from the Western hemisphere. High 

 flows are particularly noticeable 

 from late May to early July as snow 

 melt runoff from several, mountain 

 ranges averages 20,300 m /s. The 

 effect is magnified by spring tides 

 that exceed 3 m. Estuarine hydraulic 

 forces combine to naturally deepen 

 sites adjacent to jetties, peninsu- 

 las, or bridge openings. Dredging is 

 never required at these sites since 

 navigation channel depths may be ex- 

 ceeded by 3 m to 20 m. 



There is an annual removal of 

 3,000,000 m of sediments from the 

 lower Columbia river estuary with 

 most returned to the water. Es- 

 tuarine sediment deposition can 

 adversely impact many groups and 

 species of aquatic life. Particle 

 size change, smothering, and rein- 

 troduction of toxic substances are 

 several factors which can alter a 

 natural biological system. The 

 National Marine Fisheries Service 

 (NMFS) is vitally interested in 

 minimizing adverse impacts to eco- 

 nomically important fish as well as 

 food organisms they utilize. The 

 Corps of Engineers (COE) is charg- 

 ed with the responsibility of main- 

 taining a 12-m deep, 180-m wide 

 (40ft x 600ft) navigation channel for 

 ocean shipping through the Columbia 

 River estuary. The principal means 

 of sediment removal to river km 32 

 is by hopper dredge which results 

 in an inwater disposal. Sediment 

 disposal of material dredged near 

 the mouth is often placed in the 

 ocean but several sites are utili- 

 zed within the estuary. Concern 

 over the continuing effect of 

 dredge material on demersal finfish 

 and shellfish by NMFS and COE sug- 

 gested the agencies investigation 

 of alternative sites. 



In an earlier NMFS study, Dur- 

 kin (1975) indicated relatively few 



finfish and shellfish off the Colum- 

 bia River's North Jetty, whereas 

 comparable sampling at nearby sites 

 revealed greater numbers of fish. 

 These results seemed to indicate the 

 water turbulence off the North 

 Jetty caused biological instability 

 resulting in a low standing crop of 

 demersal organisms. This concept, 

 when applied to an estuarine situ- 

 ation, indicates use of similar ha- 

 bitats for sediment deposition 

 rather than continued use of exist- 

 ing controversial inwater disposal 

 sites . 



A biological inventory of sev- 

 eral hydraulically dynamic sites by 

 NMFS was proposed to the Portland 

 District COE in order to determine 

 if estuarine hydraulic scour sites 

 normally had low biological stand- 

 ing crop, were unstable, and sup- 

 ported species tolerant of stress. 

 The concept was accepted by the 

 COE, and inventory sampling was 

 scheduled for the conclusion and 

 beginning period of normal hopper 

 dredging activity. It was empha- 

 sized by NMFS that should a site 

 have apparent biological deficien- 

 cies more intensive sampling would 

 precede and follow any deposition 

 test by COE hopper dredges. 



METHODS AND MATERIALS 



Four sites were selected for 

 inventory studies, each near the 

 navigation channel and in the lower 

 18 miles of the estuary (Figure 1). 

 Sites were named after nearby land 

 promontories or structures. Thirty 

 pelagic finfish surveys were made 

 with a 200-m purse seine whereas 

 forty demersal finfish surveys were 

 made with an 8-m shrimp trawl. Each 

 sample effort was five minutes in 

 duration. Purse seine and trawl sets 



437 



