Relative Tidal Range Research Articles

Vulnerability of the rip current phenomenon in marine environments using machine learning models

Hidden and perilous rip currents are one of the primary factors leading to drownings of beach swimmers. By identifying the coastal areas with the highest likelihood of generating rip currents, it becomes possible to prevent fatalities and mitigate economic losses associated with these hazardous currents. Rip currents are characterized as streams of water moving towards the open sea, forming within the area where waves break, due to variations in wave-induced radiation stresses and pressure along the coastline. This study utilized nine different Machine Learning (ML) models, including M5 Model Tree (MT), Multivariate Adaptive Regression Spline (MARS), Gene Expression Programming (GEP), Evolutionary Polynomial Regression (EPR), Random Forest (RF), Support Vector Machine (SVM), Extreme Gradient Boosting (XGBoost), Adaptive Boosting (AdaBoost), and Stacked ML models, to estimate the Relative Tide Range (RTR) values for 50 southern beaches in China. Through this approach, we gathered a reliable dataset from prior research conducted on the southern coast of China. In this study, two parameters, namely dimensionless fall velocity parameter (Ω) and tide range (TR) are used to predict the vulnerability of rip current event. The results of the AI models were assessed by various statistical analyses (Correlation of Coefficient [R], Root Mean Square Error [RMSE], violin diagram, heatmap, and taylor diagram) for training and testing stages. Accordingly, the MARS model exhibited superior performance compared to other AI models in accurately predicting the RTR value. The outcomes substantiated the significant effectiveness and capability in estimating the RTR with high accuracy. Southern China coasts have relative high risk level of rip current, necessitating the attention and strategic management of this dangerous current by the beach managers.

Beach morphodynamic classification using high-resolution nearshore bathymetry and process-based wave modelling

Classification of beach morphodynamic state relies on accurate representation of breaking wave conditions, Hb (plus grain size and spring tidal range). Measured breaking wave data, however, are absent from all but a handful of sites worldwide. Here, we apply process-based wave modelling for propagating offshore waves to the breaking zone using high-resolution nearshore bathymetry, obtaining representative and accurate Hb values for multiple beaches at regional scale, and thereby derive meaningful morphodynamic classifications that accord with observed beach state. Ninety-five beaches on the north coast of Ireland were investigated, with observed beach types and states compared to predictions based on morphodynamic parameters determined using wave, tide and sediment data, obtained from field surveys and detailed numerical wave modelling. The coast is exposed to micro-through meso-tides (0.43–3.90 m) and low sea through high swell waves (Hb = 0.13–1.18 m) and is composed of fine to medium sand resulting in a full range of beach types (wave-dominated, tide-modified and tide-dominated) and most beach states, thereby providing a comprehensive field laboratory to undertake such a comparison. We found that modal beach types reside within their predicted Relative Tide Range (RTR) and modal beach states close to the predicted dimensionless fall velocity (Ω) range. The use of high-resolution nearshore wave modelling to determine Hb was deemed the most appropriate approach for deriving predicted beach classification. The work follows the investigation of the same coast by Jackson et al. (2005) who found shortcomings in relating beach types to breaker wave conditions. However, advances in inshore wave modelling and access to high-resolution nearshore bathymetry since then have enabled improved estimates of breaker height, producing more accurate results and enhancing previous work. The results highlight the need to obtain accurate estimates of Hb and Tp if they are to be used effectively in predicting beach parameters. This work therefore sets a precedence for other coastal sites worldwide where detailed nearshore bathymetry is available and Hb can be derived from process-based wave modelling, improving the classification and prediction of morphodynamic beach type and state.

Exploring RPAS potentiality using a RGB camera to understand short term variation on sandy beaches

Remotely Piloted Aircraft Systems (RPAS) is a low-cost and useful alternative to track spatial-temporal variations in a rapidly changing environment. However, there is a lack of studies on beach geomorphology characterization in association with visible spectrum reflectance potentialities. The objective of this study was to embrace this technology for coastal change detection. For this purpose, the data set samples are covering the winter season of 2019. The materials used were digital orthophotos, digital terrain models, and geomorphological parameters, such as the Relative Tide Range (RTR) and Omega (Ω). The goals are to (i) classify the beach morphodynamics; (ii) identify the berms, cusps, and rip current channels; (iii) extract RGB indexes to detect the shoreline variability; (iv) assess beach profiles and (v) evaluate the volume of sediments. The study area, Paiva beach, is located in the Northeast of Brazil, which presents significant morphodynamic variations. The results indicate three morphodynamic stages, namely: Rhythmic Bar and Beach (RBB); Transverse Bar and Rip (TBR), and Low Tide Terrace (LTT). The wave climate for the region averaged Dir of 120°, Tp of 9 s, and Hs of 1.8 m. Between June and July, the shoreline had the most significant advance with 51% of the beach extension. On the other hand, between July and August, the beach registered a considerable 88% retreat. The profiles showed a maximum variation of 1.5 m vertically on the berm, a common characteristic of winter profiles, detected in August. For the sediment volume, July and August showed erosion processes with sediment loss of 12,508.58 m3 in the south sector and accretion of 23,052.97 m3 in the north. The planimetric and altimetric mean square error were 2.7 and 4.5 cm, respectively, showing the advantage of high spatial resolution data for morphodynamic classification, and combining it to identify vegetation indexes to detect shoreline variability.

ADV-Based Investigation on Bed Level Changes Over a Meso-Macro Tidal Beach

Beach intra-tidal bed level changes are of significance to coastal protection amid global climate changes. However, due to the limitation of instruments and the disturbance induced by wave motions superimposed on water levels, it was difficult to detect the high-frequency oscillation of the submerged beach bed level. In this study, an observation, lasting for 12 days and covering the middle tide to the following spring tide, was conducted on a meso-macro tidal beach, Yintan Beach, to simultaneously detect the characteristics and influence mechanism of bed level changes at intra-tidal and tidal cycle scales. The collected data included water depth, suspended sediment concentration (SSC), waves, high-frequency three-dimensional (3-D) velocity, and the distance of the seabed to the acoustic Doppler velocimeter (ADV) probe, which were measured by an optical backscatter sensor, two Tide & Wave Recorder-2050s, and an ADV, respectively. The results showed that the tidal cycle-averaged bed level decreased by 58.8 mm, increased by 12.6 mm, and increased by 28.9 mm during neap, middle, and spring tides in succession, respectively, compared with the preceding tidal regimes. The net erosion mainly resulted from large incident wave heights and the consequent strong offshore-directed sediment transport induced by undertows. Moreover, the variations in the bed level were more prominent during a neap to middle tides than during middle to spring tides, which were jointly caused by the wave-breaking probability regulated by water depth and the relative residence times of shoaling wave, breaker, and surf zones that were determined by relative tidal range. In terms of the intra-tidal bed level, it displayed an intra-tidal tendency of increase during floods and decrease during ebb tides, i.e., the intra-tidal bed level changes were controlled by water depth, which modulated the effects of waves on sediment resuspension and vertical sediment exchange. To be specific, waves and SSC were responsible for the intra-tidal bed level changes under low-energy wave conditions, while mean current and bedform exerted important influences on the variations of the intra-tidal bed level under moderate wave conditions, which broke the foregoing interrelation between bed level, waves, and SSC. This study, therefore, emphasizes the usage of ADV measurement to investigate bed level changes in sandy coasts.

Beach morphodynamic characteristics and classifications on the straight coastal sectors in the west Guangdong

Currently beach morphodynamic classification is the most important foundation to conduct associated coastal geomorphological studies. This paper carried out beach morphodynamic classifications for 12 straight beaches on headland-bay coasts based on field survey and evaluated the applicability of the most widely used dimensional fall velocity parameter (Ω) and relative tidal range parameter (RTR). One reflective, five intermediate and six non-barred dissipative beaches were visually classified and sand size seemed to be a key factor to differentiate these beaches. The studied beaches were in relatively low wave energy environments (Hs < 1 m) and the absolute deep-water wave energy level of P0 = 3 KWm−1 was supposed to a critical threshold to characterize the applicability of the Ω and RTR parameters. These two morphodynamic parameters were applicable for the beaches with P0 &gt; 3 KWm−1 and MSR &lt; 2 m. It was found that the model of the traditional winter-and-summer profiles was not applicable in the study area in despite of distinct wave seasonality. The studied beaches were more possible to hover around a limited range due to relatively low background wave environments and variability without considering typhoon impacts, which needs further research on actual breaker wave conditions and beach morphodynamic type responses to typhoon events.

Rip current occurrence probability at selected recreational beaches along Pahang coastline

Purpose Pahang beaches draw more than thousand visitors throughout the year. From the year 2006 to 2018, more than 30 drowning and near-drowning cases were recorded mainly from rip currents. Rip currents are defined as unexpected currents that carried beachgoers away to seaward direction more than approximately 50 m from shore. The prediction of rip current development is very important for the protection of human life. This study aims to conduct preliminary survey and field works to identify rip current hazards. Design/methodology/approach The output would be an early warning preventative mitigation to public in Pahang. Beach state model, dimensionless fall velocity, littoral environment observation and relative tidal range were recorded for five recreational beaches during two different months (March and April 2018). The morphodynamic parameters such sediment fall velocity, sediment grain size and beach slope are then analysed using software PROFILER. Classification of risks was done based on beach morphodynamic model. The morphodynamics are classified as low tide bar rip, barred and low tide terrace associated with rip current, bar dissipative, reflective, non-bar dissipative, low tide terrace and ultra-dissipative. Findings Result shows three out of five recreational beaches may develop high-risk rip currents. During the first month of the survey, Batu Hitam (BH) was recorded the only one recreational beach that may develop high-risk rip current followed by Teluk Cempedak (TC) and Kempadang (KEM) as middle-risk rip current beaches, while Balok (BA) and Sepat (SEP) as low-risk rip current beaches. Different during second month of the survey, BA, BH and SEP were recorded as high-risk rip current beaches while TC and KEM as low-risk rip current beaches. Originality/value The results are consistent with beach incidents (drowning and near-drowning) reported.

The geomorphology and evolution of intermittently open and closed estuaries in large embayments in Victoria, Australia

Intermittently open and closed estuaries (IOCE) are common landforms on open-ocean microtidal coasts. They are often viewed as evolutionary end members of open estuaries where all the accommodation space has been infilled by sediment. While IOCE are typically recognised to form in wave-dominated, microtidal environments, they can also form within embayments where the relative balance between waves and tides is highly spatially, and temporally, variable. This study examines the geomorphology and infill of two such embayed IOCE in Victoria, southern Australia, in order to assess how these systems compare to their open ocean counterparts in order to gain an understanding of the boundary conditions of such landforms. It is found that IOCE’s can occur in embayments where there is sufficient energy to form a beach berm. The infill of these systems broadly follows the transgressive – stillstand pathways of open-coast systems, but the facies are modulated by the size of the catchment and open-ocean wave exposure. These boundary conditions also affect the evolution of the coastal plain in which the embayed IOCE may form and in turn the estuary planform. The entrance dynamics of these estuaries are highly variable, and it appears that they may switch between permanently open or closed states in relation to modification of boundary conditions such as roughness. It is inferred that the relative tidal range (RTR) of the marine environment at the estuary mouth is an important determination of entrance condition with the observed systems being close to the maximum RTR value on the open coast at which these landforms can exist.

Morphodynamics of a wave dominated embayed beach on an irregular rocky coastline

Abstract Wave-dominated embayed beaches on irregular rocky coastlines are highly appreciated for their landscapes and tourism potential. Yet our understanding about the interaction of the oceanographic processes with the geological inheritance in this type of beaches still needs further investigation to better understand their natural balance. In this study, we apply the classical approach of morphodynamics to describe for the first time the variations in the Boiçucanga beach morphology, an embayed beach located in São Sebastião City on an irregular rocky coastline that is well known for its beautiful beaches embedded in the valleys of Serra do Mar. Field surveys were performed over 15 months, between April 2008 and September 2009, seeking to evaluate the interactions among the morphology, sediments and hydrodynamic characteristics at Boiçucanga. All data generated during the field surveys have supported the application of the following morphodynamic models: Classification of morphological beach stages [O]; Number of nearshore sandbars [B*]; Relative tide range [RTR]; Beach exposure on embayed coasts [Ro/a and ß]; and Embayment beach scaling parameter [d] to determine the geomorphological behavior of the beach on monthly and annual time scales. From these models, Boiçucanga is classified as a deep embayed beach exposed to high-energy waves, with a predominant reflective profile, which favors the development of beach cusps and topographically controlled rip currents. The combined results of the field observations and applied models allowed us to better understand the role of geological heritage in the two morphodynamic signatures found at the same beach arch. For future studies, we will focus on numerical models to increase the understanding of the hydrodynamic processes that govern the sediment transport in Boiçucanga.

Intermittently Closed/Open Lakes and Lagoons: Their global distribution and boundary conditions

Intermittently Closed/Open Lakes and Lagoons (ICOLLs) are a particularly dynamic form of estuary characterised by periodic entrance closure to the ocean. Closure occurs when a subaerial sand berm stabilises across the entrance channel during times of low fluvial discharge. ICOLLs are of global importance as they provide valuable ecological habitats for many species and are associated with a wide range of management issues due to their cycle of entrance closure and opening. ICOLLs are found to be more widespread globally than previously described with 1477 of these estuaries being identified in this study. This constitutes an estimated 3% of the world's estuaries and 15% of all estuaries along microtidal coastlines. ICOLLs are concentrated along microtidal to low mesotidal coastlines in the mid-latitudes and predominantly on coasts with temperate climates. This distribution is related to greater wave heights as driven by high intensity winds and a longer fetch distance. The highest proportion of ICOLLs are present in Australia (21% all global ICOLLs), South Africa (16%) and Mexico (16%). In Australia, a comparison with fluvial input found that it is less important than marine processes in determining ICOLL formation and that ICOLLs are associated with a relative tidal range of <3.22. Additionally the majority of ICOLLS are small systems with catchments <2000km2 and tidal prisms <30×106m3, forming at the mouths of rivers with generally low mean annual and specific discharges.

Wave-dominated, mesotidal headland-bay beach morphodynamic classsfications of the Shuidong Bay in South China

Beach morphodynamic classifications have achieved extensive acceptance in foreign coastal geomorphological studies. Three beaches located in different zones of a headland-bay coast are classified according to a dimensionless fall parameter, a relative tide range parameter and a dimensionless embayment scaling parameter. Synchronous data, including wave, tide, sediment and beach morphology, are respectively collected from the tangential beach, the transitional beach and the shadow beach of the Shuidong Bay during each spring tide for 16 successive months. The research results indicate that (1) the beach in the tangential zone falls between two major categories which are low tide terrace beaches with rips and barred beaches; the beach in the transitional zone exhibits two main types which are low tide bar/rip beaches and barred dissipative beaches; and the beach in the shadow zone mainly mirrors dissipative states with presence or absence of bars; and (2) the sequential changes and differences of beach states in different coastal zones reflect spatial and temporal variabilities of the headland-bay coast, totally meeting the actual measured beach morphology changes, showing that studies on wave-dominated, meso-macrotidal beaches need to consider the influences of the tides. Meanwhile, the research mainly provides a framework about beach state studies, due to different beach states with different erosion patterns, which requires the need to strengthen the researches in this respect, in order to further enrich theoretical basis for a beach topography evolution, beach morphodynamic processes and beach erosion prevention in China.

Seasonal morphodynamic classification of beaches in Necochea municipality, Buenos Aires Province, Argentina

The seasonal morphodynamic classification of Necochea and Quequén beaches (Buenos Aires Province, Argentina) was determined. Based on 102 seasonal beach profiles and sediment sampling between February 2006 and December 2009, variations in morphology and sediment budgets of five beaches were studied. According to the dimensionless fall parameter and the relative tide range, the beaches were classified depending on their modal morphodynamic state. In Quequén, beaches presented intermediate and reflective states, whereas in Necochea they presented dissipative states. The Iribarren number showed that plunging and spilling breakers predominated in Quequén and Necochea, respectively. In winter, the beaches became more dissipative, while in summer-autumn they were more reflective. This general behavior agrees with the erosion/accretion cycles. Beach profile variability was higher in Quequén. These results have been used to elaborate the coastal management program of the area.

Applicability of parametric beach morphodynamic state classification on embayed beaches

Abstract Use of parametric classification of beach morphodynamic state has been steadily increasing in coastal research, despite identification of several shortcomings of their representativeness as elementary beach descriptors. In this paper, we analyse the parametric classification of beach morphodynamic state in a set of six embayed beaches in southwestern Portugal, exposed to diverse settings, from high-energy (dissipative to intermediate) to low-energy (intermediate to reflective) conditions. Applicability of parametric approaches considered within the dimensionless space defined by Ω (dimensionless fall velocity) and RTR (relative tidal range) according to averaged wave, tide and sediment characteristics of beaches, was assessed in association with a probabilistic analysis, implemented through a Bayesian network model, that considered the full range of wave, tide and sediment conditions at each site. Both parametric approaches were compared to field-based beach state classification implemented using a novel hierarchical framework for beach state analysis. The classification obtained within a probabilistic framework provided an innovative approach for analysis of beach state and mobility, extending the insights on beach morphodynamic behaviour obtained from averaged environmental parameters. Reflective to lower-intermediate beach conditions showed better agreement with parametric approaches, while poor beach state differentiation was achieved for intermediate beach types. Limitations in the application of beach classification models result from (i) an inadequacy of existing beach state types in differentiating beaches, particularly within the intermediate domain and for geologically controlled embayed beaches, and (ii) shortcomings involved in the parametric approaches. The beach state models disregard the major role of geological control in embayed beach morphodynamic behaviour (in modulating beach shape and segmentation, influencing sediment size and availability, causing alongshore variations in the wave field and creating topographically induced nearshore circulations). Existing beach state models are unable to adequately represent the widely variable conditions observed in embayed beaches.

Experimental simulation of sandy beaches under waves and tides: hydro-morphodynamic analysis

Khoury, A., Jarno-Druaux, A., and Marin, F., 2013. Experimental simulation of sandy beaches under waves and tides: hydro-morphodynamic analysis Proceedings 12th International Coastal Symposium (Plymouth, England), Journal of Coastal Research, Special Issue No. 65, pp. 1791–1796, ISSN 0749-0208.-->Numerous studies have been carried out on sandy beach morphology; however, the physical processes which govern beach morphodynamic are still not well understood, despite the significance of this subject in view of the direct applications for coastal erosion. The present work brings a contribution to the study of these processes from well controlled tests carried out in a 10-m-long and 0.49-m-wide wave flume with macro – and mega-tidal regime simulations. The tests were carried out with very fine or fine sand of relative density s=2.65. The incident waves and the free surface in the shoaling zone were measured with resistive probes. The wave breaking height and the free surface in the swash zone were recorded with an optical method. The temporal evolution of bottom profiles was obtained using an acoustic method. Intertidal bars were generated; such bars were previously not observed in physical modeling to the authors' knowledge. Present experimental results are compared with field observations. Formation processes of intertidal bars are analyzed; we show in particular the significant effect of the relative tide range, of waves asymmetry, and of subtidal bars on these processes. Small local variations of the beach profile in the surf zone exhibit significant outcomes on the runup.

Does beach nourishment have long-term effects on intertidal macroinvertebrate species abundance?

Coastal squeeze is the largest threat for sandy coastal areas. To mitigate seaward threats, erosion and sea level rise, sand nourishment is commonly applied. However, its long-term consequences for macroinvertebrate fauna, critical to most ecosystem services of sandy coasts, are still unknown. Seventeen sandy beaches – nourished and controls – were sampled along a chronosequence to investigate the abundance of four dominant macrofauna species and their relations with nourishment year and relevant coastal environmental variables. Dean's parameter and latitude significantly explained the abundance of the spionid polychaete Scolelepis squamata, Beach Index (BI), sand skewness, beach slope and latitude explained the abundance of the amphipod Haustorius arenarius and Relative Tide Range (RTR), recreation and sand sorting explained the abundance of Bathyporeia sarsi. For Eurydice pulchra, no environmental variable explained its abundance. For H. arenarius, E. pulchra and B. sarsi, there was no relation with nourishment year, indicating that recovery took place within a year after nourishment. Scolelepis squamata initially profited from the nourishment with “over-recolonisation”. This confirms its role as an opportunistic species, thereby altering the initial community structure on a beach after nourishment. We conclude that the responses of the four dominant invertebrates studied in the years following beach nourishment are species specific. This shows the importance of knowing the autecology of the sandy beach macroinvertebrate fauna in order to be able to mitigate the effects of beach nourishment and other environmental impacts.

Distribution patterns of interstitial polychaetes in sandy beaches of southern Brazil

AbstractThis study describes the distribution patterns of interstitial polychaetes along morphodynamic gradients on six exposed sandy beaches in Santa Catarina and Paraná (South Brazil). Three random transects were sampled at two points on each beach, one at the swash and another at the surf zone, in winter and summer conditions. Six sediment replicates were collected at each sampling point using a corer of 4.6 cm internal diameter that removed 10 cm into the sediment. Abundance and composition of interstitial polychaete were correlated to wave height, slope, grain size, CaCO3, chlorophyll a, omega indexes, temperature and relative tide range using a canonical correspondence analysis (CCA). A factorial ANOVA showed that taxa richness, mean density and Shannon’s diversity were significantly higher at the reflective beaches, but average values differ significantly between transects and these differences change according to the beach zones on both sampling dates. PERMANOVA showed that polychaete associations differ among transects according to the beach zones. The composition of interstitial polychaete associations was significantly correlated to beach morphodynamics and features (P &lt; 0.01). Polychaete associations of reflective beaches were more diverse than in other morphodynamic states. Intermediate beaches may also sustain diverse associations due to temporal variability of the morphodynamic patterns. Beaches presenting extreme dissipative morphodynamics and compacted sediments appear to be unfavourable for the occurrence of interstitial polychaetes.

Erosion and Accretion of Beach and Spit Systems in Northwest Spain: A Response to Human Activity

Abstract Three beach and spit systems have been studied in northern Galicia, along the northwest coast of Spain, within the regional context of sea level rise and coastal erosion. Each system forms part of an estuary's mouth complex within the inner part of the Ortigueira, Barqueiro, and Viveiro rias. Erosive processes along the coast have been characterised and been found to affect cliffs, beaches, and archaeological sites. To compare both long-term (decadal) and short-term (annual) erosion and accretion trends among estuaries, we analysed the morphodynamic characteristics, the degree of human occupancy, and the historical evolution of each system and monitored two profiles at each beach. Dynamic parameters—dimensionless fall velocity and relative tidal range—were calculated for the characterisation of beaches, and maritime climate data—significant wave height (Hs), peak period (Tp), wave fetch direction, and wave period were obtained, and wave height reduction was estimated for all estuaries. Detailed a...

Community structure and intertidal zonation of the macroinfauna in intermediate sandy beaches in temperate latitudes: North coast of Spain

Nineteen intermediate exposed sandy beaches, located along the northern coast of Spain, were sampled during the summer 1999. Data from 10 of the beaches, located at the eastern part of this coast, were previously reported to evaluate environmental factors affecting benthic macrofauna. Data from nine of the beaches, located at the western part of this coast, were included to compare community structure and intertidal zonation of the macroinfauna on intermediate sandy beaches in temperate latitudes. Morphodynamic parameters such as Dean's parameter ( Ω), Beach State Index (BSI) and relative tide range (RTR) were estimated at each beach. Beach length, width, intertidal slope, medium grain size, sorting, swash amplitude and wave characteristics were also analyzed. The highest macroinfaunal densities and biomass occurred at the mid and lower shore levels of each beach. Crustaceans, mainly cirolanid isopods, were the dominant group found on these beaches, whereas molluscs were the least representative. In general, the relationship between community structure and beach morphodynamics was similar to that found for the macroinfauna worldwide suggesting that macroinfauna in intermediate sandy beaches is affected, in the same way, by the physical processes associated with different beach types. Histograms and kite diagrams representing the intertidal distribution of the macroinfauna and multivariate analysis were used to show the zonation pattern on these exposed beaches. Intertidal slope values and beach profile pattern were found similar in all the beaches sampled. We hypothesized that this particular beach profile could influence the pattern of macroinfauna zonation. All the 19 beaches have two zones in common: the supralittoral zone of air breathers present on all shores at and above the drift line and the littoral zone extending from the drift line down the midshore to just above the water table outcrop. Ordination analyses identified two possible zones within the lower beach levels on seven of the beaches, but this cannot be clearly established. The Monte Carlo permutation test was used to select beach slope, length and wave height as the best predictor variables of macroinfaunal characteristics and it seems that the species most affected by the main variables showed the clearest zonation on the 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...

Persistence of storm-induced morphology on a modal low-energy beach: A case study from NW-Iberian Peninsula

The morphology of low-energy beaches is inherited from high-energy events showing a non equilibrium state with the prevailing conditions. An example of a sheltered, low-energy beach (Rodas Beach, NW-Iberian Peninsula) is examined in this paper. The evolution of six beach profiles was analysed during three years in order to investigate the response of this beach under fair-weather and storm conditions. The beach presented significant morphological differences alongshore due to its geographical location with respect to the wave approach. These differences determined the sediment transfer pattern (longshore or cross-shore sediment transport) from the emerged beach towards the adjacent inner shoreface zone. Significant morphological changes at each profile seem to be related to the incidence of sea waves along the beach superimposed on persistent swell during winter. Morphological changes were recorded under high-energy storms, during winter, whereas the recovery to prestorm conditions occurred under prevailing fair weather conditions, during summer. The traditional beach classification parameter Relative Tidal Range (RTR), which takes into account the effect of the tide range, was found unsuitable to properly classify such a mesotidal low-energy beach. Therefore, a new parameter, the Relative Tidal Range Maximum (RTR max) was introduced, which is a modification of the commonly used RTR. RTR max uses the highest wave breaking height, observed during high-energy storm conditions, instead of the modal wave breaking height. By using this parameter, the studied beach could be properly classified into the traditional beach classification models taking into account the tide range. Since low-energy beaches generally show a morphology that is inherited from higher energy conditions than the prevailing conditions, it is expected that the RTR max will be applicable for the classification of other low-energy sheltered beaches.

Geological control of beach morphodynamic state

The concept of beach morphodynamic states has achieved widespread acceptance in the coastal geological literature since its inception in the mid-1980s and expansion in the 1990s. Much of the pioneering work was undertaken in Australia under a range of environmental conditions in microtidal environments and a close empirical relationship between beach 3-dimensional morphology and the Dean's parameter ( H b/ W s T) was established. Subsequently, the Relative Tidal Range parameter ( H b/TR) was extended to beaches of all tidal ranges. In this paper, observations are presented from 25 beaches around the north coast of Ireland. These beaches exist on an environmental gradient that encompasses marked tidal and wave energy variability (micro to macrotidal and low to high wave energy). Each beach was visually categorised into one of several established beach states described in the literature, on the basis of field observations. For each beach, the RTR and Dean's parameter were calculated for the immediately antecedent period and used to predict the beach state using published relationships. Observed and predicted beach states were then compared. Comparison of observed and predicted beach states showed that while beaches with observed dissipative morphology typically matched the expected criteria, most other beach states did not. Lack of agreement between predicted and observed beach states has been reported elsewhere and attributed to failings in the RTR and Dean's parameter. In addition, this study identifies geological factors as important constraints on actual beach state. In the majority of beaches studied, inherited geological factors appear to be more important determinants of beach morphology than contemporary dynamics.