon coast (northern Brazil). The study focused on three sandy beaches, first compiling their physical characteristics (waves, currents and morphodynamic state), and then sampling biological and sediment samples at five different levels across the intertidal zone. Meiofauna was composed of 11 different groups, but was dominated by Nematoda. The nematode assemblage had a total of 89 genera, of which Daptonema and Theristus (both from family Xyalidae) were the most abundant on all studied beaches, at most intertidal levels. The diversity of nematode genera increased toward the low tide mark, while nematode density peaked in either the upper (on the protected and tide-dominated beaches) or intermediate levels (on the exposed, tide-modified beach). Distinct faunal zonation patterns were identified on the three beaches, which were influenced by their level of exposure to oceanic conditions, their granulometry, and the moisture of the sediment. While the variation in the characteristics of the meiofauna can be attributed to the level of exposure of beaches, horizontal distribution patterns were also closely related to habitat heterogeneity, including morphological features and freshwater inputs.

Biological and functional responses of the benthic surf zone community to different beach types

In this study, we analyzed the biological descriptors and functional traits of the benthic community inhabiting the water/bottom layer in the surf zones of three sandy beaches: a tide-dominated flat, and two intermediate beaches, from tide-modified to wave-dominated. Samples were collected seasonally in the inner surf zone by hand-towing a benthic sledge equipped with two nets, one above the other, across transects parallel to the shore, capturing the benthic community in two levels, close to the seafloor. A total of 116 species were collected, with a total of 327,678 specimens. Arthropods were 99.63% of all individuals caught across the three beaches, mainly represented by peracarid crustaceans. An important species turnover was detected along the shore, with a significant change in community composition. The biological descriptors and some functional traits vary among beaches: the total density, the density of individuals of small (5–10 mm length) and very small sizes (<5 mm length), the density of larval forms, and the presence of colonial species were higher in the tide-dominated flat (sometimes also in the tide-modified beach). More arthropods and more mobile individuals were found in those beaches, while mollusks and sedentary individuals were found in high number in the wave-dominated beach. Stratification was present across the three studied beaches, with higher densities in the near-bottom layer. In the tide-dominated beach, there was also a higher richness in this layer, with a nested community between levels. In the wave-dominated beach, similar richness was registered between levels, with a different community composition (and some differences in functional traits), indicating that some species can maintain their position close to the bottom despite the turbulent conditions experienced on this beach. Differences in wave conditions among beach types could be an important factor driving the biological descriptors and functional traits of the benthic community in surf zone ecosystems. Therefore, acknowledging their role is crucial in deciphering global patterns in surf zone biodiversity.

Spatial patterns of the gastropod Olivella minuta reveal the importance of tide-dominated beaches and the subtidal zone for sandy beach populations

The main ecological hypotheses on spatial patterns of intertidal sandy beach populations predict that they are mainly influenced by morphodynamic features, with most population parameters (e.g., number of individuals, reproductive effort, recruitment rates) increasing from wave-dominated reflective to wave-dominated dissipative beaches. Yet, these hypotheses did not take into account tide-modified and tide-dominated environments due to the lack of data from these habitats. Also, they were based on species inhabiting the intertidal and supratidal zones while those living in the intertidal–subtidalbeach gradient (marine component of the Littoral Active Zone) remain largely overlooked. We investigated differences in abundance and size of the sea snail Olivella minuta in the intertidal and subtidal zones of two beach types: a wave-dominated dissipative beach and a tide-dominated sand–mud flat. Samplings were performed at three different times (September and December 2011, and March 2012). Abundance was higher at the tidal flat, with a high number of small (young) and large (old) individuals. On the other hand, individuals from the dissipative beach mainly belonged to larger size classes. Furthermore, we observed that individuals were more homogeneously distributed in the across-shore gradient of the tidal flat, with a similar number of individuals inhabiting both intertidal and subtidal zones, whereas most individuals (especially young ones) from the dissipative beach were found in the subtidal zone. Overall, our results support the importance of beach morphodynamics as a main driver of sandy beach populations along the Littoral Active Zone and emphasize the relevance of tide-dominated environments for coastal species. Importantly, our results demonstrate the ecological role of the subtidal zone for sandy beach macrobenthic populations and the necessity of performing ecological investigations along the whole Littoral Active Zone.

Microplastics on beaches along the eastern Gulf of Thailand – A preliminary study

Several studies have shown the ubiquitousness of microplastics across ecosystems worldwide including significant amounts in beach sand. In Thailand, however, there is a lack of studies about the microplastic pollution of beaches. This study aimed to quantify microplastics at the high-tide line of 21 beaches along the eastern Gulf of Thailand. Observed amounts ranged from 420 to >200,000 counts/kg. Anthropogenic and environmental factors affect distribution and amount of microplastics. Tide-dominated beaches and beach sections protected by beachrocks exhibit higher microplastic amounts due to lesser hydrodynamics. While human activities have a visible impact, in some cases environmental factors seem to predominate. Despite effective protection efforts led by the government and NGOs, our study shows that the substantial microplastic pollution of beach sand requires a proper management system with appropriate laws and regulations, and a public awareness campaign to reduce effects of microplastics on organisms and their ecosystems.

Relating Hydrodynamic Forcing and Topographic Response for Tide-Dominated Sandy Beaches

To relate hydrodynamic forcing and topographic response for a tide-dominated sandy beach, extensive field measurements were carried out in the intertidal zone. Hydrodynamics and beach topography were monitored during a total of 12 weeks at two different study sites: one with a featureless intertidal zone and one with intertidal bars. The results of both study sites indicate that the intertidal beach grows when wave steepness is small, whereas it erodes when wave steepness is large. Spring-neap variations in tidal current direction heavily distort this trend: strong spring tidal currents transport sediment away from the beach, resulting in enhanced erosion. Tide-induced beach volume changes are on the same order of magnitude as wave-induced changes. Besides waves and tides, the effect of variations in the amount of sediment supply is substantial, with enhanced accretion when the sediment supply is large. The effect of variations in sediment supply on the intertidal beach topography is subordinate to the effect of waves and tide, though. From this study, it is concluded that larger waves are primarily erosive, but they can also enhance the natural sediment supply. Furthermore, it is found that tidal currents can be equally important as waves in shaping the beach topography, especially during spring tide on macrotidal beaches.

A Tide-Dominated Beach from the Cambro-Ordovician Cabos Formation of Northwestern Spain

Abstract: Beaches on which tidal processes play a significant role, as opposed to purely wave-dominated beaches, are little known from the rock record due to a lack of suitable sedimentological criteria and facies models. Cambrian strata of the Cabos Formation in Asturias, Spain, with a wealth of tide-generated sedimentary structures and a close similarity to modern tide-dominated beaches, provide an opportunity to advance our understanding of ancient tidal beaches. Our field-based analysis of the Bres and Taramundi members identifies three lithofacies: Facies 1—simple bedsets of fine sandstone, divided into (1A) sandstone with tabular and wedge-shape geometries and horizontal to low-angle laminae, (1B) sandstone with tabular, wedge-shape, and wave-form geometries and decimeter-scale planar cross-bedding, and (1C) sandstone with a channel form and erosional base; Facies 2—composite bedsets of mudstone and fine sandstone; and Facies 3—intraformational breccias composed of (3A) rip-up clasts, (3B) sandstone clasts, and (3C) skeletal clasts. The numerous tidal structures testify to bed-load transport by unidirectional and bidirectional tidal currents, alternating deposition from bed load and suspended load, emergence during the ebb stage of tidal cycles, tidal scour, and regular fluctuations of tidal-current velocity. In contrast, structures indicative of swash–backwash, oscillating waves, and storms are much less conspicuous. This study argues that the Cabos sandstone and mudstone accumulated on a tide-dominated, wave-influenced beach distinguished by four morphologic zones: a flat sandy supratidal beach (Subfacies 1A), a sandy intertidal beach characterized by small 2-D dunes of a ridge-and-runnel system (Subfacies 1B), cross-shore channels (Subfacies 1C), and the subtidal nearshore with a mix of mud and rippled sand (Facies 2). Rare storm processes on the tidal beach are suggested by the breccias (Facies 3). As increasingly more local examples like the Cabos are recognized in the rock record, sedimentologists can begin to construct a generalized facies model for this largely unexplored sedimentary environment.

Stability of artificial beaches in Port Phillip Bay, Victoria, Australia.

Lowe, M.K. and Kennedy, D.M., 2016. Stability of artificial beaches in Port Phillip Bay, Victoria, Australia. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 253–257. Coconut Creek (Florida), ISSN 0749-0208.This study investigates the drivers of beach morphodynamics on the highly modified fetch-limited beaches of the urbanised north-eastern coast of Port Phillip Bay in south-eastern Australia. Repetitive beach profiling, sediment characterization, and aerial photo analysis were conducted to quantify morphodynamic change across six distinct beach systems on a seasonal to annual-decadal scale. The observed morphologies contained features similar to those found on open-ocean wave-dominated and tide-dominated beaches, and included reflective unbarred beaches and intermediate beaches with low-tide terraces or transverse bar-rip systems. Sediment typically ranged from medium to coarse or very coarse in size. The consistency of wave energy across the study sites suggests that sediment size is the primary determinant of beach morphodynamic state, and the relatively low energy of Port Phillip Bay suggests that only storm conditions are energetic enough to mobilise sediment and alter beach morphology. On a seasonal scale, alongshore sediment transport is a major driver of beach change, and groynes and other coastal modifications have considerable influence on planform beach morphology. Over the medium term it appears that these beaches are eroding towards a landward position of equilibrium. With current projections of sea level rise it is expected that rates of beach erosion and sediment loss will accelerate over the coming decades, leading to an increased necessity for beach renourishment or other management interventions if wide beach profiles are to be maintained.

Wave farm impact on beach modal state

Abstract The extraction of wave energy by the Wave Energy Converters (WECs) forming a wave farm results in a milder wave climate in its lee, which can have an impact on coastal processes. The objective of this work is to determine whether the beach morphology can be altered by the operation of the wave farm, and if so, to quantify this alteration. For this purpose, we examine how the farm affects the modal state of the beach with reference to a baseline (no farm) scenario. The modal state is defined based on an empirical classification that accounts for wave conditions, tidal regime and sediment size. As a beach typically goes through different modal states, we determine the percentages of time in an average year corresponding to each state in the baseline scenario, and how these percentages are altered by a wave farm as a function of its distance from the coast. This methodology is illustrated through a case study: Perranporth Beach (UK), an area of great potential for wave energy development. High-resolution numerical modelling is used, with two levels of grid refinement. We find that the wave farm has a relevant impact on the modal state of the system, which passes from wave-dominated to tide-dominated during significant periods of time. The sensitivity analysis, involving three cases with the farm at distances of 2 km, 4 km and 6 km from the beach, showed that the farm-to-coast distance plays a major role. Thus, the shift from a wave- to a tide-dominated beach is exacerbated in the case of the wave farm closest to the coastline, with the submarine bar vanishing over long periods of time. We conclude that the presence of the wave farm drastically alters the morphological response of the beach, and that this alteration is strongly dependent on the farm-to-coast distance.

Swash zone moisture dynamics and unsaturated infiltration in two sandy beach aquifers

The intertidal zone of coastal aquifers is a dynamic region of mixing between saline surface water and fresh groundwater. Groundwater circulation in this zone is affected by complex forcing mechanisms that operate on a range of timescales and can regulate chemical fluxes to marine environments. We evaluated wave swash-induced infiltration and associated flow dynamics in the unsaturated region of two sandy beach aquifers with differing wave conditions and beach morphologies. Moisture and pressure sensors were used to measure fluctuations in water content, water table elevation, and hydraulic gradients at high frequencies (5 Hz) in the swash zone at mean lower low water, mean sea level, and mean higher high water. Water content in the unsaturated region of the swash zone responded to wave overtopping and swash infiltration, with a rapid rise in water content followed by a slower decline. Swash-induced unsaturated infiltration rates, calculated from water content response, were lowest near low tide and increased up the beachface with inflow highest near high tide at both sites, consistent with an increase in water table depth up the beach. Unsaturated infiltration was 1.6 m3/m per tidal cycle at the wave-dominated beach and 0.4 m3/m per tidal cycle at the tide-dominated beach. Saturated pore pressure measurements show that a water table mound formed as a consequence of swash infiltration that migrated up the beach during rising tide, leading to divergent seaward/landward groundwater flow. The results demonstrate the significant and spatially variable effects of wave swash on moisture dynamics in the unsaturated zone of beach aquifers, and show that these effects depend on wave conditions and beach characteristics. Results have implications for understanding transport and reaction of solutes in this biogeochemically active zone.

Uma abordagem morfodinâmica na caracterização fisica das praias estuarinas da Baia de Paranaguá, sul do Brasil

In this study, thirteen estuarine sandy beaches distributed along of Paranaguá Bay were characterized regarding its morphology, sedimentary composition, wave regime and morphodynamism. The beaches were characterized by a narrow and steep beachface fronted by a wide, very low-gradient intertidal flat. The strong influence of tidal currents seems to inhibit the intertidal flat formation at some beaches. Sedimentary composition of beachface ranged from very-well sorted fine sand (beaches near to the mouth of the bay) to poor sorted coarser sand at the inner bay, while the intertidal flat ranged from sandy to muddy sediments towards to the inner estuary. Observed waves were small (Hb< 0.25m) and of short period (T < 5s), in general, increasing with tide and decreasing towards the inner bay. Although the application of morphodynamic models has been limited by wave data quality, observed beach profile were similar to described for tide-modified and, especially to tide-dominated beaches.

Uma abordagem morfodinâmica na caracterização fisica das praias estuarinas da Baia de Paranaguá, sul do Brasil

In this study, thirteen estuarine sandy beaches distributed along of Paranagua Bay were characterized regarding its morphology, sedimentary composition, wave regime and morphodynamism. The beaches were characterized by a narrow and steep beachface fronted by a wide, very low-gradient intertidal flat. The strong influence of tidal currents seems to inhibit the intertidal flat formation at some beaches. Sedimentary composition of beachface ranged from very-well sorted fine sand (beaches near to the mouth of the bay) to poor sorted coarser sand at the inner bay, while the intertidal flat ranged from sandy to muddy sediments towards to the inner estuary. Observed waves were small (Hb< 0.25m) and of short period (T < 5s), in general, increasing with tide and decreasing towards the inner bay. Although the application of morphodynamic models has been limited by wave data quality, observed beach profile were similar to described for tide-modified and, especially to tide-dominated beaches.

Australian Beach Systems—Nature and Distribution

Abstract The Australian coast contains 10,685 beach systems, which occupy half the coast and can be classified into 15 beach types. These include six wave-dominated, three tide-modified, and four tide-dominated types which are a product of wave-tide and sediment conditions and two types which are influenced by intertidal rocks and fringing reefs. Wave-dominated beaches occupy the higher energy, microtidal southern coast exposed to persistent Southern Ocean swell. Tide-modified and tide-dominated beaches are most prevalent around the more tropical northern coast, which experiences meso-, macro-, and mega-tides and receives lower seas, as well as some sheltered and mesotidal southern locations. This article assesses the roles of waves, sediment, and tide range in contributing to beach type, particularly through the dimensionless fall velocity and relative tide range. It also describes their regional distribution, together with the occurrence of rip currents, multibar beach systems, and the influence of geol...