Loss Of Sand Research Articles

Recent Transport and Deposition of Littoral Sand Across the Inner-Shelf of Central Oregon: Further Constraints on Estimating Depths of Closure (30–34 m) during Future Sea Level Rise in the Pacific Northwest Region, USA

In this article, geologically recent sedimentation rates across a high wave- and wind-energy inner-shelf are used to constrain depths of closure, which are needed to estimate potential offshore displacements of littoral (beach) sand that could result from future sea level rise (SLR). Seven shallow vibracores (1.0–2.3 m subsurface depth) were analyzed from a single transect across the inner-shelf (19–72 m water depth) at the South PacWave study site in the high-wave energy (peak wave Hs= 10–15 m) coast of Central Oregon. The vibracores were 14C dated to establish 1) near-modern mixing depths and 2) net sedimentation rates that equaled or exceeded rates of coeval SLR (10 cm century-1) during very latest-Holocene time (≤1.0 ka). Sedimentation rates of 17 cm century-1 and 31 cm century-1 for vibracore P1-2A22 in 34 m water depth do exceed coeval SLR, even after accounting for apparent mixing depths of 60–100 cm. But sedimentation rates in deeper core sites (47–53 m water depth) do not approach coeval SLR rates. These results support a proposed near future (one century) 30 m depth of closure in the innermost-shelf of northern Oregon. Vibracore sand grain sizes (mean 0.20±0.03 mm 1σ, n=18) are similar across the inner-shelf, but heavy-mineral sand tracers confirmed that the latest-Holocene inner-shelf sand accumulations were supplied from seaward transport of littoral sand. The net loss of littoral sand to the inner-shelf sand sink accounts for the narrowing and thinning of beach deposits in northern Oregon during latest-Holocene time. A 1.0 m thickness of littoral sand displaced across the innermost-shelf (5–30 m water depth) following a 1.0 m SLR, or equivalent increase in offshore accommodation space, would yield a cross-sectional area of 1.5x103 m2. That value is three times larger than the mean cross-sectional area of the modern adjacent beaches (mean 4.8x102 m2) in the South PacWave study area. Following a possible near future SLR of 1.0 m, the popular sandy beaches of northern Oregon could be converted to intertidal gravel/algae covered bedrock platforms.

Beach nourishment provides resilient protection for critical coastal infrastructure

Hurricanes this century have produced almost a trillion dollars in damages in the U.S., often to critical infrastructure that requires large costs and unacceptable times to repair or replace. There is a need for resilient protection of critical infrastructure where the protection must have the “ability to anticipate, absorb, adapt to, and/or rapidly recover from a potentially disruptive event” and be cost-effective. Coastal infrastructure can be protected by moving infrastructure back from the ocean (retreat), building protective structures, or by beach nourishment to effectively move the ocean back from the infrastructure. Retreat is very costly and highly unpopular on developed shores. Structures are expensive and lack resilience because their failure is usually catastrophic and repair slow. Beach nourishment is the favored protection option on developed shorelines because it significantly reduces infrastructure damage, provides resilient protection, and is cost effective with a high return on investment. The aftermath of Hurricane Sandy provided an example of the tremendous reduction of infrastructure damage due to beach nourishment. Dr. Stewart Farrell, director of the Coastal Research Center in New Jersey, reported: “It really, really works. Where there was a federal beach fill in place, there was no major damage — no homes destroyed. Where there was no beach nourishment, the destruction was complete. Older homes were ripped from foundations and tossed about.” A post-Sandy analysis showed that Corps of Engineers’ beach nourishment projects saved an estimated $1.3 billion in avoided damages. Beach nourishment provides resilient protection. It is partially self-healing, because during a storm some of the sand moves to offshore bars where it causes waves to break and reduces infrastructure damage, and then much of it returns to shore after the storm passes. It can be repaired relatively rapidly by use of a mobile dredge to replace net sand loss. It is a highly adaptable approach to climate change because its rate of sand placement can be varied to raise profiles to offset increased sea level rise. Beach nourishment pays for itself as nice, wide beaches sit in readiness to protect critical coastal infrastructure from storms, while in the meantime, tourists typically generate more than $100 in taxes annually to local, state, and the federal governments for every $1 these governments invest in beach nourishment.

Experimental study for joint leakage process of tunnel lining and particle flow numerical simulation

Most of urban ground collapses and tunnel failures are caused by joint leakage of shield tunnel lining. This paper conducts a series of model tests and particle flow simulations aiming to investigate the geo-hazards and explore the associated failure mechanism due to tunnel leaking. Based on critical width of leaky joint, taking leaky joint location, overburden depth and height of overlying water level as influencing factors, the settlement of the sand layer and the law of the water and sand loss is effectively predicted. Then, the focus is on designing a seepage tracer device to explore the distribution of the seepage field and its flow line variation. Finally, the particle flow numerical model of tunnel-sand is employed for the soil arching effect and flow line changes during seepage erosion to discover the fine scale influences of sand particle migration and loss around the shield tunnel on the surrounding environment.

Intra‐Annual Variation of High and Low‐Flow Extremes Associated With Land Use and Climate Change in the Upper Tekeze of the Nile River Basin

AbstractIn northern Ethiopian highlands, climate variability and land use/land cover (LULC) change has been observed during the past decades. However, it remains unclear that to which extent and how these key drivers contributed to changes in hydrological extremes. As a case study, the respective impacts of LULC change and climate variability on hydrological extremes with respect to magnitude, duration, and frequency metrics were assessed in the Upper Tekeze basin, Ethiopia. A scenario‐based approach using LULC and hydro‐climatological data was developed and five simulation experiments were conducted using Soil and Water Assessment Tool model. Results showed that, during 1986–2015, low‐flow duration has decreased by 5.0 days/yr, and the magnitude and occurrence of high flow has increased by 5.23 m3/s/yr and 5.11 days/yr, respectively. Meanwhile, about 47.42% of the landscape has changed its category while no significant change was detected in annual rainfall during the past 31 yr. Particularly, rocky area increased by 82% which was mostly contributed by losses of bare, sand, and low biomass areas. Significant positive and negative contributions to the changes in high and low‐flow extremes, respectively, were detected from LULC change, while no significant contribution was detected from climate change. The increased rock area tends to be one of the major contributors to the increased high flow while climate change seemed to play a minor role. The potential mechanism is the expansion in rock area increased runoff and high flow, which may lead to significant land deterioration and loss of water storage capacity in the mountainous basin.

Responses to Lake Michigan water level rise: Trends in exposed sand cover at North Avenue Beach, Chicago

From 2013 to 2020, water levels in Lake Michigan rose from an all-time low to the highest levels observed in nearly four decades, causing shoreline changes throughout the Great Lakes. These changes are particularly noticeable at North Avenue Beach in Chicago, an artificial beach where federal, state, and city agencies have mitigated rising waters by importing sand and constructing groins. Using spring season aerial imagery from 2012 to 2020, we calculated beach area for each year and compared sand cover loss between years to water level change per the USGS station located just south of the study area. Analysis reveals year-to-year loss in sand cover since 2013, with the largest single-year change occurring between 2018 and 2019. An inverse relationship with a slight lag exists between water level and these beach area changes. We calculated sand-groin distances from 2000 to 2020 to identify north–south effects. Of the six beach cells separated by groins, the northernmost two cells failed over the study period, and experienced the largest individual sand-groin distance losses. We modeled inundation to investigate whether the sand loss was explainable by lake level change alone, with particular attention given to hardened shoreline implemented north of the beach in 2015. Observed sand cover loss markedly exceeded predictions from the inundation modeling. In addition to water level changes, a local response to shoreline modification and obstruction of sediment transport at this site may influence sand cover.

Understanding meso-scale processes at a mixed-energy tidal inlet: Ameland Inlet, the Netherlands – Implications for coastal maintenance

For successful and sustainable management of barrier islands, a thorough understanding of the ebb-tidal delta dynamics and interactions with the adjacent shorelines are of the utmost importance. Such understanding requires detailed observations and interpretations of the morphodynamics of smaller-scale features such as the individual channels and shoals (referred to as intra-delta dynamics). The intra-delta dynamics of Ameland Inlet (the Netherlands) are studied through analysis of sixteen high-resolution bathymetric surveys, supplemented with an extensive dataset of hydrodynamic observations collected in 2017. The observations are compiled into a synthesis of the morphodynamics of the ebb-tidal delta and its neighboring shorelines, to provide a basis for present day and future coastal management.Our observations show that Ameland Inlet as a whole can be classified as a typical mixed-energy, wave-dominated system. However, the ebb-tidal delta contains distinct areas that are wave or tide dominated, and these areas evolve with the changing morphodynamics of the ebb delta. Between 2005 and 2021, large morphodynamic changes have occurred on the ebb-tidal delta and continuous erosion of the island tips occurred. Limited wave-sheltering by the ebb-tidal delta exposes the shorelines of the adjacent barrier islands to significant wave-driven sand transports and sand losses. Sediment supply from longshore transport and the erosion of the updrift island Terschelling contributed to the formation, growth and migration of a series of ebb-chutes and lobes, which eventually led to complete relocation of the main channel on the ebb-tidal delta. This main channel relocation took 15 years to complete and is an example of the ebb-delta breaching model of sand bypassing. Changes in the sediment bypassing patterns result in a sediment starved western island tip of Ameland, necessitating repeated sand nourishments under the Dutch coastal maintenance policy. Our observations also confirm the role the ebb-tidal delta as a sand reservoir for the downdrift barrier island. The delta sand body is not a reservoir for the back-barrier basin, since the basin is predominantly supplied with sand eroded from the updrift island of Terschelling.As demonstrated in this study, the intra-delta dynamics of an ebb-tidal delta are complex and can change drastically through time. Only through detailed measurements and observations can all the intricate interactions that take place be unravelled.

Complex drivers of reef-fronted beach change

Royal Hawaiian Beach in Waikīkī plays an essential role in Hawai‘i's tourism-based economy. To inform development of management policies, we conduct two years of weekly ground and aerial surveys (April 2018 to February 2020) to track change on this chronically eroding beach. We use multiple linear regressions, Self-Organizing Maps (a form of cluster analysis), remotely sensed nearshore sand fields, hydrodynamic modelling, and monitoring of key physical processes to identify the principal drivers of beach change. Our results show 12 months of subaerial accretion (+2400 ± 59 m3) followed by 10 months of erosion (−3090 ± 51 m3) for a net loss of 690 ± 51 m3, and document that interannual variations in beach width and volume overprint seasonal patterns. Notably, a seasonal signal is recorded in the topographic structure of the beach. We test the relationship of beach volume and width to variations in wind, water level, wave energy flux generated from southern hemisphere swell, and wave energy flux from locally generated trade-wind waves. We identify three beach segments and three nearshore sand fields that form a sand-sharing, source-sink network, yet operate quasi-independently. Our analysis reveals that individual beach segments and their adjacent sand fields experience coherent (simultaneous) gains and losses of sand, suggesting that alongshore sediment exchange is dominant over cross-shore exchange. The main drivers of beach change are variations in water level and wave energy flux. Beach volume and width both vary with nearshore sand cover, indicating that free exchange with nearshore sources is intrinsic to beach variability. Our results suggest that rising sea level and extreme El Niño-Southern Oscillation events will contribute to Royal Hawaiian Beach destabilization, which may amplify erosional events and increase the cost of future beach maintenance.

Experimental Study of Seepage Characteristics of Filling Structures in Deep Roadway

In order to study the seepage failure mechanism of roadway filling medium consisting of cohesive soil under complex hydrogeological conditions, a large-scale triaxial stress-seepage test system was utilized to investigate the influence of kaolin content and seepage loading rate on the seepage characteristics of filling medium. Through the analysis on the variation rules of sand loss and particle size distribution, the seepage characteristics and whole process of seepage instability of filling medium were explored in depth. It is concluded that (1) The seepage instability process of filling medium can be categorized into three stages: the initiation loss of fine clay, the accelerating loss of soil, and the stable status of soil loss. (2) The seepage failure process rate is proportional to the seepage loading rate and inversely proportional to the content of kaolin. (3) The kaolin and sand content of remaining mixture presented initial>bottom>middle>top status. The research results have guidance value for exploring the instability evolution mechanism of filling medium in deep roadway.

Assessing Storm Response of Multiple Intertidal Bars Using an Open-Source Automatic Processing Toolbox

Intertidal bars are common features of sandy beaches in meso- and macro-tidal environments, yet their behaviour under storm impact and subsequent recovery remain poorly documented. Intensive surveys provide valuable information; however, it takes time to process the vast amount of data. This study presents the morphological response of a multibarred macro-tidal beach along the Belgian coast after a severe storm that happened on 8–12 February 2020, and to develop and apply an oPen-source Raster prOcessing Toolbox for invEstigation Coast intertidal bar displacemenT (PROTECT) in Python for automated bar extraction. This toolbox was applied to the digital surface models of pre- and post-storm airborne LiDAR surveys of a multibarred intertidal beach. The PROTECT toolbox is capable of detecting the position and elevation of intertidal bars accurately. The uncertainty in the elevation characteristics of the bars induces an error in the elevation dimension of 0.10 m. Using the toolbox, the results showed that the intertidal bars changed in term of variations in bar number, dimensions and shape across the storm event. Overall, the storm significantly eroded the dune and the upper-beach zone with a sand loss equivalent elevation decrease of −0.14 m. This was followed by a continuous and full recovery after 9 months under fair weather conditions. In contrast, the sand budget in the intertidal zone did not change over the entire monitoring period although the bars showed significant morphological change. Applying the PROTECT toolbox on high-resolution 3D topographic datasets allows to increase the temporal mapping resolution of intertidal bars from long-term (years) to short (storm events) time scales. Similar assessments at locations worldwide would allow the improvement of our knowledge on the morphodynamical role of multibarred beaches and to forecast their evolution, thus contributing to manage future storm response and the progressively accelerating sea level rise.

THE STATE OF COASTAL EROSION IN PUERTO RICO AFTER HURRICANE MARIA

A study of the state of the coast of Puerto Rico was conducted in 10 municipalities of Puerto Rico for 2017 to 2018 period. The main goal of this evaluation is to identify the state of the beach Post- Hurricane María (September 2017) at the municipality level. The study was conducted using the integration of remote sensing techniques (high resolution images; unmanned aerial vehicles (UAV), Geographic Information Systems (GIS), beach geospatial database design and field work. Findings indicate the presence of two main types of coastal erosion after the occurrence of Hurricane Maria. These are: beach erosion and coastal bluff erosion. Important loss of sand was occurred in beaches located on the northwest, north-cantral and southeast coastlines at the island after Hurricane Maria. In 2018, a beach recovery was identified in most of beaches in the study sites. One of the most important findings is this study is the identification of beach migration inland in the municipalities of Rincón, Añasco, Barceloneta and Humacao. Beach erosion and beach migration define a new coastal scenario that may increase the physical, social and infrastructure vulnerability of the coastal zone. These findings are an important contribution to the management and planning of the Puerto Rico coastal territory, especially facing new extreme events and climate change scenarios.

Geomorphological Changes of a Migrating Sandbank: Multidecadal Analysis as a Tool for Managing Conflicts in Coastal Use

While beach erosion and sand loss are typically of great concern to the tourism industry, managing rapid morphological changes linked to large amounts of moving sediments is the challenge facing Grado, an important seaside resort in the northern Adriatic, Italy. The cause of the unusual management conflict is the presence of the Mula di Muggia Bank, a nearshore depositional system made up of relict and active migrating sandbanks extending up to 2 km seawards from the touristic beachfront. A reconstruction of the morpho-sedimentary evolution of the coastal system over a 200-year period was done using a large dataset which includes historical cartography, topographic maps, aerial photos and topo-bathymetric surveys. The results show the growth of a significant urban development aimed at creating a tourist destination by occupying the waterfront along fetch-limited coastal tracts with very shallow water and scarce hydrodynamics. Furthermore, a number of sandy dynamic landforms (longshore migrating bars, a bypass corridor, an ebb-tidal delta) and accumulation zones attest to a sediment excess which can be mostly attributed to the eastern river supplies. The progressive constant migration rate of 12.6 my−1 allowed the bank to induce the expansion of the low-energy silty backbarrier environment, characterised by abundant seagrass meadows a short distance directly in front of the tourist beaches of Grado. As a result of historical analysis and more current observations, areas with diverse morphosedimentary features and with varying tourist/recreational, ecological, and conservation values have been identified. These can be considered as basic units for future accurate planning and re-evaluation of coastal management choices to balance environmental protection and tourist use. A soft coastal defence approach is proposed which includes either the preservation of specific environments or the proper use of excess sand for beach nourishment via periodic dredging or sediment bypassing.

Cost Comparison Between Hard and Soft Approaches Adapted as Preventive Methods of Beach Erosion

Yeon, Y.J. and Lee, J.L., 2021. Cost comparison between hard and soft approaches adapted as preventive methods of beach erosion. In: Lee, J.L.; Suh, K.-S.; Lee, B.; Shin, S., and Lee, J. (eds.), Crisis and Integrated Management for Coastal and Marine Safety. Journal of Coastal Research, Special Issue No. 114, pp. 519–523. Coconut Creek (Florida), ISSN 0749-0208. To protect the properties behind a beach, submerged breakwater, which is a representative hard approach, or beach nourishment, which is a representative soft approach, has been performed. The submerged breakwater protects the facilities behind the beach by controlling waves to mitigate erosion. This study estimates the cost required to secure a buffer section for the wave inflow of 30-year return period using submerged breakwater and beach nourishment methods for Sokcho Beach (Sokcho-si, Gangwon-do), one of the coastal maintenance project areas, and conducts economic assessment of the two methods. For the submerged breakwater method, the construction cost was calculated using the shoreline observation data, which were observed four times a year for about 8 years. For the beach nourishment method, the construction cost was calculated using the sand loss half-life (shoreline retreat over time) considering that the nourished sands cannot be maintained. The result showed that beach nourishment could obtain a higher economic feasibility. By enhancing sand maintenance, beach nourishment was evaluated as more economical than the hard approach when the sand loss rate (k), which determines the half-life of beach nourishment, was lower than 0.167 yr–1. Furthermore, beach nourishment is highly evaluated because it is an eco-friendly construction method, and it will be more effective when combined with other soft approaches.

The Cross‐Shore Component in the Vertical Structure of Wave‐Induced Currents and Resulting Offshore Transport

AbstractA comprehensive field survey was conducted, and a numerical model based on the Princeton Ocean Model was established to investigate the vertical structure of current induced by surface waves and identify its effect on sand loss from a beach. Previous studies have examined wave‐induced longshore transport, whereas this study focused on cross‐shore transport caused by waves. The introduction of vertically dependent radiation stress revealed that wave‐induced vertical gyres existed with onshore and offshore flows in the upper and lower layers, respectively, besides the well‐known wave‐induced longshore flow. It was found that the vertical gyres were caused by the onshore wave force (a gradient of radiation stress) in the upper layer and the offshore wave force usually existed in the lower layer, as well as the horizontal imbalance of local wave force. The locations of wave‐induced vertical gyres were found to correspond to the location of sediment erosion, and thus the lower part of the vertical gyres drove the offshore transport of eroded sediment. Moreover, the vertical gyres were located in areas with a highly variable topographic gradient (e.g., at a bar), and their driven offshore currents (undertow/return flow) extended far beyond the surf zone. The topographic slope had a profound effect on the vertical structure. Numerical experiments showed that an extended breakwater from the eastern headland of the bay could prevent sediment from being eroded. Furthermore, the shear front at the rim of a horizontal gyre could retain suspended sediment in the center of the gyre.

Land cover changes on a barrier island: Yearly changes, storm effects, and recovery periods

Ecosystems on barrier islands provide socio-ecological services to terrestrial and aquatic endangered species, as well as human inhabitants. The management of these coastal ecosystems is challenged by changes in annual and storm time scales driven by atmospheric, oceanographic, geologic, and human processes. Thus, the need for data and methods to accurately quantify and assess ecosystem and land cover evolution to inform stakeholders is on the rise. A dataset of high-resolution color infrared images of a U.S. National Wildlife Refuge is used to quantify annual land cover changes at a barrier island scale and to identify the effects of hurricanes and their recovery periods. Geospatial analysis and change matrices depict the interconnection between 13 land cover classes. Vegetation growth over regions of bare sand formed by storms leads to the creation of successional habitats, while the loss of bare sand dune to beach, and beach to water are indicators of erosional processes. Storms passing along the ocean and sound side of a barrier island result in different land cover changes that can last anywhere from 4 to more than 7 years, respectively. Management practices for coastal regions and the presence of infrastructure partially control the expansion of marshes, bare sand, maritime brush, and dunes.

Assessment of government supervision on the loss of sea sand resource in China

Illegal mining activities on offshore sands have recently increased dramatically in China owing to the strong demand of the construction industry and restriction of river sand mining. By studying the loss mechanism of marine sand resources, this study proposes a simplified linear programming model to quantitatively analyse the control effects related to resource loss and law enforcement costs. To accurately simulate the effectiveness of law enforcement activity, a set of variables is designed in the model to describe the severity of illegal mining and enforcement skills of the officers. Subsequently, based on different settings of law enforcement capability, the model can not only make reasonable projections for sand losses but also provide a minimum cost solution for marine sand control for government agencies. Finally, various regulatory measurements and suggestions are discussed to improve the effectiveness of the government’s regularisation and cost optimisation for law enforcement.

Catastrophic beach sand losses due to erosion from predicted future sea level rise (0.5–1.0 m), based on increasing submarine accommodation spaces in the high-wave-energy coast of the Pacific Northwest, Washington, Oregon, and Northern California, USA

The U.S. Pacific Northwest (PNW) coastline (1000 km) has been analyzed for conditions that could impact beach erosion from potential near-future (100 year) sea level rise (SLR). Heavy mineral analysis of river, beach, and shelf samples (n = 105) establish the sources of the beach deposits. River bedload discharge and intervening estuarine sinks for river sand supplies (n = 31) were normalized to the one century time interval. Twenty-six subcell beaches (657 km in combined length) were surveyed (153 profiles) for beach sand widths (20–412 m) and sand cross-sectional areas (20–1810 m2) above wave-cut platforms and/or 0 m tidal datum. Cross-sectional areas were multiplied by beach segments to yield subcell beach sand volumes (0.4 × 106 m3–35.8 × 106 m3 ± 20% uncertainty). Innermost-shelf profiles were measured for distance to the 100-year depth of closure (30 m) to digitize the areas of inner-shelf accommodation space. Both innermost-shelf and estuarine accommodation space volumes for beach sand displacements were established for 0.5 and 1.0 m SLR. The existing subcell beach sand volumes and computed new beach sand supplies (rivers and longshore transport) were subtracted from the estimated sand volumes lost to submarine accommodation spaces to establish potential beach sand deficits from near-future SLR. Of the 26 surveyed active-beaches, some 60% and 80% (by length) are predicted to be lost, respectively, from the 0.5 m and 1.0 m SLR or equivalent littoral sand sedimentation in submarine accommodation spaces. Projected losses reach 90% for all PNW beaches (~900 km total length) from 1.0 m SLR. The computed beach sand deficits are used to estimate soft-sand retreat distances or erosional beach step backs (50–590 m ± 35% uncertainty) in unrevetted barrier spit and beach/dune deflation plains from 1.0 m SLR. Such empirical accommodation space analyses should have worldwide relevance to predicting beach erosion from near-future SLR.

Marine storms in coastal tourist areas of the Canary Islands

The small island areas oriented to coastal tourism are highly vulnerable to marine storms, given the fluctuation of this economic sector and the increase in its exposure due to the increasing anthropogenic presence on the coastline. In this context, the storms between 1958 and 2017 are studied here in the most important tourist enclaves of Tenerife and Gran Canaria, located in the municipalities of Arona and Adeje (SW of Tenerife) and in San Bartolomé de Tirajana and Mogán (S-SW of Gran Canaria). In order to perform the analysis, wave data from State Ports (Spain) (SIMAR-44 nodes, Ministry of Transport, Mobility and Urban Agenda of Spain) are used. A statistical study of the phenomena can help establish a threshold for the identification of a marine storm based on a significant wave height (Hs) of 2.7 m in Arona and Adeje and 1.7 m in San Bartolomé de Tirajana and Mogán. The application of this threshold identified 144 episodes in the SW of Tenerife and 154 in the S-SW of Gran Canaria. Their behavior is examined from, on the one hand, the duration, seasonality, type of waves and degree of severity that characterizes them; and, on the other, from the state of the atmosphere that concurs in its genesis by means of the Wetterzentrale synoptic maps. Finally, a first assessment of the effects of these stormy phenomena is made using local press reports on drowning, damage to urban furniture and port infrastructures and loss of sand on the beaches.

Reducing aeolian sand transport and beach erosion by using armour layer of coarse materials

A man-made dune-beach-spit system at the south-east side of the island of Texel (Prins Hendrik site) has been built in 2018–2019 to strengthen the traditional dike. The core of the dune-beach-spit system consists of medium fine sand with a d50 of 0.25–0.3 mm. The beach is covered with an armour (protection) layer of coarse materials with relatively large gravel and shell fractions to reduce wind erosion and thus maintenance costs. In the design phase of the project the aeolian sand transport model of Bagnold was used to estimate the long-term erosion losses of sand at the new dune-beach system. This transport model was validated in the design phase by using detailed sand transport and bed roughness measurements at a nearby site called The Hors. This site is a wide natural beach plain of sand (d50 = 0.23 mm), where 147 high-quality datasets have been collected using a wind mast equipped with 5 cup anemometers and various sand traps. It is shown that the measured sand transport rates at the Hors can be reasonably well represented by the modified Bagnold-equation for dry sand. After completion of the new dune-beach system, a field experiment was performed at the Prins Hendrik site to verify the sediment transport predictions and erosion loss of sand. Data from two permanent wind masts and one short, mobile wind mast were used to derive the effective roughness of (stationary) bed forms. Sand transport rates were measured at various locations using a new trap sampler. The measured sediment transport in the armoured beach zone can be reasonably well represented by the Bagnold-equation using a multi-fraction approach with hiding-exposure coefficient. The predicted transport rates have been used to estimate the annual loss of sand from the Prins-Hendrik site.

ESTRATIGRAFIA E EVOLUÇÃO DE UM ESPORÃO ARENOSO EM AMBIENTE MACROMARÉ: PONTA DA AREIA - SÃO LUÍS - MARANHÃO - BRASIL

Na Ilha do Maranhão os sistemas de barreiras costeiras podem ser divididos em dois morfotipos principais: (i) Barreiras de Praias Anexadas, que se caracterizam por uma praia anexada transversalmente a topografia antecedente exibindo um gradiente íngreme onde há perda contínua de areia na costa erodida; e (ii) Barreiras de Esporões Arenosos ligadas a Cabeços de Promontórios, que se caracterizam por um sistema laguna-barreira-esporão ancorado longitudinalmente à topografia antecedente. Este último morfotipo origina-se de um amplo transporte de sedimentos via deriva litorânea, cujo prolongamento é geralmente interrompido pelo efeito espigão hidráulico, junto a elevados prismas de maré nas desembocaduras fluviais. O presente estudo utiliza-se de sondagens do tipo percussão e vibrocore para recuperação do registro sedimentar, o qual é descrito quanto à sua compactação, textura, estruturas e fácies sedimentares. Os resultados obtidos demonstram a natureza estratigráfica da barreira costeira na Praia da Ponta da Areia como uma sequência retrogradacional caracterizada pela migração em direção ao continente de um esporão arenoso. A datação radiométrica de sedimentos lagunares aflorantes na praia atestou a idade de 7.240±30 anos AP indicando que neste tempo, este sistema laguna-barreira-esporão estendia-se mar adentro. Recentemente a construção de um espigão costeiro alterou esta natureza estratigráfica, passando a comportar um sistema progradacional nas imediações do espigão, onde ambientes distais (antepraia) são sotopostos por ambientes proximais (foreshore).

Two years and two hurricanes later: Did the dunes recover?

In many places along the U.S. East and Gulf of Mexico coasts, barrier islands are the first line of defense against extreme weather events threatening our coastlines. The trademark of these barrier islands are sand dunes that are intricately bound, from a sedimentary perspective, to the beach. Coastal storms, such as Hurricanes Matthew (2016), Irma and Maria (2017), and Florence (2018) have devastating impacts on these environments. This study investigated the volumetric changes of an anthropogenic and controlled beach-dune system on Isle of Palms, South Carolina, for approximately one year following Hurricanes Matthew (2016) and Irma (2017). This research reveals that these systems did not recover. The average loss of sand at the beach was -15.5% (nv = -0.89), whereas the dunes gained an average of 13.3% (nv = 0.79), when compared to the already diminished post-storm volumes. When considering the pre-Hurricane Irma to pre-Hurricane Florence temporal period, the recovery percentages for the anthropogenic and control dunes was -15.5% and -40.1%, respectively, suggesting a net loss of sand. Cumulative storms, such as those experienced on the coast of South Carolina and many other coasts, pose a substantial threat to the long-term viability of coastal dune systems. However, recovery at the control site in the form of incipient foredune growth is promising. This paper concludes with a list of influencing factors to dune recovery.