Shallow coastal embayments are typical features of former glacial landscapes in parts of Scandinavia and North America. An increasing concern over the impact of accelerating sea‐level rise, calls for a better understanding of how coasts respond to sea‐level changes. Studying the response of coastal environments, such as submerged embayments, to sea‐level changes in the past, can provide important insights into the response of present‐day coastlines to future sea‐level rise. Kalø Bay is an embayment situated in south‐western Kattegat, north of the Aarhus Bay, Denmark. This shallow embayment was influenced by sea‐level changes governed by global sea‐level rise and glacio‐isostatic rebound from the Scandinavian Ice Sheet during the latest Pleistocene and Holocene. In this study, we analyse the palaeolandscape in the bay to identify the depositional succession preserved in the bay and understand the dominant geological processes occurring after the last glaciation in response to sea‐level changes. Four major depositional units reflect the variable environment in the bay as it changed from a glacial to proglacial setting through coastal and lagoonal infill stages, and gradually developed into a shallow marine environment as the area was inundated approximately 9–6 cal. ka BP. During a relative sea‐level fall in the Mid‐ and Late Holocene, the deposits in the bay reversed to more coastal facies. Our study highlights the sensitivity of coastal embayments and their dynamic response to sea‐level changes. Our results show how the bay changed from a wave‐dominated setting in the Early Holocene to a current‐dominated setting in the Late Holocene, and how the former glacial landscape and coastal deposits were affected differently by the sea‐level rise and associated erosion and redeposition. These results are important for understanding the impacts of future accelerating sea‐level rise.

In this paper, a new framework – RoadRAT - for analyzing the probability of inundation, wave runup, and erosion is applied within the context of risk management for coastal roads. The analysis focus on a case study in south Sweden and consists of risk identification, calculation of probability, and discussion of consequences and mitigation methods. The results show that future risks are highly dependent on the future greenhouse gas emissions.

Bottom boundary layer processes are key for sediment transport. To estimate bed shear stresses, wave friction factors are often used. Experimental data on wave friction factors are limited to sandy environments. Here, numerical simulations conducted with a 1D model show that for hydraulically rough beds with presence of vegetation, wave friction factors deviate from existing data.

Designing coastal protection solutions that combines hard and soft techniques can be an appropriate measure to reduce wave impact on structures (Steetzel et al., 2017). The elevated bed level in front of the hard protection dissipates energy and thereby limits wave runup and overtopping. This can increase the expected lifetime of the protection while also limiting the design dimensions and hence be a cost-effective alternative. In addition, the implementation of soft coastal protection measures in combination with hard structures can provide possible additional recreational and environmental functions. A beach nourishment was conducted in front of the rock revetment with the objectives to reduce wave overtopping onto the adjacent road and to restore the beach for recreation (Baden and Aarosiin-Hansen, 2017). Field measurements and observations, combined with numerical modelling has been conducted with the aim to monitor the morphological evolution of the nourishment and adjacent coastlines in order to assess the performance of the protection.

This paper introduces a new framework - RoadRAT- to calculate the probability of inundation, wave runup, and storm erosion impacting coastal roads. Extreme value analysis is applied to annual maxima of observed and simulated still water level levels (SWL), total water levels (SWL + runup), and storm erosion volumes. The probability of impact on the road is derived both for the present conditions and for future conditions considering long-term evolution of the coastline in response to sea level rise and projected continuation of historical trends. RoadRAT is intended for screening at a regional scale (>100 km) to identify vulnerable road segments that need further attention. A case study was conducted on the south coast of Sweden to demonstrate the framework. The results indicate that the main coastal road has a low probability of impact under present conditions, but that it will increase in the future under changing climatic conditions. In 2150, which is the target year for the analysis, several kilometres of the road will be lost to erosion, and flooding and runup will frequently impact parts of the remaining road. In future applications, RoadRAT could be coupled with models that describe the consequences of inundation, wave runup, and storm erosion for road serviceability and transport.

The October 2023 storm surge, denoted Babet, caused severe flooding and unprecedented damage along the southwestern Baltic Sea coasts. The beginning of October 2023 was dominated by several westerly low-pressure systems over the Baltic Sea region. The abundance of westerly winds pushed water into the Baltic Sea basin through the Danish straits resulting in elevated water levels of +50 cm above normal in the basin. Around the 18th of October the wind direction shifted from west to north and subsequently to east while also increasing in intensity, with mean wind speeds of 25 m/s and gusts exceeding 30 m/s. This gave strong wind setup in the southwestern part of the Baltic Sea and the strong winds generated large waves as well as increasing the water levels further. Notably, the area experienced the most extreme storm conditions in over a century with the storm peak was reached during the night between the 20th to 21st October. We present a study with results of the numerical model simulation using SWAN set up for the southwestern part to the Baltic Sea basin. The simulation combines the wave conditions derived from wind forcing and observed water levels from a network of observation gauges. These levels are compared to historical event statistics from an existing long-term hindcast model of wave climate conditions for the region. Finally, the results of storm surge levels are assessed in relation to observed flooding and erosion impact on natural coastal areas and impact to existing coastal protection.

Coastal overwash where water and sediment flow over the beach crest can be highly damaging to human properties and infrastructure. This involves a need for accurate overwash prediction for planners and engineers. On the other hand, on undisturbed coastlines, overwash makes an important sediment contribution to the system. Contributions which are key for spits and barrier islands to keep up with predicted future sea level rises. Based on a recent 100-year storm event in the eastern Baltic Sea in 2023, we asses both the predictive capability of a storm impact model (Sallenger, 2000), and the cross-shore sediment exchange associated with washover fans.

This paper introduces a comprehensive protocol leveraging open-access techniques to create small- to medium-scale 3D representations of the environment by using iPhone and iPad light detection and ranging (LiDAR). The protocol focuses on two capabilities of the iPhone LiDAR. The first capability is 3D modeling: iPhone LiDAR rapidly generates detailed indoor and outdoor 3D models, providing insights into object size, volume and geometry. The second capability is change detection: the 3D models created by the LiDAR sensor can be used for precise measurement of changes over time. Compared to other 3D topographic surveying methods, this method is rapid, high resolution, low cost and easy to use. The protocol outlines iPhone LiDAR scanning practices, model export and change detection. The expected results after executing the protocol are (i) a detailed 3D model of a small- to medium-sized object or area of interest and (ii) a distance point cloud revealing change between two point clouds of the same object or area between different times. The entire protocol can be conducted within 2 h by anyone with an iPhone with the LiDAR sensor and a computer. This protocol empowers scientists, students and community members conducting research with a cheap, easy-to-use method for addressing a range of questions and challenges, thus benefiting experts and the broader community.

Beaches are important coastal features that provide vital ecosystem services; however, these systems are threatened by coastal erosion, sea-level rise, and coastal squeeze. Beach nourishments are a commonly applied coastal protection measure to mitigate erosion and flood risks while maintaining or enhancing recreational values. Nourishments vary in scale from mega-nourishments to small-scale nourishments, where the latter has typically been less studied due to the limited resources for monitoring. Meanwhile, with rising sea levels, the implementation of small-scale nourishments is expected to increase, and there is a need for more knowledge about the morphological evolution and technical lifetime of these interventions. In this study, the morphological responses of small-scale beach nourishment (total volume 20,000 m3 which amounts to 30 m3 added per m alongshore) are observed and quantified over various timescales, considering the initial adjustment, long-term development, and event-driven response. The investigated nourishment is implemented in a partly sheltered coastal embayment in the semi-enclosed Baltic Sea, which has a complex interaction between waves and water levels. Furthermore, the beach is surrounded by hard structures, a rock revetment at the back, and a harbor mole and a groin, influencing the longshore and cross-shore sediment transport. The results show that substantial reduction in subaerial volume can be attributed to specific events. In addition, we observed considerable spatial variation in the sediment re-distribution induced by hard structures and variability in the nearshore bathymetry. The lifetime of the beach nourishment is just over two years. The nourished material remains in the system at the end of the lifetime but is not available for beach recovery. Still, the added subaerial volume has eroded at the midsection, and the protective beach width has been reduced, leaving the rock revetment exposed with reduced protection for the hinterland. The energy conditions at the site are highly episodic, which impacts morphological evolution, and observations indicate that the development is event-driven.

Access to local nearshore wave climate conditions on a detailed spatial scale is important for many coastal engineering practices. These include assessing the flood risk of coastal infrastructure, designing coastal protection measures, and estimating sediment transport processes and wave run-up. The present study displays a multi-scale wave modelling approach using the numerical wave model SWAN (Booij et al., 1999) together with field data applied in the southern Baltic Sea. The main objective of the study was to investigate the possibility of employing a single wave model for seamless simulations over several scales in time and space, from offshore to nearshore, including the effects of grid size and resolution. Validation with extensive field data was a crucial part of the study.

Abstract Groundwater springs in permafrost regions provide pathways for solutes and dissolved gases to escape from sub‐permafrost groundwater systems, which otherwise are completely isolated from the surface environment and atmosphere. Yet, fundamental questions as to the mechanisms driving groundwater flow to the surface remain unsolved. In this study, basal permafrost aggradation is explored as a mechanism for generating groundwater flow and driving groundwater spring systems. We employ process‐based numerical modeling to test the hypothesis of permafrost‐aggradation‐driven spring systems in a range of environmental settings. The model results show that permafrost aggradation can generate spring flow on a multi‐millennial timescale and with discharge rates up to a couple of liters per second. Permafrost aggradation deserves attention as a groundwater flow driving mechanism in areas of recent glacio‐isostatic uplift and glacial retreat.

This study presents 62 years of hindcast wave climate data for the south coast of Sweden from 1959- 2021. The 100-km-long coast consists mainly of sandy beaches and eroding bluffs interrupted by headlands and harbours alongshore, making it sensitive to variations in incoming wave direction. A SWAN wave model of the Baltic Sea, extending from the North Sea to the & ANGS;land Sea, was calibrated and validated against wave observations from 16 locations distributed within the model domain. Wave data collected from open databases were complemented with new wave buoy observations from two nearshore locations within the study area at 14 and 15 m depth. The simulated significant wave height showed good agreement with the local observations, with an average R2 of 0.83. The multi-decadal hindcast data was used to analyse spatial and temporal wave climate variability. The results show that the directional distribution of incoming waves varies along the coast, with a gradually increasing wave energy exposure from the west towards the east. The wave climate is most energetic from October to March, with the highest wave heights in November, December, and January. In general, waves from westerly directions dominate the annual wave energy, but within the hindcast time series, a few years had larger wave energy from easterly directions. The interannual variability of total wave energy and wave direction is correlated to the North Atlantic Oscillation (NAO) index. In the offshore, the total annual wave energy had a statistically significant positive correlation with the NAO DJFM station-based index, with a Spearman rank correlation coefficient of 0.51. In the nearshore, the correlation was even stronger. Future studies should investigate the possibility of using the NAO index as a proxy for the wave energy direction and its effect on coastal evolution. & COPY; 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Climate change will increase the duration of annual sea‐ice‐free periods and shift precipitation patterns across the Arctic. Those factors are likely to increase erosion rates along its coasts. Large parts of the Arctic coast consist of hard rock. However, glacial, deltaic, and coastal sedimentary deposits occur in deglaciated areas and isostatic uplift following glaciations has created beach ridge plains and pocket beaches with coarse soft‐sediment cliffs. Hitherto, very little was known about the spatial distribution, erosion rates, and morphodynamics of soft sediment cliffs along the coast of Greenland. Here, we investigate a 3‐km sedimentary cliff section on the south coast of Qeqertarsuaq (Disko Island). We measured 2D cliff top erosion over 50 years between 1964 and 2014 as well as 3D cliff profile change over 2 years between 2019 and 2021. Morphometric indices of the gravel beach and cliff were calculated based on a series of cross‐shore elevation profiles. Wave run‐up at the beach fronting the cliff was modeled with XBeach‐G for a series of storm events under present day sea‐ice conditions and for a reduced sea‐ice scenario. Cliff top erosion rates varied along the cliff with maximum rates of 0.3 m y −1 . The investigated coastal cliff erodes by two coupled processes: (a) precipitation‐driven surface runoff downslope the cliff and (b) wave‐driven erosion at the cliff toe. In a continuously warming climate, this study shows that erosion of soft coastal cliffs in Greenland thus can accelerate due to increased storminess and prolonging open water periods.

Coastal Sediments 2023, pp. 1272-1285 (2023) No AccessDRIVERS OF COASTAL CLIFF EROSION IN DENMARKGREGOR LUETZENBURG, ANDERS A. BJØRK, KRISTIAN SVENNEVIG, and AART KROONGREGOR LUETZENBURGDepartment of Geosciences and Natural Research Management, University of Copenhagen, Øster Voldgade 10, 1350 Copenhagen, Denmark, ANDERS A. BJØRKDepartment of Geosciences and Natural Research Management, University of Copenhagen, Øster Voldgade 10, 1350 Copenhagen, Denmark, KRISTIAN SVENNEVIGGeological Survey of Denmark and Greenland (GEUS), Øster Voldgade 10, 1350 Copenhagen, Denmark, and AART KROONDepartment of Geosciences and Natural Research Management, University of Copenhagen, Øster Voldgade 10, 1350 Copenhagen, Denmarkhttps://doi.org/10.1142/9789811275135_0118Cited by:0 PreviousNext AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack CitationsRecommend to Library ShareShare onFacebookTwitterLinked InRedditEmail Abstract: Denmark has an 8,750 km long coastline with a heterogeneous set of coastal cliffs in previously glaciated landscapes. The erosion of those cliffs is a complex interplay between a number of marine, coastal, terrestrial, anthropogenic and atmospheric factors. Currently, we lack a basic understanding of processes leading to cliff erosion and factors influencing coastal cliffs morphology. In this study, we delineate cliff profiles along all the shores of Denmark and combine the morphological indices of those cliff profiles with coastal environmental factors. Most cliffs are located in areas of Weichselian glacial deposits and they show different cliff morphologies than those in pre-quaternary bedrock outcrops. The highest rates of cliff top and cliff toe change are observed at the west coast of Denmark, where cliffs are consisting of sand and are exposed to high-energetic wave conditions from the North Sea. To protect coastal communities effectively, it is crucial to better understand the processes that drive coastal cliff erosion and its associated erosion rates. FiguresReferencesRelatedDetails Coastal Sediments 2023Metrics History PDF download

Detailed maps of the seabed and knowledge of its habitats are critical for a wide range of tasks, such as sustainable development, and environmental protection. Boulders on the seabed form an important environment for ecosystems, but the detection of them is challenging. In this study, we aim to improve the understanding of boulder predictors and to determine connections between predictors and boulder environments on different spatial scales. The Relief-F filter feature selection algorithm was used on four 30 m × 30 m areas in Rødsand lagoon, containing one boulder each, to determine the most relevant predictors. The predictors could be divided into four groups detecting different boulder characteristics: colour contrast, height, boulder boundaries, and spherical geometry. Twelve different types of boulder environments were evaluated. Bare, spherical boulders on sandy seabeds can be predicted from all four predictor groups. It is not possible to detect non-spherical boulders on seabed covered by vegetation. The best predictors for boulder detection depend on the shape and size of the boulder and the surrounding sediment and vegetation. The predictors were evaluated on a larger 400 × 2500 m area. When up-scaling the boulder detection area, larger seabed structures may affect the results. Therefore, knowledge about these structures can be used to remove errors and uncertainties from machine learning input data.

Seabed geodiversity comprises abiotic seabed structures and functions that form valuable natural resources, foundation for benthic habitats and marine ecosystems, and requires knowledge based, sustainable management. Geomorphological mapping involves delineation of surface features based on form, material composition and formative processes. We present an approach that applies methods of scale analysis and geomorphometric classification to characterize seabed morphology and interpretation of geomorphic units in a dynamic and complex marine meander bend. Seabed morphology was delineated using the morphometry as template sup-ported by the DEM and associated surface derivatives. The seabed morphology served as input to an interpre-tation of geomorphic units applying a fluvial classification scheme in channelized marine settings. We demonstrate the potential of using a (semi-) automated morphometric classification scheme to support the characterization of high-resolution seabed morphology based on descriptive definitions and the potential of translating a fluvial classification scheme in channelized marine settings.

Abstract. Landslides are a frequent natural hazard occurring globally in regions with steep topography. Additionally, landslides are playing an important role in landscape evolution by transporting sediment downslope. Landslide inventory mapping is a common technique to assess the spatial distribution and extend of landslides in an area of interest. High-resolution digital elevation models (DEMs) have proven to be useful databases to map landslides in large areas across different land covers and topography. So far, Denmark had no national landslide inventory. Here we create the first comprehensive national landslide inventory for Denmark derived from a 40 cm resolution DEM from 2015 supported by several 12.5 cm resolution orthophotos. The landslide inventory is created based on a manual expert-based mapping approach, and we implemented a quality control mechanism to assess the completeness of the inventory. Overall, we mapped 3202 landslide polygons in Denmark with a level of completeness of 87 %. The landslide inventory can act as a starting point for a more comprehensive hazard and risk reduction framework for Denmark. Furthermore, machine-learning algorithms can use the dataset as a training dataset to improve future automated mapping approaches. The complete landslide inventory is made freely available for download at https://doi.org/10.6084/m9.figshare.16965439.v1 (Svennevig and Luetzenburg, 2021) or as web map (https://data.geus.dk/landskred/) for further investigations.