Coastal Erosion Research Articles

Coastal Storm-Induced Sinkholes: Insights from Unmanned Aerial Vehicle Monitoring

In recent decades, the scientific community has increasingly focused on extreme events linked to climate change, which are leading to more intense and frequent natural disasters. The Mediterranean can be considered a hotspot where the effects of these changes are expected to be more intense compared to other regions of the planet. Italy is not exempt; in fact, with its extensive shoreline, it is particularly vulnerable, especially to high sea levels and coastal erosions. In this framework, from late October to early November 2023, six storm surges occurred in the Gulf of Trieste (NE Italy). These events, characterized by winds from 190°N to 220°N and the significant wave height, which reached up to 1.81 m nearshore—an uncommon meteorological condition in the northern Adriatic Sea—caused the occurrence of eight coastal sinkholes and substantial damages to man-made structures. Thanks to Unmanned Aerial Vehicles (UAVs) and their derived products (high-resolution orthomosaics, Digital Elevation Models—DEMs, and point clouds), it was possible to study these features over time, enabling long-term coastal dynamics monitoring, which can be crucial for timely and effective response and restoration efforts.

Remote sensing applications to identify devastated lagoons of the Indus Delta Pakistan

A reduction in river flows is a major cause of the shrinking of river deltas. The Ramsar protected Indus Delta is one such example. Due to a consistent reduction in the flows of the Indus River, 15 out of 17 allied creeks facing back flows from the sea, while the remaining two are flowing during flooding years only. The connected wetlands and lagoons of these creeks have turned brackish, resulting in the devastation of associated habitats and ecosystems. This situation also increased seawater intrusion and coastal erosion. This study spatially detect the devastated lagoons, employing the Arc-Hydro tools in ArcGIS, conduct community meetings and draft evidence-based recommendations to revive the abandoned wetlands. The study identified 130 waterbodies using maximum likelihood and supervised classification methods on Landsat imagery. Through ground trothing 20 abandoned waterbodies have been visited and verified with community engagement. The revival of wetlands will improve biodiversity and coastal habitat, along with the re-plantation of mangrove, which provides a shield against tsunamis and cyclones and is also home to hundreds of species of shrimp. The sustainable wetlands may also provide immediate drinking and agricultural needs for the local population, as well as repel seawater from intruding inland.

Coastal Dune Erosion and Slumping Processes in the Swash‐Dune Collision Regime Based on Field Measurements

AbstractThis paper studies hydrodynamic and morphodynamic field measurements of two storms with dune erosion in the swash‐dune collision regime. It analyses (a) the behavior and change of the total dune profile over the course of both storms (b) the erosion rate at the dune base, (c) the slumping frequency, and (d) the volumes of individual slumps. The erosion rate at the dune base shows a strong positive correlation with the square of the total water levels that were exceeded for 2% of the time, recorded approximately 5–6 m in front of the dune face (r = 0.91). Individual slumping events occurred when nearly all sediments from previous slumps at the dune base were transported away from the dune. A strong positive correlation was found between the time between two consecutive slumps, and the volume of the first slump divided by the mean erosion rate between the two slumps (r = 0.90). As a consequence, smaller slumps were followed more rapidly by a new slump than larger slumps, under identical erosion rates. The majority of the slumping events occurred after the last wave impact before a slumping event, when the instantaneous water level in front of the dune was still retreating. No clear process based on the incident hydrodynamics could be identified that determined the size of individual slumps. Overall, the results of this study suggest that the morphodynamic behavior of the upper dune face and dune crest is primarily steered by the erosion at the dune base.

Determination of Submerged Breakwater Efficiency Using Computational Fluid Dynamics

Wind-induced waves can lead to the partial or complete wash-over of beaches, causing erosion that impacts both the landscape and tourist infrastructure. In some regions of the world, e.g., Croatia, this process, which usually occurs during a harsh winter, has a major impact on the environment and the economy, and preventing or reducing this process is highly desirable. One of the simplest methods to reduce or prevent beach erosion is the use of innovative underwater structures designed to decrease wave energy by reducing wave height. In this study, submerged breakwaters are numerically investigated using various topologies, positions, and angles relative to the free surface. Not only is the optimal topology determined, but the most efficient arrangement of multiple breakwaters is also determined. The advantage of newly developed submerged breakwaters over traditional ones (rock-fixed piers) is that they do not require complex construction, massive foundations, or high investment costs. Instead, they comprise simple floating bodies connected to the seabed by mooring lines. This design makes them not only cheap, adaptable, and easy to install but also environmentally friendly, as they have little impact on the seabed and the environment. To evaluate wave damping effectiveness, the incompressible computational fluid dynamics (ICFD) method is used, which enables the use of a turbulence model and the possibility of accurate wave modelling.

Sea Level Rise and Coastal Erosion in Miami

Purpose: The aim of the study was to analyze the sea level rise and coastal erosion in Miami. Methodology: This study adopted a desk methodology. A desk study research design is commonly known as secondary data collection. This is basically collecting data from existing resources preferably because of its low cost advantage as compared to a field research. Our current study looked into already published studies and reports as the data was easily accessed through online journals and libraries. Findings: Sea level rise and coastal erosion in Miami are growing environmental concerns due to the city's low elevation and proximity to the ocean. Studies have shown that rising sea levels, driven by climate change, are accelerating the erosion of Miami's coastline, threatening infrastructure, homes, and ecosystems. The increased frequency of tidal flooding and storm surges exacerbates the problem, making coastal areas more vulnerable. Unique Contribution to Theory, Practice and Policy: Resilience theory, social vulnerability theory, ecosystem-based adaptation (EBA) Theory may be used to anchor future studies on sea level rise and coastal erosion in Miami. Implement local ICZM strategies that involve stakeholders in decision-making processes, ensuring that community needs are met while enhancing coastal resilience. Advocate for policies that support adaptive management practices and funding for local ICZM initiatives.

Characterization of Seismic Signal Patterns and Dynamic Pore Pressure Fluctuations Due to Wave-Induced Erosion on Non-Cohesive Slopes

Wave erosion of slopes can easily trigger landslides into marine environments and pose severe threats to both the ecological environment and human activities. Therefore, near-shore slope monitoring becomes crucial for preventing and alerting people to these potential disasters. To achieve a comprehensive understanding, it is imperative to conduct a detailed investigation into the dynamics of wave erosion processes acting on slopes. This research is conducted through flume tests, using a wave maker to create waves of various heights and frequencies to erode the slope models. During the tests, seismic signals, acoustic signals, and pore pressure generated by wave erosion and slope failure are recorded. Seismic and acoustic signals are analyzed, and time-frequency spectra are calculated using the Hilbert–Huang Transform to identify the erosion events and signal frequency ranges. Arias Intensity is used to assess seismic energy and explore the relationship between the amount of erosion and energy. The results show that wave height has a more decisive influence on erosion behavior and retreat than wave frequency. Rapid drawdown may potentially cause the slope to slide during cyclic swash and backwash wave action. As wave erosion changes from swash to impact, there is a significant increase in the spectral magnitude and Power Spectral Density (PSD) of both seismic and acoustic signals. An increase in pore pressure is observed due to the rise in the run-up height of waves. The amplitude of pore pressure will increase as the slope undergoes further erosion. Understanding the results of this study can aid in predicting erosion and in planning effective management strategies for slopes subject to wave action.

Innovative Coastal Resilience: Design and Application of Hydraulic Geotextile Tubes as Sustainable Breakwater Cores in La Union

The constant assault of waves contributes to the loss of valuable coastal land of La Union, necessitating innovative and sustainable methods to protect the shoreline. In the pursuit of sustainable solutions, innovative technologies such as hydraulic geotextile tubes have emerged as promising contenders for enhancing shoreline protection. This study explores the design and application of hydraulic geotextile tubes as breakwater cores along the La Union shoreline. Due to their permeability and flexibility, hydraulic geotextile tubes offer a viable substitute for conventional breakwater materials. The research aims to provide valuable insights into sustainable coastal management by determining how these tubes can be designed to resist wave forces, ensure stability against hydrodynamic pressures, identify various installation methods, and evaluate their advantages and disadvantages in preventing shoreline erosion and potentially reclaiming sand. The study's findings could inform strategies that balance shoreline protection with environmental preservation. It highlights the interaction between creative engineering solutions and environmental stewardship in addressing evolving coastal challenges.

Sustaining the shell middens: A coastal vulnerability assessment of shell midden sites within the Nansemond River tributary

Shorelines have always been hubs of human activity and development meaning much of our cultural heritage is concentrated in coastal settings. In recent decades, changing environmental conditions and the effects of global warming (i.e., shoreline erosion, sea-level rise, land subsistence) threaten to destroy much of our remaining global coastal heritage. To prevent the further loss of archaeological contexts, this study seeks to develop a coastal vulnerability index through geospatial analysis to assess the vulnerability of 35 precontact shell midden sites along the Nansemond River in Suffolk, Virginia. The Nansemond middens offer a long-term history of how coastal inhabitants interacted with their surrounding landscape, with occupation of the area ranging from the Early Archaic period through European contact. This research considers various environmental and cultural variables used to determine which archaeological sites are most threatened by environmental changes and have the greatest potential to contribute valuable data to understand the past.

Comparative Study of the Coastal Geomorphology of Kajirbhati Sand-Spit Using Google Earth Pro Images (2005, 2011, 2023) and Landsat Satellite Data (2009, 2016, 2023): An Approach Towards the Impact of the Casuarina Plantation

Coastal geomorphology undergoes constant transformation due to a combination of coastal and fluvial processes and human intervention. Remote sensing and GIS tools are invaluable in identifying and studying these changes. Due to the dynamic interaction between land and sea, the coastline requires careful monitoring to detect hotspots and understand the spatial and temporal impacts of climate change on the coastal environment. Remote sensing data offers a comprehensive means of studying coastal landform changes. In a recent study, the focus was to analyze the impact of the Casuarina plantation on the coastal geomorphology of Kajirbhati spit. This involved studying various depositional features such as sand bars, sand spits, dunes, and beaches. The study utilized Google Earth Pro images from 2005, 2011, and 2023 to digitize 13 classes each year, enabling the identification of changing geomorphic classes. These include agriculture, swash zones, dunes on sand spits, berm lines, Casuarina and coconut plantations, estuary, mangroves, mudflats, open land, sea, settlement, and vegetation. The results revealed dramatic changes in land use and land cover classes from 2005 to 2023. In the years from 2011 to 2023, the area of sandspit covered by Casuarina plants expanded rapidly. To analyze the changes, Landsat 5, 8, and 9 data were used to check the intensity of NDVI (Normalized Difference Vegetation Index) in 2009, 2016, and 2023. NDVI is a critical factor in this research. The mean NDVI values for 2009, 2016, and 2023 were -0.002, 0.02, and 0.04 respectively. The changes in higher NDVI values from 2009 to 2023 were -0.10, 0.27, and 0.28, while the lower values were -0.10, -0.10, and -0.07 for the same years. The correlation calculation between the mean NDVI values and the years indicates a strong positive correlation with an R-value of 0.99. Casuarina plants play a crucial role in protecting the coast from strong winds and dynamic sea waves. They help protect mudflats, mangroves, settlements, and estuary land use and cover classes along the coast of Kajirbhati.

Erosion of mangrove dominated muddy coasts in Vietnam and Indonesia: Processes and accelerating factors

Although there have been extensive studies of the erosion of mangrove-dominated muddy coasts, the information on the processes and drivers of erosion at fine scales of analysis is still lacking. Without this knowledge, the existing efforts to minimize erosion are just piecemeal solutions that only address the symptoms of the erosion process. The coastlines of the Mekong Delta in Vietnam (VMD) and Brebes Regency in Indonesia have been selected as case studies to address this issue. The aim of the paper is to document coastal erosion and the factors that accelerate the erosion process. This is achieved by using the participatory diagramming technique, which combines the analysis of photographs of erosion sites taken during field trips, detailed field observations, and responses from semi-structured interviews with erosion-affected communities in VMD and Brebes Regency, Indonesia. The results show that five dominant erosion processes identified in these two regions were burrow-induced erosion, clearcut-induced erosion, farming-induced erosion, pond-induced erosion, and boating-induced erosion. Of the five erosion processes, human activities have altered the characteristic of the mangrove forests, and are likely to have exposed areas to erosion, with wave action providing a tipping point by severely reducing the structural integrity of the coastal soil in sensitive areas and making them susceptible to collapse. However, many other areas in VMD and Brebes Regency, Indonesia have remained stable over time. The methodological approach proposed here appears to be applicable to other mangrove-dominated muddy coasts, which are characteristic of most anthropogenically affected tropical deltas. As human activities are closely linked to forestry policies in Vietnam and Indonesia, enforcement should be strengthened to significantly increase the impact of these policies in controlling coastal erosion and minimize the vulnerability of these areas to erosion.

Integrating a multi-variable scenario with Attention-LSTM model to forecast long-term coastal beach erosion

Beach erosion is an adverse impact of climate change and human development activities. Effective beach management necessitates integrating natural and anthropogenic factors to address future erosion trends, while most current prediction models focus only on natural factors, which may provide an incomplete and potentially inaccurate representation of erosion dynamics. This study enhances prediction methods by integrating both natural and anthropogenic factors, thereby enhancing the accuracy and reliability of erosion projections. By extracting historical shorelines through CoastSat model from 1986 to 2020, we develop multivariable scenarios with Attention-LSTM model to predict the regional impacts of natural and anthropogenic factors on erosion to sandy beaches along the typical shoreline of Shenzhen in China. Results reveal that Shenzhen's beaches experienced erosion up to 12 m over the past 35 years. Here we project a decrease in the mean erosion rate of the beaches, identifying population growth (21.0 %) as the main controlling factor before the mid-century in a range of scenarios. We find that Attention-LSTM multi-model ensemble approach can provide overall improved accuracy and reliability over a wide range of beach erosion compared to scenario prediction model of Attention-LSTM and statistical model of Digital Shoreline Analysis System (DSAS), yielding an average uncertainty of 10.99 compared to 13.29. These insights reveal policies to safeguard beaches because of the rising demand for beaches due to human factors, coupled with decreased impervious surfaces through ecological conservation, lead to mitigation for beach erosion. Accurate forecasts empower policymakers to implement effective coastal management strategies, safeguard resources, and mitigate erosion's adverse effects. Our study offers finely-tuned predictions of coastal erosion, providing crucial insights for future coastal conservation efforts and climate change adaptation along the shoreline, and serving as a foundation for further research aimed at understanding the evolving environmental impacts of beach erosion in Shenzhen.

Characterizing fluvial impact on the biochemical composition of particulate organic matter in the Laptev Sea and Western East Siberian Sea during the late summer of 2018

The Laptev Sea (LS) and Western East Siberian Sea (W-ESS) are paradigmatic examples of seas dominated by terrestrial organic matter, attributed to substantial Siberian River discharges and coastal erosion. The influx of terrestrial organic matter significantly alters the biochemical composition of particulate organic matter (POM) in these Arctic coastal regions, potentially reducing the nutritional quality available to higher trophic levels. This study investigated the origin and qualitative characteristics of POM in the LS and W-ESS during the late summer of 2018 by analyzing elemental ratios (C/N ratio), stable carbon isotopes (δ13C), and biochemical compositions (biomolecular and amino acid (AA) compositions). The conspicuously depleted δ13C values (mean ± standard deviation (SD) = −30.2 ± 0.5 ‰) and alongside elevated molar C/N ratios (mean ± SD = 18.1 ± 6.2) suggest that terrestrial organic matter is the predominant source of POM in the study area. Although carbohydrates (CHO) were the dominant biomolecules, their prevalence was higher in the river-influenced W-ESS region (67.7 ± 6.6 %) than in the LS region (58.6 ± 13.9 %; p < 0.05). Furthermore, the CHO composition was closely associated with freshwater content and river fraction, suggesting that the heightened contribution of CHO may stem from terrestrial organic matter delivered by river inputs. Lower concentrations of particulate hydrolyzable AA (PAA) and carbon and nitrogen normalized yields of AAs (AA-POC% and AA-PON%) along with reduced contribution of glycine suggested a substantial contribution of terrestrial POM to both LS and W-ESS POM. Overall, this study provides valuable insights into the terrestrial influence on POM composition in Arctic marine ecosystems, emphasizing the need for continued monitoring of the consequences of terrestrial carbon inputs in the changing Arctic environment.

Spatiotemporal dynamics and transformation of the Parana State coastline: A 34-year analysis using RS, GIS, and machine learning

The coastal zone is a critical and vibrant area within coastal cities. Analyzing the changes in the coastal zone of Parana State helps determine the spatiotemporal evolution patterns and driving forces of this region, providing guidance for resource protection and utilization. This study employs remote sensing (RS), Geographic Information System (GIS), and Machine Learning techniques, using Landsat data sets with eight distinct scenes from 1990 to 2024, to extract and analyze the coastline. Specifically, methodologies such as Shoreline Extraction, the Coastline Diversity Index (CDI), and the Coastline Utilization Index (CUI) were applied to assess the coastline's characteristics. The spatiotemporal characteristics of the coastline development in Parana are meticulously examined to ensure accuracy. The findings reveal that: 1) Over the past 34 years, the coastline of Parana State has shown a consistent increasing trend. Natural coastlines have been declining by 45% annually, while artificial coastlines have been increasing by approximately 55% annually. 2) The nature of the shoreline is transitioning from natural to sea-reclamation, engineering-enhanced, and degraded forest. 3) The coastline changes have occurred in three phases: The Built-up Land phase, the Port Petrochemical phase, and the Reducing Coastal Erosion phase. Significant shoreline extension is observed near both biological and ecological coasts. 4) The primary factors influencing the coastline alterations in Parana State include natural forces, human activities, and regional policies. These insights into the spatiotemporal dynamics of the Parana coastline can inform better coastal management and conservation strategies.

Interrelationship between Wall and Beach Erosion in Loc An, Vietnam: Remote Sensing and Numerical Modeling Approaches

Beach erosion and coastal protection are complex and interconnected phenomena that have a substantial impact on coastal environments worldwide. Among the various coastal protection measures, seawalls have been widely implemented to mitigate erosion and protect coastal assets. However, the interrelationship between beach erosion and seawalls remains a critical topic for investigation to ensure effective and sustainable coastal management strategies. Seawalls impact the shoreline, particularly through the “end effect”, where the seawall functions similarly to a groin, causing erosion on the downdrift side relative to the direction of wave approach. This study provides a detailed analysis of the interplay between beach erosion and seawall structures in Loc An, Vietnam, employing both remote sensing and numerical approaches. Sentinel-2 images were employed together with an analytical solution to observe the shoreline change at the Loc An sand spit and to determine input values for the numerical model. Based on the shoreline dynamics, a numerical scheme was employed to study the shoreline evolution after the construction of a seawall. Our findings show that the shoreline evolution can be divided into three stages: (1) The first stage corresponds to the elongation of the sand spit without interference from coastal structures. (2) The second stage shows the effect of jetties on the shoreline, as signaled by the buildup of sand updrift of the jetties. (3) The third stage shows the effectiveness of the seawall, where the shoreline reaches its equilibrium condition. The study provides a quick and simple method for estimating shoreline diffusivity (ε) in situations where measured data is scarce.

Shore ice control on coastal geomorphic evolution in cold regions

Shore ice is a common feature on cold climate coasts, which are abundant in mid- and high-latitude regions, however it is understudied. Previous research has reported both beach protection and erosion as potential impacts from shore ice presence. Altered ice dynamics resulting from a changing climate are likely to intensify these impacts. To address this discrepancy and improve future coastal change predictions we conducted the first combined field, laboratory and modeling study of shore-ice processes and impacts. Beach and nearshore morphology mapping, experiments with a novel cryogenic wave tank, and 3D coastal evolution modeling revealed that shore ice protected the beach from storms, but scoured the nearshore at the ice edge and transported sediment offshore, likely past the depth of closure. This resulted in enhanced beach erosion during the ice-free and non-storm season, countering the protective benefit from the ice. This study indicates that shore ice plays an important and likely evolving role in geomorphic evolution along cold climate coasts.

Modeling cross-shore profile evolution in response to climate change: A case study for the Southwestern Black Sea Coast

Changes in wave climate and sea level as a result of global climate change cause significant effects on coastal morphology. Especially increasing wave heights, more frequent storms, and sea level rise (SLR) significantly alter the morphology of cross-shore profiles and diminish the security of coastal areas. In this study, profile surveys were carried out in two distinct regions along the Western Coast of the Black Sea, and the profile evolutions were analyzed using the XBeach numerical model. The XBeach model was executed using both its default parameters and the parameters derived from on-site measurements. This study was also conducted under the influence of hydrodynamic conditions (wave parameters) that vary according to the RCP4.5 and RCP8.5 climate scenarios, along with the effects of sea level rise (SLR), to analyze the potential impacts of climate change on profile evolution. The results indicated a linear relationship between the upper beach erosion and sea-level rise (SLR). The increased water level in front of the upper beach leads to greater erosion volume. The model results for the scenarios demonstrated moderate sensitivity to variations in offshore wave height, peak wave period, and storm duration, but were predominantly sensitive to accelerated sea level rise (SLR).

Reconciling short- and long-term measurements of coastal cliff erosion rates

Oblique terrestrial laser scanning (TLS) enables topographic change detection at scales (10−1 –100 cm) that are appropriate for coastal cliff erosion monitoring. Despite this, published applications of TLS on cliff are limited to a small number of sites around the world. Here we report new TLS point cloud datasets from 9 years of monitoring (2014–2023) at Rothesay Bay within the Hauraki Gulf, New Zealand, which has relatively low wave energy and a meso-tidal range. The 120 m-length scan area includes cliffs of 10–30 m height, formed of horizontally bedded soft sedimentary flysch rock. The cliffs are fronted by an 140 m wide near-horizontal shore platform that terminates in an abrupt seaward edge. Previous research at this site has estimated long-term cliff erosion rates within a range of 1.4 ± 0.1 to 14.3 ± 0.1 mm/year on the basis of measured shore platform width, assuming that the shore platform has widened over time over 6000 years of stable Holocene sea level, and that the seaward edge of the shore platform has not retreated. Volumetric cliff-face erosion rates were detected through 17 scans over a 9-year window (2014–2023), including intensive monthly TLS scanning between July 2021 and July 2022. Results show that the average cliff recession rate over the past decade has been 41 ± 2 mm/year, and monthly scans show a range in erosion rates of 30 to 288 mm/year. The cliff recession rate detected with TLS is 3 to 30 times higher than erosion rates derived based on the shore platform width. If erosion had been constant at this rate over approximately 6000 years, a total cliff retreat of >245 m would be expected, whereas the contemporary shore platform is only 140 m wide. We discuss two possible hypotheses for the confounding width of the modern shore platform: 1) that modern cliff retreat rates are faster than past erosion rates; 2) that the seaward edge of the shore platform does not reliably demarcate Holocene cliff recession. We present new bathymetric survey mapping seaward of the shore platform edge that reveals multiple rocky features that are distinguished by steep slope breaks and planar surfaces. Understanding the evolution of the intertidal shore platforms during the Holocene era may necessitate new insights on how cliffs formed toward the end of the last marine transgression. This could potentially be investigated through the study of subtidal marine bathymetry.

Temporal Shoreline Changes From 1984 to 2022 Along Beymelek Beach and Beymelek Lagoon, Antalya, Türkiye

Coastal zones are important transition zones between land and sea, and the shoreline is subject to dynamic change on both spatial and temporal scales. Accurate measurement and modelling of the shoreline is therefore essential for coastal sustainability and coastal zone management. In this study, the shoreline change of Beymelek Beach and Beymelek Lagoon was analyzed over both short and long periods by using End Point Rate (EPR), Net Shoreline Movement (NSM) and Linear Regression Rate (LRR) statistics from the Digital Shoreline Analyses System (DSAS) tool. The long-term shoreline statistics of the Beymelek Beach indicates that the maximum shoreline accretion was 128.4 m for NSM and 4.3 m/yr for EPR, while the maximum shoreline erosion was -62.6 m for NSM, and -1.8 m/yr for LRR in 1984 and 2022. The maximum shoreline erosion rate of Beymelek Lagoon was -148.5 m for NSM and the maximum shoreline accretion was 5.3 m for NSM between 1984 and 2022. As a result, Beymelek Beach and Beymelek Lagoon have experienced significant shoreline changes over both short and long time periods. Therefore, determining the shoreline change in the study area is crucial for making efficient decisions about the coastal zone and contributing to its sustainability.

Large Eddy Simulation of Cross‐Shore Hydrodynamics Under Random Waves in the Inner Surf and Swash Zones

AbstractA 3D large eddy simulation coupled with a free surface tracking scheme was used to simulate cross‐shore hydrodynamics as observed in a large wave flume experiment. The primary objective was to enhance the understanding of wave‐backwash interactions and the implications for observed morphodynamics. Two simulation cases were carried out to elucidate key processes of wave‐backwash interactions across two distinct stages: berm erosion and sandbar formation, during the early portion of a modeled storm. The major difference between the two cases was the bathymetry: one featuring a berm without a sandbar (Case I), and the other, featuring a sandbar without a berm (Case II) at similar water depth. Good agreement (overall Willmott's index of agreement greater than 0.8) between simulations and measured data in free surface elevation, wave spectrum, and flow velocities validated the model skill. The findings indicated that the bottom shear stress, represented by the Shields parameter, was significant in both cases, potentially contributing substantial sediment transport. Notably, the occurrence of intense wave‐backwash interactions were more frequent in the absence of a sandbar. These intense wave‐backwash interactions resulted in a pronounced horizontal pressure gradient, quantified by high Sleath parameters, exceeding the criteria for momentary bed failure. Additionally, a more vigorous turbulence‐bed interaction, characterized by near‐bed turbulent kinetic energy, was observed in the case lacking a sandbar, potentially augmenting sediment suspension. These insights are pivotal in understanding the mechanisms underlying berm erosion and how sandbar formation serves to protect further beach erosion.

Nature‐based shoreline protection in newly formed tidal marshes is controlled by tidal inundation and sedimentation rate

AbstractMany tidal marshes have been lost by past land use changes, but are nowadays increasingly restored and created to provide valuable ecosystem services such as nature‐based flood and erosion protection along estuarine shorelines. To be functional for flood and shoreline erosion protection, restored and created tidal marshes should develop erosion resistant sediment beds. Here, we investigated which factors drive the spatial variations in sediment strength and erosion resistance in a developing tidal marsh restoration site. Our results show that decreasing tidal inundation frequency, decreasing sedimentation rate, and better drainage led to stronger consolidation in deeper sediment layers. This consolidation resulted in greater sediment strength, quantified here by shear strength and penetration resistance. Generally, sediment strength was greater when sediment had higher bulk density, while a higher water and fine fraction (= clay and silt) content decreased sediment strength. Overall, all measurement locations were relatively erosion resistant, likely caused by the dense root network and cohesive sediment. To restore or create resilient tidal marshes for nature‐based flood and shoreline erosion protection, we should thus aim for sites with relatively low tidal inundation frequency, moderate sedimentation rates, and cohesive sediment mixtures of clay, silt, and sand, which are well drained and have potential for vegetation establishment. These conditions have a high likelihood of resulting in restored or created tidal marshes that contribute to nature‐based flood and shoreline erosion protection.