Dredged Material Placement Site Capacity Analysis for Navigation Improvement Project at Grays Harbor, WA.

摘要

The U.S. Army Engineer District, Seattle requested that the U.S. Army Engineer Research and Development Center, Coastal and Hydraulics Laboratory perform a numerical modeling study for the purpose of performing a dredged material placement (DMP) site capacity analysis for a Navigation Improvement Project for the Federal Navigation Project at Grays Harbor (GH), WA. The project would deepen the inner harbor channel reaches up to two additional feet to reach the authorized project depth of -38 feet. This would require dredging up to an additional 1.7 million cubic yards (MCY) in addition to the 2.8 MCY available for dredging through the Corps O&M program. A project goal is to maximize the dredge volume capacity within existing open water sites while ensuring navigation safety. This study provides estimate of the short- term and long term fate of channel deepening sediments as well as the annual O&M dredge material placed at the DMP sites in the entrance channel to GH. The model simulations indicated a) potential navigation obstruction for the scenario with additional 2.0 MCY; b) potential obstruction for the scenario with additional 1.0 MCY; and c) channel obstructions were significantly reduced at the PCDS for Scenario 3 where the maximum channel obstruction was 170 ft. Two recommendations are made: a) Scenario 3 is preferred as it produces a minimal obstruction to the navigation channel and less channel sedimentation; and b) Modify placement strategy at the SJDS by placing more material in the eastern half than in the western half of the site rather than the uniform placement strategy used at present.