Search Results (562)

Human activities have led to severe aquatic pollution and significant concerns about the ecological health of the Lianjiang River Basin (LRB). These concerns resulted in the implementation of comprehensive policies and treatments to improve the sediment and water quality. Herein, we explore the concentrations, sources, and degree of metal contamination in filtered water (FW), suspended solids (SSs), and surficial channel sediments (SCSs) in streams of the LRB. Calculated enrichment factors, an ecological risk index, and a principal component analysis were employed to understand the degree of elemental contamination, ecological risks, and their potential sources. Elements (e.g., Hg, Cd, Sn, Sb, Cu, and Mo) were mainly detected in FW, SSs, and SCSs in the Bergang, Hucheng, Xiashan, and Zhonggang rivers, and the mainstream of the LR. Four potential anthropogenic sources were identified, including electronic waste recycling (e.g., Cu, Sb, Pb, and Ni), mixed pollution (e.g., Se, Zn, Mn, and Mo), metal processing (e.g., Hg, Cr, Sn, and Cd), and battery manufacturing and recycling (e.g., Co, Ni, and Mn). Overall, Sn, Sb, Hg, Cu, and Cd were enriched by 37.5–79.2% and 34.8–91.3% at the SS and SCS sites, respectively. Mercury, Cd, Sn, Sb, Cu, and Mo posed the most risk both in the SSs and SCSs. Overall, the SS and SCS samples from the LRB remain severely contaminated with metals after recent environmental remediation. The implementation of pollution source control, sewage interception, and dredging operations should be further enhanced. Full article

Anchored sheet-pile walls (ASPWs) are widely used as earth-retaining structures in engineering practice. The difficulty in analyzing sheet piles arises because the loading on the wall is a function of the deformation of the soil and the sheet-pile configuration. This paper discusses the predictions of different theoretical solutions for ASPWs, and it briefly presents and discusses four main theories of ASPWs: the two distribution theories, the finite element method, and Rowe’s theory. The effect of different influencing factors on the behavior and design of ASPWs is also examined. The above theoretical solutions are evaluated experimentally through measurements of strains, deflections, tie-rod force, and tie-rod yield on a small-scale sheet-pile model tested in a sandbox. The four theories provide an acceptable analytical solution for the ASPW problem under the given conditions. However, no theory fully predicts the behavior of ASPWs over the entire range of the different design parameters: soil conditions, sheet-pile flexibility, dredge depth, anchor location, and anchor yield. This paper proposes simple charts and tables for SPW design based on extrapolation between distribution theories while accounting for sheet pile flexibility and other influencing parameters. Illustrating examples for the proposed design procedure are provided. Full article

Rivers, vital for life and civilizations, face severe threats from human activities such as hydropower development, with heavy metal pollution emerging as a critical concern due to altered biogeochemical cycles. Understanding how river damming affects heavy metal transport processes and developing targeted remediation strategies are essential for safeguarding the health of river-reservoir ecosystems and enabling the sustainable utilization of hydropower resources. Therefore, this review first summarizes the global hydropower development, details how damming disrupts hydrology, environments, and ecosystems, and analyzes heavy metal distribution and transport in reservoir water, suspended sediments, and riverbed sediments. It reveals that river damming promotes heavy metal adsorption onto suspended particles, deposition in riverbed sediments, and re-release during reservoir regulation, and anthropogenic activities are a primary driver of significant pollution in key reservoirs worldwide. Additionally, we further evaluate in situ (e.g., stabilizing agents, sediment capping, and phytoremediation) and ex situ (e.g., dredging, chemical washing, electrochemical separation, and ultrasonic extraction) remediation techniques, highlighting the challenges of phytoremediation in deep, stratified reservoir environments. Moreover, solidification/stabilization emerges as a promising in situ strategy, emphasizing the need for specific approaches to balance pollution control with hydropower functionality in dammed river systems. Full article

As crucial transportation hubs and economic nodes, the underwater security and infrastructure maintenance of harbors are of paramount importance. Harbors are characterized by high vessel traffic and complex underwater environments, where traditional underwater inspection methods, such as diver operations, face challenges of low efficiency, high risk, and limited operational range. This paper introduces a collaborative survey and disposal system that integrates a deformable unmanned surface vehicle (USV) with a lightweight remotely operated vehicle (ROV). The USV is equipped with a side-scan sonar (SSS) and a multibeam echo sounder (MBES), enabling rapid, large-area searches and seabed topographic mapping. The ROV, equipped with an optical camera system, forward-looking sonar (FLS), and a manipulator, is tasked with conducting close-range, detailed observations to confirm and dispose of abnormal objects identified by the USV. Field trials were conducted at an island harbor in the South China Sea, where simulated underwater objects, including an iron drum, a plastic drum, and a rubber tire, were deployed. The results demonstrate that the USV-ROV collaborative system effectively meets the demands for underwater environmental measurement, object localization, identification, and disposal in complex harbor environments. The USV acquired high-resolution (0.5 m × 0.5 m) three-dimensional topographic data of the harbor, effectively revealing its topographical features. The SSS accurately localized and preliminarily identified all deployed simulated objects, revealing their acoustic characteristics. Repeated surveys revealed a maximum positioning deviation of 2.2 m. The lightweight ROV confirmed the status and location of the simulated objects using an optical camera and an underwater positioning system, with a maximum deviation of 3.2 m when compared to the SSS locations. The study highlights the limitations of using either vehicle alone. The USV survey could not precisely confirm the attributes of the objects, whereas a full-area search of 0.36 km² by the ROV alone would take approximately 20 h. In contrast, the USV-ROV collaborative model reduced the total time to detect all objects to 9 h, improving efficiency by 55%. This research offers an efficient, reliable, and economical practical solution for applications such as underwater security, topographic mapping, infrastructure inspection, and channel dredging in harbor environments. Full article

Dredged silt, characterized by high moisture content, low shear strength, and poor permeability, presents significant challenges for direct engineering application, leading to excessive land occupation and unsustainable resource management. To address these issues, solidification-lightweight composite technology has emerged as a promising approach to transform dredged silt into sustainable geo-materials. This review systematically evaluates international research progress on silt solidification, focusing on (1) the chemical reaction mechanisms of varied solidification agents, (2) the quantitative effects of key factors (e.g., agent dosage, curing time, and organic content) on the mechanical properties (unconfined compressive strength and shear strength) of treated silt, and (3) a critical discussion on technological limitations and future research directions. The findings provide insights for optimizing treatment protocols and advancing large-scale applications. Full article

Lightweight-foamed soils are mixed soils with foam and cement to enhance the solidity and lightness of soils. Marine wastes, especially waste fishing nets, can be additives to reinforce the engineering properties of lightweight-foamed soils. In this paper, lightweight-foamed soils reinforced with waste fishing nets were investigated. Dredged soil and waste fishing nets were collected and pre-processed for testing. For optimization, the water content, foam ratio, cement ratio, net ratio, net conditions, and curing days were evaluated with respect to workability, unit weight, and strength. The variables were narrowed down based on the performance criteria. The results found that a water content of around 100%, cement ratio of 20%, foam ratio of 5%, and net ratio of 4% with shredded nets provide the best engineering performance of lightweight-foamed soils. The use of nets presented a superior increase in critical strength rather than an obvious increase in peak strength. A normalized factor was used to predict the required strength of lightweight-foamed soils. Finally, this study proposes field implementation methods in terms of the initial conditions of soils and optimal conditions of soils, resulting in the depletion of waste fishing nets. Full article

Thermal discharge from power plants causes significant concerns in aquatic environments. The purpose of this study is to evaluate how river mouth morphodynamics, particularly spit development and removal, influence the dispersion of thermal plumes. To achieve this, a case study was carried out at a coastal power plant in southwest Türkiye, where thermal effluent is conveyed to the sea through a low-flow river. Field measurements combined with numerical modeling were used to analyze plume dynamics under varying spit configurations. Results revealed that the evolution of a spit on one side of the river mouth influences plume dispersion and redirects the mixing zone toward the opposite shoreline. Numerical simulations demonstrated that spit development reduces dispersion efficiency (by over 75%), while the physical removal of the spit significantly improves it, reducing temperature excess from 4–5 °C to 0–1 °C within the mixing zone, meeting safe environmental standards. The findings highlight the pivotal role of morphological changes in governing thermal discharge behavior and emphasize the importance of continuous monitoring and management strategies, such as periodic dredging, to ensure compliance with environmental regulations. 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

Due to high sedimentation rate up to ~1 m/year, mud-capped dredge pits (MCDP) are often considered natural laboratories for studying sedimentary processes, slope stability and the impacts of dredging activities on marine environments. Although many studies have been performed on the Louisiana shelf, there is a lack of high spatial resolution research covering the eastern, central and western Louisiana shelf to comprehensively investigate sediment infilling. Eighteen vibracores were collected from the Peveto Channel dredge pit (PC), Raccoon Island dredge pit (RI) and Sandy Point dredge pit (SP), and more than 1300 samples were analyzed to study the spatial variation in surficial sediment using statistical analyses. Our results indicate that the inner Louisiana continental shelf is silt-dominated, and there was no consistent grain size variation when comparing the sediment within the pits with that outside the pits. Skewness emerged as a prominent factor in the RI and SP, while standard deviation was the most influential in the PC. Our analysis shows also that two principal components are confirmed and account for more than 95% of the total grain size variance. Full article

The disposal of waste slurry in engineering construction and water environment remediation has become increasingly prominent. The physicochemical composite method integrating flocculation, solidification, and precompression has emerged as an efficient treatment approach, yet the permeability characteristics of slurry reinforced by this method remain insufficiently understood. This paper takes the high-moisture-content sludge generated from lake dredging projects reinforced by the physicochemical composite method as the research objective. Through permeability tests, the permeability characteristics of the physicochemical composite-modified slurry under different factors are tested, and its permeability characteristics are quantified through fitting methods. The research results show that the permeability coefficient decreases with the extension of curing time, decreases with the increase in curing agent dosage, increases with the increase in initial moisture content, and decreases with the increase in pre-stress. Full article

Port maintenance causes large quantities of dredged sediment throughout the world. The disposal of this material in authorised landfills is economically disadvantageous, as well as being at odds with a circular economy model with a reduced impact on the environment. The application of stabilization/solidification treatment to dredged marine sediments allows an improvement of their physical and mechanical properties, together with the production of cement-based materials that can be used for road construction, as well as for making blocks and bricks. In this study, an experimental laboratory investigation is carried out on two samples of sandy sediments collected from the Mola di Bari harbour (Southern Italy), to identify sustainable management options for recovering materials that will be dredged. To assess the influence on mortars made from sediments with variable organic matter content and seawater, these were characterised from a chemical–physical point of view before and after washing treatment and oxidative processes. The products of the Stabilization/Solidification (S/S) treatment were evaluated in terms of workability, flexural and compressive strengths, and, furthermore, a microstructural study was conducted using SEM-EDX and optical microscopy to analyse the internal structure of the materials. The mechanical performance evaluation clearly demonstrated organic matter’s negative impact on strength development, resulting in a 16% reduction. Pre-treatments, such as sediment washing, effectively improved the performance of treated sediments (e.g., 24% increase in compressive strength). This study aims to demonstrate the benefits of recycling marine sediments in cement-based materials, highlighting how this process can enhance circularity and sustainability while reducing the environmental impact of dredging activities. Full article

With intensifying watershed pollution pressures and growing ecological vulnerability, scientifically revealing and enhancing the water environmental carrying capacity is crucial for ensuring the long-term health of the basin and the sustainable socioeconomic development of the region. However, the dynamic regulatory mechanisms linking narrow-sense and broad-sense water environmental carrying capacity remain poorly understood, limiting the development of integrated management strategies. This study systematically investigated the changing trends of both the narrow-sense and broad-sense water environmental carrying capacity in the Harbin section of the Songhua River basin through model calculations, along with the regulatory mechanisms of its key influence indicators. The results of the study on the carrying capacity of the water environment in the narrow sense show that permanganate, total phosphorus, and ammonia nitrogen exhibited partial carrying capacity across water periods, while dissolved oxygen decreased during flat and dry periods, with only limited capacity remaining at the Ash River estuary and in the Hulan River. The biochemical oxygen demand in the Ash River was consistently overloaded, and total nitrogen showed insufficient capacity except during the abundant water period. Broad-sense analysis indicated that improving urbanization quality, water supply infrastructure, and drinking water safety could effectively reduce future overload risks, with projections suggesting a transition from critical to loadable levels by 2030, though latent threats persist. Correlation analysis between narrow- and broad-sense indicators informed targeted control strategies, including stricter regulation of nitrogen- and phosphorus-rich industrial discharges, restoration of aquatic vegetation, and periodic dredging of riverbed sediments. This work is the first to dynamically integrate pollutant and socio-economic indicators through a hybrid modelling framework, providing a scientific basis and actionable strategies for improving water quality and achieving sustainable management in the Songhua River Basin. Full article

Reservoir sedimentation, a global challenge causing an annual loss of 0.8–1% of reservoir storage capacity, disrupts fluvial sediment continuity and impacts ecology and societal needs. This study focuses on the Pulangi IV reservoir in the Philippines, a shallow and wide reservoir facing significant sedimentation issues. The research aims to investigate drawdown flushing and dredging of a flushing channel for future sustainable drawdown sluicing. A test flushing event was conducted and monitoring data, including discharge, suspended sediment concentration, bathymetry, and grain size distribution, were collected. Laboratory analyses, such as critical shear stress tests, were performed for model calibration. A 3D reservoir model and a 1D sediment transport model were applied incorporating cohesive sediment behavior. Scenarios were simulated to assess drawdown flushing, dredging and downstream impacts. Results highlight the importance of drawdown level, with cohesive sediment properties playing a critical role. Sedimentation downstream of the dam, resulting from dumped or flushed sediments, was low. However, downstream ecological and morphodynamic monitoring was found to be essential for all modeled strategies. This study demonstrates potential for establishing a flushing channel enabling future sustainable drawdown sluicing during floods by conducting repeated drawdown flushing in combination with dredging in the upper reservoir. Full article

Green and low-carbon filling materials, primarily composed of dredged waste fills, are commonly used in the foundation of coastal highways. These materials possess high water content and under-consolidation characteristics, which can lead to differential settlement between piles and the surrounding environment. However, mechanical models of negative friction in piles within recycled dredged waste fills are insufficiently developed and presented. A mechanical model for the negative friction of a single pile in a composite foundation, consisting of dredged waste fills and other materials, is established based on the load transfer method. Through centrifugal model testing and numerical simulations, the development of negative friction and the migration pattern of the neutral point are analyzed and clarified. The results show that the theoretical model based on improved transfer function can effectively predict the neutral point position and negative friction value (average relative error < 6.5%). The theoretical analysis and experimental results indicate that the downward load due to negative friction increases nonlinearly. The loading strength exhibits a clear relationship with the consolidation process. Additionally, the dynamic evolution of the neutral point position is strongly correlated with consolidation of dredged fills. The size of pile foundation significantly influences the distribution of negative friction. Results show that the increment in negative friction for a pile with a 1.05 m diameter is 7.3% higher than that for a pile with a 1.5 m diameter. Smaller-diameter piles are more susceptible to negative friction due to the higher friction strength per unit area. The negative frictional resistance will enter a stable period after 50 months of settlement. The investigation can provide significant references for the design of pile foundations in areas with reclaimed materials, improving the stability and safety of pile foundations in practical engineering. Full article

Reusing dredged sediments as cement-stabilized fill material offers a sustainable solution for high-fill construction projects, particularly in regions with limited land resources and strict environmental regulations. Nonetheless, the curing pressure from their weight heavily affects these materials’ mechanical properties. This research examines the impact of high curing pressure on the stress–strain behavior, unconfined compressive strength (UCS), and stiffness properties of cement-stabilized dredged sediments containing high moisture levels. Laboratory experiments were conducted under controlled conditions, varying initial water content, cement dosage, and curing pressure. Experimental results demonstrate that initial water content and cement dosage are pivotal in determining the material’s strength, regardless of curing pressure. Curing pressure enhanced peak stress and stiffness while increasing brittleness, resulting in a 41.7% increase in secant modulus for specimens cured under elevated pressure. A novel strength prediction model incorporating a curing pressure correction term was developed to quantify material behavior accurately. Microstructural analysis revealed that curing pressure improved material performance through physical densification and chemical activation, enhancing mechanical properties. This study lays scientific groundwork for the optimal design and application of cement-stabilized dredged sediments in large-scale construction projects, addressing the challenges of high water content and high-fill applications. Full article