Saltmarshes provide numerous ecosystem services, contributing to climate change mitigation (carbon sequestration) and adaptation (coastal protection). While capable of accreting sediments in a dynamic equilibrium with changing sea levels, uncertainty remains regarding their continued resilience under accelerated rates of sea level rise (SLR). Ultimately, an improved understanding of how saltmarsh systems develop and evolve under changing conditions is needed to inform management and restoration strategies. Numerical frameworks that couple hydro-morphodynamics and vegetation dynamics (“eco-geomorphic” models) are emerging to support such advancements. Challenged by conflicts of scale and high computational costs, however, saltmarsh modelling studies often implement simplifications that ignore short-term vegetation dynamics such as seasonal growth cycles. Consequently, it remains poorly understood how seasonal variation impacts saltmarsh eco-geomorphic processes on sub-annual to multi-decadal timescales, and if there are implications for ecosystem vulnerability to SLR.To address this, a numerical study was developed based on seasonal stem measurements of Sporobolus alterniflorus from the St. Lawrence Estuary (Québec, Canada). Coupling hydro-morphodynamics (TELEMAC-2D, GAIA) with a cellular automaton for vegetation dynamics, a novel eco-geomorphic framework was applied to simulate saltmarsh development under scenarios with explicit seasonal variation, versus vegetation properties averaged over the growing season. For each scenario, the model was used to simulate 180 years of eco-geomorphic development for an initially bare, idealized tidal domain.This study demonstrates, for the first time, how sub-annual seasonal processes contribute to ecosystem development over the long-term (decades to centuries). Simulations that incorporated explicit seasonal variation in stem characteristics yielded more rapidly accreting saltmarsh platforms, with denser tidal channel networks; both supporting improved resilience under SLR. Sediment delivery to saltmarsh interiors was promoted during seasons of low biomass, while seasons of peak biomass strengthened flow routing around vegetation patches, enhancing channel network development. Identifying new mechanisms underlying long-term saltmarsh evolution and resilience, this work highlights the critical importance of integrating seasonality into eco-geomorphic models.

ABSTRACT Predicting the long‐term evolution of saltmarshes using numerical tools could significantly aid management and restoration efforts. However, limited geographic diversity in the present body of saltmarsh eco‐geomorphic literature highlights a significant barrier to model development and widespread application. To address this gap, a comprehensive field study was conducted for meso‐tidal saltmarshes within the St. Lawrence Estuary (Petites‐Bergeronnes, Québec, Canada). From eight field campaigns performed between July 2023 and August 2024, a novel hydro‐eco‐geomorphic database is presented for the study site. Spatial variation in eco‐geomorphic drivers supported observations of contrasting historical marsh edge evolution; differences in inundation frequency, sediment supply, deposition rates and vegetation properties are reinforcing marsh progradation in one area of interest, and edge erosion within another. Within the former, suspended sediment concentration was significantly correlated with temporal variation in spring tidal heights, indicating that short‐term hydrodynamic changes could critically influence sediment supply. Analysis of stem measurements for seven saltmarsh species demonstrated a significant difference in stem length and diameter between pioneer ( Sporobolus alterniflorus ) and high marsh communities ( S porobolus pumilus – and Plantago maritima –dominant). Repeated measurements throughout the snow‐free season also revealed significant temporal variation in stem properties, often disregarded in numerical models. Pioneer S. alterniflorus exhibited the largest magnitude of change, with increases of 2.53 mm in mean diameter and 59.5 cm in mean length between early and peak season. Overall, this work presents important advancements for system understanding of saltmarsh evolution across diverse geographies and provides novel datasets for addressing spatial and temporal complexity in eco‐geomorphic processes.

Salt marshes play a crucial role in coastal defense, yet quantifying their protective contribution requires understanding the seasonal and regional variability of their biomechanical properties. Stem characteristics such as bending stiffness, diameter, and geometry determine plant motion and the resulting hydrodynamic forces under wave and current exposure. The first field-based quantification of flexural stiffness and its seasonal variation for Canadian Spartina alterniflora was obtained through in situ measurements. To link these measurements with hydrodynamic processes, the fluid-structure interaction solver in REEF3D::CFD was employed to simulate stem-scale flow field alterations. Extending the analysis to a broader geographical context, biomechanical properties of Spartina anglica from Southeast North Sea marshes were incorporated to assess the influence of seasonal and regional variation on the local flow field. Field data for S. alterniflora indicates pronounced seasonal changes, with stems increasing substantially in stiffness and size from early-season to adult stages. Comparison with S. anglica shows, for the first time, that Canadian stems are smaller and more flexible. Numerical results demonstrate that stem-induced flow modifications, expressed as turbulence intensity in currents and turbulent kinetic energy in waves, exhibit stronger regional than seasonal differences. Corresponding drag coefficients, differentiated by season and region and ranging from 1.5 to 2.0, are provided for future hydrodynamic modeling. The findings highlight that regional variation in stem biomechanics influences the flow-vegetation interaction, emphasizing the importance of cross-regional assessments for nature-based coastal protection strategies.

Arctic permafrost coastlines are retreating faster as climate warming intensifies. Accurate modelling of the thermomechanical process is hindered by a lack of direct measurement of heat flux or heat transfer coefficients (h(w)) at the water-permafrost interface. This study presents the first, direct laboratory measurements of wave-induced convective heat transfer coefficients. In twelve wave-flume experiments, artificial permafrost samples were exposed to air, still water, and irregular waves (0.02-0.04 m height; 0.8-1.2 s period). Embedded resistance temperature detectors tracked temperature changes at high spatial and temporal resolution, allowing for precise heat flux and heat transfer coefficient calculations. Under wave action, thaw-front advanced rapidly into the permafrost blocks at about 160-350 mmh(-1) compared to 3.24 mmh(-1) in air and 50.14 mmh(-1) in still water. Similarly, heat transfer coefficient ranged from 459 to 1210 Wm(-2) K-1 in wave tests, significantly exceeding those for still water (similar to 165 Wm(-2) K-1) and air exposure (similar to 4.4 Wm(-2) K-1) tests. Heat flux correlated most strongly with wave height; higher ice content slowed thawing but did not evidently affect h(w) magnitude. A novel empirical model was developed that pioneers the linking of h(w) to surf similarity and dimensionless wave height and period. With strong predictive performance (R-2 = 0.89, RMSE = 81.1 Wm(-2) K-1), the model provides a practical, experimentally validated tool for specifying h(w) in coastal permafrost erosion models, eliminating the reliance on parameter tuning required by previous analytical approaches. Overall, this study demonstrates the critical role of waves in heat delivery to permafrost coastlines.

Coastal regions are increasingly vulnerable to erosion, flooding, and habitat loss due to climate change-driven sea-level rise, intensified storm surges, and amplified wave energy, necessitating the development of innovative, sustainable coastal protection strategies. While traditional methods remain effective, they are often saddled with environmental drawbacks and high maintenance costs. The floating breakwater concept is a well-established coastal protection measure, offering adaptability to varying water depths and minimal ecological impact; however, optimizing its efficiency-particularly through advanced porous designs-remains an active research challenge. This study explores integrating triply periodic minimal surface (TPMS) geometries into breakwaters design to enhance and optimize their hydrodynamic performance and promote innovative coastal protection measures. Twelve three-dimensional-printed models with varying TPMS architectures, relative densities, and cell sizes (uniform and graded) were experimentally tested in a small-scale flume under 54 wave-current scenarios, analyzing wave reflection, transmission, and dissipation coefficients for their performance assessment. Unlike many previous studies that focused solely on waves, this research incorporates wave-current interactions to better simulate coastal environments. The results showed that diamond TPMS outperformed other geometries due to higher tortuosity and surface complexity, showing lower energy reflection and transmission and greater dissipation. Models with lower relative density and larger cell sizes (required up to 46% less material for printing) exhibited improved energy reflection performance. Additionally, cell grading proved effective in enhancing dissipation and minimizing wave transmission. The findings demonstrate the potential of TPMS-based floating porous breakwaters as a cost-effective, adaptable, and high-performance solution for future coastal protection systems.

Tsunamis and other extreme hydrodynamic events have the potential to transport large debris that, along with the flow, are capable of causing severe damage to coastal structures and infrastructures. Therefore, modelling such processes is essential when assessing the multiple hazards associated to this type of events. In harbour areas, transport inland of shipping containers and subsequent impacts are relevant examples of waterborne debris hazards. The present work addresses two gaps in the scientific research of this problem using numerical methods; the understanding of the effect of containers initial layouts and that of the flow impact angle on the transport and diffusion. To fill these gaps a numerical study was carried out using idealised flow conditions. To this end a Smoothed Particles Hydrodynamics solver (DualSPHysics), coupled with a Discrete Element Method model (Project CHRONO), was used and initially validated with experiments published in the literature. Subsequently, four layouts commonly used in shipping containers yards were simulated, including incident flow depth and impact angle variability, resulting in 76 total simulations. The results were analysed in terms of normalised standard deviation and normalised range differences with respect to the initial values of both parameters. These parameters were related to the flow impact angle, water depth to containers height ratio DhR, and normalised displacement of the container clusters centroids. Standard deviation and range are shown to reach, for almost all results, a quasi-steady state by the end of the simulations. It is shown that the standard deviation and range are more sensitive to the impact angle for DhR <= 1.7. In this case, the configurations with flow impacting orthogonally to one of the containers axes show larger values of the two parameters than for intermediate angles. For larger values, DhR drives the standard deviation and range, independently from the impact angle. DhR is shown to be a physical parameter that well describes the relative importance of dispersion and advection of containers transported in extreme hydrodynamic events. Finally, existing relationships, that assume an infinite growth of the range, are shown to overestimate numerical results at the stage in which dispersion does not grow further. Two new regression formulae are numerically derived to predict the dispersion parameters at this stage. They include the effects of the cluster layout, impact angle a and DhR making them a valid alternative to existing relationships.

Field surveys following major coastal disasters, such as the Chile tsunami in 2010 or the Tohoku tsunami in Japan in 2011, have pointed out the lack of resilience of coastal communities to such events and the need to better understand the risks associated with them (Takahashi et al. [2010]; Palermo et al. [2013]; Esteban et al. [2015]). While the primary cause of destruction during tsunamis remains associated with the hydraulic loads (hydrostatic, hydrodynamics, wave impact, etc.), it has been demonstrated that debris loading is also a major cause of damage on structures, mainly through debris impact and damming (Yeh et al. [2014]). In the past decade, multiple studies have addressed debris transport and loading in extreme events (Shafiei et al. [2016]; Ikeno et al. [2016]; Stolle et al. [2018]). However, those studies mainly focused on positively buoyant debris, like wood logs or empty containers, leaving a gap in knowledge. Indeed, Stolle et al. [2020], in a field survey following the Indonesian tsunami in 2018, identified the study of neutrally and negatively buoyant debris as one of five major needs in debris loading research, with even ASCE7-16 Chapter 6 containing limited recommendation on the load associated with those type of debris.

Novel approaches to evaluating marsh eco-geomorphic evolution are being developed using mathematical models that incorporate ecological, hydrological, and geomorphologic considerations. Such works have predominantly been implemented for marshes located in the Netherlands (e.g., Gourgue et al., 2022), with a couple case studies in the United States (e.g., Brand et al., 2022) and Australia (Kumbier et al., 2022). Inputs to such models are often highly site-specific and intrinsically tied to geographically variant parameters (species, sediment supply, hydrodynamic context, seasonal effects). Numerical models of marsh eco-geomorphic evolution developed thus far have not been validated for field sites within Canada. Presently, vegetation-based coastal adaptation strategies, including coastal marsh restoration design and erosion risk assessment, are hindered in Canada by a lack of numerical predictive tools that can accurately assess marsh eco-geomorphologic evolution.

Understanding growth patterns, survival, and seasonal variations in plant characteristics is essential for newly established vegetated slopes to ensure their long-term effectiveness in dissipating wave energy, particularly in cold climate regions with extended winters and short summers. This study investigates the growth patterns, seasonal and interannual variations in plant morphological properties, and their corresponding effect on wave energy attenuation under controlled conditions, to evaluate the wave dissipation characteristics of newly established vegetated slope over multiple seasons, based on experimental data from large-scale physical modeling experiments. These experiments capture the one-year growth cycle of a newly constructed marsh with live saltmarsh vegetation native to eastern Canada and the USA. The findings reveal that even a newly established marsh with young, relatively sparse plants can contribute to wave energy dissipation. A clear seasonal variation in plant morphological properties was observed, resulting in a significant increase in vegetation-induced wave dissipation after one year of growth. Different species exhibited different responses against wave forces leading to different wave dissipation characteristics depending on their plant traits. However, under conditions of considerable depth-induced wave breaking, the effectiveness of vegetation in dissipating wave energy was considerably reduced. Overall, our data with young saltmarsh plants showed a maximum of about 60% contribution by vegetation to total wave energy dissipation under minimal depth-induced breaking conditions, and a maximum of about 25% contribution to total wave energy dissipation under significant depth-induced breaking conditions, indicating a considerable reduction in percentage contribution to total wave energy dissipation by vegetation with wave breaking.

Permafrost coastal systems are critical to Arctic environmental processes, and understanding their erosion dynamics is essential for addressing climate change impacts. These coastlines undergo unique thermomechanical erosion, where wave action, rising sea levels, and thermal degradation jointly drive a rapid coastline recession. This study demonstrates advancements in physically modeling coastal permafrost erosion using a laboratory setup that replicates natural Arctic coastal conditions. A wave flume with a representative nearshore slope and reproducible permafrost specimen preparation methodology allowed isolation of the hydrodynamic and thermodynamic effects. Distinct erosion patterns and rates were quantified under varying wave heights, periods, and thermal conditions. Results indicate that wave height is a dominant mechanical driver, with mean erosion rates increasing by over 100% from low to high wave conditions. Even low-energy waves (H = 0.02 m) enhanced erosion by more than 50% compared to still-water conditions. Additionally, a higher ice content reduced niche deepening rates by 38%, which is attributed to latent heat delaying thawing. A new scalable thermomechanical model for erosional niche incision on an Arctic bluff is proposed based on a power-law relationship that integrates the Froude, Iribarren, and Stefan numbers. This dimensionless approach captures the coupled influence of wave-induced forces and permafrost thermal properties, exhibiting a strong predictive capability (R 2 = 0.90) and outperforming existing analytical models. The experimental framework and new model offer new insights into Arctic coastal retreat mechanisms and provide a promising foundation for regional-scale applications in coastal management under changing climatic conditions.

Coastal regions are confronted with an escalating threat posed by the intensification of wave-induced erosion through rising sea levels and increased storm intensities, underscoring the critical need for innovative solutions to ensure effective coastal protection. Floating breakwaters as a possible optimal solution play a crucial role in land reclamation by facilitating the creation of recreational spaces, such as promenades, and enhancing aesthetical landscapes through tree plantations. Their significance lies in their ease of maintenance and the ability to be swiftly removed during stormy seasons, providing adaptable and sustainable solutions for coastal development. This study explores the potential of the Triply Periodic Minimal Surface (TPMS) floating porous breakwaters as an optimal approach, due to their intricate geometry and structural integrity which enhances the dissipation and dispersion of wave energy, to mitigate the impact of waves on vulnerable shorelines. TPMS structures offer a sustainable solution by being printable with re-use materials, promoting recycling, and aligning with the principles of a circular economy, thus contributing to eco-friendly coastal protection. Conducted in a controlled environment within a small-scale wave flume, our comprehensive laboratory-scale experiment focuses on assessing the performance of various TPMS structures under diverse conditions of wave and current generation. Systematically varying parameters, including TPMS architecture, unit cell size, relative density of porous structures, buoyancy depth (draft), and altering wave parameters and current rates, aims to elucidate the influence of these variables on the breakwater’s ability to dissipate, reflect, and transmit wave energy. The experiments involved exposure to various regular wave conditions generated by a plunger-type wavemaker, combined with different constant current rates to mimic realistic coastal scenarios. The controlled environment enables a nuanced understanding of how TPMS floating breakwaters respond to diverse wave dynamics, providing valuable insights into optimal design parameters. The performance evaluation is conducted using three widely known parameters: reflection coefficient (Cr), transmission coefficient (Ct), and dissipation coefficient (Cd) as they quantify the efficiency of wave energy absorption, transmission through the structure, and dissipation, providing key insights into the breakwater's ability to mitigate wave impact and protect coastal areas. To determine these parameters, wave separation analysis methods have been employed, including the method developed by Suh et al (2001), which considers the presence of simultaneous waves and currents, and the method developed by Zelt and Skjelbreia (1993), utilizing an arbitrary number of wave gauges. Anticipating that the outcomes of this study will contribute to the development of a novel coastal protection solution, we strive to strike a balance between environmental sustainability and effective wave attenuation. Furthermore, our research opens avenues for integrating optimal floating breakwaters with wave energy conversion systems, enhancing functionality and addressing both environmental and energy challenges associated with coastal protection.

Successful establishment and growth of constructed saltmarshes can be evaluated through consistent monitoring of plant biophysical parameters, such as aboveground biomass and leaf area index. Monitoring during the early establishment stage is vital for ensuring the long-term effectiveness of constructed saltmarshes in delivering anticipated ecosystem services, including wave energy dissipation, which strongly depends on vegetation biophysical characteristics. Efficient, low-disturbance methods are needed for the successful adoption of such monitoring plans. This study combines laboratory measurements and remote sensing observations to evaluate the performance of vegetation indices in capturing changes in aboveground biomass, leaf area index, and wave energy dissipation in a constructed saltmarsh. Allometric equations were also investigated to predict aboveground biomass from non-destructive plant traits. Results showed acceptable correlations between vegetation indices, measured biophysical parameters and wave energy dissipation characteristics. All species performed better with NIR-R-based indices for leaf area index, while aboveground biomass predictions varied, with both NIR-R- and G-R-based indices performing best depending on species. Wave energy dissipation also correlated with vegetation indices, aligning closely with the best predictors of aboveground biomass, particularly when vegetation was submerged. These findings indicate that remote sensing combined with allometric equations offers a promising method for monitoring newly established marshes and estimating their biophysical parameters, which serve as key indicators of successful establishment and initial wave energy dissipation.

Restoration of coastal salt marshes has become progressively more common as the ecosystem services provided by these systems, including flood protection and shoreline stabilization, have been acknowledged. Recent examples in Canada include a marsh restoration in Boundary Bay (British Columbia) and a managed realignment at Belcher Street (Nova Scotia) (van Proosdij et al., 2023). To date, most laboratory-based live vegetation experiments have used transplanted natural marshes (Möller et al., 2006; Maza et al., 2022), which are representative of established marsh conditions. However, seasonal fluctuations in biomass and the reduced density of newly established (constructed) marshes compared to their natural counterparts (Tempest et al., 2015) can potentially result in significant variability in performance. There is a pressing need to understand the performance of newly established marshes to better characterize short- term benefits and ensure the long-term viability of these restoration efforts.

Extreme hydrodynamic events, such as those driven by tsunamis, most notably in Tohoku, Japan 2011 (Mori et al., 2011) and in Indonesia 2004 and 2018 (Sassa et al., 2019), have shown the need to consider debris for an accurate hazard assessment. Three main processes are relevant in this context: (I) debris transport and dispersion (Naito et al. 2014), (II) debris impact on coastal structures and infrastructures (Stolle et al., 2018, De Iasio et al., 2023) and (III) debris damming (Mauti et al., 2020). For (II) and (III), multiple design guidelines for structures, such as the FEMA P646 (FEMA, 2012) and American Society for Civil Engineers design codes (ASCE, 2016), were developed. (I) is mainly addressed either by simple empirical laws or by laboratory experiments. Numerical simulations of debris transport are still challenging in realistic conditions (Koh et al. 2023). Simple empirical rules describe debris lateral dispersion defined by a spreading area ±22.5° from the initial position (Naito et al. 2014), and by a dispersion law depending on the number of debris transported (Nistor et al., 2017). Harbours and nearby areas are exposed to container transport hazard (Naito et al. 2014., Koh et al. 2023). This makes understanding the role of tsunamis impact angle and storage yard layout on the movement of shipping containers particularly important. While dispersion at city scale can be simulated with depth integrated models (Koh et al. (2023), the analysis of the pick-up stage and near field transport requires modelling of the six degrees of freedom of the waterborne debris. Due to their nature, Lagrangian numerical models have been used to simulate these problems. More specifically Smoothed Particles Hydrodynamics (SPH) models coupled with the Multiphysics model CHRONO have recently demonstrated their capability in accurately simulating these type of phenomena (Ruffini et al., 2021, 2023). Using this numerical approach, this study aims to provide insight into the role of the initial debris layout in the hazard generated by their mobilisation, focusing on shipping containers in harbours.

Physical modeling presents a useful tool for investigating the coastal protection function provided by marsh vegetation in a controlled, repeatable environment to inform the design of nature-based coastal protection strategies or nature-based solutions (NBS). To date, such studies have been used to investigate the influence of plant biophysical parameters and hydrodynamic conditions on wave attenuation, predominantly using surrogate vegetation due to the logistical challenges associated with live plant experiments. Most studies have been performed at or near full scale to avoid uncertainties associated with downscaling vegetation, particularly where Reynolds number similitude cannot be preserved. To address knowledge gaps related to the physical modeling of NBS at the small scale, experiments (1:4 scale) were conducted at the National Research Council of Canada's Ocean, Coastal and River Engineering Research Centre, Ottawa, in collaboration with the University of Ottawa and the Institut National de la Recherche Scientifique, Quebec, Canada. This study aims to (1) investigate methods for downscaling live vegetation in laboratory settings and (2) compare various surrogate proxies for the semiflexible Spartina alterniflora salt marsh species. A solid volume fraction scaling approach was applied to select multiple stem width and stem density combinations representative of a prototype-scale S. alterniflora field while maintaining stem Reynolds numbers within a range representative of prototype conditions. Arrays of various surrogate elements were subjected to irregular waves (0.073 m < H-m0 < 0.225 m, 2.0 s < T-p < 3.2 s) at two water depths (d = 0.60, 0.75 m) across a fixed beach slope (1:20). Comparison of wave height transformations for the different surrogate array configurations indicated that downscaling of vegetation canopies is sensitive to stem diameter and spacing, even considering equivalent solid volume fractions. Flexible surrogate arrays performed similarly to rigid surrogate arrays in terms of irregular wave attenuation despite measurable deformation of the flexible element stems. This supports that wave transformations across S. alterniflora fields can be reasonably represented in scaled models using rigid cylinders for the range of array stem densities, wave conditions, and scale tested herein. This study presents novel critical guidance on small-scale physical modeling of wave-vegetation interactions to inform the design of coastal marsh-based NBS. (c) 2025 American Society of Civil Engineers.

Debris impact on critical infrastructure is a major cause of destruction during tsunami events. While the loading of positively buoyant debris (debris with a density lower than water) has been well researched, to the author's knowledge, few studies have focused on the impact of negatively buoyant debris (debris with a density higher than water). To address this knowledge gap, this paper presents the results of an experimental program investigating the impact of negatively buoyant debris on a structure using a dam-break wave. Spherical debris scaled down to a 1:60 ratio was entrained by a bore wave to impact a cylindrical structure. The final velocity of negatively buoyant debris was shown to be lower than the bore front velocity, with a relative velocity decreasing with increasing density. The Stokes number of the debris was found to be a good parameter to approximate this relative speed. For the calculation of the impact force, a single-degree-of-freedom equation based on the contact stiffness model was found to be a good fit for the experimental data. However, this fit can be improved by incorporating an extra parameter dependent on the density and diameter of the debris.

Tsunamis continue to pose an existential threat to life and infrastructure in many coastal areas around the world. One of the risks associated with tsunamis is the formation of deep scour holes around critical infrastructure and other coastal buildings, compromising their structural integrity and stability. Despite its importance, tsunami-induced scour is still given limited and simplified consideration in design guidelines for coastal structures. To further improve the understanding of tsunami-induced scour processes, and thus provide the basis for safer design of coastal structures, novel large-scale laboratory experiments have been conducted. The experiments featured a unique combination of boundary conditions, including a square coastal structure on a sloping and dry sandy beach. Single broken solitary waves were used to simulate tsunami bores. The spatiotemporal scour development directly at the square column was monitored by a high-resolution camera system, allowing a detailed description of the highly dynamic flow and scour process. Differences in the scour process between the wave runup and drawdown phases are described, and maximum and final scour depths are given as a function of inundation depth, wave height, and distance of the column from the shoreline. The scour process is characterized by several distinct phases of varying intensity and scour rate, the sequence of which varies depending on the location on the sides of the column. It is shown that the drawdown phase has a large influence on the overall scour development, adding up to 58% to the scour depth obtained during the wave runup phase. As a result of significant sediment infilling during the drawdown phase, the maximum scour depths achieved during the drawdown phase are up to twice the final scour depths at the end of a test. This discrepancy between final and maximum scour depths is greater than in previous studies using a flat sediment bed. The results of this study therefore help to interpret scour depths measured during field investigations after a tsunami event and provide a basis for extending design guidelines for coastal structures.

Post-disaster surveys of tsunamis have emphasized the need for an in-depth understanding of debris loading. Until now, empirical formulas used to estimate debris impact loads are based on single-degree-of-freedom (SDOF) models. However, the validity of these SDOF models to estimate debris impact loads has not been studied extensively. This study investigates the validity of using a SDOF model to predict debris impact forces by comparing its force response to experimental data and a multiple-degree-of-freedom (MDOF) model developed. Additionally, a comparative analysis was conducted to assess the provisions on debris impact loads in Chapter 6 of ASCE 7-22 against these alternative methods. The MDOF method was shown to model accurately the experimental force response data, while all other methods for estimating debris impact loads overestimated the force response in both magnitude and frequency. Furthermore, the impact loads generated by the MDOF model proved to be longer in duration but smaller in magnitude than loads generated using the SDOF model and Chapter 6 of ASCE 7-22. In addition, a performant numerical model was developed to simulate single and multi-debris transport and impact loads on a column. The dynamic numerical model was developed within the general-purpose finite element program LS-DYNA. Inside this modelling framework, the Arbitrary Lagrangian-Eulerian (ALE) method was used to simulate dam-break wave generated debris impact loads onto the column. The model accurately replicated the water surface elevations, hydrodynamic forces, debris transport, and debris impact forces presented in Stolle et al. (2019) and Stolle et al. (2020b). The model’s ability to simulate debris impact events demonstrates its potential as a valuable tool for designing and evaluating critical infrastructure’s resilience against extreme coastal inundation events, such as tsunamis.

Driftwood is abundant in coastal zones, and is increasingly being incorporated in nature-based shore protection and restoration projects. However, accumulations of driftwood, and their mobilization by storms or other disturbances, can pose hazards to coastal communities, infrastructure, and ecosystems. An improved understanding of driftwood dynamics in nearshore, wave-dominated environments is needed to inform sustainable use and management of wood in coastal zones. An optical tracking technique was applied to quantify mean transport and dispersion of driftwood in a 1/30 Froude-scaled coastal model exposed to oblique waves. The results provided new insight to factors controlling driftwood mobility and dispersion on beaches exposed to oblique waves, including the effects of sea state, wave-induced currents and circulation, water levels, driftwood length, driftwood roughness, driftwood buoyancy, and coastal structures.

A quantitative understanding of the migration of munitions and canonical objects in the nearshore is needed for the effective management of contaminated sites. Migrations of munitions with a density range of 2000 kg/m3 to 5720 kg/m3 were quantified in a large-scale wave flume. The forcing consisted of six cases of varying wave heights, periods, still water depths, and durations. The cross-shore profile, typical of natural sandy beaches, was sub-divided into swash, surf, and offshore zones. Overall, 2228 migration measurements were recorded with 16% and 84% of the migration observations classified as “motion” (net distance > 0.5 m) and “no motion” (net distance ≤ 0.5 m), respectively. The probability of munitions migration increased with proximity to the shoreline. There was a nearly equal probability of onshore or offshore migration in the swash zone. Migration in the surf zone tended to be offshore-directed (65%), while migration was onshore-dominant (65%) in the offshore zone. Migration in the offshore zone was preferentially onshore due to skewed waves over flat bathymetry. Less dense munitions in the offshore zone may have migrated offshore likely still related to the skewed nature of the wave profile causing transport in both directions through the majority of the wave phase. The largest migration distances occurred in the surf zone likely due to downslope gravity. Migration in the surf and swash zones is a balance between skewed/asymmetric forcing and downslope gravity, with downslope gravity tending to be pronounced provided the forcing is sufficient to initiate motion. An exception was sometimes observed in the swash zone where onshore forcing was sufficient to transport munitions to the seaward side of the berm where they became trapped in a bathymetric depression between the dune and berm. Relating overall migration (Lagrangian) to fixed hydrodynamic measurements (Eulerian) was ineffective. Parameters such as the Shields number, wave skewness, and wave asymmetry estimated from the closest measurement location were insufficient to predict migration. Large scatter in the migration data resulting from competing hydrodynamic, morphodynamic, and munitions response processes makes robust deterministic predictions with flow statistics and dimensionless numbers difficult.