AN EVALUATION OF AQUATIC LIFE FOUND AT FOUR HYDRAULIC SCOUR SITES 



IN THE COLUMBIA RIVER ESTUARY SELECTED FOR 



POTENTIAL SEDIMENT DEPOSITION 



Joseph T. Durkin, Travis C. Coley, Keith Verner, and Robert L. Emmett 



National Marine Fisheries Service, Hammond Biological Field Station 

 Coastal Zone & Estuarine Studies, Northwest and Alaska Fisheries Center 



Seattle, Washington 



ABSTRACT 



Substantial scouring of estua- 

 rine sediment occurs from flushing 

 of a major river system with an an- 

 nual spring freshet of 20,300 m /s. 

 The effect is heightened by diurnal 

 marine water intrusion combined with 

 spring tides having ranges exceeding 

 3 m. Estuary depth is maintained 

 by these forces at the end of jet- 

 ties, promontories, and adjacent 

 bridge openings. Hydraulic stress 

 in these areas suggests biological 

 instability, a low standing crop 

 and occupancy by species tolerant 

 of such physical conditions. Be- 

 cause inwater sediment disposal at 

 sites with low biological activity 

 is preferable to deposition at bio- 

 logically rich and stable sites, 

 scour sites were investigated for 

 potential dredge deposition. Bio- 

 logical inventories of aquatic life 

 were conducted in October, November 

 1978 and May 1979, at four diverse 

 scour sites in the Columbia River 

 estuary, river km 4 to river km 24. 

 Investigative timing was related to 

 the completion and initiation of 

 normal maintenance dredging. 



Benthic infauna, epifauna, and 

 pelagic; fish were studied as well 

 as food utilization of dominant fin- 

 fish. The 71 sampling efforts pro- 

 duced 42 species of finfish consist- 

 ing of 31,870 individuals. Also 

 captured in this sampling were 4 

 species of decapod crustaceans re- 

 presenting 4,957 epifauna. Numer- 

 ically important benthic inverte- 

 brates included amphipods and cope- 

 pods. Inventory studies indicated 

 low suitability for sediment depo- 

 sition due to biological richness 

 at the Tongue Point and Interstate 

 Bridge sites. Jetty A site was 

 biologically poor, and has poten- 

 tial suitability as a deposition 

 site. Tansy Point site may be 

 suitable for depositon at pre- 

 determined times. Inventory eval- 

 uation studies should be tested 

 under controlled deposition condi- 

 tions preceding sustained usage. 



INTRODUCTION 



High volume flows characterize 

 the Columbia River, the Nation's 

 second greatest river and the lar- 

 gest flowing into the Pacific Ocean 



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