Search Results (61)

Coral sands are critical in the construction of islands and harbors in tropical regions. Studying their dispersal, specifically the movement of ‘sedimentary clouds’ during marine dumping/dredging operations, is essential for optimizing construction efficiency and mitigating impacts on marine ecosystems. This study investigates the evolutionary characteristics of coral sand particles in still water via controlled indoor experiments. By manipulating parameters such as particle size, mass, nozzle diameter, and air release height, this study evaluated the impact of aspect ratio, Stokes number, and initial particle momentum on the movement of coral sand clouds. The results indicate that variations in air release height modulated the cloud’s width and corresponding diffusion angle, but exerted a negligible impact on the cloud front’s velocity and position. Empirical formulas for traditional quartz sand have limitations in reflecting the complex hydrodynamic settling behavior of coral sand. To address this, this paper establishes a modified empirical equation. This equation effectively predicts the width of coral sand plumes across different air release heights and Stokes number ranges. Furthermore, rather than directly quantifying microscopic morphological features, this study interprets these macroscopic transport characteristics from a process-based hydrodynamic perspective. Ultimately, the resulting predictive data and empirical framework provide a practical reference for evaluating sediment dispersion in reef engineering projects. Full article

This study evaluates the feasibility of 1% xanthan gum-treated sandy soils (natural sand and recycled glass sand) as sustainable materials for coastal restoration applications. The long-term durability and water erosion resistance of treated soils were systematically investigated through wet–dry cycling, pH durability testing, Erosion Function Apparatus (EFA) tests, and rainfall simulation experiments. Particular attention was given to the combined use of xanthan gum and recycled glass sand (RGS) as an environmentally friendly alternative to conventional geomaterials. The results demonstrated that soil gradation and soil type significantly influenced the performance of the xanthan gum–soil matrix. Xanthan gum-treated pure recycled glass sand specimens lost their structural integrity within one day of water immersion, whereas xanthan gum-treated natural sand specimens resisted water erosion for up to 20 days. In contrast, xanthan gum-treated mixed sand (XTMS), prepared using RGS and natural dredged sand, exhibited significantly improved durability and erosion resistance. Although the unconfined compressive strength (UCS) of XTMS decreased by approximately 70% after three wet–dry cycles, accompanied by only 0.21% soil loss, the specimens maintained structural integrity throughout the testing period. The UCS results further indicated that XTMS exhibited relatively good durability under artificial seawater conditions but experienced significant degradation under acidic and alkaline environments. EFA results classified XTMS as having medium erodibility, representing a substantial improvement in water erosion resistance compared to untreated sand. In addition, rainfall simulation tests demonstrated that XTMS specimens were capable of withstanding very heavy rainfall conditions (120 mm/h) with minimal soil loss. Overall, the findings suggest that the combined use of xanthan gum and RGS provides a promising, sustainable, and environmentally friendly approach for improving soil stability and erosion resistance in coastal restoration applications. Full article

Introduction: The sea lamprey (Petromyzon marinus) is an anadromous jawless fish that migrates between marine and freshwater environments, spawning once in rivers before dying. It is distributed along both coasts of the North Atlantic. In Asturias (northern Spain), P. marinus is classified as Vulnerable, and a conservation plan is currently under development. In the present study, Critical Conservation Areas (CCAs) are defined as river reaches requiring urgent protection due to their high ecological value for the species. Objective: This study aimed to identify key reproductive and larval habitats (spawning grounds and silt–sand banks) to support the designation of CCAs for the conservation of the sea lamprey in Asturias. Methodology: Fieldwork was conducted in the main salmonid rivers of Asturias (Deva, Nalón, Narcea, Navia, Eo, and Sella basins). During spring 2025 and 2026, habitats were characterized and spawning sites identified using transects. In autumn 2025, larvae were sampled by electrofishing within defined areas (10–30 m²), measured and weighed, and densities were extrapolated using an inverse distance weighting (IDW) model. Basin use and critical areas were assessed based on species distribution and habitat quality. Results: A total of 1886 larvae were recorded across 27 river sections, of which 1366 were measured. Sea lamprey was present in 74.1% of sections, whereas brook lamprey (Lampetra planeri) was detected only in the Deva basin. Mean larval size was 9.5 ± 3.7 cm and 2.3 ± 2.19 g, with marked spatial variability. The highest larval densities occurred in the Eo (21.5 ind/m²) and Narcea rivers (15.1 ind/m²). Additionally, 94 spawning records were identified, and 65% of the 83 assessed sections were classified as good or very good habitat. Conclusions: A total of 31 CCAs (~300 km) were proposed, including 97 km classified as “of interest”, 21 km as “important”, and 180 km as “highly important”. Habitat use was greatest in sinuous middle river reaches with riffles, pools, and fine sediment deposits. Transversal barriers, dredging, and channel simplification were identified as the main drivers of habitat loss. These findings provide a robust scientific basis for conservation planning and management of the species in Asturias. Full article

Deep stormwater drainage tunnels are increasingly being used to mitigate urban flooding, but in-tunnel sediment deposition reduces their discharge capacity and complicates their maintenance. With direct field observation constrained, numerical simulation is essential, and river-based total sediment load formulas require reassessment for use in deep tunnels. The three-phase (air–water–sediment) CFD solver SedInterFoam is first validated against a benchmark open-channel suspended sediment experiment, and is then applied to a horseshoe tunnel under a fixed design discharge for multiple inlet sediment concentrations spanning urban stormwater conditions. Four classical formulas (Yang, Shen–Hung, Ackers–White, Engelund–Hansen) are evaluated at the CFD-resolved hydraulic state; Toffaleti is omitted because its zone-based formulation is incompatible with the partially filled horseshoe geometry. The CFD consistently shows persistent retention of a substantial fraction of the inlet sediment load, whereas the transport capacity-limited interpretation of the classical formulas predicts near-complete sediment throughput—indicating structural inadequacy for the dilute, supply-limited regime typical of urban stormwater. A Universal Soil Loss Equation (USLE)-style dimensionless deposition formula is therefore proposed, with inlet sediment loading as the explicit independent variable and a tunnel correction factor $K_{tunnel}$ absorbing the geometric, hydraulic, and sediment variations. Its regression yields an almost linear scaling and a nearly constant deposition ratio, while analysis of the internal flow and concentration fields shows that the retained sediment is strongly concentrated near the bed and that near-bed turbulent mixing weakens moderately with a rising inlet concentration. While calibrated for a single non-cohesive settleable sand fraction, the framework provides a transferable basis for inlet-loading-dependent deposition prediction in deep stormwater drainage tunnels, and subsequent extension of $K_{tunnel}$ to broader sediment conditions with field-based validation is expected to enable maintenance planning, dredging volume estimation, and sediment retention risk assessment. Full article

This paper develops foamed mixture lightweight soil (FMLS) using dredged soil for ecological floating landscapes applications, focusing on key performance indices including dry density, compressive strength, splitting tensile strength, water absorption, and fluidity. Orthogonal experiments determined the optimal mix ratio, while CaO expansion agent, MgO expansion agent, polypropylene fiber (PPF), and basalt fiber (BF) were employed to modify material properties. The microstructural mechanisms of FMLS before and after modification were characterized by scanning electron microscopy (SEM). The results show that FMLS achieves optimal comprehensive performance at a cement-to-sand ratio of 0.4, foam content of 10%, and water-to-sand ratio of 0.35, with all parameters conforming to technical specifications. The optimal dosage for both CaO and MgO expansion agents is 5%, PPF is 0.3% and BF is 0.5%, respectively. MgO expansion agent and PPF demonstrate superior suitability for floating landscapes due to enhanced pore-filling efficiency and crack-bridging effects by SEM. Finally, correlation analysis further indicates that the water–binder ratio critically governs the strength characteristics of FMLS. This paper not only provides a new direction to promote the effective use of dredged soil resources, but also provides new ideas for carrier materials for ecological floating landscapes. Full article

The sustainable management of dredged sediments poses a major environmental and economic challenge, particularly in Morocco, where large quantities are annually discarded as waste. Contributing to resource efficiency and circular economy objectives, this study represents the first systematic application research of Moroccan Mehdia Harbor sediments in mortar formulations. Three substitution strategies were investigated at substitution rates of 5–30%: (i) replacement of cement with fine sediments (series MA); (ii) replacement of sand with intermediate sediments (series MB); (iii) replacement of sand with sandy sediments (series MC). Mechanical testing at 28 days showed that both compressive and flexural strengths remained comparable to the reference mortar for substitution levels up to 10–15%, depending on sediment type. Beyond these limits, a marked strength reduction was observed, particularly for cement replacement with fine, clay-rich sediments. Mortars incorporating sandy sediments (MC) exhibited the best performance, maintaining over 80% of the reference compressive strength up to 15%. Leaching tests confirmed the environmental stability of all formulations, which remained within the “inert” waste classification up to 15% substitution. These findings demonstrate that dredged sediment incorporation in mortar is both technically and environmentally feasible for non-structural applications, promoting sustainable materials within a circular economy framework. Full article

Egypt’s largest coastal lagoon, Manzala Lagoon, has undergone severe degradation due to sediment infilling, aquatic vegetation proliferation, and untreated wastewater. It has shrunk from 805 km² in 1985 to 525 km² by 2017, with poor water quality and heavy metal accumulation. The 2017–2022 restoration project deepened the lagoon to 3–4 m, restoring 750 km² of open water and temporarily improving water quality. However, the reuse of dredged sediments to construct 13 elongated sand barriers and man-made islands inadvertently created semi-isolated sub-basins, disrupting east–west circulation, fostering localized stagnation, and coinciding with vegetation resurgence and seasonal algal blooms. This study employs coupled CMS-Flow and CMS-Wave modeling to evaluate hydrodynamic conditions and test innovative restoration strategies. Four scenarios were analyzed: pre-purification (2017), post-intervention project (2025), and two proposed interventions aimed at restoring connectivity, either through complete barrier removal or selective channel excavation, to enhance east–west water circulation and reduce stagnation. This study demonstrates that targeted, data-driven interventions can rapidly restore water circulation, revive ecological function, and optimize management strategies, providing a conceptually transferable framework for hydrodynamic assessment and sustainable management of coastal lagoons subject to similar anthropogenic pressures. Full article

The utilization of treated dredged sludge as a partial replacement for natural sand and gravel in construction projects offers a promising approach to reducing the exploitation of natural resources. The conventional vacuum preloading (VP) method, while widely used for soft soil improvement, is often associated with prolonged consolidation periods and high energy consumption in its later stages. Conversely, the electroosmosis (EO) technique is effective in enhancing drainage in low-permeability soft clays but is constrained by issues including anode corrosion, high operational costs, and uneven soil reinforcement. This study presents an experimental investigation into an alternating vacuum preloading and electroosmosis method for sludge treatment based on the underlying reinforcement theory. A series of laboratory model tests was conducted using a self-made vacuum–electroosmosis alternating test device. The reinforcement efficiency was assessed through the continuous monitoring of key performance indicators during the tests, including water discharge, surface settlement, electric current, electrode corrosion, and energy consumption. Post-test evaluations of the final soil shear strength and moisture content were also performed. The test results demonstrate that the alternating vacuum–electroosmosis yielded more significant improvement than their synchronous application. Specifically, the alternating vacuum–electroosmosis increased total water discharge by 46.1%, reduced final moisture content by 20.8%, and enhanced shear strength by 35.6% relative to the synchronous mode. Furthermore, an alternating VP-EO mode was found to be particularly advantageous during the electroosmosis phases, facilitating a more stable and sustained dewatering process. In contrast, the application of vacuum preloading alone resulted in inefficient performance during the later stages, coupled with relatively high energy consumption. Full article

Ship Shoal, a large transgressive sand body on the Louisiana continental shelf, is a critical sediment source for coastal restoration. This study evaluates spatial and temporal variability in sediment grain size, percents organic matter (%OM), and carbonate (%CO₃) across the shoal crest (REF), Caminada Dredge Pit (CAM), and Terrebonne Dredge Pit (TER). Sediment samples were collected between 2020 and 2022 using box cores and analyzed for grain size, %OM, and %CO₃, with temporal and spatial patterns assessed through statistical comparisons, correlation analyses, and random forest regression models. Results show that dredged areas act as sinks for fine-grained, organic-rich sediments, with CAM consistently exhibiting the smallest median grain sizes and highest %OM, while REF maintained coarse, well-sorted sands. Carbonate enrichment reflected long-term depositional regimes, with REF exhibiting the highest %CO₃ due to the absence of dredging disturbance. Grain size and %CO₃ were identified as the strongest predictors of %OM, while %CO₃ was only weakly correlated with other sedimentary variables. Collectively, these findings demonstrate that dredge pits function as persistent repositories, with implications for benthic habitat resilience, sediment management, and coastal restoration planning. Future integration of hydrodynamic modeling with sediment transport and biogeochemical processes is needed to enhance predictive capability for managing dredged environments. Full article

Coastal lagoons are dynamic and highly productive systems that offer a remarkable number of ecological services and benefits for humans. However, our understanding of them is still far from adequate. The Mar Menor lagoon is an ecosystem subject to anthropogenic pressures that have worsened in recent years. These pressures include coastal works, such as dredging and sand dumping, as well as changes in agricultural regimes that have induced a process of eutrophication that set off alarms after the eutrophic crisis that occurred in 2016. Benthic organisms, and in particular mollusks, are very sensitive to environmental variations, often serving as indicators of these changes. This work analyzes the malacofauna of the Mar Menor from 1981 to 2019 in the context of the environmental changes that have occurred in it during these years. Eighty-six species have been recorded throughout our study period, and species richness, abundances, local assemblage structures, along with changes in the main environmental parameters of the water column (salinity, temperature, and chlorophyll a concentration) have been used to explain the composition of the communities of the main lagoon habitats and to detect their spatial and temporal variations. With the information provided, the complete inventory of mollusks reported in the lagoon has been updated to 126 species. The results indicate that, during these almost 40 years, the total number of species has remained relatively constant, but with a high percentage of occasional and very rare species, along with a high rate of change from one species to another over time, accompanied by variations in the abundance and dominance of some species compared to others depending on the environmental conditions and pressures that the lagoon has undergone. The high spatial and temporal heterogeneity detected is determined by the restricted connectivity with the open sea, the diversity of environments and habitats, and the changes in environmental conditions due to human actions. Full article

The Yangtze River Economic Belt in China, a major economic and ecological region, faces critical challenges in the sustainable management of dredged sand, exacerbated by illegal sand mining practices. This study advances the understanding of integrated management models for dredged sand utilization by systematically analyzing six pilot projects through field investigations and theoretical methods. It identifies three novel management models: the traditional government-led model, the integrated “operation + concession” model, and the separated “operation + concession” model. These models provide structured approaches to enhance stakeholder collaboration, streamline resource distribution, and standardize regulatory frameworks. Furthermore, this study underscores the necessity of tailored strategies to align with local conditions, enabling sustainable and resource-efficient practices. By addressing critical gaps in prior research and proposing an actionable framework, this research offers valuable insights for global efforts to mitigate the sand scarcity crisis through innovative sand management. Full article

From both economic and environmental points of view, the reuse of dredged sediments in the direct onsite casting of concrete represents a promising method for replacing sand. The aim of this study was to develop a cementitious material that (i) reuses the thin particles of sediments; (ii) has a low density due to the incorporation of air foam in the material; and (iii) achieves a minimum mechanical strength of 0.5 MPa for embankment applications. This study focused on the characterization of a non-standard “concrete”, which is a mixture of a synthetic soil (80% montmorillonite and 20% calibrated sand) and cement. To reduce its density, air foam was incorporated into the material during the manufacturing process (air-foamed lightweight clay concrete—AFLCC). The study results highlight that a density around 1.2 (unit: g/cm³/1 g/cm³) can be obtained. This density reduction can be obtained with a certain degree of workability when the material is in a fresh state. To obtain this workability, a certain amount of water must be added; however, the addition of water has a significant impact on the compressive strength of the AFLCC. As such, a mathematical equation correlating the compressive strength, the density, and the percentage of cement is proposed in this study. The mechanical strength results of the AFLCC at different times, in conjunction with the Vicat results, show that the porosity created by the air foam has the effect of slowing down the hydration mechanism of the cement. The porosities obtained are consistent with the density results. The characteristic radii indicate large pore sizes for formulations with low fluidity in the fresh state when air bubbles are incorporated. Full article

The study of dredged fill in Guangdong (GD), China, is of great significance for reclamation projects. Currently, there are relatively few studies on dredged fill in Guangdong, and there are many differences in the engineering characteristics of dredged fill foundations formed through land reclamation and natural foundations. In order to have a more comprehensive understanding of the physico-mechanical properties of blowing fill in the coastal area of GD and to understand the effect of its long-term creep row on the long-term settlement and deformation of buildings, the material properties, microstructure, elemental composition, triaxial shear properties, and triaxial creep properties of dredged fill in Guangdong were studied and analyzed through indoor geotechnical tests, scanning electron microscopy (SEM), X-ray diffraction (XRD), and conventional triaxial shear tests and triaxial creep tests. The test results showed that the Guangdong dredged fill is characterized by a high water content, high pore ratio, and high-liquid-limit clayey sand, and the mineral composition is dominated by quartz and whitmoreite. The scanning electron microscopy results showed that the particles of the dredged fill showed an agglomerated morphology, and the surface of the test soil samples had scaly fine flakes and a fragmented structure. In the triaxial shear test, the GD dredged fill showed strain hardening characteristics, and the effective stress path showed continuous loading characteristics; the consolidated undrained shear test showed that the GD dredged fill had shear expansion characteristics under low-perimeter-pressure conditions. It was found that, with an increase in bias stress, the axial strain in the consolidated undrained triaxial creep test under the same perimeter pressure conditions gradually exceeded the axial strain in the consolidated drained triaxial creep test. The results of this study are of theoretical and practical significance for further understanding the mechanical properties of silty soils in the region and for the rational selection of soil strength parameters in practical engineering design. Full article

As a strategically important resource with stable properties, high-purity quartz plays a crucial role in various fields such as high-purity quartz crucibles, semiconductors, and electronics. Currently, the availability of high-quality quartz resources is gradually diminishing, and there are no high-quality quartz deposits in some areas, making the improvement of low-quality quartz essential. This study focuses on the quartz sand produced through river dredging in Yueyang. The detected SiO₂ content is 92.31%, which enables the secondary utilization of waste resources and provides significant environmental benefits. In this study, the iron oxide removal efficiency achieved through magnetic separation pretreatment can reach 87.24%. Following flotation, calcination, and leaching processes, high-purity quartz products with a total impurity content of less than 100 ppm were successfully obtained. In addition, the factors affecting magnetic separation and calcination effect were studied, and the process parameters for reference were obtained. The mechanism of microwave impurity removal was investigated using SEM, TG-MS, and in-situ XRD, demonstrating the feasibility of producing high-purity quartz from low-quality quartz. Full article

Water jet scouring technology is extensively applied in marine engineering, harbor maintenance, river training, and various other fields, showcasing a broad spectrum of potential applications. However, achieving a comprehensive understanding of the transient sand scouring characteristics of water jets remains challenging due to the inherent complexity of the coupled flow structure involving submerged jets and environmental fluids, along with the intricate dynamics of two-phase flow. This study, rooted in numerical simulation and experimental validation, introduces pulse characteristics into a submerged jet. A thorough investigation is conducted to explore the transient sand scouring characteristics and sand transport laws of the submerged jet under diverse working conditions. The results of this study revealed that the main reason for the asymmetry of the sand pit morphology is not the non-uniform distribution of sand grains, but more likely caused by turbulence effects. Simultaneously, within the initial 0.25 s of the pulse cycle, suspended sediment resulting from the pulsed jet in the preceding cycle gradually transports to the dune and its surrounding areas. Subsequently, from 0.25 s to 0.5 s, sediment on both sides of the pit’s bottom undergoes movement and amalgamation with the sediment that remained unsettled during the previous cycle. The findings reveal that higher jet velocities significantly enhance sediment suspension, migration, and redeposition, leading to deeper erosion and the rapid formation of the sand pit’s outline within 2 s. Additionally, the jet velocity and the impact distance are identified as critical factors influencing erosion depth and sediment dynamics. These insights advance the understanding of erosion mechanisms driven by pulsed jets, highlighting their impact on sediment transport processes. The research findings provide important guidance for dredging and ocean engineering fields and offer a theoretical basis for improving the understanding of submerged jet scouring mechanisms. Full article