Northwest Fisheries Science Center

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Document Type: Contract Report
Center: NWFSC
Document ID: 7758
Title: Portland Harbor pre-dredge and disposal study
Author/Editor: Theodore H. Blahm, Joseph T. Durkin, Robert J. McConnell, Lawrence G. Davis, Travis C. Coley
Publication Year: 1979
Publisher: National Marine Fisheries Service
Contracting Agency: U.S. Army Corps of Engineers. Portland, Oregon
Contract Number: DACW57-78-F-0575

The Portland Harbor study proposal specified three data collection efforts:  before, during, and after disposal of dredged material (from the Willamette River) at Columbia River mile 101.  Each effort was to include benthic invertebrate counts, general water quality, finfish abundance, and analysis of fish stomach contents.

A preliminary survey was conducted on 15, 16, and 17 May 1978.  Subsequently the overall study was cancelled because the Washington State Department of Ecology would not grant the required permits.

This report outlines data collected during the preliminary survey.  Water quality data are minimal because that particular portion of the sampling was to be done 1-2 d prior to the disposal operation, which did not occur.  Based on preliminary collections, we concluded the following:

  1. Benthic abundance and diversity at the disposal site (and in and near the ship channel habitat) is much less than off-channel habitat areas of the lower Columbia River and its estuary.
  2. Fish abundance compared favorably with that recorded in earlier studies in the Columbia River.
  3. Stomach contents of fish captured during the study consisted mainly of insects, Amphipoda, Bivalvia, and Oligochaeta.
  4. Water quality at the disposal site was within natural limits expected during the sampling period.
  5. Increased turbidity and decreased dissolved oxygen was evident near the dredging operation (in the Willamette River) and in Ross Island.  However, it is questionable if the degree of degradation exceeds that which occurs naturally in the Willamette River.