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Modeling the Fate and Water Quality Impact of the Proposed Dredged Material Placement at Site 104

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Final rept.,

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Several numerical models CH3D-WES, MDFATE, STFATE, SURGE, and CEQUAL-ICM have been employed to provide information on potential losses of dredged material proposed to be placed at Site 104 in the Upper Chesapeake Bay and on potential water quality impacts. Placement of the material was assumed to either be from bottom-releasing barges or from hydraulic pump out from a barge with the material released near the bottom. CH3D-WES is a three-dimensional hydrodynamic model that was employed to provide bottom shear stresses and vertically averaged currents to the MDFATE model. MDFATE computes the building of sediment mounds because of the placement of material at the site and the possible erosion of sediment from those mounds. STFATE computes the fate of dredged material from the moment of its release into the water column until its initial placement on the seafloor. Therefore, STFATE provided estimates of the potential sediment loss to the water column during placement. SURGE was employed to provide insight into the effect of bottom slopes on the extent of bottom surges generated by the impact of the dredged material striking the seafloor and gravitational forcing. An existing CEQUAL-ICM model of the entire Chesapeake Bay was applied to assess the impact of the placement of dredged material at the site on the water quality of the overlying waters. Model results show that up to about 17 percent of the placed material could potentially leave the site with bottom release of the dredged material from barges and about 6 percent might potentially leave the site if the material is pumped out of the barge and placed near the seafloor. However, because of factors such as using erosion parameters that are probably slightly larger than would exist for a composite of material from all the proposed dredging sites and using bottom shear stresses that are likely too large, these predicted sediment losses are considered quite conservative.

Subject Categories:

  • Hydrology, Limnology and Potamology
  • Solid Wastes and Pollution and Control
  • Water Pollution and Control

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