Showing papers on "Dredging published in 1976"

Floating apparatus for weeding and dredging waterways

Abstract: A floating apparatus including a barge having a plurality of hydraulically actuated stabilizers for positioning the barge at a location. An hydraulically actuated, articulated boom is rotatably mounted on the barge and provided with any of a plurality of instrumentalities at the free end thereof for weeding, dredging or cleaning waterways.

Environmental aspects of dredging in the coastal zone

Abstract: (1976). Environmental aspects of dredging in the coastal zone. C R C Critical Reviews in Environmental Control: Vol. 6, No. 2, pp. 91-109.

Turbidity caused by dredging

Abstract: This paper discusses the turbidity due to two dredging methods. One is turbidity caused by pump dredger, and the other is grab dredger, using a closed type grab bucket and a conventional one. These experiments were conducted out in the field. In the former case, the paper shows the relationships between turbidity and dredging conditions. Turbidity is measured around the cutter head and at the several points farther than 20 m from the central point of dredging. In the latter case, the experiment concentrates on the comparison between the properties of turbidity caused by the closed type grab bucket, which has covers attached to rods and shells.

Dredging and Its Environmental Effects

Abstract: Proceedings of the Specialty Conference on Dredging and its Environmental Effects, held in Mobile, Alabama, January 26-28, 1976. Sponsored by the Task Committee on Dredging and its Environmental Effects of the Committee on Sedimentation of the ASCE Hydraulics Division and the Alabama Section of ASCE. Dredging and Its Environmental Effects contains many papers covering a broad range of relevant issues in dredging. Topics include legislative impacts on dredging, how dredging relates to environmental policy acts, types of dredging, and the ultimate fate of suspended material in estuaries. These proceedings will be of interest to both practitioners and researchers working with dredging or concerned with its environmental effects.

Techniques for reducing turbidity associated with present dredging procedures and operations

Abstract: Techniques for reducing turbidity associated with present dredging procedures and operations fall principally in the categories of the cutter, ladder, suction, hull, pipeline, connections, barges, tenders, personnel, inspection, contracts, plans, and specifications These techniques consist principally of good dredging procedures already known but not always followed by dredging contractors and their personnel When these techniques are consistently applied, not only will dredge-induced turbidity be reduced, but economical operation will prevail in most instances Other techniques for reducing dredge-induced turbidity tend to increase dredging costs and should be used only when necessary Dredge-induced turbidity is normally apparent only in the immediate vicinity of the dredge plant and the levels of this turbidity are not usually as high as those created by open-water disposal of the dredged material In addition to applying good dredging techniques to reduce turbidity, better inspection is needed on Corps of Engineers (CE) and CE-related projects More CE supervision of dredging operations needs to be implemented More training is required for inspectors, whether CE or private-company personnel Consideration should be given to a nationwide school or short courses where dredge personnel could obtain basic technical knowledge of dredging Contracts should clearly and uniformly specify requirements for turbidity-reduction measures and measurements Contracts should be written to include smaller dredges Where turbidity is a problem, dredging should be accomplished when natural background levels of turbidity are high /Author/

Dredged material research problems and progress

Abstract: The U.S. Army Corps of Engineers has $30 million earmarked for the DMRP. The author describes how the program may be optimized. Some suggested approaches to this research are presented. The primary concern of this research is the significance of chemical contaminants in dredged sediments. Under certain conditions, disposal of dredged sediments (even independent of chemical composition) can be adverse to aquatic life, particularly benthic organisms at the disposal site. This situation is related to the problem of burying of organisms. This kind of problem must be approached differently from that associated with chemical contaminants in dredged sediments.

Decrease in Harbor Maintenance Dredging through the Use of Pile Dikes and Related Structures Together with an Analysis of Estuarine Sedimentation Problems

Abstract: : Most harbors in the continental United States of interest to the U.S. Navy are located within estuaries. Because of the presence of fresh water as well as salt water, special sedimentation problems are created. Eight sources of sediments in an estuary are discussed. Most estuaries are the repository for fine-grained sediments ranging from clay to fine sand in size which would eventually fill the estuary. This report discusses a system to remove sediments by means other than dredging. Part of the system is to entrap estuarine sediment by means of pile dikes to prevent it from entering dredged shipping channels. The pile dike, which consists of two to seven rows of clusters of concrete piles extend perpendicularly to the river bank. The rows are spaced approximately 5 feet apart; the clusters 15 feet to 20 feet apart. Stringers are placed between each row and secured to pile clusters; and piles are driven about 20 feet to 30 feet below the bottom of the estuary. The second part is to remove periodically the accumulated sedimentary material by a back-flushing and slurry pumping system. The slurry may be pumped to barges, used as landfill, or pumped to off- shore spoil disposal areas such as submarine canyons.

Dredging Pollution and Environmental Conservation in the United States

Abstract: Dredging operations are often needed for the improvement of a channel and/or harbour area. Unavoidably the water resources close to the dredging site will be contaminated to some degree. This paper initially presents the main feature and operation methods of new-work dredging and of maintenance dredging. The former comprises the improvement (i.e. deepening or widening) of a channel and/or harbour area mainly by removing stones and compacted sediments which were deposited through geologic ages. The latter is employed mainly to remove the loose sediments which tend to fill up previously excavated channels and harbours. The clamshell dredge, the dipper dredge, the pipeline dredge, and the hopper dredge, are four common types of dredges that are used for river and harbour excavation by the U.S. Army Corps of Engineers. Their functions, operations, and cost data, are indicated.In general only the sediments excavated from maintenance dredging operations are polluted with obnoxious or toxic contaminants that are detrimental to the land, air, and water, environment. The sources of pollution that are associated with the channel and harbour sediments may be categorized as being from municipal and industrial discharge, storm-runoff, agricultural runoff, soil erosion, and accidental spills.Typical dredged materials from Ashtabula and Fairport Harbors in Ohio were collected and analyzed for investigation. It was found that the sediments varied widely, in their physical and chemical characteristics, between harbours and even at different locations within each harbour. Nevertheless, the pollutants in the dredged materials of a specific harbour (or channel) can be generally characterized. Settleability of the dredging samples was investigated in detail. It was observed that oil and grease and heavy-metals were intimately associated with sediments and could be removed with settlement of solids.The current dredging practices in the U.S.A. includes the disposal of dredged materials in open sea, open lake, along-shore diked areas, off-shore diked areas, abandoned strip-mine areas, and other disposal sites. Due to the excellent settleability of the dredged materials, it is desirable that the polluted dredgings be stored on a disposal site for some time prior to any treatment. A disposal area can be used to create new land if satisfactory fill is produced. The satisfactory fill can be the non-polluted dredged materials from the new-work dredging operations, or well-treated sediments from maintenance dredging operations. The treated sediments or particles should be free from oil and grease, from toxic heavy-metals, and from any substances which are putrescent, deleterious, or odorous. They should not cause any organic decomposition or ground-water contamination.The dredged materials can be separated into the sediment and the supernatant water (i.e., spoil) by settling. From the dredging-settling data presented in this paper, it appears that sufficient settling of dredging in a diked disposal area, followed by discharge of supernatant to Great Lakes water, will not contravene the proposed Great Lakes Water Standards, and so the goal of water resources conservation could be achieved.

Effects of dredging and disposal on some benthos at Monterey Bay, California

Abstract: : The specific objectives of this study were to document; (a) Natural temporal variations in benthic assemblages and changes related to substrate stability, (b) the initial effects of dredging and subsequent recolonization, (c) the effects of disposal of dredged material on the benthos and subsequent recovery of the fauna, and (d) the role of faunal distribution and reproductive abilities upon recovery or recolonization of disturbed areas The natural benthic assemblages differed with changes in the amount of sediment movement or substrate stability Many animals characterized the relatively stable submarine ridges but few inhabited the unstable terrace slopes of the submarine canyon in Monterey Bay, California (Monterey Canyon); even fewer animals were found in channeled areas Dredging in the channel areas removed 60 percent of the original population of bottom animals After 15 years, the number of individuals was low but the species diversity and evenness indexes were higher than before dredging The ultimate recovery of a disturbed area depends upon the timing of the action in relation to the reproductive cycles and distributive abilities of the benthic organisms in the area Underwater disposal of dredged material should be made in unstable bottom areas if possible

Water quality effects of a dredging disposal area.

Abstract: The effect of the settling-basin concept on the water quality associated with a typical disposal site for polluted maintenance dredgings, and the fate of pollutants during a typical dredging and disposal cycle were determined between Aug.20, 1972 and Dec.20, 1972 in Toledo, Ohio. Over 100 samples of slurry influent, overflow effluent, ground water, ambient river water, bottom sediments, and material from the hopper bins and overflow waters were collected and analyzed for standard physical, chemical, and microbiological parameters. It was concluded that only a small fraction of the pollutants are discharged via the overflow weir into the ambient river water; this is attributable to the fact that the polluting substances tend to associate with the solid particles, which settle out of the suspension and are retained within the diked enclosure. The water quality of the effluent resembled that of the ambient river water used as a carrier to pump the dredgings in slurry form from the hopper dredge into the disposal area.

Sediment transportation and deposition models for mobile bay, alabama

Abstract: The objective of this study is the application of hydrodynamic and material transport mathematical models for Mobile Bay in predicting sediment transport and deposition profiles within the bay system. Of particular importance are the seasonal variations of sediment distribution which are critically influenced by current patterns within the estuary. Both point and non-point sources of sediment will be included in the analysis. Results will be presented in two ways. The first or long term variations in sediment distribution will be assessed by correlation with tidal cycle average velocities at various locations within the bay. Calculated distribution patterns will be compared with observed bathemetic data over the past century. The net effect of the construction of the Mobile ship channel on deposition patterns within the bay will also be evaluated. Secondly, short term variations in sediment transport and deposition resulting from man-made and natural disturbances will be analysed using a sediment transport model. This model will include deposition, bulk fluid transport and resuspenslon characteristics and will be capable of predicting localized, short term sediment patterns from maintenance dredging operations within the bay. Model trend results will be compared with field data collected during recent dredging activities and high altitude photographic data obtained for the bay area.