Virginia Capes Range Complex Final Environmental Impact Statement

VACAPES Range Complex FEIS/OEISChapter 3 Affected Environment andEnvironmental Consequences3.1 – Bathymetry and Sedimentsexplosions and the accumulation of training debris on the ocean bottom. Factors that were included in theevaluation of impacts included the geographic dispersion of training activities, density of debris, andpersistence or decomposition of debris on the ocean bottom.The VACAPES Marine Resource Assessment (MRA) (DoN, 2007) was a key data source that was usedfor assessing the existing conditions for bathymetry and sediments. The MRA compiled and synthesizedavailable scientific literature, including information in journals, periodicals, theses, dissertations, projectreports, and other technical reports published by government agencies, private businesses, and consultingfirms. These included National Marine Fisheries Service (NMFS) reports, including stock assessmentreports, recovery plans, and survey reports. The MRA summarized the physical environment, includingmarine geology, circulation and currents, and hydrography for the study area. Unless otherwise indicated,the existing conditions information provided in this chapter was taken from the VACAPES MRA.Internet keyword searches were performed to determine if information was available that was notcaptured in the MRA. The searches on bathymetry and sediments produced a number of websites thatwere evaluated for information quality and relevance, and that were used as appropriate.3.1.1.2 Warfare Areas and Associated Environmental StressorsAspects of the proposed actions that likely would act as stressors to bathymetry and sediments wereidentified by analyzing the warfare areas, operations, and specific activities that would be associated witheach alternative. As shown in Table 3.1-1, four stressors would have at least one operation that wouldaffect bathymetry or sediments.Table 2.2-5 in Chapter 2 indicates the types of military expended materials (MEM) that would result fromeach alternative. The types of types of training materials and locations of use were detailed in Tables 2.2-6 and 2.2-7.3.1.2 Affected EnvironmentThe bathymetry and sediments features in the VACAPES Study Area are shown in Figure 3.1-1 andFigure 3.1-2.3.1.2.1 BathymetryWithin the VACAPES Study Area, the continental shelf has an average depth of 246 feet. Thecontinental shelf ranges in width from about 24 nm off Cape Hatteras to about 87 nm off Delaware Bay.It has a seaward gradient of less than 1:1,000 (Hollister, 1973; Kennett, 1982).The shelf break is the seaward limit of the continental shelf and the beginning of the continental slope. Atthe continental shelf break, the ocean bottom drops abruptly along the continental slope in a gradient ofabout 1:10. The continental slope, the most prominent physiographic feature along the mid-Atlanticcontinental margin, extends to water depths of between about 2,000 meters and 4,000 meters.Four submarine canyons, designated Norfolk, Washington, Accomac, and Baltimore, are found within theVACAPES Study Area. These large canyons dissect the continental slope and continue as deep-seachannels on the continental rise.The Chesapeake Bay is relatively shallow, with an average depth of 21 feet. The bay is shaped like ashallow tray, except for the large channel, believed to be remnants of the ancient Susquehanna River, thatruns the entire length of the bay. At the mouth of the bay, the channel terminates at a shallow sill that canrestrict deeper water flow into and out of the bay (Reshetiloff, 2004; Kemp, et al., 2005).3-2 March 2009