Search Results (50)

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

Reliable coastal and offshore sediment transport data is a requirement for many engineering and environmental projects including port and harbour design, dredging and beach nourishment, sea shoreline protection, inland navigation, marine pollution monitoring, benthic habitat mapping, and offshore renewable energy (ORE). Novel sediment transport numerical modelling approaches allow engineers and scientists to investigate the physical interactions involved in these projects both in the near and far field. However, a lack of confidence in simulated sediment transport results is evident in many coastal and offshore studies, mainly due to limited access to validation datasets. This study addresses the need for cost-effective sediment validation datasets by investigating the applicability of four new suspended load validation techniques to a 2D model of the south-western Irish Sea. This involves integrating an estimated spatial time series of suspended solids concentration (${SSC}_{solids}$) derived from acoustic Doppler current profiler (ADCP) acoustic backscatter with several in situ water sample-based ${SSC}_{solids}$ datasets. Ultimately, a robust spatial time series of ADCP-based ${SSC}_{solids}$ was successfully calculated in this offshore, tidally dominated setting, where the correlation coefficient between estimated ${SSC}_{solids}$ and directly measured ${SSC}_{solids}$ is 0.87. Three out of the four assessed validation techniques are deemed advantageous in developing an accurate 2D suspended sediment transport model given the assumptions of the depth-integrated approach. These recommended techniques include (i) the validation of 2D modelled suspended sediment concentration (${SSC}_{sediment}$) using water sample-based ${SSC}_{solids}$, (ii) the validation of the flood–ebb characteristics of 2D modelled suspended load transport and ${SSC}_{sediment}$ using ADCP-based datasets, and (iii) the validation of the 2D modelled peak ${SSC}_{sediment}$ over a spring–neap cycle using the ADCP-based ${SSC}_{solids}$. Overall, the multi-disciplinary method of collecting in situ metocean and sediment dynamic data via acoustic instruments (ADCPs) is a cost-effective in situ data collection method for future ORE developments and other engineering and scientific projects. Full article

As a critical intervention for enhancing inland navigation efficiency, waterway regulation projects profoundly modify riverine hydrodynamic conditions while optimizing navigability. This study employs the MIKE21 hydrodynamic model to establish a two-dimensional numerical framework for assessing hydrological alterations induced by channel regulation in the Hui River, China. Through comparative simulations of pre- and post-project scenarios across dry, normal, and wet hydrological years, the research quantifies impacts on water levels, flow velocity distribution, and geomorphic stability. Results reveal that channel dredging and realignment reduced upstream water levels by up to 0.26 m during drought conditions, while concentrating flow velocities in the main channel by 0.5 m/s. However, localized hydrodynamic restructuring triggered bank erosion risks at cut-off bends and sedimentation in anchorage basins. The integrated analysis demonstrates that although regulation measures enhance flood conveyance and navigation capacity, they disrupt sediment transport equilibrium, destabilize riparian ecosystems, and compromise hydrological monitoring consistency. To mitigate these trade-offs, the study proposes design optimizations—including ecological revetments and adaptive dredging strategies—coupled with enhanced hydrodynamic monitoring and riparian habitat restoration. These findings provide a scientific foundation for balancing navigation improvements with the sustainable management of fluvial systems. Full article

Sediment transportation on coasts can be significantly affected by rivers, wave–wind effects, and human activities. As a result, undesirable effects such as shoaling or erosion may occur in fishery shelters. This study examines the “Sandıktaş a Fishery Shelter”, a coastal structure in the Eastern Black Sea region of Turkey, and its susceptibility to shoaling. Bathymetric measurements were performed within the nearshore and onshore, and sediment samples were taken periodically from selected points and analyzed in the laboratory. The characteristic grain diameters of the sedimentation were obtained. It was revealed that the average grain diameter was d₅₀ = 0.30–0.91, caused by an increase of 11,611 m³ in shoaling, which caused the decrease of 8 cm water depth that occurred between 2019 and 2022. The entrance of the fishery shelter has become progressively shallower, making it difficult for boats to navigate. Existing breakwater configurations played a role in trapping sediments, requiring optimized breakwater designs/modifications for improved sediment control. The Mann–Kendall test showed an increasing trend in sediment accumulation, particularly in coarser fractions. The findings highlight the necessity of periodic dredging and potential structural modifications to mitigate shoaling and ensure the long-term sustainability of the fishery shelter. Moreover, they emphasize the critical challenges caused by sedimentation in fishery shelters and provide data-driven recommendations for enhancing coastal engineering practices and maintenance strategies. 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

This paper deals with the dewatering and handling of dredged sediments in the context of sustainability and renewability of natural resources. Dewatering is a critical part of sediment management, as the high water content of dredged sediments becomes a challenge for transportation, final storage and/or recycling. This is why it is necessary to reduce their water content before transportation. Conventional methods suggest using land-based drained basins, which is a sustainable solution. However, this solution has certain drawbacks: dewatering the sediment is time-consuming and involves the use of large land areas. The main problem with this method of dewatering can be solved by proposing mechanical dewatering in the vicinity of the dredging operation. Once the sediment has been sufficiently dewatered, it should be shoveled and transported again. The proposed paper covers the study of the dewatering and shoveling ability of sediments. After introducing why dewatering is a critical phase in the recycling process of sediment, some techniques for dewatering large volumes of high-water sediments are briefly reported. Typical dewatering laboratory tests are detailed, demonstrating their usefulness for understanding the mechanisms of natural dewatering. A laboratory dewatering press machine is reported and the procedure used for a sediment sludge. The last section concerns a recent innovative test implemented for the study of the shoveling ability and adhesion of sediments. This study improves our understanding of the phenomenon of sediment dewatering, for both natural and mechanical dewatering. It also provides the protocols for typical laboratory tests on sediment dewatering and shoveling ability. Full article

This study comprehensively explores the intricate hydrodynamic and geomorphological processes that affect the Sulina Channel and bar area. It employs advanced hydrodynamic, wave, and sediment transport models to simulate the influence of marine currents, waves, and shipping traffic on sediment transport and deposition patterns, providing valuable insights for maintaining navigable conditions in the Sulina Channel. It is shown that sediment deposition is highly dynamic, particularly in the Sulina bar area, where rapid sediment recolonization occurs within one to two months after dredging. The simulation indicates that vessels with drafts of 11.5 m cause notable erosion. In comparison, drafts of 7 m have a minimal impact on sediment transport, emphasizing the importance of managing vessel drafts to mitigate sediment disturbances. This research highlights and quantifies the siltation phenomenon from the Black Sea to the mouth of the Sulina Channel, effectively addressing the challenges posed by natural and anthropogenic factors to ensure the Channel’s sustainability and operational efficiency. Full article

Sedimentation is the natural process of sediment transportation and deposition in quiescent water conditions. Sedimentation can affect the functionality of ports, harbours and navigation channels by reducing water depth, making navigation difficult, if not impossible. Different solutions are available to guarantee infrastructure functionality against sedimentation, with maintenance dredging being the most widely adopted. Alternative technologies for dredging have been developed and tested to reduce the environmental concerns related to dredging operations. Among other solutions, applying a sediment by-pass system based on a jet pump emerged as one of the most promising. While the existing literature covers the techno-economic aspects of sediment by-pass systems, the environmental impacts must be better evaluated and assessed. This paper aims to resolve this gap by evaluating, through the ReCiPe2016 life cycle assessment (LCA) methodology, the environmental impact of an innovative sediment by-pass system called an “ejectors plant”. The LCA results are based on the demonstrator established in Cervia Harbour in Italy, which was extensively monitored for 15 months during its operation. This paper shows how energy consumption during the operation phase highly affects the considered midpoint and endpoint categories. For example, the GWP100 of the ejectors plant, considering the Italian electricity mix, equals 1.75 million tons of equivalent CO₂ over 20 years, while under a low-carbon scenario, it is reduced to 0.17. In that case, material consumption in the construction phase becomes dominant, thus highlighting the importance of eco-innovation of ejectors plants to minimise oxidant formation. Finally, this paper compares the ejectors plant and traditional dredging through environmental LCA. The ejectors plant had a lower impact in all categories except for GWP-related categories. The sensitivity analysis showed how such a conclusion may be mitigated by considering different electricity mixes and maintenance dredging working cycles. Full article

Despite the fact that the first red tide reported on the coasts of the Iberian Peninsula was due to Lingulodinium polyedra, knowledge about their frequency and, particularly, about the environmental conditions contributing to bloom initiation is still scarce. For this reason, L. polyedra bloom episodes were observed and studied in three Galician rias during the summer season based on the 1993–2008 record database period; additionally, samples were collected in summer 2008. Proliferations of L. polyedra occurred in the rias of Ares and Barqueiro in June and August, respectively, while in the Ria of Coruña, they persisted from the end of June to early September. Red tides developed when the surface temperature reached 17 °C, with “seasonal thermal window” conditions, and when salinities were ≥30, i.e., an “optimal salinity window”; when these parameters were lower than these thresholds, cyst germination decreased. A cyst transport mechanism from sediments to the surface must also exist; this mechanism was found to be natural (tidal currents) in the ria of Barqueiro or anthropogenic (dredging) in the rias of Ares and Coruña. Surface temperatures during summer were usually favorable for cyst germination (85 to 100%) during the 1993–2008 period; however, water temperatures below 10 m depth only rarely reached the 17 °C threshold (2 to 18%). During this 16-year period, dredging activities could explain 71% (Coruña) and 44% (Ares) of the recorded bloom events. When a bloom episode developed in early summer, favorable conditions did not lead to a new red tide, probably due to the lag period required by cysts for germination. Moreover, blooms did not develop when high densities of diatoms (>1,000,000 cells·L⁻¹) remained in the water column as a result of summer upwelling pulses occurring in specific years. The temperature–sediment disturbance pattern found in this study provides a useful tool for the prevention of eventual risks resulting from red tides of this dinoflagellate. Full article

Sandy beaches high in recreation value make up 16% of the over 4000 km long shoreline of Estonia. The shore processes associated with climate change have remarkably accelerated over recent decades. Many sandy shores have suffered from strong erosion, including an excellent former beach at Valgeranna. The jetties, which were built in the 1860s to protect the navigation channel of Port Pärnu from clogging, have prevented natural sediment transport along the coast from south to north. At the same time, the sandy beach in Pärnu is expanding, and part of the sand accumulates with strong storms also in between the jetties, reducing the width of the shipping channel. The channel needs regular dredging, but, so far, the dredged sediment has been taken far away to the open sea and accumulated on the seabed. The current paper addresses the possibilities of using that sand for beach restoration in destructed and eroded areas. An overview of the applied methods and measurements during field studies is given. The results of modelling the processes of wave activity and sediment transport are discussed. The recycling of shore sediments is an important measure in sustainable coastal zone management. Different options and scenarios are analysed in order to find the most reasonable ways to bring sand back onto beaches and stabilize natural processes. Support from the state by working out respective laws and regulations would be motivating as well. Full article

The ornamental nursery industry is steadily growing in Europe, and a consequent increase in the demand for substrates related to container plant cultivations is expected in the coming years. Currently, substrates consist in part or entirely of peat, a non-renewable resource with concerns about its environmental impact due to extraction, transport, and use. Therefore, it is essential to focus on alternative materials, particularly waste by-products to be recycled as components of substrates to achieve more sustainable cultivations. In this study, substrates obtained by mixing co-composted dredged sediments (S) and green waste (GW) in different ratios (1:3; 1:1; 3:1) were tested for cultivation, and plant growth was compared with a control growing media (peat and pumice in a 1:1 ratio). The cultivation trial lasted for one year and was carried out on two potted ornamental evergreen shrubs (Photinia × fraseri and Viburnum tinus). The results showed that the plant growth parameters of both species, occurring in substrates with co-composted materials, were not significantly affected compared to the control, with the exception of below-ground biomass in V. tinus. Moreover, a Life Cycle Assessment (LCA) analysis was carried out to quantify the greenhouse gas emissions (GHG) deriving from the replacement of peat with the other proposed substrates. The functional unit was 10 L (Ø 24 cm) potted plants and the results were expressed in kg of CO₂ equivalent (kg CO₂eq). We demonstrated that the replacement of peat-based substrates with the alternative substrates was able to reduce the GHG emission by an average of 11.56 to 23.13%. Higher GHG emissions were related to the cultivation phase (0.9 kg CO₂eq/plant), and while comparing substrates, we obtained an average percentage reduction of 28.1% to 59.6%. Thus, our results suggest that co-composted mixtures of dredged sediments with green waste could be used as sustainable techno-soils for pot nursery cultivation of ornamental species with reduced environmental impact. Full article

The reduction in the usable capacity of reservoirs, which is linked to the ongoing silting phenomenon, has led to the need to remove sediments to allow the storage of greater quantities of water resources. At the same time, however, the removal of sediment from the bottom results in the need to manage a large quantity of materials, for which the current prospect of discharge is both economically and environmentally unsustainable. This research work concerns the assessment of the silting volume increment of the Camastra reservoir and the phenomenon of progressing speed based on topographic and bathymetric surveys carried out in September 2022 through the use of a DJI Matrice 300 RTK drone with ZENMUSE L1 LiDAR technology, multibeam surveys, and geophysical prospecting using a sub-bottom profiler. It was possible to estimate the increase in dead volume and compare this value with that obtained from the surveys through a literature calculation model and previous silting data. The used model, which slightly underestimates the silting phenomenon, estimates the volume of accumulated sediment from the original capacity of the reservoir, which is understood as the volume that can be filled with sediment in an infinite time, from which an amount is removed depending on the characteristic time scale of reservoir filling and the level of complexity of the silting phenomenon for a specific reservoir. Furthermore, there is evidence of an increase in the speed of sediment accumulation, which is linked to the more frequent occurrence of high-intensity and short-duration meteoric events caused by climate change, which can lead to an increase in erosion and transport phenomena. Further evidence is provided by the occupation of approximately 50% of the Camastra’s reservoir capacity, which makes sediment dredging policies and interventions a priority, contributing to the practical significance of the present study. In this regard, the main recovery and reuse alternatives are identified and analyzed to make the removal of accumulated material environmentally and economically sustainable, such as through environmental and material recovery applications, with a preference for applications for which sediment pretreatment is not necessary. Full article

Dredging is a common technique for managing eutrophication problems in waters, reducing the accumulation of pollutants by removing sediments from the bottom of water bodies. However, dredging can have complex impacts on lake ecosystems, and it is crucial to understand its benefits and mechanisms for the environment. In this paper, the dredged and undredged areas in the Caohai portion of Dianchi Lake were studied to analyze the effects of dredging on nitrogen–phosphorus transport and conversion and changes in nitrogen–phosphorus morphology content and its mechanisms by comparing the nitrogen–phosphorus morphology content and percentage, the nitrogen–phosphorus ratio, and the release contribution of the two areas. It was found that the ratio of stabilized nitrogen (SN) to stabilized phosphorus (SP) in the dredged area was lower than that in the undredged area and the BD-P and TOC content had a large turnaround at the 16–20 cm position of the sediment in the dredged area. The main conclusions were that the dredging would disrupt the internal equilibrium of the lake system for many years, with the greatest effect on the balance of the BD-P in the phosphorus forms of the sediment, and that the column cores of the dredged area at 0 to 16 cm might be newly accumulated sediments after the dredging project. However, with time, the distribution of nitrogen and phosphorus forms in the newly accumulated sediments will gradually reach a new equilibrium. In addition, dredging will also cause significant changes in the retention efficiency of nitrogen and phosphorus in the sediment, and the stable nitrogen and phosphorus forms will be released and transformed into unstable nitrogen and phosphorus forms. Full article

Proper orthogonal decomposition (POD) is used to examine the release of highly concentrated water–sediment mixture in water, with or without ambient current. This technique allows us to extract the dominant features in spatio-temporal data sets and the POD total energies associated to the base parameter of the decomposition. Both one-component and two-component POD techniques are, respectively, applied on data relative to the solid volume fraction and on the solid volume fraction velocities. The analysis is based on an experiment in the literature and data sets provided by a two-phase flow solid-fluid numerical simulation. For release phenomenon without ambient current, the analysis of the POD results highlights that the impact of the particle diameter on the solid phase dynamics and the particle dispersion is modest during the falling time, but that it becomes preponderant during the formation of a turbidity current. Aided by POD, the impact of the ambient current is studied for a given particle diameter. As the ambient current becomes strong, we can observe the effect of the resistance of the bottom against the water–sediment mixture transport. According to the strength of the ambient current, the POD results show that the dynamics of the release phenomenon have two different regimes on either side of a clearly identified threshold value. Full article

Estuaries around the world are facing numerous threats, including urbanization, industrialization, resource scarcity, and the impacts of climate change. To increase estuarine resilience, it is crucial to manage these ecosystems to maintain their functionality. Sediment transport resilience is a critical factor that affects the performance objectives of navigation, storm damage reduction, and ecosystem restoration. This paper focuses on an integrated resilient sediment transport risk management (IRSTRIM) approach for estuaries. The framework quantifies resilience indexes such as reaction amplitude, graduality, and recovery rates of “sediment transport” to “river and sea interaction” in the Arvand Estuary, the Persian Gulf. Additionally, three indexes, the tidal asymmetry index (TAI), saltwater intrusion vulnerability index, and infill rate, are developed to aid in resilient sediment management. The quantified indexes successfully incorporated tidal asymmetry, sediment characteristics, bed properties, and flow hydrodynamics. Different resilience and resistance management scenarios are evaluated using a decision support system. Based on the results, tidal barrier application, as a resilience scenario, is the best scenario, and the dredging scenario, as a resistance one, is the worst scenario. The reaction amplitude with a weight of 0.39, and the TAI with a weight of 0.27 are determined as the most effective indexes. Full article