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Equilibrium Beach Profiles: Characteristics and Applications
Abstract
When beaches are nourished with a sediment of arbitrary but uniform size, it is found that three types of profiles can result: 1) submerged profiles in which the placed sediment is of smaller diameter than the native and all of the sediment equilibrates underwater with no widening of the dry beach, 2) non-intersecting profiles in which the seaward portion of the placed material lies above the original profile at that location, and 3) intersecting profiles with the placed sand coarser than the native and resulting in the placed profile intersecting with the original profile. -from Author
... Aeolian transport can bring sediment from the intertidal zone and beach to the dunes at different timescales [20,21], with many processes influencing the magnitude of wind-driven sediment transport [22]. The resulting beach width is closely related to the shape of the dynamic equilibrium profile, as described by [23,24]. As such, the remaining dry beach width after nourishment can depend significantly on the size of nourished grains compared with native [3,24]. ...
... The resulting beach width is closely related to the shape of the dynamic equilibrium profile, as described by [23,24]. As such, the remaining dry beach width after nourishment can depend significantly on the size of nourished grains compared with native [3,24]. ...
... The subaqueous profile was designed as a Dean [24] profile fitted to observed profiles of the adjacent coast. Although in practice placed steeper, the placed subaqueous volume was sufficient to accommodate adjustment to a profile slope close to this expected dynamic equilibrium slope. ...
Sandy nourishments can provide additional sediment to the coastal system to maintain its recreational or safety function under rising sea levels. These nourishments can be implemented at sandy beach systems, but can also be used to reinforce gray coastal infrastructure (e.g., dams, dikes, seawalls). The Hondsbossche Dunes project is a combined shoreface, beach, and dune nourishment of 35 million m3 sand. The nourishment was built to replace the flood protection function of an old sea-dike while creating additional space for nature and recreation. This paper presents the evolution of this newly created sandy beach system in the first 5 years after implementation based on bathymetric and topographic surveys, acquired every three to six months. A significant coastline curvature is created by the nourishment leading to erosion in the central 7 km bordered by zones with accretion. However, over the five-year period, net volume losses from the project area were less than 5% of the initial nourished sand volume. The man-made cross-shore beach profile rapidly mimics the characteristics of adjacent beaches. The slope of the surfzone is adjusted within two winters to a similar slope. The initially wide beaches (i.e., up to 225 m) are reduced to about 100 m-wide. Simultaneously, the dune volume has increased and the dune foot migrated seaward at the entire nourished site, regardless of whether the subaqueous profile gained or lost sediment. Our results show that the Hondsbossche Dunes nourishment, built with a natural slope and wide beach, created a positive sediment balance in the dune for a prolonged period after placement. As such, natural forces in the years after implementation provided a significant contribution to the growth in dune volume and related safety against flooding.
... To some degree, all these issues were considered earlier [10,12,13,19], which, however, does not exclude the need for further studies. This article also attempts to solve the identified problems. ...
... Segment characterizes the subaqueous part between points and , where is the position of the shoreline at the storm level (Fig. 1). The depth profile here is approximated by Dean's equilibrium profile [12,13], (1) where is a function of the size of solid particles (on the order of 10 -1 m 1/3 ). Segment characterizes the width of the wave runup zone (between points and ), and segment corresponds to the berm width, i.e., the distance between the maximum level of and on the artificial and natural profiles, respectively (Fig. 1). ...
... The conditional boundary between them is the position of the shoreline in calm conditions ( Fig. 1). Material volumes and in the corresponding areas are determined as (12) where z and are the elevations of the design and actual profiles, respectively. ...
... The volume of lost sand, that causes the beach erosion, is equal to the rise in the sea level within the active portion of the beach profile. The same approach was also used by Dean [7]. Here, the effect of the wave set-up is also included, but the method only works for a vertical profile of the emerged Water 2022, 14, 1305 2 of 20 beach followed by the Dean's equilibrium profile [8]. ...
... In the present paper, a semi-analytical model has been developed for a fast evaluation of the shoreline recession of a beach protected by submerged/emerged breakwaters only due to the cross-shore sediment transport. The approach is an extension of the Dean's method [7] where some limitations are overcome. The Dean's equilibrium profile cannot always describe field data adequately and their main parameters are found also to change with time [15]. ...
... On the contrary, the model here proposed can be applied to beach profiles of any shape, not only the Dean's equilibrium beach profile. The proposed model is also valid for steeper beaches in which the approach of Dean [7] cannot be applied due to the assumption of small shoreline recession with respect to the width of the breaker zone. In addition, the contribution of submerged or emerged breakwaters to the wave height reduction and water level variation is taken into account. ...
The climate change process is leading to an increase in the sea level and the storm intensity. The associated shoreline recession can damage coastal facilities and also beaches protected by submerged/emerged breakwaters whose defense action can become ineffective. The application of cross-shore numerical models does not allow the performance of long-term analyses. In this paper, a semi-analytical model for the evaluation of shoreline recession due to waves and sea-level rise for free and protected beaches is proposed. The model is an extension of the Dean’s approach in which some limitations on the beach profile are overcome and the effects of breakwaters on the wave height (wave transmission) and on the water level (piling-up) are considered. The model takes into account a wide range of parameters for wave, sea level, beach profile, and breakwater characteristics. Among the breakwater parameters, the freeboard and the berm width are found to mainly affect the shoreline recession. For submerged breakwaters, an optimal value of the freeboard can be computed depending on the sea level and the offshore wave characteristics. The results of the model are then used to find prediction relations of the shoreline recession, with r2 > 0.99, for both free and protected beaches, depending on the main hydrodynamic/geometrical characteristics.
... Perturbations related to seawalls depend upon several factors, such as the sedimentary context and shoreline evolution [5,6], the type and design of the structure [7,8], wave conditions [3,[9][10][11], the characteristics of the beach water table [12] or the position of the seawall relative to the shoreline [4]. This last point is crucial to evaluate the impact of the seawall on the topo-bathymetric beach profiles [13][14][15]. Other authors have reported contrasting conclusions about adverse effect, such as scours at the base of the wall [16][17][18][19] or end-effect, at the directly adjacent shore [6,[20][21][22]. ...
... The impacts of different kind of built structures on beach morphology and erosion hazard are theoretically well-known (Figure 9; see References [1,2,13,48,49]), but, in fact, magnitudes of the perturbations are related to multiple and complex non-linear factors. In the literature, conclusions appear often discordant, site-dependent and strongly related to the approach taken (flume experiment, model and field observation). ...
... Finally, a few quantitative approaches are available to anticipate the topo-bathymetric impacts of sea walls [13]. Promising works were recently presented [14,15] to draw expected perturbations related to seawall and sea-level rise on nearshore topo-bathymetric profiles. ...
Seawalls are commonly used worldwide to protect urbanized sea fronts. These alongshore protection structures are often blamed for hydro-sedimentary dynamics perturbations, but without clear and generalizable conclusions on long-term morphodynamic effects. In this paper, evolutions of beaches are studied from 1966 to 2021, comparing the urbanized sea front of Lacanau seaside resort (Aquitaine France) and adjacent natural areas. A large-scale spatiotemporal multisource dataset is used to derivate several indicators and evaluate the characteristics and magnitude of passive and active erosion related to a large riprap seawall at a highly energetic meso–macro tidal coast. The most dramatic manifestation of the presence of the seawall (passive erosion) is the beach lowering and the reduction of beach variability at the seasonal and interannual timescale in front of the seawall. However, recent evolutions are roughly similar at the seawall-backed beach than at the natural sector, indicating no specific active seawall influence on beach erosion or recovery. The perturbations directly attributable to the seawall (active erosion) are limited to temporary end-effect, slight perturbation of outer bar pattern and the setup of a slight platform around the depth of closure. The adverse effects are currently manageable, but they require a new strategy in view of the chronic shoreline retreat at adjacent sectors and the expected effects of climate change.
... The results obtained from this approach look encouraging (Broker et al., 1995;Roelvink et al., 1995, Nicholson et al., 1997Leont'yev, 1999 The best known and most commonly used equilibrium beach profile form is Dean's profile, which determines the shape of equilibrium beach profile with regard to the offshore distance and the sediment. The profile does not consider the effects of wave climate, and coastal currents (Dean 1991; Türker and Kabdaşlı 2006; Gonzalez et al. 1999). Several equilibrium beach profiles have been characterized to represent cross-shore profiles subject to different conditions (Dean 1991, Özkan-Haller and Brundidge, 2007, Bodge 1992Holman et al. 2014).Beach profiles are likely to stay the same under long-term wave climate and persistent sediment size, which means that the sediment transport is equal to zero (Bowen 1980). ...
... The profile does not consider the effects of wave climate, and coastal currents (Dean 1991; Türker and Kabdaşlı 2006; Gonzalez et al. 1999). Several equilibrium beach profiles have been characterized to represent cross-shore profiles subject to different conditions (Dean 1991, Özkan-Haller and Brundidge, 2007, Bodge 1992Holman et al. 2014).Beach profiles are likely to stay the same under long-term wave climate and persistent sediment size, which means that the sediment transport is equal to zero (Bowen 1980). Bruun (1954) proposed the power law approach, most used form of equilibrium beach profile, but it is commonly known as Dean's profile. ...
... The equilibrium profile described by Dean (1991), h = Ax 2/3 , is mainly based on sediment characteristics, in particular grain size (Karunarathna et al. 2011).( Figure 6) compares cross-shore profiles measured by INCC and Dean's profile corresponding to A=0.02, which was determined based on the sediment characteristics in the study area. It was noticed that there was a considerable difference between the cross-shore profiles and Dean's profile. ...
Addressing the interaction of the presence of coastal structures, breakwaters for instance, and morphological changes is of great importance. The purpose of this paper is to investigate the influences of the extended breakwaters of Astara Port on sediment transport and beach morphological evolution in the vicinity of them so as to identify how the extension of breakwaters altered the sea bed topography. In order to describe evolving cross-shore profiles in the study area, beach profile surveys were conducted by a single-beam echo sounder. Results showed that the breakwaters considerably affected their surroundings, and scouring in front of them was obvious. Furthermore, comparisons of measured beach profiles with Dean's profile model for the equilibrium beach profile illustrated that the Dean's profile was not able to precisely represent the time-mean profiles. As a result, Dean's equilibrium profile was modified and a new model was developed so that it can represent more correctly cross-shore morphodynamics of the study area. The results revealed that modified equilibrium profile can be a better representative for the cross-shore profiles of the study area.
... Fig. 1 shows a sketch of the initial experimental setup as well as the positions of the wave gauges along the length of the flume. Included in the figure (solid red line) is also the expected equilibrium profile based on Bruun (1954) and Dean (1991Dean ( , 2002: ...
... where is the offshore distance from the shoreline and is a proportionality constant, which was fitted on a case-to-case basis by Bruun (1954), while Dean (1991Dean ( , 2002 obtained the following grain/fall velocity dependent parameter in = 0.067 0.44 ...
Experimental results involving shoreface nourishment scenarios are presented. The experiments are performed at small scale and the effects of nourishment placement and timing in relation to long-term cross-shore profile development are investigated. Four different nourishment scenarios are tested experimentally, with nourishment positioned both in the trough of a pre-developed profile as well as along the bar of the profile. The results demonstrate that under all scenarios the erosion of the shoreline slows relative to the case without nourishment. The two cases where the nourishment was placed along the bar reduced erosion of the shoreline more compared to the two cases with nourishment in the trough onshore of the bar. Compared to past experiments on nourishment presented in the literature, the present experiments were run for a longer duration, and the concepts of equilibrium profile and the development towards such an equilibrium were investigated. Curiously, the experiments showed a reversal of the sediment transport rate from being primarily offshore directed across the entire profile to onshore directed in the inner surf zone region closest to the shoreline. This reversal of transport rate occurred without changing the incoming wave conditions and resulted in deposition at the shoreline. This either questions the existence of equilibrium beach profiles or at the very least shows that the development towards such an equilibrium will not always be monotonic in time.
... Despite active changes in the upper shoreface, the general shape of the shoreface profile derived from averaging over a significantly long period appears to follow an equilibrium shape. Theoretically, a profile with such an equilibrium shape is able to effectively dissipate incident wave energy so that net sediment transport is zero at any location of the profile (Bruun, 1954;Dean, 1991). ...
... This relationship assumes a balance between the sediment yield from the horizontal retreat of the profile, and the sediment demand to fill the increased accommodation space from a vertical rise in the profile. The equilibrium shoreface profile formulation was later confirmed by more field data worldwide and has gained its popularity in coastal engineering applications over decades (e.g., Ashton et al., 2011;Davidson-Arnott, 2005;Dean, 1977Dean, , 1991Deng et al., 2014;Wolinsky & Murray, 2009;Zhang et al., 2015). ...
Coastal morphology refers to the morphology and morphological development of the coast in response to a combined influence of atmospheric, oceanic and anthropogenic forcing. Coastal morphology comprises a wide variety of landforms (exposed to air) and bedforms (submerged in water) manifested in a large spectrum of spatial scales (10-10 m scale) and shapes ranging from mildly sloping lower shoreface to steep cliffs, from small ripples to large river deltas. Coastal zones are cradles for life. About 40% of the global human population and 50% of marine life are living in low-lying coastal zones with elevation less than 10 m above the mean sea level. Coasts contain the highest biodiversity in the surface earth system yet are highly vulnerable to environmental stressors associated with human activities and climate change. Climate impacts coastal morphology in multiple ways, including ice cover/melting, precipitation, temperature, and wind. In response to a changing climate, adaptation of coastal morphology can be categorized into three basic states: erosional, stable, and accretionary. Each state may persist or iterate at any given part of a coast, even in the context of a persistently warming or cooling climate. Anthropogenic protection has been globally implemented to ease erosion and protect human property. However, it remains largely unknown whether the existing measures would be able to counteract the effects of climate change in the upcoming decades.
... Beach orientation, sediment classification, morphology, bottom composition, currents, and prevailing wind-generated waves are the main parameters for the morphodynamic variability that acts along and across the shore. The identification of the equilibrium in the beach planform could be characterized as static equilibrium, dynamic equilibrium, or unstable or natural reshaping [24]. Such parameters can help to determine the wave effect on sediment transport, to determine the duration of wave action, and to identify if there is a potential threat to the wider area. ...
... For each section, the sediment volumes transported on either side of each section for each scenario were quantified annually. The total sediment volume for Section 1 was estimated at 3047 m 3 , directed to the southwest, and for Section 2, at 4744 m 3 Taking into account the data of wind and wave conditions for the study area [31][32][33][34] Taking into account the data of wind and wave conditions for the study area [31][32][33][34] and the orientation of the coast, the most extreme event was on 24 (Figure 13). For the specific time period, the average velocity of the coastal current was 0.22 m/s and the maximum value was 2.95 m/s, located at the southern part of the area with a NE direction. ...
Myrtos Beach (Cephalonia Island, Ionian Sea, Greece) represents a pocket beach with strong touristic, economic and natural interest. In this research, the morphodynamic behavior of the coastal area (e.g., hydrodynamic and sedimentary state, morphology, orientation, etc.), the current wave conditions (extreme and dominant waves, wave exposure), and also external factors, such as human impact and the geotechnical condition of the wider area, are examined. Short- and medium-to-long-term analysis took place, such as mapping, sediment analysis, wave/wind analysis, numerical modeling, and satellite monitoring, in order to identify the dynamic forcing parameters related to geomorphology, sedimentology, and hydrology that prevail in the area. Additionally, the intense tectonics, the karstified limestones, and the steep slopes of the cliffs in combination with the frequent seismic events on the island set up a geotechnically unstable area, which often cause landslides on the beach of Myrtos; these supply the beach with a large amount of aggregates, constituting the main sediment supply. Wave exposure forcing conditions, longshore–rip current direction, and other hydrodynamic processes are stable with high values in the area, causing notable sediment transport within the bay boundaries. As a result, at Myrtos Bay there is a dynamic balance of the natural system, which is directly affected by human interventions. Taking also into consideration that Myrtos is one of the most famous beaches in Greece and one of the main attractions of Cephalonia Island with thousands of visitors every year, beach management must be focused on preserving the natural system of the coastal area.
... Indeed the maturity of the profile data set, especially in the US, is such that it is considered that \.the present lack of understanding of nearshore processes precludes quantitative prediction of beach profiles..' (Dean, 1991). It is considered that the understanding of beach profile behaviour is at a stage where modelling is considered possible. ...
... It is considered that the understanding of beach profile behaviour is at a stage where modelling is considered possible. The concept of the 'equilibrium profile', although long-established (Brunn, 1954), has been revisited, qualified (Dean, 1991) and applied to beach profile models (e.g. Hansen and Kraus, 1989). ...
p>Meso-scale (tidal time-scale) shingle beach processes are examined, using a combination of direct (trapping, tracing and core) and indirect (survey) data on an open shingle beach at Shoreham, W. Sussex.
Traditionally, studies of the coastal zone have been restricted to macro-scale investigations; these utilise morphometric comparisons, which are indirect and record the superimposition of many processes occurring over long periods. In order to gain an insight into the processes themselves, there is a need to study the appropriate processes at meso- and micro-scale (Horikowa, 1981). The technology to study micro-scale processes is still under development. Similarly, although approaches to the understanding of meso-scale processes have been available for the past two decades, there has been a reluctance to use such technology; this is due to the highly variable results produced, especially during high energy conditions. Against this background the present investigation seeks to develop more definitive measurement techniques, to study processes which influence shingle beach behaviour.
The literature review undertaken identified that results of transport experiments are sensitive to the various methods used. In particular, a number of fundamental requirements are identified; these have resulted in the development of the 'electronic' pebble.
Shingle transport was monitored during a (5 week, 2 Phase) field measurement programme, during a range of wave energy conditions. The first phase involved the coordinated deployment of trapping and tracer studies, using the 'electronic' and aluminium pebbles. The deployments were supported by daily measurements of beach form, together with the automatic recording of breaking waves. The results demonstrate that reliable transport measurements were possible during storms, using tracers (especially the 'electronic' types where recoveries of 78% were achieved). In contrast, the traps were susceptible to damage and, similarly, interacted with the processes being measured.
The second phase of the field programme involved a high intensity (1 to 2 tide resolution) morphometric study, incorporating transport layer thickness measurements and the monitoring of shingle beach behaviour. Wave observations were obtained at the same time. The morphometric study allowed Powell's (1990) SHINGLE beach profile model to be validated. The transport layer experiments reveal a direct relationship between breaker wave height and disturbance depths. Furthermore, shingle beaches display transport layer efficiencies which are comparable to morphometrically-similar sand beaches. At the same time, tracers record reliably the mobile layer thicknesses. Using novel (Grid and Column) tracer injection methods, shingle transport is shown to vary within the beach system. Differential across-shore transport is most pronounced during storm conditions (where an association with breaker zone transport, rather than swash, was found). Longshore transport is found also to decay with depth. The assumption that tracer material which moves vertically also undergoes horizontal advection was validated. Transport rate calculations indicate that shingle transport efficiency (K) increases with increased wave power. The reliability of the measurements obtained were confirmed by use of morphometric data.</p
... In our contribution, we only applied an equilibrium model based on that developed for the shoreline by [41]. However, different equilibrium response frameworks exist [21,22,29,48,49]. The model of [21] was also tested here, showing similar skill. ...
Beach slope is a critical parameter to, e.g., beach safety, wave reflection at the coast and longshore transport rate. However, it is usually considered as a time-invariant and profile-average parameter. Here, we apply a state-of-the-art equilibrium model to hindcast beach slope variability from the time scales of days to years at the high-energy meso-macrotidal sandy beach of Truc Vert, southwest France. We use 9 years of bimonthly beach surveys to compute beach slope time series at different elevations. Results show that beach slope exhibits an equilibrium response with contrasting behaviors along two distinct areas of the beach profile. From 0 to 2 m above mean sea level, which is located under the berm crest, a slope response predominantly at the storm time scale is observed. The beach slope steepens under low energy waves, with the equilibrium model explaining up to 40% of the observed beach slope variability. In contrast, from 2.5 to 4 m above mean sea level, which is above the berm crest, the beach slope steepens under high-energy waves. Within this region of the beach profile, the response time scale increases upwards from seasonal (~2.5 m) to seasonal (~4 m), with the model explaining up to 65% of the observed beach slope variability. Such behaviors are found to be enforced by the berm dynamics developing from the end of the winter to early autumn, providing new perspectives to model and predict beach slope on sandy beaches.
... Once the weather calms the constructive equilibrium profile of the beaches [79] in a long-term building trend (accreting conditions), the sand drift slowly moves great sand volumes longitudinally along the beach. This is the most important sedimentary dynamic that requires sustainable management and which the construction of the breakwater has been unable to slow down. ...
Since the 1970s, dredging sands have been poured onto the embayed beaches of La Magdalena in the western mouth of the estuarine Bay of Santander (N Spain) in order to increase beach width. Up until the year 2000, the sands were systematically fed by a trailing suction dredge, which was later replaced by truck sand transfers from the surplus sands of the western beach to the eastern ones and by mechanical redistribution to create artificial berms. A recent project aimed to solve sand losses after each storm by building two perpendicular breakwaters about 620 m apart.
... Shoreface morphologies are variable globally (Athanasiou et al., 2019), and while the general assumption is that shorefaces adopt an equilibrium profile (Dean, 1991), in nature such morphologies are only rarely developed and many observed profiles are not well fitted by equilibrium parametrizations (Hamon-Kerivel et al., 2020). Equilibrium morphologies, in fact, appear to be more an exception than the general rule, especially under geologically-constrained conditions and/or sediment scarcity (Pilkey et al., 1993;Thieler et al., 1995). ...
Shorefaces are transitional zones between the shelf and surfzone/beach systems. They are subdivided into ‘upper’ and ‘lower’ shoreface sectors, which display particular morphodynamic behaviour. The upper shoreface is morphologically active over short (annual) time scales, while the lower shoreface changes over much longer time scales (decadal and beyond).
Shoreface morphodynamics is examined using three distinct examples from the high-energy coast of Ireland. Numerical modelling (SWAN) is used to characterise energy dissipation across the shoreface.
Our results show that zonation patterns and the physical extent of shorefaces display distinct spatial, as well as, temporal variations. The shoreface’s physical limits and internal zonation are driven by the combination of local wave forcing and pre-existing shoreface morphology. Shoreface behaviour seems to fall within a spectrum between gradual and intensive energy dissipation.
We show that particular seabed morphology controls the extent of, as well as the bed shear stress distribution across the shoreface. This may have significant implications for any adjoining beach systems, as waves arriving at the surf zone acquire specific characteristics, depending on the shoreface configuration, even under similar offshore wave conditions. Additionally, the variation of shoreface extent impacts the volume of sediment available for transport, both to the nearshore zone and therefore beach systems. The influence of shoreface morphology is an important, but largely overlooked element in the study of mesoscale coastal behaviour as well as coastal response to global climate change and secular sea-level rise.
... The calculation domain of the generic study area in LTC was defined by regular topohydrography with an area of 8 × 10 km 2 , Figure 1, represented by a regular square grid (20 m spaced), with 401 × 501 points (respectively, in the cross-shore and longshore directions). Dean profile, h = Ax m [28], was considered to define the bathymetry of the study area in which the sediment-dependent scale parameter (A) was defined to be equal to 0.127, according to Portuguese beaches sediment grain size, and the parameter related to the beach exposure to wave energy (m) was defined to be equal to 2/3 (value generally considered for intermediate beaches). The topography was defined with a constant slope equal to 2%. ...
Worldwide, artificial nourishments are being considered as one of the main coastal erosion mitigation measures. However, this solution is not permanent, since the natural removal of sediments that occurs after the sand deposition leads to the need of re-nourishment projects; thus, its performance and longevity dependent on several design parameters (placement site and extension alongshore, frequency, and volume, etc.) In this work, a methodological approach for cost–benefit assessment is applied to analyze the performance of artificial nourishments from a physical and economical point of view, by analyzing the effectiveness of different scenarios. The study was developed considering two study areas: a hypothetical situation (generic study area) and a real coastal stretch (Barra-Vagueira, located in the Portuguese west coast). The findings show the complexity in defining the best nourishment option, being dependent on the wave climate, site specific conditions, and main goal of the intervention. The proposed cost–benefit approach allows one to obtain and compare the physical and economic performance of artificial nourishments to mitigate coastal erosion, aiding the decision-making processes related to coastal planning and management.
... Para isso, devem-se ter informações adicionais dos parâmetros meteocenográfi cos como ondas, correntes, marés, ventos e granulometria dos sedimentos na face praial. Através do cálculo do perfi l de equilíbrio (Equação 9) proposto por Dean (1977;1991), utilizando valores médios de granulometria (AMARO et al., 2012b), foi encontrado o perfi l de equilíbrio para cada perfi l indicado na Fig.8. ...
Este trabalho apresenta metodologia desenvolvida para levantamento, geração e avaliação de Modelos Digitais de Elevação (MDE) de superfícies praiais (setores emersos e submersos) de litorais arenosos a partir da integração de dados topográficos e batimétricos in situ, georreferenciados com precisão compatível aos estudos geomorfológicos da dinâmica costeira de curto prazo. A metodologia desenvolvida consiste em: a) levantamento topográfico da porção emersa da praia, pelo posicionamento relativo cinemático do GNSS (Global Navigation Satellite Systems) com apoio de um quadriciclo motorizado; b) levantamento batimétrico da porção submersa do perfil praial, apoiado por embarcação equipada com ecossonda e receptor GNSS operando em modo relativo cinemático; e, c) integração de dados de levantamentos topográficos e batimétricos para obtenção de MDE mais realista do perfil de praia. Os posicionamentos GNSS envolvidos nos levantamentos topográficos e batimétricos foram executados em relação às estações de controle da rede geodésica para a área de estudo, que fornecem referencial geodésico vinculado ao Sistema Geodésico Brasileiro (SGB), o qual é unívoco, fixo e relativamente estável no tempo. A metodologia foi aplicada para a praia de Ponta Negra, região nordeste do Brasil, caracterizada pela intensa ocupação humana e drástica erosão costeira, que oferece uma demanda motivadora para a potencialidade do procedimento proposto, relacionada à produtividade dos levantamentos e à precisão dos resultados, sem dúvida provando o progresso alcançado em comparação com os métodos clássicos de levantamento de perfis completos de praia.
... However, the crescentic bar appears to have migrated further offshore in the March-2022 bathymetry dataset, while in the November-2021 bathymetry dataset appears to be closer to the coastline. It is hypothesized that wave action during the winter storms resulted in dissociation of the "summer" structure of the bar, and a slow build-up of the deeper part of the bar as usually happens with typical beach profiles [73]. The only difference here is that this change occurs on a crescentic bar instead of a standard straight bar. ...
Short-term changes in shallow bathymetry affect the coastal zone, and therefore their monitoring is an essential task in coastal planning projects. This study provides a novel approach for monitoring shallow bathymetry changes based on drone multispectral imagery. Particularly, we apply a shallow water inversion algorithm on two composite multispectral datasets, being acquired five months apart in a small Mediterranean sandy embayment (Chania, Greece). Initially, we perform radiometric corrections using proprietary software, and following that we combine the bands from standard and multispectral cameras, resulting in a six-band composite image suitable for applying the shallow water inversion algorithm. Bathymetry inversion results showed good correlation and low errors (<0.3 m) with sonar measurements collected with an uncrewed surface vehicle (USV). Bathymetry maps and true-color orthomosaics assist in identifying morphobathymetric features representing crescentic bars with rip channel systems. The temporal bathymetry and true-color data reveal important erosional and depositional patterns, which were developed under the impact of winter storms. Furthermore, bathymetric profiles show that the crescentic bar appears to migrate across and along-shore over the 5-months period. Drone-based multispectral imagery proves to be an important and cost-effective tool for shallow seafloor mapping and monitoring when it is combined with shallow water analytical models.
... Deigaard et al., 1986) Les évolutions morphologiques à l'échelle de la zone pré-littorale ont été conceptualisées avec des prols d'équilibres le long desquels le transport net de sédiment, moyenné sur une grande période de temps, est supposé nul en tout point (e.g. Dean, 1991;Larson et al., 1999). Sur des échelles de temps annuelles à décennales, cet équilibre implique que la somme des ux sédimentaires orientés vers la côte compense la somme des ux sédimentaires orientés vers le large. ...
Ces travaux traitent de la dynamique hydro-sédimentaire de la zone pré-littorale en combinant l'exploitation de mesures in situ acquises dans des conditions modérément énergétiques à paroxysmales avec des simulations numériques d'un système de modélisation morphodynamique 3D qui s'appuie sur une approche "force vortex". Nous mettons d’abord en évidence une sous estimation de la hauteur significative des vagues modélisée dans des conditions paroxysmales, associée à une contribution surestimée du terme de dissipation par déferlement bathymétrique. Pour pallier à ce problème, nous introduisons une nouvelle paramétrisation du coefficient de déferlement qui contrôle la saturation des vagues déferlantes dans ces modèles. Nous présentons ensuite une étude qui porte sur la dynamique hydro-sédimentaire de la zone pré-littorale interne. Nous étudions la distribution spatiale et les mécanismes d'entraînement de la circulation transversale induite par les vagues en s'appuyant sur une caractérisation spatiale des processus de dissipation et nous analysons la dynamique du transport en suspension. Le transport opéré par le courant moyen apparaît dominant et on observe, en particulier, un transport net orienté vers le large associé au courant de retour forcé par les vagues. Enfin, nous présentons une dernière étude qui porte sur la dynamique hydro-sédimentaire et les évolutions morphologiques saisonnières à annuelles de la zone pré-littorale externe au niveau d’une concession d'extraction de granulats marins. Nous mettons notamment en évidence une dynamique de comblement des souilles d'extraction qui se produit essentiellement sous des conditions incidentes fortement énergétiques.
... In order to simplify this process, coastal engineers commonly use empirical expressions based on previous parameterization efforts. Shoreline movement is estimated through widely accepted methodologies (e.g. the Bruun rule (Bruun 1954) and the EBP method (Dean 1990)), whereas the estimation of wave run-up excursion is based on theoretical formulae that suggest that the excursion is controlled by the incident wave energy and the nearshore seabed slope (e.g., Holman 1986;Stockdon et al. 2006) Over the recent years, emphasis has been given to the development of image processing algorithms/techniques, capable to record/monitor with high accuracy specific coastal features of interest on specialized optical datasets deriving from coastal video monitoring systems (e.g., Vousdoukas et al. 2010;Vousdoukas 2014;Velegrakis et al. 2016). ...
Shoreline and wave run-up positions and their changes are crucial morphodynamic parameters for coastal engineering works and coastal zone management. In this contribution, the variability of the shoreline and wave run-up positions of an urban perched beach (Ammoudara, Herakleion - Crete, Greece) is presented for a 4-month energetic wave period. Specialized algorithms capable to detect/record the 2-D shoreline and wave run-up/swash maxima positions with high spatio-temporal resolution, were developed and used in geo-rectified time series of optical images derived from a Beach Optical Monitoring System (BOMS). It was found that the maximum shoreline and wave run-up positions at representative examined cross-shore sections of the beach ranged at 15 m and 5 m, respectively. No significant shoreline changes have been recorded during the 4-month energetic period; however, several beach sections show different patterns of sediment loss or gain. The proposed approach appears to provide an efficient and accurate coastal monitoring tool with high geo-spatial resolution. The latter is extremely important for beach managers, planners and policy makers, as the wave run-up plays a most significant role in the definition of the landward boundary of the Public Maritime Domain, and could define the swash maxima (i.e., the “aigialos” line).
... This synthetic bathymetry is based on the equilibrium shoreface profile concept detailed in Dean (1991), where the depth h at a cross-shore distance x from the mean sea level contour is given by the equation h = Ax 2/3 . The parameter "A" is determined based on the best fit to the cross-shore position of the 5 m depth contour, as determined from the average of all bathymetry surveys at each site. ...
Coastal hazard early warning systems (EWS) are an evolving disaster risk reduction tool that can provide information on coastal flooding and erosion along coastlines several days in advance of an impending storm, potentially providing a “window of opportunity” to implement a range of emergency responses. However, prototype and operational EWSs that provide quantitative predictions of storm impacts have to date focused primarily on the flooding component of coastal hazards. As such, it is unclear whether the modelling frameworks utilised by these EWSs are effective at forecasting coastal erosion along dynamic wave-dominated sandy coastlines where storm hazards are associated with rapid wave-driven morphological change of the sub-aerial beach. Herein, a prototype EWS modelling framework is developed at an erosion ‘hot-spot’ on the southeast coast of Australia and its performance evaluated to provide insight on forecasting coastal erosion on wave-dominated sandy coastlines.
Immediately pre-storm surveyed bathymetry is considered as the ideal nearshore bottom boundary condition for carrying out EWS erosion predictions but is logistically impractical to survey at short notice whenever a storm approaches. As such, a more practical approach of using time-invariant synthetic/representative bathymetries was explored and found to be an appropriate alternative for carrying out operational erosion forecasts.
The skill and accuracy of a new nearshore wave forecasting system and two established water level forecasting systems along the southeast coast of Australia were evaluated to identify the met-ocean systems that can be incorporated within the modelling framework of an operational coastal erosion EWS implemented along this coastline.
The synthetic/representative alternative bathymetry and the met-ocean forecasting systems are incorporated into the modelling framework of a prototype ‘hot-spot’ scale coastal erosion EWS. The performance of this system was evaluated, and the magnitude of error introduced into the EWS predictions from uncertainty within the modelling framework quantified. The results identified that the error in EWS erosion predictions was predominantly due to uncertainty in the morphodynamic model. This study demonstrates a prototype modelling framework that can be utilised by an EWS implemented along wave-dominated sandy coastlines and has identified areas for improvement that can potentially increase the accuracy of EWS erosion predictions.
... The most often used form is h(x) = Ax 2/3 in which h is the water depth at a distance x from the shoreline and A is the sediment-dependent scale parameter (e.g. Dean [101]). The equilibrium profile concept has proven to be useful in areas where longshore transport gradients can be neglected, and where the profile is able to reach equilibrium. ...
Coastal zones are the most important areas for human activities and infrastructure development. In addition, the coastal zone behavior is dynamic and need to be investigated extensively before any structure is planned so as to avoid damages due to natural processes such as erosion and flooding. For example, for the design of any submerged structures, it is necessary to study the beach profile change and the bathymetry due to the hydrodynamic conditions (wave and current actions) and the prevailing sediment transport patterns in the study area. Another example is the implementation of shoreface nourishments. The study of the beach profile behavior not only provide a means of determining the most effective location for the nourished sediments, but also give information on the behavior of the nourishment during the design life of the project.
Nearshore sandbars are sand deposits (i.e. shallow areas) occurring in the surf zone of sandy beaches. They also play as a submerged breakwaters that protect the beach during storms because waves dissipate part of their energy on the bar crest. They can also provide sand to the beach if they migrate onshore direction. These bars can grow as a result of natural morphodynamic instabilities, forced by the wave-induced current. In addition, these features have a strong effect on the nearshore hydrodynamics. The predominated morphological features in the nearshore zone are longshore sandbars. For these reasons, the sandbars morphology and the surf zone hydrodynamics are extremely important coupled. Understanding sandbar dynamics and the physical processes related to phenomena are also essential not just in a scientific perspective but in their effects on human activities, such as beach nourishments, protection structures or harbors, and environmental issues (water quality, pollutant dispersion, biologic activity, etc). For these reasons, this research aims to:
• Get more insight into the cross-shore hydrodynamic processes that responsible for the near-shore sandbars formation and development by using numerical simulation.
• Apply a new finite difference scheme which has not been used extensively for morphological calculations, and the results here represent the central contribution of this study.
... While acknowledging that a combination of storm tide, wave energy, storm duration and beach "character" determine the magnitude of coastal erosion, Zhang et al. (2001) make the case that storm tides determine the onshore distance influenced by storm waves and therefore, have a greater impact on beach erosion than wave energy. Furthermore, Zhang et al. (2001) point to several studies which corroborated their claim that storm tides contribute more to beach retreat than storm waves (Edelman, 1968;Edelman, 1972;Dean, 1991;Steetzel, 1991;Steetzel, 1993, among others). Finally, Zhang et al. (2001) indicate that continuous long-term wave data that correspond to water level data do not exist because wave buoy data contain relatively short-term data (e.g., 14 years at the buoy closest to the tide gauge data used in this study; Station 44099-Cape Henry, Virginia; Appendix A). ...
This paper presents a new empirical model, called the cumulative storm impact index (CSII), that quantifies the impact of coastal storms on sandy beaches. The new model utilizes user‐defined storm data to incorporate both individual storm magnitude and the cumulative effect of successive storms into an index, which is a proxy for beach erosion at a given time. Applying this model to long‐term water‐level data from a Virginia tide gauge showed that the greatest storm impact resulted not from the larger individual storms, such as the Ash Wednesday nor'easter of 1962, the “Perfect Storm” of 1991, or Hurricane Sandy of 2012, but rather from especially stormy winter seasons that occurred during the twenty‐first century. Additionally, the CSII model uncovered a trend—not detectable by single storm impact analyses—toward greater storm impacts, which began c. 1980 and continued to the present day. Finally, comparative analyses using wave power as a storm index shows CSII can capture decadal or seasonal scale storminess. We expect this model to have utility in many areas of the coastal sciences and engineering, including developing holistic response models, quantifying erosion potential at other locations, and managing coastal ecosystems.
... After that, Dean (1977) applied constant wave energy dissipation in a unit volume, and theoretically derived the relational expression presented by Bruun (1954). In various fields such as beach nourishment (Dean, 1991), beach management (Park et al., 2019), and sea-level rise (Bruun, 1962;Dubois, 1990), it has become a means to obtain various engineering solutions to predict and solve catastrophic problems caused by coastal erosion. Recently, Kim et al. (2021) expressed the vulnerability of ultimate erosion in terms of sand grain size by applying the equilibrium beach profile equation of Dean (1977). ...
Recently, the impacts of short-term erosion caused by storm waves on coastal damages are increasingly recognized as social issues, compared to those of long-term erosion from climate change or coastal development. The erosion caused by the storm wave has an episodic characteristic that the shoreline recovers gradually after retreating for a short-term. Furthermore, if shoreline changes caused by longshore sediment transport are not taken into consideration, the shoreline position is determined by following two physical parameters based on the bulk response model. The beach response factor determines converging ultimate erosion on the assumption that incident waves constantly affects a beach, which can be estimated according to the concept of Dean’s profile. On the contrary, the beach recovery factor affects the velocity of the shoreline retreat and recovery. Therefore, the parameter plays an important role to predict the peak erosion due to the storms. However, there are still insufficient researches to utilize it as an engineering design for erosion reduction. In this study, the two methodologies (i.e., approximation formula and statistical analysis) that estimates peak erosion width caused by the storms are compared to extract the beach recovery factor. During the process, it is confirmed that peak wave height has little impact on the beach recovery factor. Instead, it is mainly determined by the median grain size. Also, the beach recovery factor is estimated as a function of median grain size based on the shoreline and sand survey data conducted over ten years. Among the 41 surveyed sites along the east coast, 11 sites of straight-type shorelines that directly react to the incident waves were applied to consider only the short-term recovery process. To prove validity, the estimated applied into the real sea and then the results were compared to the shoreline data extracted from CCTV images. Using these results, the peak erosion width for a target wave event can be predicted with only median grain size. These study results are expected to be used as a concrete and practical means to manage the coast, in preparation for the current and future shoreline erosion threats.
... To assess the contribution of MSLR, a MSLR rate of 3.4 mm/yr [71] was used in the absence of more accurate local information; this amounts to a MSLR of about 0.14 m for the period of consideration . Using an ensemble of cross-shore morphodynamic models [34], consisting of the models from Bruun, Edelman and Dean [72][73][74] models, and 74 beach profiles (Table 1 and Figure 2), maximum shoreline retreat due to MSLR was estimated as about 6 m. Thus, MSLR cannot explain by itself the observed high beach losses. ...
Coastal and marine ecosystems are supplying a wide range of services. With accelerated Sea Level Rise, intensification of waves and storm surge severity and increasing anthropogenic pressures, these areas are under multiple threats and society may not receive the same level of ecosystems services. This study aims at measuring the trend of beach erosion and at identifying and quantifying the role of some coastal and marine ecosystems in mitigating beach erosion in the region of Negril (Jamaica). In this location, the tourism industry provides the main source of economic revenue. Even at the national level, the two beaches are important assets linked with 5% of the national revenue as 25% of the hotel rooms are located around Negril. In Jamaica, the tourism industry is a significant component of national GDP. 25% of hotel rooms are located around the two beaches of Negril, which have lost an average of 23.4 m of width since 1968. Given the importance of Negril’s beaches to their economy, the Government of Jamaica asked UNEP to conduct a study to identify causes of beach erosion in Negril and potential solutions to address trends of beach erosion, in the context of future sea level rise scenarios induced by climate change. This paper addresses the current beach erosion status and future trends under different climate scenarios. We explain how, by using remote sensing, GIS, wave modelling and multiple regressions analysis associated with national, local and community consultations, we were able to identify and quantify the role of ecosystems for mitigating beach erosion. We show that larger widths of coral and seagrass meadows reduce beach erosion.
... The processes that drive beach evolution are inadequately understood (Hoefel and Elgar, 2003;Ludka et al., 2015;Ruggiero et al., 2016), especially in nearshore regions where sand ripples are ubiquitous (Clarke and Werner, 2004;Hay and Mudge, 2005). Established equilibrium coastal profile models generally poorly reproduce the beach shape in the surfzone when ripples and sandbars are dominant morphologic features (Dean, 1991;Clarke and Werner, 2004;Ludka et al., 2015). Moreover, coastal morphologic change models are shown to under-predict large-scale coastal adjustment in regions that are populated by dynamic sand ripples and sandbars (Terwindt and Wijnberg, 1991;Sherman, 1995;Brakenhoff et al., 2020). ...
Field observations of small scale seabed morphology were obtained over 4 weeks at two locations separated 66 m along a cross-shore transect during the 2014 MEGAPEX Experiment conducted as part of the longer term Sand Engine mega-nourishment project along the North Sea Coast of The Netherlands. The seafloor was continuously covered by dynamic bedforms with amplitudes ranging 0.02–0.40 m and wavelengths ranging 0.20–2.5 m. Ripple migration rates were up to 3.6 m/h, dependent on the energy of the waves and currents. Under the assumption of bedload dominant transport, cross-shore and alongshore sediment volume flux by ripples was estimated from observations at the spatially separated imaging locations. The average and maximum ripple sediment volume flux was found to be 0.22 and 1.7 m³/m/day, respectively, with larger fluxes during spring flood tides and storm wave conditions. The daily averaged fluxes were usually oriented about 30° north of shore-normal, moving in the same direction as a nearby transverse sandbar migration direction. Estimated gradients in the sediment flux within the surfzone were computed from bed level change measurements of the inner surfzone including a larger scale transverse sandbar measured from subsequent jetski surveys. We find that the estimated gradients in surfzone sediment flux are conceivably driven by small variations in the sediment flux driven by sand ripple migration, supported by our observations of ripple driven sediment flux at the two ripple imaging stations. A simple conceptual model is presented that shows how small scale bedforms may contribute to the growth and decay of larger scale bathymetric features, such as sandbars. Results suggest that sediment flux by small scale sand ripples and megaripples could significantly contribute to larger scale morphologic development in the surfzone.
... The next step of the analysis aimed to project shoreline retreat based on widely used analytical models (i.e., Bruun 1988;Edelman 1972;Dean 1991) that take into account morphodynamic characteristics (beach and subaqueous slope, sediment texture, and wave conditions) under different scenarios of SLR. Sediment texture and slope information relied on data acquired from previous steps, while maximum wave forcing was abstracted from the "Wind and Wave Atlas for the Hellenic Sea" information (1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006) (Soukissian et al. 2007). ...
Sea level rise could result in the loss and shrinkage of coastal habitats, jeopardizing the persistence of a number of species that rely upon these highly dynamic and sensitive areas. With reproduction and population recruitment depending exclusively on low-lying sandy beaches, marine turtles are among the organisms for which sea level rise represents a major threat. Here, we provide an assessment of the potential impacts of sea level rise upon sandy beaches located at the Ionian Archipelagos, which host some of the main nesting sites of the Mediterranean population of the loggerhead marine turtle Caretta caretta. Our analyses focused on sandy beaches which host stable or sporadic nesting as well as on sites that could potentially serve as nesting grounds for the species. We demonstrated that more than 60% of the stable nesting sites (accounting for about half of the total nesting activity in the region) are likely to fail to act as nesting sites under moderate and worst case scenarios of projected sea level rise by 2100. We found that only about one fifth of the stable and the sporadic nesting beaches were characterized by high resilience to SLR, meaning that the effective zone for nesting can migrate landwards and fit in the remaining upper beach part. Potential nesting sites were subjected to even lower resilience to sea level rise, suggesting that even if marine turtles could shift to new, nearby nesting sites, the efficiency of such a response would be limited. These alarming findings call for the prioritization of conservation and restoration efforts towards sandy shores of moderate and high resilience to sea level rise which are currently used for stable or even sporadic nesting.
... The theoretical equilibrium profile shape is determined by the local sediment and wave climate characteristics (Dean, 1991). Therefore, the preservation of the equilibrium profile shape implies that the local wave climate characteristics remain roughly constant. ...
Shoreline change along sandy coasts responds to a myriad of processes interacting at different spatial and temporal scales, making shoreline predictions challenging. Shoreline modelling inherits uncertainties from the primary driver boundary conditions (e.g. sea-level rise and wave forcing) as well as uncertainties related to model assumptions and/or misspecifications of the physics. Despite the recent progresses in addressing uncertainties related to sea-level rise (SLR), the uncertainties related to wave-driven shoreline response are still poorly understood. This thesis gathers wave-driven equilibrium shoreline models, SLRdriven recession models, and variance decomposition methods into a probabilistic framework to investigate the roles of several sources of uncertainty in modelled shoreline change. The framework is applied to analyse the uncertainties associated with past and future multi-decadal shoreline evolution at the cross-shore transport dominated sandy beach of Truc Vert (France). As the physics of the combined action of waves and sea-level rise has not yet been described in detail, the thesis also presents a novel physical interpretation of the beach response to sea-level rise to support the integration of SLR-driven recession into equilibrium shoreline models. Shoreline response under the coupled effects of waves and SLR reveals complex patterns and interplays of the several contributions of uncertainties to shoreline predictions. Overall, uncertainties on Truc Vert shoreline predictions across the 21st century are driven by the uncertain model free parameters and wave conditions over the first half of the century. Then, the uncertainties on SLR become the dominant driver over the last decades. When uncertainties on SLR are negligible, the uncertainties of wave conditions variability are responsible for up to 83% of the uncertainties in modelled shoreline. It is also observed that the uncertainties in modelled shoreline trajectories depend on the underlying physical assumptions of different equilibrium shoreline models and future climate scenario.
... The average profile is often assumed to represent a state of equilibrium. Profile averaging has been used in various studies to obtain equilibrium beach profiles (e.g., Dean, 1977Dean, , 1991Karunarathna et al., 2016;Davis, 1998, 1999). Variation from the equilibrium profile is assumed to be a measure of the degree to which a set of profiles deviates from equilibrium at a particular time. ...
Beach nourishment has been widely used for coastal protection in China. However, few beaches have been monitored after nourishment, and the evolution of nourished beaches has not yet been elucidated. This paper presents a study of two nourished beaches, both of which are in low-wave-energy environments but have different tidal ranges: Huizhan Beach, with a large tidal range, and Meiliwan Beach, with a small tidal range. To gain a better understanding of the evolution of these nourished beaches, beach profile surveys were carried out repeatedly over 4 and 2 years after nourishment, respectively. The nourished beach evolutions were analyzed in terms of profile morphology, foreshore slope, dry beach width, and remaining sand volume. From the results obtained, it can be seen that Huizhan Beach profiles demonstrated major changes during the initial adjustment, followed by a stable state, while Meiliwan Beach profiles demonstrated major changes both during the initial adjustment and after a storm. Moreover, Huizhan Beach presented a rapid volume loss during initial adjustment, which was related to both the steeper foreshore slope and longshore spreading. For the analysis of profile equilibration, Huizhan Beach profiles changed rapidly and achieved equilibrium in several months, while Meiliwan Beach changed in stages and approached final equilibrium after the first postnourishment storm. The different mechanisms of profile equilibration at the two beaches were closely related to the tidal ranges of the sites. On the basis of the observed evolution, two types of profile evolution patterns of nourished beaches with different tidal ranges were proposed. ADDITIONAL INDEX WORDS: Remaining volume, profile equilibration, tidal range, storm response.
... The breaking criterion to limit the active profile during individual storms (e.g. Dean, 1991;Dean and Dalrymple, 2004) is circa − 10 m MSL for Christina storm. This depth is clearly located outside the rocky embayment framing the sand beach as shown by bathymetric data in Fig. 1B. ...
Understanding time scales of beach response (erosion and recovery) to extreme storms is particularly relevant for management of coastal land and risk. Observations show that rock-bounded platform beaches are generally remarkably stable and only occasionally respond to extreme storm wave forcing with abrupt morphological changes. The present work aims to understand the conditions leading to the disruption of beach stability (storm thresholds for morphological changes) and to comprehend the conditions of the subsequent recovery.
Results obtained at two rock-bounded beaches of the western Portuguese coast over five years provided the foundations of a new conceptual morphodynamic model. This model explains abrupt beach disruption as a consequence of full inundation of the beach profile during extreme storms, together with strong wave reflection at the rigid landward boundary, causing major erosion of the subaerial beach. We argue that the timescale of post-storm recovery depends essentially on the fate of the sediment transported offshore during the storm event. If sediments remain within the beach sediment cell (underwater beach section) beach recovery to pre-storm conditions is very fast, while recovery is much slower if sediments exit the beach sediment cell. In the latter case, beach recovery depends on external sand sources, which can lead to recovery time scales of several years.
... Generally, the stability of a sandy coast can be assessed by the equilibrium beach profile during a long period of observation [39][40][41][42]. However, the exact movement of bar and berm induced by the cross-shore process during the recovery process was difficult to determine due to the complex movement of sediment or the disturbance caused by tsunami. ...
The 2011 Great East Japan earthquake and tsunami caused significant damage along the coastal region in Miyagi Prefecture. In the Natori River of Miyagi Prefecture, the recovery process of the estuarine morphology has been observed since the tsunami arrived. In this study, detailed analyses of collected aerial photographs and beach topography in front of the river mouth were conducted to evaluate whether the river mouth has reached a new equilibrium. The shoreline analysis suggests that the river mouth has obtained an equilibrium state after 2014 in which the sediment volume can be preserved within the littoral system. In addition, the convergence process to the stable topography was detected by the first spatial and temporal eigenfunctions obtained from the empirical orthogonal function (EOF) analysis of the beach profiles. From the results, it can be concluded that the river mouth has obtained a new equilibrium of morphology after the tsunami. As the recurrence of the tsunami can be expected in the next several centuries, the findings of this study can be useful for long-term coastal and riverine management against future disasters in this river mouth, and other coastal regions that are prone to large-scale disasters in the near future.
... Although many beach nourishments have been carried out over the past decades, there are still some uncertainties about their technical design and execution. It is hypothesized, for example, that larger nourishments lead to more initial erosion (Leonard et al., 1990;Dean, 1991). Furthermore, it is hypothesized that beach nourishments have a longer lifespan if they are carried out in spring, just after the storm season (e.g. ...
The Dutch coast is one of the most heavily nourished coasts globally. An average of 12 mln. m³ is annually added to the coastline of only 432 km for dynamic coastline conservation. This study provides an overview of the operational aspects of the more than 300 nourishments for coastline maintenance that have been performed since the 1990s and discusses the evolution of the nourishment approach and lessons learned with regard to the nourishment design. The first nourishments were beach and dune nourishments to repair local beach and dune erosion. In the 1990s the nourishment efforts increased when nourishing the coastline was set in policy as the formal strategy to dynamically preserve the coastline. Simultaneously shoreface nourishments emerged, which aim to feed the coast gradually over a longer period than beach nourishments. In 2001 the volume of sand used for nourishments increased from 6.4 to 12 mln. m³ per year, to enable the coastal zone to stay in equilibrium with sea level rise. Channel wall nourishments were introduced around that time because they can slow down the landward migration of tidal channels and can accommodate large volumes of sediment. Nowadays, underwater nourishments are preferred because of the lower costs associated, but the decision for a beach, shoreface, or channel wall nourishment also depends on the morphology, the local setting, and the purpose of the nourishment. All nourishments combined have succeeded in conserving the coastline at its desired position over the past 30 years.
... Cross-shore beach profiles can be approached using the theoretical equilibrium beach profiles proposed by Bruun (1967) [24] and Dean (1995) [25]. These equilibrium profiles derived from field observations have the following form: ...
Low tide terrace (LLT) beaches are characterised by a moderately steep beach face and a flat shallow terrace influencing the local hydro-morphodynamics during low tide. The upper beachface slope (β) and the terrace width (Lt) are the main morphological parameters that define the shape of LTT cross-shore beach profiles. This work aims at better understanding the behaviour of β and Lt and their link with the incoming wave forcing. For this purpose, our results are based on 3.5 years times series of daily beach profiles and wave conditions surveys at two different microtidal LTT beaches with similar sediments size but different wave climate, one at Nha Trang (Vietnam) and the other one at Grand Popo (Benin). While they look similar, two contrasting behaviour were linked to two sub-types of LTT regimes: the first one is surf regulated beaches (SRB) where the swash zone is highly regulated by the surf zone wave energy dissipation on the terrace, and the second is swash regulated beaches (SwRB) acting in more reflective regime where the terrace is not active and the energy dissipation is mainly produced in the swash zone, the terrace becomes a consequences of the high dynamics in the swash zone. Finally, extending the common view of an equilibrium beach profile as a power law of the cross-shore distance, the ability of a simple parametrized cubic function model with the Dean number as unique control parameters is proposed and discussed. This simple model can be used for the understanding of LLT environments but it can not be extended to the whole beach spectrum.
Depth of closure (DOC) is defined as the most landward depth seaward of which there is no significant change in bed elevation and no significant net sediment exchange between the nearshore and the offshore over a certain period of time, such as 5 to 20 years. DOC is an essential parameter used in beach and shore protection, sediment management, and many other aspects of coastal studies. Taking advantage of advancements in wave hindcast and bathymetry measurement in the past 20 years (2000-2019), this study determined the DOC at 12 locations along the Florida coast, including three from the northwest Gulf coast, three from the west Gulf coast, and six from the east Atlantic coast. The 12 sites covered a wide range of coastal morphodynamic conditions, with considerable difference in tidal ranges, incident wave heights, as well as nearshore and offshore morphology. Hindcast wave data from WAVEWATCHIII, available since 2005, were analyzed and applied to calculate the closure depth using various empirical formulas. At all the 12 study sites, time-series profiles demonstrated an apparent convergence point indicating the presences of a DOC. The bed-level change at DOC, as quantified by the standard deviation of elevation variation, ranged from 0.05 m to 0.19 m. Along the studied northwest Florida Gulf coast the DOC ranged from 9.12 m to 9.76 m. The DOC along the studied west Florida Gulf coast ranged from 1.59 m to 4.06 m and is influenced by the shallow flat inner continental shelf. Along the studied east Florida Atlantic coast, the DOC ranged from 4.35 m to 8.20 m, with considerable alongshore variation. The Birkemeier formula yielded the closest predictions to the measured values. A linear relationship between the seaward slope of the outer bar and DOC was identified. Incorporating the seaward slope of the outer bar into the Birkemeier formula improved the accuracy of DOC prediction.
Climate change is resulting in global changes to sea level and wave climates, which in many locations significantly increase the probability of erosion, flooding and damage to coastal infrastructure and ecosystems. Therefore, there is a pressing societal need to be able to forecast the morphological evolution of our coastlines over a broad range of timescales, spanning days-to-decades, facilitating more focused, appropriate and cost-effective management interventions and data-informed planning to support the development of coastal environments. A wide range of modelling approaches have been used with varying degrees of success to assess both the detailed morphological evolution and/or simplified indicators of coastal erosion/accretion. This paper presents an overview of these modelling approaches, covering the full range of the complexity spectrum and summarising the advantages and disadvantages of each method. A focus is given to reduced-complexity modelling approaches, including models based on equilibrium concepts, which have emerged as a particularly promising methodology for the prediction of coastal change over multi-decadal timescales. The advantages of stable, computationally-efficient, reduced-complexity models must be balanced against the requirement for good generality and skill in diverse and complex coastal settings. Significant obstacles are also identified, limiting the generic application of models at regional and global scales. Challenges include the accurate long-term prediction of model forcing time-series in a changing climate, and accounting for processes that can largely be ignored in the shorter term but increase in importance in the long term. Further complications include coastal complexities, such as the accurate assessment of the impacts of headland bypassing. Additional complexities include complex structures and geology, mixed grain size, limited sediment supply, sources and sinks. It is concluded that with present computational resources, data availability limitations and process knowledge gaps, reduced-complexity modelling approaches currently offer the most promising solution to modelling shoreline evolution on daily-to-decadal timescales.
The IPCC sixth assessment report shows that the world will probably reach or exceed 1.5 degrees C (2.7 degrees F) of warming within just the next two decades and the oceans will rise between 10 and 30 inches (26–77 cm) by 2100 (Globally). The report highlights that the sea levels in South Asia could rise by 0.4 m in the low emissions scenario, about 0.5 m in the current pledges scenario, and 0.7 m in the high emissions scenario. Sea levels rise (SLR) has been rapidly increasing, with devastating effects on coastal habitats farther inland, it can cause destructive erosion, wetland flooding, aquifer and agricultural soil contamination with salt, and lost habitat for fish, birds, and plants. Studies by Indian scientists reveal that the trends of sea level rise are estimated to be 1.3 mm/year along the Indian coasts during the past 40–50 years (Unnikrishnan et al., Curr Sci 90(3), 2006). Also, impacts of storm surges, tsunamis, coastal floods, and coastal erosion in the low-lying coastal area cause gradual loss of coastal land. In the present study, the impact of sea level rise on the sandy coast of the Nagapattinam sector is assessed to understand the devastation incurred in both physical and socioeconomic aspects. In the analysis, it is further noted that the exposed vulnerable sectors to sea level rise are increasing with changing climate. The quantitative SLR impact assessment method suggested in the study forms the basic framework for coastal planners in disaster mitigation and building a climate-resilient community.
The bathymetry and geometry of coastal seas, barrier coasts and estuaries strongly influence tides and currents, and the associated transport of sediments. In turn, these transports result in a constantly evolving bathymetry and geometry, thus resulting in a feedback loop between bathymetry and geometry, water motion and sediment transport. To capture this evolution, morphodynamic models are employed. In this chapter, first the conservation laws are derived, resulting in a system of strongly coupled partial differential equations that model the morphodynamic evolution. Subsequently, two different solution strategies, indicated as the initial value and the bifurcation approach, are discussed. In the former approach, the emphasis is on the temporal evolution of bathymetric patterns, whereas the latter approach focuses on the direct identification of asymptotic states of the system under consideration. To exemplify these two approaches, the morphodynamic evolution and asymptotic states of a short, rectangular tidal inlet are considered, showing that these two model approaches result in different and complementary insights.
Plain Language Summary
River deltas are ecologically and economically important, and each delta is unique in terms of its environmental conditions and overall form. We test a 50‐year‐old hypothesis that qualitatively relates the overall form of a delta (in terms of its shoreline and channel network) to the balance between river and marine influence. We develop a suite of simulated river deltas using a physics‐based numerical model. We quantitatively describe the overall form for each of the simulated deltas and for a globally‐distributed set of real‐world deltas. The simulations and global deltas indeed exhibit relationships between their overall form and the balance of river and marine influence. Deltas with little to no marine influence have abundant channel mouths and rough shorelines. Tides act to roughen the shoreline but do not affect the number of distributary channel mouths. Waves tend to smooth the shoreline and reduce the number of distributary channel mouths. Waves may also lead to the formation of barrier islands and sand spits, though these features do not necessarily indicate wave “dominance.” These results confirm the hypothesis from the 1970's while adding important information about the morphological transitions between different end‐member “type” deltas.
Flooding and erosion are among the most relevant hazards for coastal regions and although they are linked, their inherent complexity has typically led them to be addressed separately, potentially leading to highly uncertain estimates. This paper has three aims: (a) to present a methodology for coupling coastal flood projections with shoreline changes; (b) to quantify the effects of neglecting the coupling of flooding and erosion on future projections at a case study location; and (c) to analyse the relative importance of the climate-related uncertainty sources. We use a suite of statistical, process-based, and physics-based models to generate and downscale storms, compute water levels affected by storm morphodynamics and long-term profile changes and propagate flooding over topo-bathymetries that are in turn modified to incorporate the impact of sea-level rise, longshore sediment transport and storm-driven erosion. We sample climate uncertainty by considering storm variability (synthetic generation) and ensembles of radiative forcing scenarios, regional climate models, and sea-level rise trajectories. For illustration purposes, we consider a 40-km coastal stretch in the Spanish Mediterranean. We find that if the effect of erosion is neglected, the mean values of the total water level and flooded area can be either over- or underestimated by up to 18% and 22%, and up to 7% and 85%, respectively, with respect to our coupled results. The factors that most influence total water levels are storm erosion and profile geometry, highlighting the relevance of using real profiles in shoreface translation. In the flooded area, longshore transport can play a fundamental enhancing role. We also find that the coupling approach used can contribute more to the projection of flooded areas than the choice of climate models and sea-level rise trajectories even by 2100 (up to 76% versus 8% and 16%, respectively). We conclude that neglecting erosion effects on coastal flooding can have management implications, especially for urban beaches, leading to poor adaptation planning and maladaptation.
Beaches, barrier islands and tidal inlets are valuable coastal resources and provide desirable environments that are often densely populated. They are dynamic landforms that change constantly, driven by both normal processes and energetic storms. They behave as one interconnected system and must be understood and managed as such. This book discusses their various morphologic features, as well as the processes that shape them and future challenges due to environmental change. A major focus is placed on the interaction between sandy beaches and tidal inlets, and the sediment exchange among various morphologic features. Balancing these valuable sediment resources while maintaining the natural sediment exchange constitutes a major goal of modern shore protection and coastal management. Illustrated with numerous aerial photographs to demonstrate how beaches and tidal inlets interact, this book provides a valuable reference for graduate students, researchers and professionals working in coastal management and geomorphology.
1) Large scale and coordinated restoration of coastal and marine ecosystems will benefit our natural assets and improve our capability to mitigate and adapt to climate change, while also generating jobs and providing communities with economic and social benefits.
2) Scaling up restoration requires a national scale science-based plan adopted at state/territory and local levels, and a new economic model which is blended between government funding as well as investment pipelines from the private sector and philanthropy.
3) Coastal and marine restoration projects co-designed with diverse stakeholders (e.g., research, practitioner, community, Aboriginal and Torres Strait Islander Organisations) provide greater value than those designed by single groups; In particular, Traditional Custodians are rights holders and there is a need to work towards improved models of culturally appropriate and meaningful engagement.
In this study, we derived an ordinary differential equation governing temporal changes in shoreline position by analyzing the horizontal behavior of suspended sediment due to storm waves. The derived governing equation has a mathematical form similar to that of current empirical models. However, because the equation was derived physically, it clearly reveals the characteristics of each physical coefficient. Therefore, coefficient estimation using the derived equation improves the accuracy of the model results. The model was applied to wave and shoreline data of Tairua Beach, New Zealand for a period of 11 years; the results confirm that the model has satisfactory field applicability. Further, we observed that the model accuracy with respect to the shoreline position extracted from video images, improved when the wave setup effect was considered. The degree to which the wave setup affects the improvement in model accuracy is evaluated by correlation and spectral analysis of the observed and predicted shoreline positions. This study provides a clear theoretical background for shoreline models and improves the prediction accuracy and model generality.
Engineered and natural submerged coastal structures (e.g., submerged breakwaters and reefs) modify incident wave fields and thus can alter hydrodynamic processes adjacent to coastlines. Although submerged structures are generally assumed to promote beach protection by dissipating waves offshore and creating sheltered conditions in their lee, their interaction with waves can result in mean wave-driven circulation patterns that may either promote shoreline accretion or erosion. Here, we analyse the mean flow patterns and shoreline water levels (wave runup) in the lee of idealised impermeable submerged structures with a phase-resolved nonhydrostatic numerical model. Waves propagating over submerged structures can drive either a 2-cell mean (wave-averaged) circulation, which is characterised by diverging flows behind the structure and at the shoreline, or 4-cell circulation, with converging flows at the shoreline and diverging flows in the immediate lee of the structure. The numerical results show that the mode of circulation can be predicted with a set of relationships depending on the incoming wave heights, the structure crest level, and distance to the shoreline (or structure depth). Qualitative agreement between the mean flow and proxies for the sediment transport using an energetics approach suggest that the mean flow can be a robust proxy for inferring sediment transport patterns. For the cases considered, the submerged structures had a minimal influence on shoreline wave setup and wave runup despite the wave energy dissipation by the structures due to alongshore wave energy fluxes in the lee. Consequently, these results suggest that the coastal protection provided by the range of impermeable submerged structures we modelled is primarily due to their capacity to promote beach accretion.
近年来风暴潮等海洋灾害日趋频发,沙质海岸侵蚀问题也愈发突出,沙滩稳定防护显得日益重要。为研究风暴浪作用下沙质岸滩稳定机制问题,设计了一系列的水槽试验,对风暴浪作用下沙质岸滩的稳定机制和演变过程进行了录像观察和研究分析。试验中采用图像处理技术,根据水和岸滩床面的像素值差异,对岸滩整体剖面进行实时动态提取;对比和分析了不同入射波高、波周期、水深、岸滩初始坡度以及波高连续变化下沙质岸滩演变过程。试验结果表明,岸滩稳定与岸滩初始坡度和沙坝的发育直接相关,而波参数主要影响岸滩扰动幅度和沙坝以及前滩侵蚀边界的位置变化。当入射波高连续变化时,沙坝迅速响应并向离岸迁移。岸滩变化幅值与入射波能流存在明显正相关关系,波能流越大对岸滩稳定性的危害越大。而水位升高会增强前滩向岸侵蚀风险。此外,在本试验尺度下,前滩以侵蚀为主。当岸滩初始坡度小于稳定坡度且波陡较小时,即Dean参数Ω'较小时,岸滩才发生明显的前滩淤积,这对于试验尺度下岸滩恢复工况研究至关重要。具体来说,当岸滩整体坡度为1:10且前滩坡度达到1:5~1:2.5时,岸滩稳定性最好,岸滩形态最接近最终平衡剖面,岸滩趋于稳定的时间最短。
Recently, studies have been conducted that long-term changes in shoreline position can be sufficiently interpreted using an ordinary differential equation that includes only erosion and recovery processes. Here, the erosion process term is given as a function of the breaking wave energy, which causes the shoreline to retreat to the ultimate erosion position by the incoming wave energy. The recovery process term is given as a function of the concentration of suspended sediment and allows it to recover to its shoreline position. Therefore, in this study, we propose a numerical technique that simulates long-term changes in the beach profile by extending the ordinary differential equation to be applied to the change in seabed constituting the beach profile by applying the parabolic equation of the equilibrium beach profile of the surf zone. This model also consists of a term that allows the beach profile to converge to the equilibrium beach profile due to the breaking wave energy and another term that allows it to converge back to the linear shoaling profile when the wave is extinguished. Therefore, it is possible to simulate the repeated formation and disappearance of scarp and berm whenever a storm wave passes, and it can also be applied to the morphological change at the beach with a large tidal range. The validity of the proposed methodology was verified by comparing the long-term shoreline observation data of Tairua Beach, New Zealand, where the tidal difference is about 2 m, with the results of the long-term beach section convergence model of this study. In addition, short-term observation data were also compared and analyzed to investigate the ability to simulate morphological changes due to episodic erosion and recovery processes. The results of this study are expected to be applied not only to the beach profile but also to the three-dimensional morphology change of the beach, and it is expected that it will serve as a cornerstone for a more detailed topographic change prediction study due to sea level rise.
The subaerial zone of the beach is a highly dynamic area that supports recreation and different habitats; as such, it has been the focus of many past studies. Accordingly, this paper reports a study of the assessment of the erosion and accretion over subaerial beach profiles and their relationship to the upper beach width. To this end, the erosion and accretion balanced approach (EABA) which was initially developed for beach profiles in the offshore direction is employed and tested over 934 subaerial beach profiles from the southwestern Maine coastline in New England region of the USA. The results indicated that the calculated average profile over 14 years does represent the equilibrium profile and the model can be used for subaerial beach profiles with high accuracy. Moreover, the results verified the application of the erosion and accretion balanced approach even in natural phenomena such as strong storms and abrupt sea level rises.
Digha is one of the largest sea resorts in eastern India, facing a long history of erosion and has been engineered extensively since 1970s. It extends for 5.45 km along the Medinipur coast, which can be divided into three sectors viz. New Digha, Old Digha and Gangadharpur based on the beach character. The current study aims to identify the erosion-accretion trend of the coast and link it with the phases of construction of the coastal engineering structures in this zone, understanding the nearshore wave climate, and finally quantify the influence of these structures on the spatio-temporal variability of beach dynamics. Keeping these objectives in mind, DSAS was used to generate data on erosion-accretion regimes of the study area. A number of beach-profiles have been systematically surveyed during 2011–2019. The results show that between 1973 and 1998, the coastline at Old and New Digha retreated by about 200 m and 180 m, respectively, and were later constrained by the sea wall, while Gangadharpur suffered severe erosion (about 350 m) due to the impact of the refracted waves at the abrupt termination of the sea wall after Old Digha. Due to the low chance of energy dissipation , the beach at Old and New Digha has lowered drastically (average 3.50 m and 1.5 m respectively) and has largely moved away from the equilibrium condition. At Gangadharpur, the effect of the groyne in raising the beach elevation is jeopardised by a newly constructed wall in this sector, which has interrupted the process of beach-dune sediment exchange in this area.
This chapter charts developments in the study of coastal processes and landforms in the period between the 1960s and the end of the millennium, focusing on efforts to better understand sandy beaches, barriers and barrier islands, deltas and estuaries, tidal flats and marshes and coral reefs. The period saw the emergence of a dual focus on, first, the elucidation of landscape history from morphological and, later, stratigraphic evidence; and second, the relationships between shoreline morphology and processes of sediment movement. Particularly noteworthy was the integration of a broad spectrum of space and time scales in a conceptual framework that became known as ‘coastal morphodynamics’.
Pocket beaches bounded by coastal structures are widely used as coastal systems that are in equilibrium for shoreline stabilization. Throughout the literature, several equations can be found to obtain the static equilibrium planform (SEP) of these embayed beaches, such as the parabolic bay shape equation (PBSE). The literature has already addressed some methodologies used to determine the location of the down-coast control point from which the parabolic shoreline is applicable for pocket beaches to the leeward side of a single headland structure. However, a methodology for locating this down-drift limit for double-curvature pocket beaches behind breakwater gaps is still lacking. This paper explores a methodology for locating this down-drift limit, hereafter called the intersection point (Pi), and investigates the role of the breakwater gap configuration as well as the directional wave climate close to the gap by employing 32 prototype beach cases along the Spanish coast. Moreover, an extensive series of numerical simulations using a spectral wave model was carried out to model the wave refraction-diffraction conditions on the leeward side of a breakwater gap under different wave conditions and various gap configurations. The results show the importance of the gap width and its orientation (θgap) with relation to the direction of the mean wave energy flux (θEF) at the gap as well as the ratio of the widths of the two parts of the bay beach that are affected by the breakwaters, denoted as the breakwater influence ratio (BIR), on the location of the intersection point (Pi). The results also indicated that a symmetrical pocket beach with a gap orientation (θgap) parallel to the θEF direction has an intersection point (Pi) around the mid-width point of the breakwater gap. On the other hand, the larger the difference angle (Δθgap) between θgap and θEF is, resulting in asymmetrical beach cases, the wider the eccentricity of the location of the intersection point (Pi) from the gap centerline towards the shallower landward breakwater of the gap is. New formulae were derived for calculating the angles used to locate the intersection point (Pi) from the two diffraction points of the gap as a function of the gap width, BIR and the offshore distances of the diffraction points. The model showed good results, with R² = 0.9571 and an RMSE value of 0.9731° in estimating the location of the intersection point (Pi) in various prototype beach cases, confirming its utility for coastal engineering practices. Accordingly, a design procedure was proposed for the design of new equilibrium pocket beaches behind breakwater gaps.
Atoll islands are among the places most vulnerable to climate change due to their low elevation above mean sea level. Even today, some of these islands suffer from severe flooding generated by wind-waves, that will be exacerbated with mean sea-level rise. Wave-induced flooding is a complex physical process that requires computationally-expensive numerical models to be reliably estimated, thus limiting its application to single island case studies. Here we present a new model-based parameterisation for wave setup and a set of numerical simulations for the wave-induced flooding in coral reef islands as a function of their morphology, the Manning friction coefficient, wave characteristics and projected mean sea level that can be used for rapid, broad scale (e.g. entire atoll island nations) flood risk assessments. We apply this new approach to the Maldives to compute the increase in wave hazard due to mean sea-level rise, as well as the change in island elevation or coastal protection required to keep wave-induced flooding constant. While future flooding in the Maldives is projected to increase drastically due to sea-level rise, we show that similar impacts in nearby islands can occur decades apart depending on the exposure to waves and the topobathymetry of each island. Such assessment can be useful to determine on which islands adaptation is most urgently needed.
As our climate continues to change, it is increasingly clear that natural landscapes are being affected in a variety of ways. Managers of the Apostle Islands National Lakeshore have observed notable changes in their own backyard, and they are rightfully concerned that continued change will challenge their mission to preserve and enhance the ecological and cultural legacy of this remarkable place. Therefore, the National Park Service has undertaken this vulnerability assessment to gather the best available information on how climate change may affect the park’s terrestrial ecosystems. This assessment, created by a team of local experts representing diverse institutions and disciplines, is designed to provide information about what ecosystems are vulnerable, how vulnerable they are, and why they are vulnerable. It is not designed to give management recommendations to managers of Apostle Islands National Lakeshore. Our intent is to improve the understanding of local vulnerabilities to climate change and to draw conclusions about potential ecosystem vulnerability and change across a range of plausible future climate scenarios by the end of the 21st century.
This vulnerability assessment summarizes the physical environment, ecological character, and cultural history of the Apostle Islands in Chapter 1. The park’s island setting and location within Lake Superior fundamentally shapes its ecology, for example by creating a more maritime climate, limiting deer abundance, and exposing the park’s vegetation to persistent winds and waves. The cultural history of the Apostle Islands has also shaped the landscape that we see today, from several eras of indigenous inhabitation to the intense period of extraction and disruption following European settlement, and finally to the most recent 50 years as a part of the National Park System.
Low elevation coastal zones around the world are increasingly threatened by the effects of climate change, and adaptation in these areas is becoming urgent. One of these threats, especially to sandy beaches, is the slow chronic landward movement of the coastline, known as coastal recession. The Probabilistic Coastline Recession (PCR) Model is a physics-based approach that is specifically designed to support modern day risk informed coastal zone management. Here, the PCR model is applied at the highly monitored Hasaki Beach in Japan, which presents challenges that have hitherto not been experienced in previous applications of the model elsewhere in the world (e.g. lack of a clear correlation between high wave events and beach erosion, no storm erosion of dunes but only of the beach strong seasonal variation in erosion events). Therefore, the model is here applied following a novel approach to derive projections of coastal recession (here indicated by shoreline retreat) at Hasaki, under the two end-member IPCC scenarios (RCP 2.6, RCP 8.5.)
Shoreline retreat is computed in two different ways that may be useful for two different management purposes; method (a) for computing the probability of erosion reaching and damaging an infrastructure or settlement at any time, and method (b) for computing the average shoreline retreat by a certain future time horizon. Projections for the end of the 21st century obtained with PCR method (a) indicate median shoreline retreats of 17 m (RCP 2.6) and 29 m (RCP 8.5), while those obtained with PCR method (b) are −15 m (RCP 2.6) and −7 m (RCP 8.5) (positive values indicate retreat and negative values indicate progradation). Bruun rule projections, which are comparable with those obtained from PCR method (b), indicate end-century shoreline retreats of 36 m and 66 m at Hasaki, for RCP 2.6 and RCP8.5 respectively. These projections fall at around 34% and 21% exceedance probability PCR method (b) projections respectively, consistent with several previous studies which also show that Bruun rule provides larger coastal recession projections compared to the PCR model. Furthermore, the Bruun Rule appears to provide increasingly conservative (relative to the PCR model) recession projections with increasing time horizons.
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