Reports
Placement, consolidation, and erosion studies at open-water placement Site 92, 2006-2007 (Year 9)
2008, Offerman, K.A., and Panageotou, W.
File Reports, Coastal and Estuarine Geology, File Report 2008-01
Abstract
The ninth year (Year 9) of dredged sediment placement at Site 92 occurred between December 6, 2006 and March 13, 2007. A clamshell-bucket dredge excavated approximately 0.86 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 141.8-acre designated drop zone in the northern portion of Site 92. Placement occurred in water depths that ranged from −16 ft to −22 ft mean lower low water.
The volume of placed sediment identified by Maryland Geological Survey at the completion of placement was 0.63 ± 0.09 mcy. This represented a mean volumetric deficit of 0.29 mcy, or 31.5%, when compared to the average of the dredged volumes reported by the contractor and the U.S. Army Corps of Engineers, Philadelphia District. The total area covered by placed sediment, 0.86 million square yards, or approximately 177.5 acres, was slightly greater than the drop zone area. The majority of the deposit was 1.0 to 4.0 ft thick with a maximum thickness of 6.0 ft.
The placed sediments underwent elevation, volumetric, and sediment mass changes during the following six months. The maximum thickness of the placed sediments at six months was 4.3 ft, a decrease of 1.7 ft. There was a 47.8% volumetric reduction at six months following placement. It was estimated that approximately one-quarter of the volumetric change resulted from consolidation and three-quarters from erosion. During the combined placement and post-placement periods, the placed sediments experienced a sediment mass loss of approximately 59.7% (-241,961 tons) at Site 92.
Year 9 placement utilized 0.33 mcy, or approximately 5%, of the site volume capacity. To date, dredged sediment placement has used approximately 56% (3.91 mcy) of the total site volume capacity, and 44% (3.09 mcy) is available for future placements.
