Sedimentation Control to Reduce Maintenance Dredging of Navigational Facilities in Estuaries Report and Symposium Proceedings (1987) / Chapter Skim
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Session C: Optimizing Dredging Procedures
Session C: Optimizing Dredging Procedures
Pages 177-238
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From page 177... ...
SESSION C OPTIMIZING DREDGING PROCEDURES CHAIR Henry B .
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From page 178... ...
Army Engineer Waterways Experiment Station Although there is no one type of dredging apparatus designed solely for work in an estuary, the majority of estuarine dredging in the United States is performed by one of three kinds of conventional dredges. In addition, there are many types of nonstandard dredging equipment or techniques that can be used in an estuarine environment.
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From page 179... ...
has a clamshell bucket capacity of 50 yd3. As with other types of bucket dredges, the grab or clamshell must depend on hopper barges to carry material away ; the farther the distance between dredging and disposal, the more barges are needed to keep a steady flow of excavation.
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From page 180... ...
As an example, some modern hopper dredges are equipped to automatically shunt low-density suction material overboard (Figure 4) , allowing the hoppers to be filled only with more productive higher-density slurry.
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.. _3'i _~= _a suction dredge components are its pumps, power plant, swing winches, spuds, and discharge pipeline.
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From page 190... ...
b. The foregoing pertains not only to projects on which dredging operations are relatively continuous throughout the year, but also to those projects on which dredging is performed periodically and by application of this additional dredging principle dredging intervals could be extended with attendant savings or justified needs of commerce can be satisfied.
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From page 191... ...
The key to the effectiveness of advance maintenance is the depthshoaling rate relationship at the site being considered. Three basic scenarios will be discussed: the channel shoaling rate increases dramatically with depth; the channel shoaling rate is independent of depth; and the channel shoaling rate increases only slightly with depth.
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From page 192... ...
advance maintenance could be used over the above depth range to reduce the required dredging frequency without any penalty from overall dredging volumes. If the channel shoaling rate increases only slightly with depth, the cost of advance maintenance must be evaluated considering the increased overall maintenance dredging volumes versus reduced dredging frequency and the improved project quality.
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From page 193... ...
Prom 1952 to 1962, no advance maintenance was used on the project; from 1962 to 1976, 3 to 5 ft of advance maintenance was used. The following tabulation summarizes the shoaling volumes and dredging intervals with and without advance maintenance.
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From page 196... ...
The first example is the TABS-2 numerical modeling system, used to study sediment transport in Kings Bay, Georgia, by the Hydraulics Laboratory at the Waterways Experiment Station. The primary purpose of the model investigation was to estimate the required maintenance dredging which would result from navigation channel enlargement.
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From page 197... ...
In many cases the addition of advance maintenance to a project causes some increase in the amount of material trapped, which means that the increased shoaling rate must be weighed against the reduction in dredging frequency or improved project quality to determine the worth of advance maintenance. Since the potential benefits can be substantial, advance maintenance should be given consideration in any navigation channel requiring periodic maintenance.
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From page 198... ...
U.S. Army Engineer Waterways Experiment Station Environmental considerations during dredging operations focus primarily on water quality changes.
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would occur only under combined conditions of extremely high suspended solids and high oxygen demand. Dissolved oxygen depressions observed during dredged material disposal operations are higher (> l.O mg/liter)
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From page 206... ...
The processes acting under conditions of dredged material disposal are either too slow or are too quickly reversed to allow sediment constituents to become dissolved.
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From page 207... ...
Nutrients Quantitative information about the release of nutrients during dredging operations is not available. Qualitative information on the behavior of nitrogen and phosphorus compounds during dredged material disposal in open water can be viewed as applicable as long as the differences in dredging and dredged material disposal operations are recognized in terms of the concentrations and volumes of sediment that they suspend.
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From page 208... ...
BIOLOGICAL CONSIDERATIONS Restrictions (most commonly seasonal) are applied to federal and permit dredging projects in order to protect sensitive life history stages of important aquatic animals from the physical and chemical alterations of aquatic habitats caused by dredging operations.
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Vicksburg, Miss.: U.S. Army Engineer Waterways Experiment Station.
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Letter report to the U.S.-Army Engineer District, Baltimore, prepared through the Dredging Operations Technical Support Program, U.S. Army Engineer Waterways Experiment Station, Vicksburg, Mississippi.
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From page 218... ...
Army Engineer Waterways Experiment Station.
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1973. Evaluation of effects of channel maintenance dredging and disposal on the marine environment in southern Puget Sound, Washington.
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From page 222... ...
. In hydrographic surveying, two basic measurements are made continuously: water depth and boat position.
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From page 224... ...
Laboratories. Photograph courtesy of Ross Efficient large-scale survey operations require much more electronic equipment than a depth sounder alone.
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From page 228... ...
to "multipath" problems. HYDROGRAPHIC SURVEY System Components The previous sections dealt with the individual depth and positioning units of a hydrographic survey system.
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Army Engineer Waterways Experiment Station, CE. Ingham, A
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From page 232... ...
Army Engineer Waterways Experiment Station (Retired) In 1962, I conducted a brief study of Savannah Harbor, Georgia to determine how shoaling rates and patterns in the harbor had responded to several changes in length and depth of the navigation channel.
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From page 234... ...
, which was by far the most drastic of those accomplished during the period covered by the study, increased total shoaling of the harbor by only about l5 percent, compared to much larger percentage increases for the earlier increases in length and/or depth. This finding suggested that shoaling in Savannah Harbor is probably source-limited to about 7
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From page 236... ...
While I am unable to make direct cost comparisons for maintenance dredging of Savannah Harbor under preand post-improvement plan conditions, it is certain that the improve~nent plan provides substantial monetary savings for the following reasons: 1. Almost 60 percent of ache total maintenance dredging is performed in ache sediment trap where only limited movement of the dredge is required and there is no interference with dredging operations by ship movements, thus maximiz ing dredge efficiency.
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