Showing papers on "Dredging published in 2021"
TL;DR: In situ inactivation by LMB is superior to dredging in the long-term control of sediment P loading, as indicated by a 360-day field investigation.
47 citations
TL;DR: Dredge sediments containing MPs were stored in piles on farmlands, whereby MPs were subsequently dispersed to surrounding soils and surface waters while awaiting a permanent disposal option.
38 citations
TL;DR: Dredging significantly reduced the N flux at the SWI, which was evident from the reduction of inorganic N release flux and N removal through denitrification and anammox, Therefore, sediment dredging has its advantages and disadvantages in managing internal N loading in lakes.
38 citations
TL;DR: In this paper, concern over environmental effects of dredging, disposal and the increasing unavailability of suitable disposal sites, has put pressure on engineers to improve dredged soils which are weak, have lo...
Abstract: Concern over environmental effects of dredging, disposal and the increasing unavailability of suitable disposal sites, has put pressure on engineers to improve dredged soils which are weak, have lo...
22 citations
29 Apr 2021
TL;DR: In this article, the authors show adverse side effects to dredging activities in several estuaries worldwide, i.e., flooding, erosion, and sedimentation of shipping fairways.
Abstract: Shipping fairways in estuaries are continuously dredged to maintain access for large vessels to major ports. However, several estuaries worldwide show adverse side effects to dredging activities, i...
17 citations
TL;DR: In this article, the authors constructed sediment budgets which quantify annual changes for the urbanized Rhine-Meuse Delta of the Netherlands, a typical urban delta experiences changing fluvial and coastal fluxes of sediment, engineering works and dredging and dumping activities.
Abstract: Deltas and estuaries worldwide face the challenge of capturing sufficient sediment to keep up with relative sea-level rise. Knowledge about sediment pathways and fluxes is crucial to combat adverse effects on channel morphology, for example, erosion which enhances bank collapse and increasing tidal penetration. Here, we construct sediment budgets which quantify annual changes for the urbanized Rhine-Meuse Delta of the Netherlands, a typical urban delta experiences changing fluvial and coastal fluxes of sediment, engineering works and dredging and dumping activities. The delta shows a negative sediment budget (more outgoing than incoming sediment) since the 1980s, due to anthropogenic intervention. Following a large offshore port expansion, dredging in ports and harbors in the region has doubled in the past 5 years, likely due to the induced change in net sediment fluxes. In addition, the deeper navigation channels, ports, and harbors are now trapping siltier sediment, changing the sediment composition in the mouth. The removal of sediment by dredging is adverse to the necessity for sediment in heavily eroding branches. To allow for sustainable sediment management in the future and to cope with sea-level rise, further measurements are required to properly quantify the amount of incoming sediment at the boundaries of the system and the internal mechanisms of transport. The varied response of the branches has important consequences for navigation, ecology and flood safety and management of the sediment in the system. These effects will be of pivotal importance in coming decades with similar implications for many urbanized deltas worldwide.
17 citations
TL;DR: In this article, the Apalachicola River in Florida was dredged from the 1950s for several decades, with disposal on sand bars, in open water on the channel margins, and on the floodplain.
14 citations
TL;DR: In this paper, sediment and water samples were collected from dredged and undredged regions around the gate-controlled estuary of northern Taihu Lake for laboratory experiments, in which they were subjected to different temperatures, depths, and disturbance levels.
Abstract: Estuarine zones are regarded as the ecotones connecting the rivers and lakes Sediment dredging is a conventional treatment technology that is widely used to remove the internal loading in estuarine zones worldwide However, what is the characteristic of nutrient release in the gate-controlled estuary and how long this practice is effective are still unclear Hence, sediment and water samples were collected from dredged and undredged regions around the gate-controlled estuary of northern Taihu Lake for laboratory experiments, in which they were subjected to different temperatures, depths, and disturbance levels The total nitrogen (TN) and total phosphorus (TP) concentrations of the dredged region were lower than those from the undredged region under stable hydrodynamic conditions A high dynamic release rate (R) of nutrients in the dredged sediments (RTN = 16475 mg/m2·d and RTP = 583 mg/m2·d) existed under dynamic release conditions (stirring speeds: 90 and 120 r/min) The effect of disturbance and temperature on release rate and nutrient form was completely different for the static and dynamic release cases The nutrient loads from dynamic release were 4–17 times greater than those from static release For unstable hydrodynamic conditions, the release rate from the bottom sediment exceeded that from the surface sediment in the undredged region These results indicated that, under stable hydrodynamic conditions, dredging improves long-term water quality However, dredging alone in unstable hydrodynamic conditions may not remove the potential risk of internal release in the long term Specific ecological and engineering measures should be combined with dredging practice to restore estuary habitats and minimize the release of internal pollutants
14 citations
TL;DR: In this paper, the authors focus on the molecula of urban environments, from the construction of ports to the dredging of access corridors for ships and the production of asphalt and concrete.
Abstract: From the construction of ports to the dredging of access corridors for ships and the production of asphalt and concrete, sand is an inextricable part of urban environments. Focusing on the molecula...
12 citations
TL;DR: The threshold values proposed by this study were lower and more effective to predict toxicity compared to international guidelines, indicating levels of contamination for this tropical region in which toxic effects may occur.
10 citations
TL;DR: In this article, a plume dispersion experiment carried out in the German license area for the exploration of polymetallic nodules in the northeastern tropical Pacific Ocean in 4200 m water depth was investigated numerically by employing a sediment transport module coupled to a high-resolution hydrodynamic regional ocean model.
Abstract: Predictability of the dispersion of sediment plumes induced by potential deep-sea mining activities is still very limited due to operational limitations on in-situobservations required for a thorough validation and calibration of numerical models. Here we report on a plume dispersion experiment carried out in the German license area for the exploration of polymetallic nodules in the northeastern tropical Pacific Ocean in 4200 m water depth. The dispersion of a sediment plume induced by a small-scale dredge experiment in April 2019 was investigated numerically by employing a sediment transport module coupled to a high-resolution hydrodynamic regional ocean model. Various aspects including sediment characteristics and ocean hydrodynamics were examined to obtain the best statistical agreement between sensor-based observations and model results. Results show that the model is capable of reproducing suspended sediment concentration and redeposition patterns observed during the dredge experiment. Due to a strong southward current during the dredging, the model predicts no sediment deposition and plume dispersion north of the dredging tracks. The sediment redeposition thickness reaches up to 9 mm directly next to the dredging tracks and 0.07 mm in about 320 m away from the dredging center. The model results suggest that seabed topography and variable sediment release heights above the seafloor cause significant changes especially for the low sedimentation pattern in the far-field area. Near bottom mixing is expected to strongly influence vertical transport of suspended sediment.
TL;DR: In this paper, the potential coupling of sediment management and bio-remediation is discussed, and the potential for such innovative sediment management to reduce dredging need and remediate contaminated mud in ports is discussed.
TL;DR: In this paper, bottom sediments from dam reservoirs in earth structures were used as research material, which, according to geotechnical standards, were classified as low permeable silt with high organic content.
Abstract: A possibility of using bottom sediments from dam reservoirs in earth structures was considered. Sediments from the Rzeszow reservoir (Poland) were used as research material, which, according to geotechnical standards, were classified as low permeable silt with high organic content. As fine, cohesive soil with a low coefficient of permeability, the sediments can be used in sealing elements of hydraulic engineering embankments. In order to verify the suitability of the sediments, stability and filtration calculations were carried out for embankments with a sealing in the form of a core made of the sediments. It was stated that by using a core made of sediments, the volume of seepage on the downstream side during continuous or variable backwater was significantly lower in relation to an embankment without a core, and the phreatic line did not extend to the downstream slope. It is estimated that, in the case of a planned dredging in Rzeszow Reservoir, the amount of dredged sediment would exceed 1.5 million m3, and therefore, the possibility of their economic use is essential. The search for materials that could replace natural soil in earthen structures is an important issue from both the ecological and economic points of view.
TL;DR: Barbier et al. as mentioned in this paper used a sediment transport model calibrated to modern conditions to assess the corresponding changes in sediment dynamics and found that sediment trapping during winter (and high river discharges) has increased more than twofold, owing to increased accommodation space, altered pathways of supply, and altered bed stresses and tidal asymmetries.
Abstract: Estuaries serve as effective sediment traps and critical interfaces between rivers and the coastal ocean, providing key infrastructure and ecosystem services (e.g., Guerry et al., 2012; Lotze, 2010; Lotze et al., 2006). Because of their prime location at the land-ocean boundary and rich species diversity, estuaries have also seen intense development pressure over the past several centuries. While some of this pressure has come in the form of overharvesting local species and degradation of water quality, many ecosystem changes result from physical restructuring of the estuary through dredging, spoils disposal, land reclamation and shoreline armoring, accelerated sediment delivery related to watershed denudation, reduced sediment delivery related to upstream damming and diking, and other sediment-related modifications (Barbier et al., 2011; Abstract Estuaries worldwide have experienced modifications including channel deepening and intertidal reclamation over several centuries, resulting in altered fine sediment routing. Estuaries respond differently based on preexisting geometries, freshwater and sediment supplies, and extents and types of modification. The Coos Bay Estuary in Oregon is a relatively small estuary with complex geometry that has been extensively modified since 1865. A sediment transport model calibrated to modern conditions is used to assess the corresponding changes in sediment dynamics. Over ∼150 years, channel deepening (from ∼6.7 to 11 m), a 12% increase in area, and a 21% increase in volume have led to greater tidal amplitudes, salinity intrusion, and estuarine exchange flow. These changes have reduced current magnitudes, reduced bed stresses, and increased stratification, especially during rainy periods. Historically, fluvially derived sediment was dispersed across broad, deltaic-style flats and through small tidal channels. Now, river water and sediments are diverted into a dredged navigation channel where an estuarine turbidity maximum (ETM) forms, with modeled concentrations >50 mg/L and measured concentrations >100 mg/L during discharge events. This “new” ETM supplies sediment to proximal embayments in the middle estuary and the shallow flats. Overall, sediment trapping during winter (and high river discharges) has increased more than two-fold, owing to increased accommodation space, altered pathways of supply, and altered bed stresses and tidal asymmetries. In contrast to funnel-shaped estuaries with simpler geometries and river-channel transitions, these results highlight the importance of channel routing together with dredging in enhancing sediment retention and shifting pathways of sediment delivery.
TL;DR: Experimental benthic dredging was conducted in an unfished, muddy area in the Baltic Proper to mimic the impact of trawling by removing surface sediment, with a focus on Benthic biogeochemical processes as mentioned in this paper.
TL;DR: In this article, the authors present a process-based model study, incorporating different strategies of dredging in an existing nonlinear sand wave model, and study the maintenance intervals and (cumulative) dredging volumes resulting from adopting a typical temporal strategy.
15 Mar 2021
TL;DR: In this paper, the effect of large-scale channel modifications via riverine dredging on flood dynamics in low-gradient river systems located in inland-coastal flood transition zones was investigated.
Abstract: The current study investigates the effect of large-scale channel modifications via riverine dredging on flood dynamics in low-gradient river systems located in inland-coastal flood transition zones. The study site is the Vermilion River in south Louisiana, US, which is characterized by complex flow regimes, reversal and bi-directional flows, presence of large swamps with significant river-swamp interactions, and large volumes of runoff contributions from lateral tributaries. The study aims to understand the interplay of these factors and how they modulate and get affected by different dredging approaches that vary in spatial extent and the modifications introduced to the channel. The study deploys a hybrid, one- / two-dimensional (1D/2D), hydrodynamic model that simulates flow and stage dynamics in the main river and its major tributaries, as well as the flow exchanges with the interconnected swamp system. Overall, the results show that the dredging activities can significantly alter the flow regime in the watershed and affect flow exchanges between the river and the swamp system. In terms of flooding impact, only dredging approaches that are extensive in spatial extent and modifications to channel longitudinal slope can result in sizeable reductions in flood stages. However, these benefits come at the expense of significant increases in the amplitude and inland propagation of the Gulf tidal wave. On the other hand, less-extensive dredging can still provide moderate and spatially limited flood mitigation; however, they further expose downstream communities to increased levels of flooding, especially during more frequent events. The results reveal that while dredging can increase the hydraulic conveyance of the river system, the large runoff volumes delivered by the urbanized tributaries seem to outweigh the added improvement in the in-channel storage, thus reducing the anticipated flood relief. The results suggest that a watershed-centered approach, instead of a riverine-centered approach is needed for flood management in these systems so that the relative benefits and tradeoffs of different mitigation alternatives can be examined.
TL;DR: Bucket dredging to mine and extract gold and tin from rivers is a global industry that has had a range of negative effects on physical environments as discussed by the authors, such as the destruction of riparian soil.
Abstract: Bucket dredging to mine and extract gold and tin from rivers is a global industry that has had a range of negative effects on physical environments. These include the destruction of riparian soil p...
TL;DR: In the Pearl River Estuary (PRE), China, the surface sediments have been intensely disturbed by human activities as discussed by the authors, and the mean surface sediment grain size in PRE is distributed between 5 and 8 ϕ, while the sorting coefficient of the sediments vary between 0.39 and 4.53.
TL;DR: Water Injection Dredging (WID) is a hydrodynamic technique involving the turbation and downstream displacement of fine sediments using vessel-mounted water jets as mentioned in this paper.
TL;DR: In this article, the authors evaluate the effectiveness of guaranteeing a minimum water depth over time at the port entrance at Marina of Cervia (Italy), wherein the first industrial scale ejector demo plant has been installed and operated from June 2019.
Abstract: The need to remove deposited material from water basins is common and has been shared by many ports and channels since the earliest settlements along coasts and rivers. Dredging, the most widely used method to remove sediment deposits, is a reliable and wide-spread technology. Nevertheless, dredging is only able to restore the desired water depth but without any kind of impact on the causes of sedimentation and so it cannot guarantee navigability over time. Moreover, dredging operations have relevant environmental and economic issues. Therefore, there is a growing market demand for alternatives to sustainable technologies to dredging able to preserve navigability. This paper aims to evaluate the effectiveness of guaranteeing a minimum water depth over time at the port entrance at Marina of Cervia (Italy), wherein the first industrial scale ejector demo plant has been installed and operated from June 2019. The demo plant was designed to continuously remove the sediment that naturally settles in a certain area through the operation of the ejectors, which are submersible jet pumps. This paper focuses on a three-year analysis of bathymetries realized at the port inlet before and after ejector demo plant installation and correlates the bathymetric data with metocean data (waves and sea water level) collected in the same period. In particular, this paper analyses the relation between sea depth and sediment volume variation at the port inlet with ejector demo plant operation regimes. Results show that in the period from January to April 2020, which was also the period of full load operation of the demo plant, the water depth in the area of influence of the ejectors increased by 0.72 mm/day, while in the whole port inlet area a decrease of 0.95 mm/day was observed. Furthermore, in the same period of operation, the ejector demo plant’s impact on volume variation was estimated in a range of 245–750 m3.
TL;DR: In this paper, the authors evaluated for the first time the discards and impact of mechanized clam dredging on the Catalan coast and found that a large proportion of the catch (between 67-82% weight) is discarded.
Abstract: There is an important small-scale fishery using mechanized dredges and targeting clams (mainly wedge clam Donax trunculus and striped venus clam Chamelea gallina) along the Catalan coast (NW Mediterranean Sea). This study evaluated for the first time the discards and impact of mechanized clam dredging on the Catalan coast. To this end, three surveys were performed on board standard clam vessels (September and November 2016 and January 2017). Surveys were conducted in the three main clam fishing areas (Rosas Bay, South Barcelona and Ebro Delta). The composition of discards and the impact caused to discarded species was assessed using a three-level scale (undamaged; minor or partial damage; and lethal damage). Our study revealed that a large proportion of the catch (between 67–82% weight) is discarded. Even though about 63% of the discarded species were undamaged, 11% showed minor or partial damage and 26% lethal damage. Infaunal and epifaunal species with soft-body or fragile shells were the most impacted by the fishing activity (e.g. the sea urchin Echinocardium mediterraneum (~89%) and the bivalve Ensis minor (~74%)). Our results showed different levels of impact by target species and fishing area.
TL;DR: In this article, the authors investigated the dispersion of the suspended sediment plume and its interaction with coastal currents in the Patos Lagoon estuary using TELEMAC-3D and SEDI-3d models.
Abstract: Management of estuarine systems under anthropogenic pressures related to port settlement and development requires thorough understanding about the long-term sediment dynamics in the area. In an era of growing shipping traffic and of ever larger ships; millions of tons of bottom sediments are dredged annually all over the world and the major question concerning dredging operations is not whether they should be done, because it is obvious that they are extremely important and necessary, but where the dredged sediments can be disposed of with the least possible ecological impact. The present study involves the evaluation of transport trends of dredged material from a turbid estuary disposed of in four different open ocean disposal sites using numerical model techniques, aiming to contribute to minimizing potential environmental impacts and maximizing efficiency of the dredging operation. The study is carried out in southern Brazil, investigating the fate of dredged material from the Port of Rio Grande, located inside the Patos Lagoon estuary. Simulations were carried with the TELEMAC-3D model coupled with the suspended sediment (SEDI-3D) module and incorporating results from the wave module (TOMAWAC) to evaluate the dispersion of the suspended sediment plume and its interaction with coastal currents. This modeling structure proved to be a valuable tool to study the hydrodynamics and sediment transport pathways in estuarine and coastal areas. Results indicate that the natural Patos Lagoon coastal plume was observed under the predominant ebb flows and NE winds, promoting fine sediment entrapment south of the mouth of the lagoon (in front of Cassino Beach). The dispersion plumes in the disposal sites responded to the wind intensity and direction and did not present any transport tendency towards Cassino Beach. Part of the dredged sediment disposed of in the proposed alternative sites located in deeper areas (Sites B and C) left the site and was transported parallel to the coast (SW–NE direction) according to the wind direction (NE–SW). The area where the disposal sites were located took around 4 days to recover from the dredging operation and reach the usual suspended sediment concentrations and the actual Port of Rio Grande Licensed Site for dredged material proved to be the best alternative among the investigated options.
TL;DR: In this paper, the authors used a random forest algorithm to extract historical bathymetric series from satellite images to determine how the seabed has behaved and how the entry of sediments into the study area occurs.
Abstract: One of the fundamental tasks in the maintenance of port operations is periodic dredging. These dredging operations facilitate the elimination of sediments that the coastal dynamics introduce. Dredging operations are increasingly restrictive and costly due to environmental requirements. Understanding the condition of the seabed before and after dredging is essential. In addition, determining how the seabed has behaved in recent years is important to consider when planning future dredging operations. In order to analyze the behavior of sediment transport and the changes to the seabed due to sedimentation, studies of littoral dynamics are conducted to model the deposition of sediments. Another methodology that could be used to analyze the real behavior of sediments would be to study and compare port bathymetries collected periodically. The problem with this methodology is that it requires numerous bathymetric surveys to produce a sufficiently significant analysis. This study provides an effective solution for obtaining a dense time series of bathymetry mapping using satellite data, and enables the past behavior of the seabed to be examined. The methodology proposed in this work uses Sentinel-2A (10 m resolution) satellite images to obtain historical bathymetric series by the development of a random forest algorithm. From these historical bathymetric series, it is possible to determine how the seabed has behaved and how the entry of sediments into the study area occurs. This methodology is applied in the Port of Luarca (Principality of Asturias), obtaining satellite images and extracting successive bathymetry mapping utilizing the random forest algorithm. This work reveals how once the dock was dredged, the sediments were redeposited and the seabed recovered its level prior to dredging in less than 2 months.
TL;DR: Results showed that after 65 days, soft, black, muddy and hypoxic sediment with high organic matter content and a characteristic foul odour was transformed into well-oxygenated sediment, which had a low organic Matter content and had lost its initial shiny black colour and odour.
Abstract: The occurrence of hypoxic muddy sediments on shallow beaches and other sheltered areas is a well-known environmental problem, which negatively affects coastal areas, tourism potential, the public use of beaches and sediment biodiversity. The usual solution is limited to dredging and removal of sludge to a landfill site. In this study, a laboratory-scale experiment was performed to determine the effectiveness of two technologies: a modification of air sparging and a new approach based on injecting oxygen-saturated seawater in hypoxic muddy sediments (oxygen-saturated seawater injections method), for remediating sludge in coastal sediments, minimizing environmental impact respect to dredging. Our results showed that both technologies significantly increased dissolved oxygen content in pore water, facilitating the oxidation of more than 90% of the organic matter, and other reduced inorganic compounds such as sulphide, with the consequent increase in sulphate concentration from 0.3 to 3.0 g·L−1. Moreover, a rise of redox potential from − 258 mV to above 200 mV, and a dramatic drop in chemical oxygen demand were also indicators that oxic conditions had been restored. After 65 days, soft, black, muddy and hypoxic sediment with high organic matter content and a characteristic foul odour was transformed into well-oxygenated sediment, which had a low organic matter content and had lost its initial shiny black colour and odour. The main difference between both technologies was the depth influenced by sediment remediation; oxygen-saturated seawater injections affected deeper areas than clean pressurized air injections.
TL;DR: In this paper, the authors discuss the importance of maintaining navigable waterways through dredging, especially as global transport and cargo loads increase, and the need for rapid techniques to e...
Abstract: Maintaining navigable waterways through dredging is vital to society and the economy, especially as global transport and cargo loads increase. Decision makers require rapid techniques to e...
TL;DR: In this article, the authors provide an update of the water quality conditions over Burullus lake by carrying out a wide water sampling program that covers the entire perimeter of the lake with an emphasis on the most problematic areas.
TL;DR: In this article, the authors used a hydrodynamic and sediment transport process-based model to simulate maintenance dredging in a macrotidal estuary: the Seine Estuary.
Abstract: This study used a hydrodynamic and sediment transport process-based model to simulate maintenance dredging in a macrotidal estuary: the Seine Estuary. This sandy-muddy estuary allows access to two major ports (Le Havre and Rouen). The model accounts for sand and mud dynamics and was previously validated for turbidity and morphodynamic coupling. Dredging is schematised as a physical process responding to simulated seabed evolutions. In coherence with port practices, (i) numerical dredging is conducted when sediment depositions exceed nautical depth limits determined by port authorities; (ii) dredged sediment are released in the water column above dumping sites. The model successfully reproduced the amount of sand and mud dredged in harbors and fairways (7MT/year) without any drift along 10 years. Moreover, the dredged quantities appeared to be considerably higher than the estuarine turbidity maximum (ETM) mass, which was successfully simulated by the model. The model was used to study relationships between maintenance dredging requirements and hydro-meteorological forcings. Dredging requirements are related to forcings in different ways depending on the exposure of dredged areas to waves, currents and ETM. Le Havre harbor and fairway are sensitive to storms, as 75% of the dredging activity is due to waves higher than 1m. The entrance of Rouen fairway equally responds to tidal range, river discharge and waves. Variabilities in dredging requirements differ depending on the type of sediment. For instance, at the entrance of the Seine navigation channel, mud dredging is strongly correlated to tidal range and secondarily to river discharge, while sand dredging is dominantly related to waves. A specific simulation (not including local wind-induced circulation) showed that the low contribution of waves to mud dredging was explained by materials in suspension hauled off-site. This process is induced by westerly winds that occurred together with waves. On the other hand, mud dredging increases with tidal amplitude in areas of intense tidal currents, and presents a counter clock-wise hysteresis with tidal amplitude, which can be compared to the one followed by the ETM mass. In addition, the dependence of mud dredging on river discharge appears to be related to the proximity of the ETM, the main source of fine sediment, which location shifts downwards when river discharge increases. At an inter-annual scale, variability in the temporal distribution of hydrometeorological forcings leads to 50% variation of annual dredged masses. In conclusion, this study has improved the understanding of the estuarine dynamics responsible of maintenance dredging.
TL;DR: It is suggested that sluggish water circulation inside these topographic depressions coupled with higher SOC rates does result in persistent low bottom O2 conditions inside these dredge pits well beyond the duration of the seasonal hypoxia period in this region.