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Dredging

About: Dredging is a research topic. Over the lifetime, 3300 publications have been published within this topic receiving 28325 citations.


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ReportDOI
01 Mar 1999
TL;DR: In this article, an approach for estimating the suspended-sediment source from cutterhead, hopper, and clamshell dredges is presented, which involves modification of an existing method developed from limited field data.
Abstract: : The purpose of this technical note is to herein presents an approach for estimating the suspended-sediment source from cutterhead, hopper, and clamshell dredges. The approach involves modification of an existing method developed from limited field data. These estimates are needed to provide input to a numerical model called SSFATE (Suspended Sediment FATE) that is being developed under the Dredging Operations and Environmental Research (DOER) Program.

8 citations

01 Dec 2001
TL;DR: In this paper, the authors present an inventory of the standards for sediment plumes caused by dredging as applied in different countries and limits set at dredging projects with their backgrounds.
Abstract: In many dredging contracts, environmental restrictions on sediment plumes must be met. Sediment plumes cause reduced light penetration, increased concentration of suspended solids and sedimentation which all can affect benthic ecosystems. Contractors confronted with these requirements get the impression that these regulations are not well founded. Because the costs of dredging increase with stricter limits, it is important to know why restrictions are necessary. Goal of this investigation was to review and clarify some aspects of the situation. This report about requirements for sediment plumes caused by dredging is divided in three parts. In the first part consists of an inventory of the standards for sediment plumes caused by dredging as applied in different countries and limits set at dredging projects for sediment plumes with their backgrounds. The possible effects of sediment plumes on different ecological environments are listed and the extent to which limits are based on well documented environmental effects is discussed. There is no international regulation or legislation about uncontaminated sediment plumes caused by dredging. It seems impossible to make limits universal because the effects of sediment plumes are site and time specific. Site specific because ecosystems and natural conditions vary from site to site and time specific because they depend on tide, day or night, seasons and hydrodynamic conditions (like monsoons, breeding and hatching seasons, currents). Per project has to be decided if the environment is sensitive to sediment plumes and whether limits are required. It is concluded that requirements for sediment plumes in dredging contracts are often not well founded. Limits usually are copied from other projects or reports without much investigation and/or based on water criteria standards or community perception. The second study focuses on the effects of sediment plumes on one specific ecosystem: coral reefs. Probably this is the most sensitive marine ecosystem. The literature on the effects of suspended sediment and turbidity on corals is reviewed and restated in the context of dredging. The effects are evaluated in terms of acceptable damage, for which a recovery time of one year is used, considering the long-term equilibrium situations, or natural conditions, of coral reefs. Most published experiments were focussed on the sublethal effects. It appears that, taking in account the observed species and sediment sizes, corals can clear themselves from 100 mg/cm2/day and can handle concentrations of suspended solids up to 100mg/l for a few days. Drastic lethal effects on corals were experimentally observed only when burial was complete. There must be an intermediate dose of sediment, but no data exist in this range. Corals can not handle burial caused by dredging activities for more than, depending on the natural conditions, 1 day to 1 week. To put the data in perspective and to give direction to future discussions about norms and limits, it is proposed to work with dose-effect curves as used in toxicology. This approach also indicates that experiments with higher sediment doses where partial but significant damage occurs and where recovery times are registered must be done to achieve higher precision in the conclusions. The impact of sediment plumes probably can be minimised by modifying dredging techniques. Dredging also can be confined to specific time windows from which sensitive seasons of the ecosystem and conditions that adversely affect the distribution and impact of the plume can be excluded. Another possibility to reduce the impact of sediment plumes caused by dredging is to remove the sediment with a flowdredge. Further an approach is given to calculate the extent of possible effects caused by dredging plumes. The third part is a contribution to the methodology of how to implement and control a set limit in real time during a dredging operation. A probabilistic description of sediment plume behaviour in the Øresund Fixed Link Dredging project is given. Very many measurements were done during this project, which gives the opportunity to investigate the minimum but required frequency of measurements to check if the actual turbidity or concentration of suspended solids complies with the limits. When measurements are taken continuously the probability that the limits are exceeded without being noted is small, but continuous measurement methods are expensive. The objective of this study is to optimise the number of measurements at a location, i.e. the number of ship crossings through a sediment plume, given the costs and the accuracy of the turbidity measurements, by a statistical data analysis. Turbidity is assumed to be a random variable and the inherent uncertainty of turbidity is described by a Binomial-Exponential (BE) distribution function. The data contain natural background values as well and the BE distribution separates the background values from the turbidity due to dredging. The BE distribution has two distribution parameters, which are calculated. as well as their uncertainty in dependence on the number of ship crossings. The statistical uncertainty of the probability distribution function of the parameters and of the turbidity depends on the number of ship crossings. The maximum allowable turbidity is probabilistically determined as function of the number of ship crossings. With this approach the number of ship crossings can be determined for a required reliability. A method is proposed and illustrated with the data to optimise the number of ship crossings by optimising total costs, consisting of the costs of ship crossings and the gains of having a smaller uncertainty. Also a sensitivity analysis of the cost parameters is given. With this method, when the costs (disadvantages) of having a smaller accuracy of the turbidity probabilistic distribution function are assessed in relation to the Øresund case and assuming the same plume behaviour, the number of ship crossings can be optimised for other cases. List of relevant terminology Background conditions Natural turbidity and concentration of suspended solids Benthic organisms, benthos Organisms that spend all or most of their life at the bottom of the water column Bleaching A phenomenon in which Zooxanthellae microalgae leave a coral, resulting in coral whitening, under the stress of high water temperature, low salinity or high turbidity. If such a stress is removed the coral will recover but if bleaching continues for an extended period, coral will die. Coral reef A coral reef is defined as the topography formed by hermatypic organisms that are mainly composed of coral. In a coral reef, animals called coral live in a colony. The reef includes the area where corals grow and the seaweed and seagrass habitats and sandy or muddy places around the coral. Cnidaria A phylum of animals including corals and jellyfish Hermatypic The property of corals that produce a skeleton of calcium carbonate in a coral reef. Most of the corals that coexistent with Zooxanthellae are hermatypic. Mitigation The policy of trying to eliminate the effects of development on the environment, through avoidance, minimization, correction, reduction, and compensation. Natural conditions Climate-, background-, and hydrodynamic conditions Phylum A taxonomic group of similar classes having common properties Planula A coral or other cnidarian larva Zooxanthellae Single-cell algae, which are symbiotic with hermatypic corals and other animals List of notation and abbreviations

8 citations

01 Jan 1997
TL;DR: The proceedings, Dredging and management of Dredged material, consists of papers presented at GeoLogan '97 Conference held in Logan, Utah, July 18, 1997 as discussed by the authors.
Abstract: This proceedings, Dredging and Management of Dredged Material, consists of papers presented at GeoLogan '97 Conference held in Logan, Utah, July 18, 1997. With dredging of ports and management of dredged material becoming a national issue, geotechnical engineers are increasingly involved with these matters. This publication discusses the latest environmentally sensitive dredging techniques, decontamination and reuse techniques for dredged sediments, and regulations on the dredging and management of dredge residues.

8 citations

Patent
22 Oct 1981
TL;DR: In this article, a setter is used to set up upper and lower limiting values suitable to the conditions of dredging site and also the moving range of the cutter 4, and an arithmetic unit is provided to compare and calculate the set value and detected value.
Abstract: PURPOSE:To raise the efficiency and accuracy of dredging operation as much as possible as well as simplify the dredging operation and save its energy by a method in which set value suitable for the conditions of dredging site and detected value obtained in actual dredging operation are compared and calculated, and on the basis of the results, a dredger is automatically controlled. CONSTITUTION:A detector 17 by which to detect the suction negative pressure 26 and discharge pressure 29 of a dredging pump 24, the flow rate of mud water flowing in a dredging pipe 25, the sludge content 28 of the mud water, the load 12 to be applied to a soil cutter 4, the load 11 to swing a dredger 1, and the position of the cutter is provided. A setter 32 by which to set up upper and lower limiting values suitable to the conditions of dredging site and also the moving range of the cutter 4 is also provided. Furthermore, an arithmetic unit 31 to compare and calculate the set value and detected value is provided. On the basis of the calculation results of the arithmetic unit 31, the operations of a ladder 7, a swing winch 10m and a cutter 4 are controlled, and dredging work is automatically performed at given dredging width and depth.

8 citations

Journal ArticleDOI
TL;DR: In this paper, a comparison of 1883-1978 hydrographic surveys shows that riverbed dredging of the Cecina river and lowland reclamation of the Ombrone river resulted in a widespread erosion of their submarine deltas.

8 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
2023189
2022438
202170
2020119
2019150
2018131