Laboratory investigations of beach morphology change under wave action are undertaken to gain insight into coastal processes, design coastal structures and validate the predictions of numerical models. For the results of such experiments to be reliable, it is necessary that they are repeatable. The equilibrium beach concept, that beach morphology will evolve to a quasi-static equilibrium shape for a given forcing suggests that experiments should be repeatable to some degree. However, sediment transport in turbulent breaking and broken waves is complex and highly variable and the level of repeatability at different temporal and spatial scales is challenging to measure, as such, previous work has restricted comparisons to small numbers of waves. Here we use the results of two identical, 20-h large-scale wave flume experiments to investigate the repeatability of sediment transport and beach morphology change under waves at timescales down to individual swash events. It is shown that while flow characteristics from identical swash events are very repeatable, the sediment transported can be very different in both magnitude and direction due to differences in turbulence, sediment advection and morphological feedback. Over longer periods containing multiple matching swash events however, the beach responds in a very similar manner, with the level of morphological repeatability increasing with time. The results also demonstrate that gross swash zone sediment transport remains high even as a beach profile approaches quasi-equilibrium, but the proportion of individual swash events that cause large sediment fluxes (>±7.5 kg/event/m) reduces with time. The results of this laboratory study indicate that beach morphology change has a level of determinism over timescales of several minutes and longer, giving confidence in the results from physical modelling studies. However, the large differences in sediment transport from apparently identical swash events questions the value in pursuing numerical predictions of sediment transport at the wave-by-wave timescale unless the reversals in sediment transport between apparently near identical swash events can also be predicted.

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The swash zone is a highly dynamic region of the nearshore in terms of both hydro- and sediment dynamics. Previous work has demonstrated that the majority of swash events transport only small amounts of sediment and net beachface volume change over several hours tends to be small. However, a small number of individual swash events can deposit or remove hundreds of kilograms of sediment per metre width of beach. These events are typically associated with swash flows that involve one or more highly turbulent swash-swash interactions, causing enhanced suspension and transport of sediment (Blenkinsopp et al. 2011). The timing and location of these interactions is complex and small changes in either can lead to very different local flow conditions. The complexity of these flows make sediment transport prediction on a swash-by-swash basis very challenging, and raises the question whether deterministic physical and numerical modelling of swash sediment transport is warranted.@en

The continual sea-level rise predicted over the next century poses a significant threat to coastal regions. Preserving the coastline will require innovative coastal protection techniques and structures. A potential defence is to introduce artificial gravel beaches (Loman et al., 2010), or dynamic revetments (Bayle et al., 2020), a gravel berm placed at the high tide berm(Bayle et al., 2020). A key feature of these types of defences is their ability to maintain the berm elevation relative to the water level. As the water level rises, the structure is overtopped by waves which drives sediment up and over the berm crest peak. This leads to elevation gain for the berm and limits the landward excursion of waves. Berm crest behaviour has only been recorded at frequencies that do not allow wave-by-wave analysis of the process and the resultant ‘snapshot’ profiles may not be representative of the true variability of gravel berms. Through application of continuous 2-D Lidar monitoring on several active gravel berms this paper addresses this gap. It presents new findings related to sediment transport at the berm crest, the morphodynamic behavior under wave attack and a conceptual model for berm state.@en

Pressure on the coastline is escalating due to the impacts of climate change, this is leading to a rise in sea-levels and intensifying storminess. Consequently, many regions of the coast are at increased risk of erosion and flooding. Therefore coastal protection schemes will increase in cost and scale. In response there is a growing use of nature-based coastal protection which aim to be sustainable, effective and adaptable. An example of a nature-based solution is a dynamic cobble berm revetment: a berm constructed from cobble and other gravel sediments at the high tide wave runup limit. These structures limit wave excursion protecting the hinterland from inundation, stabilise the upper beach and adapt to changes in water level. Recent experiments and field applications have shown the suitability of these structures for coastal protection, however many of the processes and design considerations are poorly understood. This study directly compares two prototype scale laboratory experiments which tested dynamic cobble berm revetments constructed with approximately the same geometry but differing gravel characteristics; well-sorted rounded gravel (DynaRev1) and poorly-sorted angular gravel (DynaRev2). In both cases the structures were tested using identical wave forcing including incrementally increasing water level and erosive wave conditions. The results presented in this paper demonstrate that both designs responded to changing water level and wave conditions by approaching a dynamically stable state, where individual gravel is mobilised under wave action but the geometry remains approximately constant. Further, both structures acted to reduce swash excursions compared to a pure sand beach. However, their morphological behaviour is response to wave action varied considerably. Once overtopping of the designed crest occurred, the poorly-sorted revetment developed a peaked crest which grew in elevation as the water level or wave height increased, further limited overtopping. By comparison, the well-sorted revetment was characterised by a larger volume of submerged gravel and a lower elevation flat crest which responded less well to changes in conditions. This occurred due to two processes: (1) for the poorly-sorted case, gravel sorting processes moved small to medium gravel material (D₅₀<70mm) to the crest and (2) the angular nature of the poorly-sorted gravel material promoted increased interlocking. Both of these processes led to a gravel matrix that is more resistant to wave action and gravitational effects. Both revetments experienced some sinking due to sand erosion beneath the front slope. The rate of sinking for the well-sorted case was larger and continued throughout due to the large pore spaces within the gravel matrix. For the poorly sorted revetment in DynaRev2, sand erosion ceased after approximately 28 h due to the development of a filter layer of small gravel at the sand-gravel interface reducing porosity at this location, hence a larger volume of sand was preserved beneath the structure. Both designs present a low-cost and effective solution for protecting sandy coastlines but from an engineering viewpoint it appears better to avoid well-sorted gravel material and greater gravel angularity has been seen to increase crest stability.

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A dynamic revetment is a cobble-gravel berm constructed around the high tide wave runup limit. These structures mimic composite beaches, which consist of a lower foreshore of sand and a backshore berm constructed of gravel or cobbles, which stabilizes the upper beach and provides overtopping protection to the hinterland. Dynamic revetments contrast with static coastal defense structures as they are “dynamic” and are expected to reshape under wave attack. The idea of a dynamic structure made of smaller material than a classic riprap type of revetment is not new, and previous laboratory and field research has investigated the use of dynamic revetments for coastal protection (Allan et al., 2016). However, applications of such a structure remain sporadic and often differ to each other in terms of their design and aim. Furthermore, few existing dynamic revetments have been monitored to evaluate their function, and therefore, the way they behave at the particle and global scale remains poorly understood. In this study, 2D Lidar, GPS topography, particle tracking, and sub-surface particle composition data were collected on the dynamic revetment at North Cove, Washington State, USA, during a spring tidal cycle. Together they enabled investigation of the revetment dynamics and evolution in response to waves and water levels. In addition, this monitoring is proposed as a suitable protocol for short and long-term monitoring of dynamic revetments.@en

Dynamic cobble berm revetments are a promising soft engineering technique capable of protecting sandy coastlines by armouring the sand and dissipating wave energy to protect the hinterland against wave attack. They also form composite beaches as they are essentially mimicking natural composite beach structure and behaviour. This type of coastal protections and beaches have recently been investigated, and this led to a better understanding of their overall behaviour under varying water levels and wave conditions. However, the short-term dynamics of the swash zone (where all bed changes occur) has never been studied at high-resolution, and this is needed to fully understand the underlying dynamics of such structures and relate it to observed processes at larger scale. To do so, the revetment at North Cove (WA, USA) was monitored for a nine-day period in January 2019 over a spring tidal cycle and with offshore significant wave height reaching 6 m. A 2-D lidar was used to survey a cross-shore profile of the revetment, and record all surface changes and interaction with swashes at high spatial (0.1 m) and temporal (swash-by-swash) resolution. The revetment was found to rapidly reshape under these energetic conditions, but reached a relatively stable state during the rising tide. The analysis of bed-level changes and net cross-shore mass fluxes over the revetment showed that revetment changes are mainly driven by very small events, with some rare large bed-level changes of a magnitude comparable to the median cobble diameter. The distribution of event mass fluxes nearly balanced out over the duration of a tide, meaning that positive and negative fluxes tended to be symmetrical. Furthermore, measured net fluxes magnitude were 18 times smaller than the absolute fluxes, which demonstrated the dynamic stability of the revetment as substantial movement occur on a wave-by-wave timescale but these balance out over time. The analysis of swash revealed that the revetment section where the swash reaches a maximum depth between 0.15 and 0.45 m undergoes the more extreme fluxes. Swashes deeper than 0.45 m only occurred in zones inundated more than 50% of the time, and smaller extreme fluxes were measured over the revetment section where these deep swashes were recorded. Bed level change oscillations over the revetment were observed, and the cross shore limit of these was correlated with the mean wave period at the toe of the revetment. Overall, the water depth at the toe of the revetment was identified as the key parameter to describe the energy reaching the revetment. This study enables the morphodynamics of dynamic revetment, observed in previous lab and field studies, to be explained at the swash scale, and brought new information on the sediment dynamics of composite beaches and dynamic revetments. These findings allow to suggest some generic guidance for dynamic cobble berm revetment design. Finally, the results are compared to a similar study on sandy beaches.@en

The development of coastal regions combined with rising sea levels is leading to an increasing risk of coastal flooding caused by wave overtopping of natural beaches and engineered coastal structures. Previous measurements of wave overtopping have been obtained for static coastal structures using fixed current meters and depth sensors or tanks. These are unsuitable for dynamically stable coastal protection structures however, because the geometry of these structures is expected to evolve under wave action. This study investigates the potential to use elevated 2D laser scanners (Lidar) to remotely sense the flow volumes overtopping the time-varying crest of a porous dynamic cobble berm revetment. Two different analysis methods were used to estimate the wave-by-wave overtopping volumes from measurements of the time-varying free surface elevation with good agreement. The results suggest that the commonly used EurOtop parameterisation can be used to estimate overtopping discharge to an acceptable precision. An advantage of the remote sensing approach reported here is that it enables the spatial distribution of overtopping discharge and infiltration rate to be measured. It was found that the overtopping discharge on a porous dynamic revetment decays rapidly landward of the structure crest, and that this has implications for safety and structure design.@en

Ageing stock and extreme weather events pose a threat to the safety of infrastructure networks. In most countries, funding allocated to infrastructure management is insufficient to perform systematic inspections over large transport networks. As a result, early signs of distress can develop unnoticed, potentially leading to catastrophic structural failures. Over the past 20 years, a wealth of literature has demonstrated the capability of satellite-based Synthetic Aperture Radar Interferometry (InSAR) to accurately detect surface deformations of different types of assets. Thanks to the high accuracy and spatial density of measurements, and a short revisit time, space-borne remote-sensing techniques have the potential to provide a cost-effective and near real-time monitoring tool. Whilst InSAR techniques offer an effective approach for structural health monitoring, they also provide a large amount of data. For civil engineering procedures, these need to be analysed in combination with large infrastructure inventories. Over a regional scale, the manual extraction of InSAR-derived displacements from individual assets is extremely time-consuming and an automated integration of the two datasets is essential to effectively assess infrastructure systems. This paper presents a new methodology based on the fully automated integration of InSAR-based measurements and Geographic Information System-infrastructure inventories to detect potential warnings over extensive transport networks. A Sentinel dataset from 2016 to 2019 is used to analyse the Los Angeles highway and freeway network, while the Italian motorway network is evaluated by using open access ERS/Envisat datasets between 1992 and 2010, COSMO-SkyMed datasets between 2008 and 2014 and Sentinel datasets between 2014 and 2020. To demonstrate the flexibility of the proposed methodology to different SAR sensors and infrastructure classes, the analysis of bridges and viaducts in the two test areas is also performed. The outcomes highlight the potential of the proposed methodology to be integrated into structural health monitoring systems and improve current procedures for transport network management.

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Worldwide, transport infrastructure is increasingly vulnerable to aging-induced deterioration and climate-related hazards. Often, inspection and maintenance costs far exceed the available resources, and numerous assets lack any rigorous structural evaluation. Space-borne synthetic aperture radar interferometry (InSAR) is a powerful remote sensing technology that can provide cheaper deformation measurements for bridges and other transport infrastructure with short revisit times, while scaling from the local to the global scale. As recent studies have shown InSAR accuracy to be comparable to that of traditional monitoring instruments, InSAR could offer a cost-effective tool for long-term, near-continuous deformation monitoring, with the possibility of supporting inspection planning and maintenance prioritisation while maximising functionality and increasing the resilience of infrastructure networks. However, despite the high potential of InSAR for structural monitoring, some important limitations need to be considered when applying it in practice. In this paper, the challenges of using InSAR for the purpose of structural monitoring are identified and discussed, with specific focus on bridges and transport networks. Examples are presented to illustrate the current practical limitations of InSAR, and possible solutions and promising research directions are identified. The aim of the paper is to motivate future action in this area and highlight the InSAR advances needed to overcome current challenges.

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The effects of climate change and sea level rise, combined with overpopulation are leading to ever-increasing stress on coastal regions throughout the world. As a result, there is increased interest in sustainable and adaptable methods of coastal protection. Dynamic cobble berm revetments consist of a gravel berm installed close to the high tide shoreline on a sand beach and are designed to mimic naturally occurring composite beaches (dissipative sandy beaches with a gravel berm around the high tide shoreline). Existing approaches to predict wave runup on sand or pure gravel beaches have very poor skill for composite beaches and this restricts the ability of coastal engineers to assess flood risks at existing sites or design new protection structures. This paper presents high-resolution measurements of wave runup from five field and large-scale laboratory experiments investigating composite beaches and dynamic cobble berm revetments. These data demonstrated that as the swash zone transitions from the fronting sand beach to the gravel berm, the short-wave component of significant swash height rapidly increases and can dominate over the infragravity component. When the berm toe is submerged at high tide, it was found that wave runup is strongly controlled by the water depth at the toe of the gravel berm. This is due to the decoupling of the significant wave height at the berm toe from the offshore wave conditions due to the dissipative nature of the fronting sand beach. This insight, combined with new methods to predict wave setup and infragravity wave dissipation on composite beaches is used to develop the first composite beach/dynamic revetment-specific methodologies for predicting wave runup.@en

Laboratory wave flume experiments in coastal engineering and physical oceanography are widely used to provide an improved understanding of morphodynamic processes. Wave flume facilities around the world vary greatly in their physical dimensions and differences in the resulting distortion of the modelled processes are reconciled using scaling laws. However, it is known that perfect model-prototype scaling of all hydro and morphodynamic processes is rarely possible and there is a lack of understanding to what extent distorted models can be used for direct morphological comparison. To address this issue, distorted scale laboratory flume experiments were undertaken in three different facilities, with the aim to measure and compare beach profile evolution under erosive waves and increasing water levels. A novel approach was developed to transform and scale the different experimental geometries into dimensionless coordinates, which enabled a direct quantitative comparison of the beach profile evolution and sediment transport rates between the differing distorted experimental scales. Comparing results from the three experiments revealed that the dimensionless scaled morphological behaviour was similar after the same number of waves – despite very different degrees of model distortion. The distorted profiles appeared to be suitable for comparison as long as a modified version of the Dean number is maintained between them. The new method was then validated with two further published datasets, and showed good agreement for both dimensionless profile shape, dimensionless sediment transport and morphodynamics parameters. The new approach scales the sediment transport by the square of the runup, proportional to HL, rather than H2, and yields good agreement between the datasets. It is further shown that the new scaling method is also applicable for comparing distorted profile evolution under water level increase, as long as the water level is raised in a similar way between the experiments and by the same total increment relative to the significant wave height (Δh/Hs).@en

In western countries, thousands of infrastructure assets have exceeded their intended design life and need continuous monitoring. Space-borne Interferometric Synthetic Aperture Radars (InSAR) are capable of wide-area monitoring, providing inexpensive and high-density measurements of buildings and infrastructure deformations with a millimetre-scale accuracy. Infrastructure catalogues can be used to associate the InSAR-based measurements with the corresponding structures. However, when large infrastructure networks are analysed, the manual extraction of the relevant InSAR-derived displacements is not feasible. In this paper, a new methodology based on the automated integration of InSAR-based displacements and infrastructure databases to warn potentially anomalous deformations over large infrastructure networks is presented. The proposed methodology is applied to the Los Angeles highway and freeway network, using Sentinel data from 2016 to 2019. Results can have a direct impact on transportation network management.@en

The original version of this Data Descriptor contained errors in the author affiliations. Peter Troch was incorrectly associated with DEME Group and the Department of Civil Engineering, Ghent University was inadvertently omitted. This has now been corrected in both the PDF and HTML versions of the Data Descriptor.

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High quality laboratory measurements of nearshore waves and morphology change at, or near prototype-scale are essential to support new understanding of coastal processes and enable the development and validation of predictive models. The DynaRev experiment was completed at the GWK large wave flume over 8 weeks during 2017 to investigate the response of a sandy beach to water level rise and varying wave conditions with and without a dynamic cobble berm revetment, as well as the resilience of the revetment itself. A large array of instrumentation was used throughout the experiment to capture: (1) wave transformation from intermediate water depths to the runup limit at high spatio-temporal resolution, (2) beach profile change including wave-by-wave changes in the swash zone, (3) detailed hydro and morphodynamic measurements around a developing and a translating sandbar.

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In many places, sandy coastlines and their associated assets are at high risk of erosion and flooding, with this risk increasing under climate change and sea level rise. In this context, dynamic cobble berm revetments represent a potentially sustainable protection technique to armour sandy beaches, reduce wave runup and protect the hinterland against wave attack. However, the behaviour and performance of such structures is not well understood. The dynamic cobble berm revetment located in North Cove, WA, USA, was monitored over a spring tidal cycle in January 2019. A representative 60 m alongshore section was monitored over 10 days using 2D laser scanner (lidar) measurements, GPS ground elevation surveys, Radio Frequency Identification of individual cobbles and revetment thickness measurements. These data were used together to assess the dynamic behaviour and functionality of the revetment throughout the experiment. Over the course of the experiment, the surface elevation changed by up to ±0.5 m, and the revetment volume reduced by an average 0.67 m ³/m. These changes were found to be caused by relatively large significant wave height and high water levels. The revetment demonstrated a dynamic stability and the capacity to quickly reshape under changing hydrodynamic conditions. The instrumented cobbles were transported along and cross-shore and accumulated at the toe of the revetment, but were never transported seaward of the toe. The revetment also managed to recover some of the lost volume under moderate wave conditions. The revetment behaviour was found to be influenced by variation in the cobble-sand matrix. The underlying sand dynamics – i.e., accumulation or removal of sand within the cobbles – were found to govern the overall volume changes and were important to the overall stability of the revetment. Seven possible transport regimes were identified, and a model of the internal sand dynamics was developed. During the spring tidal cycle measured here, the revetment protected the sand scarp immediately landward and prevented flooding of the hinterland, while armouring the underlying sand. Over time, renourishment will likely be required due to longshore sediment transport, and preliminary guidelines for this and other aspects of design are suggested.

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The two-phase flow generated by breaking ocean waves plays a crucial role in various geophysical processes, including dissipation of wave energy and atmospheric gas exchange. This paper presents a technique to measure the two-phase flow generated by breaking waves at prototype scale. We have demonstrated the validity and potential of this technique in the Large Wave Flume (Grosser Wellenkanal, GWK) facility in Hanover, Germany. Actively breaking, depth-limited waves were measured using an array of three downward-looking lidars mounted above the water surface and an upward-looking multibeam sonar below. This novel setup enabled the characterization of the complete upper boundary (free water surface and splash-up) and seaward lower boundary (entrained cavity and bubble plume) of the breaking wave. We have quantified the migration of the lower boundary as the cavity and plume are entrained in the water column - penetrating toward the seabed, moving onshore with the passage of the wave crest, and then rising as it is slowly advected offshore. We have also estimated the overall composition of the splash, cavity, and plume as the breaking wave evolves over time. Our observations are consistent with results from previous small-scale laboratory experiments and the suitability of the technique for experimentation at prototype scale has been demonstrated.

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