Beach Shape Research Articles

Predicting beach profiles for thickened tailings surface deposition

Thickened tailings deposition technology can form a stack with a certain slope by depositing high-concentration tailings slurries to reduce the footprint of tailings storage facilities and water consumption. Thickened tailings slurries exhibit complex non-Newtonian behaviors. Predicting the beach profile evolution of thickened tailings is important for the tailings storage facility design and management. A novel governing differential equation (GDE) derived from the lubrication theory is proposed in this work to capture laws of beach profile formation. Experimental data from three-dimensional laboratory-scale flume tests are analyzed using the proposed GDE. The GDE avoids the discrepancy from an inappropriate coordinate system, which exists in some state-of-the-art models and exhibits higher accuracy when predicting the beach shape near the toe of a preexisted layer. Compared with the Herschel–Bulkley (H–B) model, the Zhang’s equilibrium rheological model is preferred to determine the static yield stress, which leads to the accurate estimation of the stack profile in single- and multilayer thickened tailings depositions. The in-situ beach profile of thickened tailings is predicted using a numerical technique. A case study is included to demonstrate that the prediction based on the proposed GDE is consistent with the field measurement. The beach profile prediction of thickened tailings considering thixotropy is also discussed in this study. Results indicated that the decrease of yield stress along the flow path due to thixotropy leads to the concave beach shape of thickened tailings.

Monitoring Beach Shape Development and Sediment Dynamics on a Sandy Beach with Low Anthropogenic Influence

This study examined the evolution of the beach profile and sedimentary balance in Playa del Coco, Mexico, during one year (September 2013–September 2014) to monitor these conditions at a site with little or no anthropogenic influence. The type of beach profile was determined according to the energy profile of the geomorphology, resulting in three types of profiles: low, medium, and high energy. In addition, sediment volumes were quantified, and erosion or accumulation at each study site was described. The results showed that the medium-energy profile was characteristic of the beach most of the time. High-energy conditions were recorded only once due to the influence of a high-category hurricane (Odile, III) during the hurricane season. The dominant sediment size was medium, moderately well-classified to well-classified, coinciding with the medium-energy profile. Coarse, well-sorted sand was recorded at the end of the study, coinciding with the highest loss of sediment on the beach. Playa del Coco showed a state of quasi-equilibrium before the end of the annual cycle, recovering the characteristics of the beach at the beginning of the study. After that time, there was a great loss of sedimentary material influenced by Hurricane Odile (III), modifying the beach’s state of recovery. Therefore, the stability of this beach could be cyclical and respond to the self-organization principle rather than to seasonal parameters. However, the duration of the cycles that influence Playa del Coco seems to be determined by the hurricane season, especially the combination of two main factors: the proximity to the coast of the hurricane and the amount of rainfall associated with the hurricane.

Predicting Crenulate Bay Profiles from Wave Fronts: Numerical Experiments and Empirical Formulae

For crenulate-shaped bays, the coastal outline assumes a specific shape related to the predominant waves in the area: it generally consists of a tangential zone downcoast and a curved portion upcoast. Many coastal engineers have attempted to derive an expression of the headland bay shapes that emerge when a full equilibrium is reached (stable or dynamic). However, even though models for static equilibrium bays exist, they are merely of an empirical kind, lacking further insight on relationships between incident wave characteristics and beach shape. In addition, it is commonly believed that shoreline profiles tend to follow wave fronts, but this has been never fully verified. In this paper, we investigate a possible correlation between static equilibrium profiles and wave front shapes. Numerical experiments have been performed using the MIKE 21 Boussinesq Wave module, and the generated wave fronts have been compared to the hyperbolic-tangent equilibrium profile. A thoughtful analysis of results revealed that a single-headland equilibrium profile is merely the wave front translated perpendicularly to the wave direction at the headland tip, without any influence of wave period or in wave direction. A new function called the “wave-front-bay-shape equation” has been obtained, and the application and validation of this formula to the case-study bay of the Bagnoli coast (south-west of Italy) is described in the paper.

NEURAL NETWORK MODEL FOR IDENTIFYING THE COASTAL SAND AREA USING THE AERIAL PHOTOGRAPHS PICTURED BY UAV

Small island states formed by atolls such as Marshall Islands, Kiribati and Tuvalu require useful and efficiency method of coastal monitoring for coastal management because of lack of human resources and budget. In atoll islands, the identification of shape of sandy beach and temporally accumulation area of sand has high importance in coastal management. In this study, neural network model to classify the aerial photographs pictured by UAV was established for identifying the sand area in the coastal zone of Fongafale island in Funafuti atoll, Tuvalu. Photographs of coastal sediments especially sand, in Fongafale island were collected by digital camera. These photographs were used to make the data set for training and testing of the constructed neural network model. Additionally, aerial photographs pictured by UAV were collected to apply to the constructed neural network model. In this study the convolution neural network was constructed to classify the aerial photographs.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/trHQOmsFpD4

Dissimilar laser cladding of Inconel 718 powder on A-286 substrate: Microstructural evolution

In this work, laser cladding of a Ni-based superalloy powder (Inconel 718) on a Fe-based superalloy (A-286) substrate was performed. The microstructural evolution was studied by optical and electron microscopy techniques, aided by energy dispersive spectroscopy. Additionally, the microhardness along the as-deposited parts was analyzed and correlated with the observed microstructure. It was found that other than austenitic dendrites, Nb-rich carbides, interdendritic Laves networks, and Ti (C, N) were formed; the latter was aided by the presence of pre-existing TiC particles in the substrate. Additionally, a slag oxide layer was seen on the clad surface of the fusion zone. The formation mechanisms of an unmixed zone in the shape of beach and peninsula are discussed.

Wave Dynamics Investigation in Scope of Coastal Processes

In this research it is given the Classifying Coasts, Primary Coasts and Land Erosion Coasts, Coasts Built Out by Land Processes, Coast, Coasts Shaped by Earth Movements, Secondary Coasts,Some Features of Secondary Coasts, Shore Straightening, The Accumulation of Beaches, Beaches, The Composition and Slope of Beaches, Beach Shape,Minor Beach Features, Coastal Cells, Large-Scale Features of Secondary Coasts, Sand Spits and Bay Mouth Bars, Barrier Islands and Sea Islands, Coasts Formed by Biological Activity, Estuaries, Classification of Estuaries, Characteristics of Estuaries, The Value of Estuaries, Lagoons and Wetlands with useful data.

Exploring the Potential for Multivariate Fragility Representations to Alter Flood Risk Estimates.

In flood risk analysis, limitations in the multivariate statistical models adopted to model the hydraulic load have restricted the probability of a defense suffering structural failure to be expressed conditionally on a single hydraulic loading variable. This is an issue at the coastal level where multiple loadings act on defenses with the exact combination of loadings dictating their failure probabilities. Recently, a methodology containing a multivariate statistical model with the flexibility to robustly capture the dependence structure between the individual loadings was used to derive extreme nearshore loading conditions. Its adoption will permit the incorporation of more precise representations of a structure's vulnerability in future analyses. In this article, a fragility representation of a shingle beach, where the failure probability is expressed over a three-dimensional loading parameter space-water level, wave height, and period-is derived at two localities. Within the approach, a Gaussian copula is used to capture any dependencies between the simplified geometric parameters of a beach's shape. Beach profiles are simulated from the copula and the failure probability, given the hydraulic load, determined by the reformulated Bradbury barrier inertia parameter model. At one site, substantial differences in the annual failure probability distribution are observed between the new and existing approaches. At the other, the beach only becomes vulnerable after a significant reduction of the crest height with its mean annual failure probability close to that presently predicted. It is concluded that further application of multivariate approaches is likely to yield more effective flood risk management.

Causes of the different behaviour of the shoreline on beaches with similar characteristics. Study case of the San Juan and Guardamar del Segura beaches, Spain

Storms can alter the beach shape, relocating large volumes of sediments and generating drastic changes in the coastline. In the last 60years, beaches shoreline behaviour has been different even though the energy of the waves was similar. Therefore, it is necessary to understand the factors that affect the sandy coasts for better future management. In this research, two beaches, with different erosion rate, located in the southeast of Spain (separated by only 40km of distance) have been studied. The beaches: i) have similar orientations, ii) are open to waves with similar sand lengths of 9.8km and 6.6km, and iii) have similar median sediment size (D50).For its study, shoreline evolution has been analysed from 1956 to 2017. From the results obtained, it can be seen that: i) Between 1992 and 2017, San Juan just lost 3% of its surface, while in the previous period (1956–1990) it was 50%, and ii) Guardamar surface lost in 1992–2017 was 18%, and in the previous period it was 14%. For the analysis of the agents involved in both beaches, cross-shore profiles (volume), marine climate, biocenosis and sedimentology studies were carried out. The results showed that the energy on both beaches was very similar. The biocenosis had not changed and, however, the morphology of Guardamar seabed had increased to 1m deep in some places, which had caused part of the beach berm erosion. Furthermore, important differences were found from the sedimentological study, concluding that the content of calcites and the degree of homogeneity of the particles are the real factors that caused these two beaches to behave differently against erosion.

Mangrove canopy density analysis using Sentinel-2A imagery satellite data

Teluk Jor has alluvium surface sediment that came from volcanic materials. Sea wave that relatively calm and the closed beach shape support the existence of mangrove forest at Teluk Jor. Sentinel-2A imagery has a good spatial and spectral resolution for mangrove density study. The regression between samples and the NDVI values of Sentinel-2A used to analyze the mangrove canopy density. Mangrove canopy density was identified using field survey with transect method. The regression analysis shows field data and NDVI value has correlation R=0.7739 and coefficient of determination R2=0.5989. The result of the analysis shows area of low density 397,900 m2, moderate density 336,200 m2, the high density has 110,300 m2 and very high density has 500 m2. This research also found that mangrove genus in Teluk Jor consists of Rhizopora, Ceriops, Aegiceras and Sonneratia.

Evolution of a beach nourishment project using dredged sand from navigation channel, Dunkirk, northern France

The largest beach replenishment project ever in France was completed in February 2014 in Dunkirk on the coast of northern France. A volume of 1.5 × 106 m3 of sand extracted from a navigation channel was placed on the beach to build up a 150 to 300 m wide supratidal platform in front of a dike, called « Digue des Allies », which protects several residential districts of Dunkirk from marine flooding. High resolution topographic surveys were carried out during 2½ years to monitor beach morphological changes, completed by a hydrodynamic field experiment conducted in February 2016. Approximately −138,200 m3 of sand, corresponding to 9.2% of the initial nourishment volume, were eroded over the nourishment area in about 2 years. An obvious decrease in erosion eastward with a shift from erosion to accumulation was observed, suggesting an eastward redistribution of sand. This longshore sand drift is beneficial for the eastward beach of Malo-les-Bains where most of the recreational activities are concentrated. Hydrodynamic measurements showed that waves and wave-induced currents play a major role on the longshore sand redistribution compared to tidal flows. Strong relationships were observed between cumulative offshore wave power and beach volume change during distinct beach survey periods (R2 = 0.79 to 0.87), with more significant correlations for northerly waves. A slight decrease in erosion during the second year compared to the first year after nourishment suggests that the loss of sand should decrease after an initial phase of rapid readjustment of the beach shape towards equilibrium.

Restoring sediment to compensate for human-induced erosion of an estuarine shore

Shoreline erosion is often exacerbated by reduction of sediment inputs because of interference with sediment transport by human structures. We evaluate use of sediment dredged from a navigation channel to establish a feeder beach adjacent to a bulkhead as a solution for addressing erosion of landforms and habitats on sandy estuarine shores. The objectives are to determine how beach volume, position and shape within and downdrift of the fill area change and whether the volumes supplied by dredging match sediment losses caused by human actions. The fill was placed along a 75m length of shoreline adjacent to a marina in Great South Bay at Fire Island, New York, USA. Changes in beach shape and volume were determined from topographic surveys conducted before and after fill and at half year intervals for 18months.The quantity of fill was 1747m3. Maximum shoreline advance due to fill emplacement was 20.7m. The maximum volume placed at any transect was 28.6m3m−1 of shoreline length. Erosion of the fill occurred rapidly, with landward migration of a conspicuous scarp. The edge of the upland 18months after the fill was placed was up to 4.6m farther landward than prior to the fill. Movement of sediment alongshore downdrift of the fill occurred as wave-like pulses, extending the active foreshore bayward, causing accretion of the inner low tide terrace, burying saltmarsh peat outcrops on the foreshore and creating a higher and wider overwash platform over portions of the saltmarshes. Landforms downdrift of the fill area underwent successive stages including erosion (pre-nourishment), accretion, stability (with throughput of sediment) and then erosion. Beach nourishment compensates for human-induced sediment losses. The volume of sediment added from maintenance dredging can slow the rate of erosion but may not prevent long-term shoreline retreat.Restoration and maintenance of coastal landforms and habitats to specific target states at a given location is difficult, but augmenting longshore sediment inputs can allow those locations to undergo cycles of erosion and accretion, creating a variety of landforms and habitats where only erosional forms existed previously. Alternatively, nourishment could occur more frequently and in smaller volumes to reduce fluctuations in accretion-erosion cycles.

Character Exploration for River Ecology Condition Based on Factor Analysis

The basis of analysis of the ecological health of the river is taken into account, including water quantity, water quality, riparian zone, the physical structure of organisms and other elements to explore a new method based on factor analysis of river ecosystem health. 21 typical reaches along villages of Tang River in Beijing are measured using the method of 17 indexes system to analyze the index relevance for Tang River ecosystem health. The results showed that midstream of Tang River ecological health relevant factors are riverbed, water and biological effects, water quality, water-soil interaction, the downstream river bank only have slope factor, and significantly related reaches are distributed in water and biological effects, heart beach shape, river curvature, slope degree more. The evaluation results raised the indexes and reach affecting river ecological condition, to provide scientific guidance for the ecological restoration of Tang River (Beijing Reach).

A preliminary exploration of the physical properties of seagrass wrack that affect its offshore transport, deposition, and retention on a beach

Lay AbstractThe accumulation of seagrass wrack on beaches provides a link between the marine and terrestrial environments and has been shown to play an important role in beach ecology. However there are parts of the world where accumulations of wrack are so pronounced that the wrack piles affect beach shape, and erosion can block harbors and breakwaters. The production of poisonous gases caused by its decay can become a human health hazard. Ideally, numerical models should allow us to predict wrack accumulation under a variety of management scenarios; however, there are few data to use in such numerical modeling. Indeed our understanding of how wrack is deposited to and removed from beaches is limited. This paper provides an exploratory investigation of a range of physical properties of seagrass wrack and establishes a baseline understanding of how these physical properties might impact on its transport and accumulation onto beaches.

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.

SEDIMENT SORTING AND BEACH MORPHOLOGY UNDER PLUNGING WAVE BREAKING

This paper presents an experimental investigation into the response of coarse-grained beaches under the action of plunging wave breaking. Beach profile results allowed the identification of three main morphological responses. These are: a beach profile which presented the generation of a clear step below the SWL; a beach shape that did not form any beach step; and a beach face which evolved a bar-like step. Additionally, high-resolution velocity measurements illustrate the prevailing hydrodynamic conditions in the surf-swash transition zone. These results were validated with ADV measurements collected at two cross-shore locations. Through Euler's equation the pressure field was associated to the total acceleration in the fluid, allowing a careful assessment of the contribution of each the acceleration terms to the resulting momentum balance. In the region close to the impact point, the magnitude of the local acceleration under the plunging waves is insignificant, while at the same location the role of advective terms cannot be overlooked. Results indicate the relevance of including advection processes for the accurate calculation of sediment transport under the action of plunging breakers across the nearshore zone.

FIELD OBSERVATIONS OF SHORELINE CHANGE BY FREQUENCY-BANDED WAVE ENERGY FLUX AND FORESHORE SHAPE

In this paper, correlations between shoreline change rates and six frequency-sectioned wave energy fluxes were discussed using a 5-year data set of beach profiles and offshore waves observed at the Hasaki coast. Also, an effect of foreshore beach shape on shoreline backward movement speed was discussed. From the results, it is possible to separate shoreline erosion events from shoreline advance events and shoreline stand still events by using frequency-sectioned wave energy fluxes. Furthermore, the results revealed that the shoreline position and foreshore shape affect shoreline backward movement speed. This indicates that for the estimation of the shoreline change rate, we need to consider not only wave energy but also shoreline position and foreshore shape.

Megacusps on rip channel bathymetry: Observations and modeling

The formation of beach megacusps along the shoreline of southern Monterey Bay, CA, is investigated using time-averaged video and simulated with XBeach, a recently developed coastal sediment transport model. Investigations focus on the hydrodynamic role played by the bay's ever-present rip channels. A review of four years of video and wave data from Sand City, CA, indicates that megacusps most often form shoreward of rip channels under larger waves (significant wave height ( H s ) = 1.5–2.0 m). However, they also occasionally appear shoreward of shoals when waves are smaller ( H s ~ 1 m) and the mean water level is higher on the beach. After calibration to the Sand City site, XBeach is shown to hindcast measured shoreline change moderately well (skill = 0.41) but to overpredict the erosion of the swash region and beach face. Simulations with small to moderate waves ( H s = 0.5–1.2 m) suggest, similar to field data, that megacusps will form shoreward of either rip channels or shoals, depending on mean daily water level and pre-existing beach shape. A frequency-based analysis of sediment transport forcing is performed, decomposing transport processes to the mean, infragravity, and very-low-frequency (VLF) contributions for two highlighted cases. Results indicate that the mean flow plays the dominant role in both types of megacusp formation, but that VLF oscillations in sediment concentration and advective flow are also significant.

Field Investigation of Morphological Changes in Lagoonal Sandy Beach of Atoll Islands

This study focused on the morphological change in Alapi beach of Fongafale islet in Funafuti atoll, Tuvalu. Although Alapi beach is indispensable for residents, the mechanism of morphological change is not sufficiently understood because measured data of morphological change are not enough. Measurements of sandy beach's shape in Alapi using handy GPS and wave condition in lagoon were carried out by this study. Analyzed results of measured data indicated that the longshore sediment transport in Alapi beach is toward north through a year and the rare tropical cyclone has potential of rapid both northward and southward transport of sandy beach. This mechanism of morphological change becomes fundamental information for beach conservation plan in Alapi beach.

Extraction of Structural Curves, Regression Relations and Structural Regression Relations in the Tidal Limit of the Karun River

The Karun River is the most important tidal river in Iran. Two factors are governing of hydraulic conditions of tidal rivers (fluvial flows and tidal flows). Fluvial flow concerns hydrologic and physiographic conditions of watershed and characteristics of rainfall while tidal flows are produced by gravity of moon and sun, reflection wave from beach, effects of shallow water in estuaries and the shape of beach. Because tidal flows move to upstream and fluvial flows go toward downstream in the tidal limit of the tidal rivers, hydraulic conditions of this part are very complex. The measurement of discharge and velocity of current is impossible in this part. For determination of discharge-stage curve in tidal limit, an especial approach was applied in this research. Structural curves (an especial type of discharge-stage curve) were developed by using of discharge of fluvial flow in the upstream and tidal height in the downstream. For convenience of using of structural curves, these curves converted to regression relations. For determination of correlated water surface elevations to different return periods, structural regression relations were extracted by regression relations, joint probability method and combination coefficient. In this research, four methods made used of determination of combination coefficient. These methods are conventional method, desk study joint probability method, analytic joint probability method and developed analytic joint probability method by researcher. The results of developed analytic joint probability method by researcher have the best fitness by observed data in the Karun River. At the end structural regression relations showed correlated water surface elevation to each combined return period of fluvial flow and tidal flow.

Extraction of structural curves, regression relations and structural regression relations in the tidal limit of the Karun River

The Karun River is the most important tidal river in Iran. Two factors are governing of hydraulic conditions of tidal rivers (fluvial flows and tidal flows). Fluvial flow concerns hydrologic and physiographic conditions of watershed and characteristics of rainfall while tidal flows are produced by gravity of moon and sun, reflection wave from beach, effects of shallow water in estuaries and the shape of beach. Because tidal flows move to upstream and fluvial flows go toward downstream in the tidal limit of the tidal rivers, hydraulic conditions of this part are very complex. The measurement of discharge and velocity of current is impossible in this part. For determination of discharge-stage curve in tidal limit, an especial approach was applied in this research. Structural curves (an especial type of discharge-stage curve) were developed by using of discharge of fluvial flow in the upstream and tidal height in the downstream. For convenience of using of structural curves, these curves converted to regression relations. For determination of correlated water surface elevations to different return periods, structural regression relations were extracted by regression relations, joint probability method and combination coefficient. In this research, four methods made used of determination of combination coefficient. These methods are conventional method, desk study joint probability method, analytic joint probability method and developed analytic joint probability method by researcher. The results of developed analytic joint probability method by researcher have the best fitness by observed data in the Karun River. At the end structural regression relations showed correlated water surface elevation to each combined return period of fluvial flow and tidal flow.