Search Results (120)

Coastal areas are increasingly vulnerable to erosion, a process that can lead to severe consequences such as flooding and land loss. This study investigates strategies for preventing and mitigating coastal erosion, with a particular focus on nature-based solutions, notably artificial sand nourishment. Artificial nourishment has proven to be an effective method for erosion control. However, its success depends on factors such as the placement location, sediment volume, and frequency of operations. To optimize these interventions, simulations were conducted using both a numerical model (CS-Model) and a physical flume model, based on the same cross-section beach/dune profile, to compare cross-shore nourishment performance across different scenarios. The numerical modeling approach is presented first, including a description of the reference prototype-scale scenario. This is followed by an overview of the physical modeling, detailing the experimental 2D cross-section flume setup and tested scenarios. These scenarios simulate nourishment interventions with variations in beach profile, aiming to assess the influence of water level, berm width, bar volume, and bar geometry. The results from both numerical and physical simulations are presented, focusing on the cross-shore morphological response of the beach profile under wave action, particularly the effects on profile shape, water level, bar volume, and the position and depth of the bar crest. The main conclusion highlights that a wider initial berm leads to greater wave energy dissipation, thereby contributing to the mitigation of dune erosion. Full article

The Chacopampean Plain is a major physiographic unit in Argentina, bounded by the Colorado River to the south, the Sierras Pampeanas and Subandinas to the west, and the Paraná River, Río de la Plata Estuary, and the Argentine Sea to the east. Its subsurface preserves sediments from the Miocene marine transgression, while the surface hosts some of the country’s most productive soils. Two main geomorphological domains are recognized: fluvial systems dominated by alluvial megafans in the north, and aeolian systems characterized by loess accumulation and wind erosion in the south. The southern sector exhibits diverse landforms such as deflation basins, ridges, dune corridors, lunettes, and mantiform loess deposits. Despite their regional extent, the origin and chronology of many aeolian features remain poorly constrained, as previous studies have primarily focused on depositional units rather than wind-sculpted erosional features. This study integrates remote sensing data, field observations, and a synthesis of published chronometric and sedimentological information to characterize these aeolian landforms and elucidate their genesis. Our findings confirm wind as the dominant morphogenetic agent during Late Quaternary glacial stadials. These aeolian morphologies significantly influence the region’s hydrology, as many permanent and ephemeral water bodies occupy deflation basins or intermediate low-lying sectors prone to flooding under modern climatic conditions, which are considerably wetter than during their original formation. Full article

Thorough investigation into dune morphology is pivotal for grasping the intricacies of constructing and operating power transmission lines in desert terrains. However, there remains a notable gap in the quantitative analysis and assessment of how dune dynamics evolve under the influence of transmission infrastructure. In this study, the Real-Space Cellular Automaton Laboratory is deployed to explore how transverse dunes evolve around transmission towers under diverse wind velocities and varying dune dimensions. The results reveal that, beyond the immediate vicinity of the transmission tower, the height of the transverse dune remains largely stable across broad spatial scales, unaffected by the transmission line. As wind velocities wane, the structural integrity of the transverse dunes is compromised, leading to an expansion in the size of the trail structures. Initially, the height of the dune surges, only to decline progressively over time, with the maximum fluctuation reaching nearly $1\mathrm{m}$. The height of larger dunes escalates gradually at first, peaks, and then subsides, with the pinnacle height nearing $6.5\mathrm{m}$. As a critical metric for safety evaluation, the height of the transmission line above ground initially plummets, then gradually rebounds, and shifts backward over time after hitting its nadir. Full article

This study presents the initial scientific characterization of the recently discovered Rhizoliths Petrified Forest of Chania, located at Stavros in the Akrotiri peninsula of Crete, Greece. Unlike most known petrified forests that primarily preserve tree trunks, this site uniquely features an abundance of rhizoliths—fossilized root systems preserved through calcium carbonate mineralization. The rhizoliths exist within aeolianite formations along the coastal front, with diverse morphologies and sizes ranging from small trace-like forms to massive, branched structures exceeding one meter in length. The rhizoliths are exposed within historic Venetian quarries that operated from Minoan times through the medieval period at Stavros Bay, where quarrying operations have revealed these fossilized root systems preserved in coastal dune deposits. The site also contains in situ petrified trunks, calcrete formations, and biokarstic dissolution features that further enhance its scientific value. Microscopic examination of rhizolith samples has revealed valuable information about their internal structure, showing clear biogenic characteristics. The preservation of rhizolith structures and associated sedimentary features provides valuable insight into the Quaternary paleoenvironment, including former vegetation patterns, soil stabilization processes, and paleoclimatic conditions. The alternating layers of aeolianites and paleosols suggest cyclical environmental changes, with periods of active dune formation alternating with more stable conditions allowing soil development and vegetation establishment. This study documents the Stavros rhizoliths and their paleoenvironmental significance, contributing to the comparative understanding of similar features documented at other global sites. Full article

This study presents, for the first time, a detailed linear stability analysis (LSA) of bedform evolution under low-flow conditions using a one-dimensional vertically averaged and moment (1D-VAM) approach. The analysis focuses exclusively on bedload transport. The classical Saint-Venant shallow water equations are extended to incorporate non-hydrostatic pressure terms and a modified moment-based Chézy resistance formulation is adopted that links bed shear stress to both the depth-averaged velocity and its first moment (near-bed velocity). Applying a small-amplitude perturbation analysis to an initially flat bed, while neglecting suspended load and bed slope effects, reveals two distinct modes of morphological instability under low-Froude-number conditions. The first mode, associated with ripple formation, features short wavelengths independent of flow depth, following the relation F² = 1/(kh), and varies systematically with both the Froude and Shields numbers. The second mode corresponds to dune formation, emerging within a dimensionless wavenumber range of 0.17 to 0.9 as roughness increases and the dimensionless Chézy coefficient $C^{\ast }$ decreases from 20 to 10. The resulting predictions of the dominant wavenumbers agree well with recent experimental observations. Critically, the model naturally produces a phase lag between sediment transport and bedform geometry without empirical lag terms. The 1D-VAM framework with Exner equation offers a physically consistent and computationally efficient tool for predicting bedform instabilities in erodible channels. This study advances the capability of conventional depth-averaged models to simulate complex bedform evolution processes. Full article

Understanding aeolian sediment transport and wind erosion enhances our knowledge of desert dune formation and sand migration. The Makran region of southern Sistan and Baluchistan is prone to wind-driven erosion alongside frequent sand and dust storms (SDSs). Hourly wind data from two meteorological stations spanning 1994–2020 were analyzed to study erosive winds and sand transport. Wind energy analysis using drift potential (DP) indicated low energy (DP < 200 in vector unit) and minimal spatial variation across the Makran dune fields. The effective winds transporting sand particles were towards the east from November to May, and in the northwestern direction from June to October. The DP showed a gradual decline in the study area from 1990 to 2022, with no significant temporal trends. The sand dune morphology analysis indicates that bimodal wind regimes primarily form linear dunes and sand sheets, while crescentic, transverse, and topographic dunes are also present. Full article

This study assesses the current status of selected soil properties of an expanding equatorial agricultural region (Arauca, Colombia) across six landscapes, with the final focus being on evaluating overall soil quality. Field surveys, morphological descriptions, and laboratory analyses of 133 soil profiles were investigated. The landscapes include mountains (25 profiles), foothills (17), hills (11), alluvial plains (43), alluvial plains with dunes (21), and alluvial valleys (16). Soils are classified into six Reference Soil Groups (WRB FAO): Gleysols, Acrisols, Arenosols, Ferralsols, Leptosols, and Cambisols. The findings indicate high acidity, low fertility, and deficient exchangeable bases. Indeed, pH ranges from extremely acid to slightly acid (3.5–6.4), and exchangeable acidity saturation percentage (%SAI) values reach 100% in some areas. Soil textures vary from clay loam to sandy loam and clay. Nutrient contents are ranked in the order Cambisols > Gleysols > Arenosols > Ferralsols > Acrisols > Leptosols. Correlation analysis reveals that clay content positively influences the exchangeable basis percentage, while organic matter (OM) negatively correlates with the nutrients phosphorus, calcium, and magnesium. This study highlights that landscape position influences soil quality, with lower landscape positions having better quality than upper ones. These results provide insights into soil fertility and nutrient availability, which helps to predict suitable plant cultivation areas when increasing areas for agricultural use versus forestry in Arauca. The inclusion or maintenance of diverse tree species is a key element in maintaining the production of organic matter and, consequently, generating better soil quality. Full article

In the context of sea levels rising, monitoring spatial and temporal topographic changes along coastal dunes is crucial to understand their dynamics since they represent natural barriers against coastal flooding and large sources of sediment that can mitigate coastal erosion. Different technologies are currently used to monitor coastal dune topographic changes (GNSS, UAV, airborne LiDAR, etc.). Satellites recently emerged as a new source of topographic data by providing high-resolution images with a rather short revisit time at the global scale. Stereoscopic or tri-stereoscopic acquisition of some of these images enables the creation of 3D models using stereophotogrammetry methods. Here, the Ames Stereo Pipeline was used to produce digital elevation models (DEMs) from tri-stereo panchromatic and high-resolution Pleiades images along three 19 km long stretches of coastal dunes in SW France. The vertical errors of the Pleiades-derived DEMs were assessed by comparing them with DEMs produced from airborne LiDAR data collected a few months apart from the Pleiades images in 2017 and 2021 at the same three study sites. Results showed that the Pleiades-derived DEMs could reproduce the overall dune topography well, with averaged root mean square errors that ranged from 0.5 to 1.1 m for the six sets of tri-stereo images. The differences between DEMs also showed that Pleiades images can be used to monitor multi-annual coastal dune morphological changes. Strong erosion and accretion patterns over spatial scales ranging from hundreds of meters (e.g., blowouts) to tens of kilometers (e.g., dune retreat) were captured well, and allowed to quantify changes with reasonable errors (30%). Furthermore, relatively small averaged root mean square errors (0.63 m) can be obtained with a limited number of field-collected elevation points (five ground control points) to perform a simple vertical correction on the generated Pleiades DEMs. Among different potential sources of errors, shadow areas due to the steepness of the dune stoss slope and crest, along with planimetric errors that can also occur due to the steepness of the terrain, remain the major causes of errors still limiting accurate enough volumetric change assessment. However, ongoing improvements on the stereo matching algorithms and spatial resolution of the satellite sensors (e.g., Pleiades Neo) highlight the growing potential of Pleiades images as a cost-effective alternative to other mapping techniques of coastal dune topography. Full article

Dunes are key geomorphological features in aeolian environments, and their automated mapping is essential for ecological management and sandstorm disaster early warning in desert regions. However, the diversity and complexity of the dune morphology present significant challenges when using traditional classification methods, particularly in feature extraction, model parameter optimization, and large-scale mapping. This study focuses on the Gurbantünggüt Desert in China, utilizing the Google Earth Engine (GEE) cloud platform alongside multi-source remote sensing data from Landsat-8 (30 m) and Sentinel-2 (10 m). By integrating three deep learning models—DeepLab v3, U-Net, and U-Net++—this research evaluates the impact of the batch size, image resolution, and model structure on the dune segmentation performance, ultimately producing a high-precision dune type map. The results indicate that (1) the batch size significantly affects model optimization. Increasing the batch size from 4 to 12 improves the overall accuracy (OA) from 69.65% to 84.34% for Landsat-8 and from 89.19% to 92.03% for Sentinel-2. Increasing the batch size further to 16 results in a slower OA improvement, with Landsat-8 reaching OA of 86.63% and Sentinel-2 reaching OA of 92.32%, suggesting that gradient optimization approaches saturation. (2) The higher resolution of Sentinel-2 greatly enhances the ability to capture finer details, with the segmentation accuracy (OA: 92.45%) being 5.82% higher than that of Landsat-8 (OA: 86.63%). (3) The U-Net model performs best on Sentinel-2 images (OA: 92.45%, F1: 90.45%), improving the accuracy by 0.13% compared to DeepLab v3, and provides more accurate boundary delineation. However, DeepLab v3 demonstrates greater adaptability to low-resolution images. This study presents a dune segmentation approach that integrates multi-source data and model optimization, offering a framework for the dynamic monitoring and fine-scale mapping of the desert’s geomorphology. Full article

Coastal foredune blowout is a significant indicator of shoreline retreat, activation of backshore dune fields, and land desertification. Among current research on the terminal phase of coastal foredune blowouts, few studies explain blowouts’ morphological and airflow interaction mechanisms in the late stage through comprehensive field surveys and observations. In this study, the coastal blowout on the foredune at Tannanwan Beach, Pingtan Island, China, is investigated to explore the morphodynamics and evolutionary characteristics of blowout morphology. High-resolution RTK GPS technology and two-dimensional ultrasonic anemometers are utilized to repeatedly measure and observe the morphology of late-stage bowl blowouts. The results revealed that the following: (1) During the entire survey period, the bowl blowout is characterized by deepening erosion of the lateral walls and accretion in the deflation basin, with the maximum erosion depth on the east lateral wall reaching up to 3.99 m and the maximum accumulation height occurring in the front half of the deflation basin. (2) The wind direction and the morphology of the bowl blowout significantly impact the airflow characteristics within the blowout, and the airflow distribution within the blowout further affects the development of the blowout morphology. (3) The bowl blowout is in the late stage of its life cycle. Full article

This paper examines the long-term morphological evolution of the Bevano River sand spit (Ravenna, Italy) after an artificial intervention carried out in 2006 that artificially relocated the river mouth to improve the hydraulic efficiency, preventing flooding and reconstructing a local dune system. Using multitemporal Lidar data (2004–2019), combined with orthophotos and a storm dataset, this study analysed shoreline changes and morphological variations, highlighting the role of overwash processes in sediment transfer from the dunes to back-barrier areas. Based on the analysis, a set of washover fans was identified that began to form after a storm event in 2008 and accreted until 2015. These fans, which later coalesced into terraces and were colonised by vegetation, became stable after 2015. Despite an initial low resilience, due to insufficient nourishment and slow vegetation development, the barrier system eventually stabilised, with dunes growing higher and forming a continuous dune crest. The study illustrates the role of surge levels, waves, and low initial elevation in triggering and shaping overwash processes. Full article

Within the Rubiaceae family, the genus Randia comprises approximately 90 species, with significant morphological diversity in growth forms, leaf shapes, and floral sexuality. In particular, Randia aculeata is a taxonomically challenging species distributed from the southern United States to South America and the Antilles that exhibits high morphological variability and ecological adaptability. One of its synonyms is Randia tomatillo, originally described from coastal dunes in Veracruz, Mexico, and it has been inconsistently described in the taxonomic literature either as a distinct species or as a synonym for R. aculeata. This study aimed to resolve the taxonomic identity of R. tomatillo through morphological observations from herbarium specimens, and transverse sections from mature leaves were observed using SEM microscopy to explore crystal types. Morphological traits, such as lifeform, twig pubescence, stipule persistence, fruit size, and pericarp texture, are critical in distinguishing R. tomatillo from morphologically related species, such as R. aculeata and Randia thurberi. Anatomical features, particularly the presence of prisms in the leaf mesophyll and epidermis, are unique to R. tomatillo, suggesting their diagnostic value. Ecological adaptations, such as scandent growth and spongy pericarps for hydrochorous fruit dispersal, further support its distinction as a species adapted to coastal environments. These findings highlight the need for a comprehensive taxonomic reassessment of Randia, integrating morphological, anatomical, and ecological evidence. Full article

The influence of various factors, such as the natural properties of rock and in-situ stress conditions, results in uneven and rough fracture surfaces post-hydraulic fracturing. This significantly impacts the transport and placement of proppant within the fracture, thereby affecting the effectiveness of fracture stimulation. This study employs the rectangular wave method to characterize the roughness of fracture wall morphology, detailing the variation of roughness by altering the number and height of micro-protuberances, and constructs a three-dimensional model of rough fractures. The Euler–Euler model is utilized to simulate the placement and transport patterns of proppant within the fracture. Sand banks within the fracture profile are segmented based on proppant concentration, and the dimensionless area of each concentration interval is calculated to analyze the structure of sand banks and the suspension and settling effects of proppant. This research investigates the variation patterns of sand dune structures within fractures characterized by different levels of roughness and morphologies; it also examines the impact of injection velocity and fracturing fluid viscosity on the transport and placement of proppant within rough fractures. The findings indicate that the complex spatial structure of rough fractures modifies the edge shape of sand dunes. Moreover, it impedes proppant transport, leading to the formation of sand plugs near the wellbore. The maximum distance of sand placement for rough fractures is only 55.2% of that for fractures without considering roughness. The increase in the number and height of micro-protrusions enhances fracture roughness, leading to a stronger retarding effect. However, variations in these two types of roughness have distinct impacts on the morphology of sand dunes. Higher injection velocities facilitate the transport of proppant within rough fractures. The furthest distance of proppant placement at an injection velocity of 0.5 m³/min is only 68.4% of that at an injection velocity of 1.5 m³/min. The study’s findings contribute to a more intuitive understanding of the impact of rough fracture wall surfaces on the transport and placement patterns of proppant, providing a foundation for the optimization of fracturing design and operational parameters. Full article

Sandy barrier systems are highly dynamic, with the most significant natural morphological changes to these systems occurring during high-energy storm conditions. These systems provide a range of economic and ecosystem benefits and protect inland areas from flooding and storm impacts, but the persistence of many coastal barriers is threatened by storms and sea-level rise (SLR). This study employed observations and modeling to examine recent and potential future influences of storms on a sandy coastal barrier system in Nauset Beach, MA. Drone-derived imagery and digital elevation models (DEMs) of the study area collected throughout the 2023–2024 winter revealed significant alongshore variability in the geomorphic response to storms. Severe, highly localized erosion (i.e., an erosional “hotspot”) occurred immediately south of the Nauset Bay spit as the result of a group of storms in December and January. Modeling results demonstrated that the location of the hotspot was largely controlled by the location of a break in a nearshore sandbar system, which induced larger waves and stronger currents that affected the foreshore, backshore and dune. Additionally, model simulations of the December and January storms assuming 0.3 m (1 ft) of SLR showed the system to be relatively resistant to major geomorphic changes in response to an isolated storm event, but more susceptible to significant overwash and breaching in response to consecutive storms. This research suggests that both very strong isolated storm events and sequential moderate storms pose an enhanced risk of major overwash, breaching, and possibly inlet formation today and into the future, raising concern for adjacent communities and resource managers. Full article

We propose the hypothesis that dune gullies and seasonal “meteorological” appearances observed on the same dunes (e.g., frosting) may have a common origin. These gullies are difficult to explain through the action of liquid flow. The occurrence of a spring flowing from the crest of a dune seems impossible to explain. However, these phenomena could originate from the impact of wind on the profiles of some large Martian dunes. This aerodynamic effect could seasonally generate all the meteorological phenomena we observe on these dunes (bodies of ice, frost, moisture trails, and vapor clouds) and as a result, produce gullies with a peculiar morphology different from the standard. Thus, dune gullies could originate from meteorological liquids, but through a process unlike those known on Earth. Evidence from the Kaiser, Russell, and Korolev Craters supports the possibility of a partial water cycle (a half-cycle), potentially the remnant of a complete ancient cycle. Full article