Reports
Placement, consolidation, and erosion studies at open-water placement Site 92, 2004-2005 (Year 7)
2006, Panageotou, W.
File Reports, Coastal and Estuarine Geology, File Report 2006-01
Abstract
The seventh year (Year 7) of dredged sediment placement at Site 92 occurred between October 20, 2004 and March 5, 2005. A clamshell-bucket dredge excavated approximately 1.11 million cubic yards of clayey-silt sediment from the Chesapeake & Delaware Canal approach channel. The sediment was placed via bottom-release scows into a designated drop zone near the center of Site 92. Placement occurred in water depths that ranged from -16.5 to -24 feet MLLW.
The volume of placed sediment identified by the Maryland Geological Survey at the completion of placement was 0.95 ±0.10 mcy. This represented a mean volumetric deficit of 0.08 million cubic yards, or 8%. The total area covered by placed sediment was 0.87 million square yards, or 179.2 acres. The majority of the deposit was 2 to 6 feet thick with a maximum thickness of 7 feet.
The placed sediments underwent elevation, volumetric, and sediment mass changes during the following six months. Consolidation and erosion reduced the sediment thickness by 1 to 2 feet. There was a 7% volumetric reduction at one month, 13% at three months, and 26% 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, there was approximately a 26% loss of sediment mass (-117,800 tonnes) at Site 92.
Year 7 placement utilized 0.70 mcy, or approximately 10%, of the site volume capacity. To date, dredged sediment placement used approximately 46% of the total site volume capacity, and 54% is available for future placements. After accounting for consolidation, approximately 5.51 mcy of cut-channel sediment volume can occupy the remaining site volume capacity at Site 92.
