Contaminated Marine Sediments Assessment and Remediation (1989) / Chapter Skim
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Physical Transport Investigations at New Bedford, Massachusetts
Physical Transport Investigations at New Bedford, Massachusetts
Pages 351-364
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From page 351... ...
Army Engineer Waterways Experiment Station ABSTRACT Migrations of sediment, sediment-associated contaminant, and dissolved materials released by proposed dredging and disposal operations were predicted as part of an engineering feasibility study of dredging cleanup. Highly contaminated sediments blanket most of upper New Bedford Harbor (the Acushnet River estuary)
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From page 352... ...
FIELD DATA COLLECTION Figure 1 shows the layout and approximate dimensions of New Bedford Harbor, which is located on the north shore of Buzzards Bay and is the estuary of the Acushnet River. The mean tide range at New Bedford Harbor is 1.1 m, and the spring range is 1.4 m.
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From page 353... ...
' 4 5 6 COGGESHALL STREETS——-a I NSET AT COGGESHALL STREET BRIDGE \ ~ POPES ISLAND · ODE GAGE =2 ~= ~~ ~ it.
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From page 354... ...
Mechanisms for upstream tidal pumping were evaluated. Maximum TSM resuspension produced by the highest tidal currents, usually occurring near low water, were transported in the flood direction, producing upstream tidal pumping.
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From page 356... ...
Tidal biases were removed from the raw tidal net fluxes by summing net-f~ow fluxes (freshwater volume times mean concentration) and tidal pumping fluxes (the difference between ebb- and flood-mean concentrations times the mean tidal volume)
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From page 357... ...
This testing device was developed for this study to safely test contaminated sediments. It was a closed-conduit sediment water tunnel, open to the air only at a small expansion chamber.
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From page 358... ...
Plume predictions for dredging in upper New Bedford Harbor indicate that on average about 35 and 29 percent of the material released at the dredge head will escape from 50 and 100 m of the site, respectively. The remainder settled within this radius.
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From page 359... ...
Results indicated that only the finest or slowest settling fraction escaped from the CAD, and that the escape of this fraction was almost complete. Moderate current Figure 5 shows an a three-dimens tonal Estuarine Numerical Modeling Computer codes RMA-2V and RMA-4 of the TABS-2 numerical modeling system (Thomas and McAnally, 1985)
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From page 360... ...
Results from the hydrodynamics model were used to construct an 8 - tidal - cycle sequence for nput to the sediment transport model ~ Sediment transport modeling was performed to estimate escape probabilities from the upper harbor for various sediment materials which might be resuspended as a result of dredging. Transport of resuspended material was modeled as a steady mass loading at specified points.
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From page 361... ...
Average transport rates under the Coggeshall Street Bridge were computed for flood and ebb tidal phases after the model had reached dynamic equilibrium. The difference between ebb and flood transport rates, normalized by the mass loading rate, represents the escape probability.
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From page 362... ...
SUMMARY AND CONCLUSIONS Assessments of sediment and contaminant migration out of the upper New Bedford Harbor for proposed dredging and disposal were made from information and analyses developed by field, laboratory, and various model studies. Upper New Bedford Harbor is a sheltered area with low current speeds, typical of many areas where contaminated sediments reside.
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From page 363... ...
See Figure 6. Results from the dredge plume model indicated that an average, weighted by occurrence frequencies, of about 33 percent of the resuspended material will escape from a 100-m radius of the dredging site.
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From page 364... ...
Report 1 of 12, New Bedford Superfund Project: Acushnet River Estuary Engineering Feasibility Study Series. Technical Report EL-88-15.
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