Northwest Fisheries Science Center

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Document Type: Contract Report
Center: NWFSC
Document ID: 6181
Title: Benthic and epibenthic invertebrates, fishes, and sediments at and adjacent to a proposed new site for Area D, an in-water dredged-material disposal site in the Lower Columbia River, 1991. Final report
Author/Editor: George T. McCabe, Susan A. Hinton, Robert L. Emmett
Publication Year: 1993
Publisher: National Marine Fisheries Service
Contracting Agency: U.S. Army Corps of Engineers. Portland, Oregon
Contract Number: E96910017 and E96910040
Pages: 42
Date: 1993

The U.S. Army Corps of Engineers maintains navigation channels in the Columbia River estuary, requiring annual dredging and disposal of millions of cubic yards of bottom sediments.  A submerged disposal site in the lower estuary, commonly referred to as Area D, no longer provides safe operating depths for large dredges.  Therefore, the corps has proposed relocating the disposal site immediately downstream from the present Area D.

In February 1991, the corps contracted the National Marine Fisheries Service to conduct biological surveys in March and June 1991 at the proposed site for Area D and at two adjacent areas.  The goal of these surveys was to provide baseline information concerning species composition and abundance of benthic invertebrates, Dungeness crabs (Cancer magister), shrimps, and fishes.  Subsequently, the corps requested additional surveys in September and December 1991.

In summary, we found benthic invertebrate densities significantly higher in the proposed Area D than in the deeper-water area, and significantly lower than in the reference area (P < 0.05).  Fishes were generally more abundant in the proposed Area D than in the reference and deeper-water areas.  Juvenile or adult Dungeness crabs were generally not abundant in any of the areas during the four surveys.  In three of the surveys, shrimp densities were higher in the deeper-water area than in the proposed Area D.  The data indicate that the deeper-water area has lower standing crops of benthic invertebrates and fishes than the proposed Area D, and may be a more suitable site for relocating the present Area D.  In assessing the potential of the deeper-water area as a dredged-material disposal site, it is essential to determine the direction of sediment movement out of this area.  The deeper-water area is located southwest of the opening between East and West Sand Islands.  If it is determined that dredged material deposited in the deeper-water area would be carried by tidal currents through this opening into Baker Bay, then the deeper-water area should not be considered for disposal of dredged material.

Notes: Final Report to U.S. Army Corps of Engineers, Contracts E96910017 and E96910040, 42 p.