Ocean Dredged Material Disposal Site (ODMDS) Authorization and Short-Term FATE (STFATE) Model Analysis: 2014-2015 Working Group Findings Report
Coastal and Hydraulics Laboratory Vicksburg United States
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The U.S. Army Corps of Engineers USACE dredges hundreds of millions of cubic yards of sediment from Federal ports, harbors and waterways annually. The USACE Navigation Data Center reports on average 42 of dredged material is placed offshore in Offshore Dredged Material Disposal Sites ODMDS. Regulation of dredged material placement within waters of the United States and ocean waters is a shared responsibility of the USACE and U.S. Environmental Protection Agency USEPA under the Marine Protection, Research, and Sanctuaries Act MPRSA, also called the Ocean Dumping Act and the Clean Water Act CWA. Dredged sediments placed offshore must have limited contaminants and be shown to have minimal impact on benthic species. The Short-Term FATE of dredged material placed in open water STFATE model was created by USACE to assist with dredge material placement impact assessment. STFATE enables the computation of the physical fate of dredged material disposed in open water and simulates the movement of the disposed material as it falls through a water column, spreads over the bottom and is transported and diffused as suspended sediment by the ambient current. In 2013, STFATE model outputs resulted in operational restrictions on several projects in USACE districts in the South Atlantic Division SAD region. A working group was established to address operational restrictions such as dredging vessel bin load restrictions, restricted release zones and other issues that impacted the efficiency and cost of dredging. The working group evaluated the sensitivity of inputs into the STFATE model and found grid cell size, dredge vessel velocity and heading, water density gradient, and application factors all had significant impacts on model output. The working group found that applying a more specific, technically defensible application factor produced model outputs that result in unrestricted dredging operations in USACE Mobile District, Mobile Harbor O and M project.