Reports
Placement, consolidation, and erosion studies at open-water placement Site 92, 2007-2008 (Year 10)
2009, Offerman, K.A.; Panageotou, W.
File Reports, Coastal and Estuarine Geology, File Report 2009-01
Abstract
The tenth year (Year 10) of dredged sediment placement at open-water placement Site 92 occurred between November 29, 2007 and February 3, 2008. A clamshell-bucket dredge excavated approximately 0.64 million cubic yards (mcy) of clayey-silt sediment from the Chesapeake & Delaware (C&D) Canal approach channel. The sediment was placed via bottom-release scows into a designated drop zone in the western, central portion of Site 92. Placement occurred in water depths that ranged from -16 to -17 feet (ft.) mean lower low water (MLLW).
The volume of placed sediment identified by Maryland Geological Survey (MGS) at the completion of placement was 0.44 ± 0.10 mcy. This represented a mean volumetric deficit of 0.17 mcy, or 27.6%, after accounting for a bulking factor of 0.95. The total area covered by placed sediment was 0.89 million square yards (msy), or approximately 183.4 acres. The majority of the deposit was 1.0 to 3.0 ft. thick with a maximum thickness of 3.8 ft.
The placed sediments underwent elevation, volumetric, and sediment mass changes during the following ten months. The maximum thickness of the placed sediments decreased by 1.6 ft., from 3.8 ft. at completion of placement to 2.2 ft. at ten months. There was a 46.4 % volumetric reduction at ten months following placement. It was estimated that approximately one-sixth of the volumetric change resulted from consolidation and five-sixths from erosion. During the combined placement and post-placement periods, a sediment mass loss of approximately 58.5% (-179,755 tons) occurred at Site 92.
Year 10 placement utilized 0.24 mcy, or approximately 3%, of the site volume capacity. To date, dredged sediment placement has used approximately 59% of the total site volume capacity, and 41% is available for future placements.
