The stability formula for rock slopes under wave attack was revised in Van der Meer (2021), replacing the mean period Tm with the spectral period Tm-1.0. This rewritten formula closely resembles the Modified Van der Meer formula as in the Rock Manual (2007), with differences primarily in coefficients and the use of H2% in the Rock Manual and H1/3 in Van der Meer (2021).
The wave characteristics change significantly in shallow water due to nonlinearities and wave breaking. The result is a significant change in the wave height and period, especially when severe breaking occurs and infragravity waves become significant or even dominate the spectrum. This may lead to very large breaker parameters. At a certain point, existing stability formulas may thus become inaccurate, both the original and the Modified formula for shallow water. The primary objective of this paper is to identify when and where shallow water stability results deviate from established formulas and how these deviations can be described.
The analysis involves an in-depth examination of datasets from Van Gent et al. (2003), Eldrup (2019), and other relevant data to increase the understanding of waves in shallow water and how they affect rock slope stability.
The use of H2% in the Modified Van der Meer formula gives some difficulties as no reliable prediction method is available for that parameter when the relative depth is small, h/Hm0 depth < 1.5. The Van der Meer (2021) formula applies the significant wave height, and it may be chosen as either Hm0 or H1/3. These two parameters are almost identical in deep water for which the formula was derived, but significant differences may occur in shallow water. The application of the Van der Meer formula in shallow water indicates a preference for the use of Hm0 as it describes nonlinear waves better. The main conclusion is that the Van der Meer (2021) formula seems valid much further into the shallow water region than what the Rock Manual (2007) recommends and at least to relative water depths of h/Hm0 deep > 1.5. For shallow water with h/Hm0 depth < 1.5 no systematic trend with the energy period is observed anymore and constant combined stability numbers are given for guidance in preliminary design.
The European Green Deal (EGD) adopted in December 2019 seeks to facilitate the transition of the EU towards a climate-neutral continent and a modern, resource-efficient, and competitive economy by 2050. In addition to a set of objectives, it is also a policy program that will affect the policy landscape, by driving the development of new directives and regulation, and the amendment of existing ones. In order to facilitate a transition of EU society to better protect the marine environment, decision making and implementation processes within marine governance will need to be improved to develop and implement measures through which EGD marine protection objectives will be achieved.
The Horizon Europe PERMAGOV project aims to improve the implementation and performance of EU marine policies to reach the goals set in the EGD. The PERMAGOV project focuses on four issue areas, so-called regime complexes: Maritime Transport, Marine Energy, Marine Life and Marine Plastics. Within each regime complex, 2 to 3 case studies are used to explore and analyse how governance arrangements are emerging and changing and improving their performance through the EGD. These case studies span three European Seas, the Baltic Sea, the Mediterranean Sea and the North East Atlantic.
Fishing and sand mining in Cambodia may not appear to have much in common. However, digging deeper reveals important parallels. Both fishing and sand mining support livelihoods and are connected to a limited natural resource. Meanwhile, they are both typified by precarious livelihoods, on the one hand, and overexploitation, on the other. In bringing these two topics together, the paper combines empirical qualitative research from two separate studies conducted by the co-authors in Cambodia, one in coastal fishing villages and another in the sand mining industry along the Mekong River. We argue that the interplay between fishing and sand mining has paradoxical impacts on livelihoods, supporting one group while undermining another. Using a precarity analysis lens, we show how an unconventional, and largely invisible frontier of natural resource exploitation—sand mining—is intertwined with fisheries, and expands our understanding of the relationship between precarious labour, environmental change, and livelihoods.
Monitoring methods, such as seabed bottom-towed cameras, sediment grabs, and benthic sledges, have limitations in spatial coverage, cause seabed disturbance, are restricted to soft-bottom substrates, and offer low flexibility for marine seabed monitoring. In this study, we investigate the potential of a non-invasive and simple underwater remotely operated vehicle (ROV) to enhance marine seabed monitoring. A tethered ROV equipped with a GoPro camera was deployed in three areas of Skagerrak at depths from 15-34 m to assess accuracy in species identification and substrate classification identified from still frames. The quality of still frames varied between areas due to turbidity, motion blur, and marine snow, which reduced the number of high-quality frames by approximately 20%. Classification of substrates and taxa identification were possible in the remaining still frames. Two different substrates were detected: sand and stone reef. Stone reefs had a lower occurrence compared to sand. A total of 10 taxa were detected in the two substrate types. The highest abundance was observed in the stone reef substrate compared to the sand substrate. Identification at the species level was limited due to the quality of the still frames, which affected the detectability of morphological traits. This study demonstrates that a widely accessible ROV can be used for marine monitoring. The ROV can be used in different substrates, and still frames provide valuable information on species composition, which can enhance the replicability of monitoring programs.
The influence of directional spreading of waves is significant for wave-induced loads, wave breaking and nonlinearity of the waves. For physical model testing performed at test facilities such as the Ocean and Coastal Engineering Laboratory at Aalborg University, it is crucial to validate if the test conditions match the target sea states by measurement and analysis of the generated directional wave field. Most of the existing methods assume a double summation sea state to be present which is valid in the prototype. However, waves in the laboratory are usually generated by single summation. The current paper presents a method to analyze short-crested waves generated by the single summation method. Compared to similar methods oblique reflections are considered instead of only in-line reflections. The results show that the method successfully decomposes the incident and reflected wave fields in the time domain. Thus, for example the incident wave height distribution may be obtained. The sensitivity of the new method to additional reflective directions, noise, calibration errors and positional errors of the wave gauges was found small.
In hydraulic model tests, it is common practice to relate the response of the tested structure to the incident wave parameters at the toe. Estimation of the incident wave parameters at the toe is thus an essential part of the analysis of hydraulic model testing. In many cases, the design conditions at the toe are given by waves that are highly nonlinear or even depth limited. Modelling such conditions requires reproducing the prototype foreshore slope in the model. The present paper provide guidelines on the accuracy of a nonlinear reflection separation algorithm when applied to nonlinear waves over sloping foreshores. A simple methodology has been established to estimate the expected errors on the incident wave parameters.
Gathering real-world high-quality data from underwater environments is cost-intensive, as is labeling this data for machine learning. Given this, synthetic data represents a possible solution that delivers ground-truth training data. Nevertheless, rendering and modeling of underwater environments are challenging due to several factors, including attenuation, scattering, and turbidity. The focus of this study is on the creation of a simulated underwater environment constructed for the purposes of simulating marine growth on offshore structures. The main requirement is the creation of renderings of sufficient quality and quantity with respect to the representation of marine-species distribution and intra-class variation, and sufficiently accurate recreation of lighting and turbidity (Jerlov water type) conditions underwater. Underwater rendering has been implemented using Blender, with marine growth from 2D/3D scanned and hand-modelled entities combined with a CAD model of an actual offshore installation. The proposed approach provides for the generation of synthetic images usable for training computer vision models in marine-growth inspection applications as well as other related underwater applications. This has been demonstrated in a case study, wherein the utility of the rendered dataset has been briefly demonstrated in a neural network marine-growth segmentation task. The produced renderings are available as a dataset of 1038 scene renders, using varying poses and randomized representative marine growth; each render includes RGB images, ground-truth segmentation masks, water-free RGB images, and depth information. In future work, the expansion with additional species and objects in other oceanic and coastal environments is envisioned.
This paper introduces an interactive method which aims to map out perspectives on the state of ecosystem-based approaches (EbA) in marine spatial planning (MSP). MSP meets a need for organizing the allocation of space to maritime uses. MSP should also control and limit the pressures induced by these activities on marine ecosystems. To evaluate how EbA is actually applied, this research proposes a participatory method to assess the effectiveness of current EbA practices within the MSP process using perceptual maps. The mapping focuses on two dimensions: relevance and implementation of a set of 13 key elements of EbA. The method was tested on a sample of marine planners from ongoing MSP processes in northern European sea basins. The study shows that perceptual maps provide four main benefits: participatory, visualization capacity, qualitative and quantitative applicability, and easy to use. This tool undoubtedly has the potential to illustrate the state of integration of EbA in MSP and highlight the priority issues to develop in future plans, and consequently to provide keys to revise marine plans in a way that better takes into account EbA principles.
A tension between two opposing forces, that is, the force of division and that of unity, is increasingly sharpened in the law of the sea today. An essential question that arises is how one can protect community interests in the divided ocean. The law of dédoublement fonctionnel advocated by Georges Scelle provides an insight into this question. According to Scelle’s theory of the law of dédoublement fonctionnel, State organs perform a dual function: the national function of protecting State interests and the public service function of safeguarding community interests. The law of dédoublement fonctionnel seeks to reconcile these functions. Scelle’s harmonistic vision of international law is well worth reconsidering in the law of the sea and beyond. This article examines the relevance of Scelle’s theory in the context of the law of the sea and explores two models for the protection of community interests at sea.
Despite the relatively rich literature on the omnipresence of microplastics in marine environments, the current status and ecological impacts of microplastics on global Marine Protected Areas (MPAs) are still unknown. Their ubiquitous occurrence, increasing volume, and ecotoxicological effects have made microplastic an emerging marine pollutant. Given the critical conservation roles of MPAs that aim to protect vulnerable marine species, biodiversity, and resources, it is essential to have a comprehensive overview of the occurrence, abundance, distribution, and characteristics of microplastics in MPAs including their buffer zones. Here, extensive data were collected and screened based on 1565 peer-reviewed literature from 2017 to 2020, and a GIS-based approach was applied to improve the outcomes by considering boundary limits. Microplastics in seawater samples were verified within the boundaries of 52 MPAs; after including the buffer zones, 1/3 more (68 MPAs) were identified as contaminated by microplastics. A large range of microplastic levels in MPAs was summarized based on water volume (0–809,000 items/m 3) or surface water area (21.3–1,650,000,000 items/km 2), which was likely due to discrepancy in sampling and analytical methods. Fragment was the most frequently observed shape and fiber was the most abundant shape. PE and PP were the most common and also most abundant polymer types. Overall, 2/3 of available data reported that seawater microplastic levels in MPAs were higher than 12,429 items/km 2, indicating that global MPAs alone cannot protect against microplastic pollution. The current limitations and future directions were also discussed toward the post-2020 Global Biodiversity Framework goals.