TABLE NO- 3 



MAIN STEM VflLLMIETTE RIVER AT WILLAJTETTE FALLS 

 Mean monthly flows in cubic feet per second * 



Month June July August September 



* Data supplied by Portland District Office, Corps of Engineers 



Interpretation of Results 



Reviewing the dissolved oxygen profiles listed in Table 2, the 

 combined effects of reaeration and dilution appeared fully adequate 

 to maintain the quality of the main stem water above Wilsonville well 

 within the accepted tolerance limits of cold-water fishes. Below 

 Wilsonville, however, a rapid deterioration in water quality occurred 

 during the low-flow period. The degradation of water culminated in an 

 oxygen block (i.e., less than five parts per million) which appeared 

 in the lower river betv;een July 6 and 19, 1949o Between those dates, 

 the block developed over its maximum range, namely upstream to a point 

 below Wilsonville or, roughly, within the confines of the slackwater 

 reach locally known as the "Newberg Pool**. The block persisted through^ 

 out the entire lower river area until it was dissipated by increasing 

 river flows sometime between September 2 7 and October 12. More than 

 five parts per million of dissolved oxygen were found throughout the 

 river to its confluence with the Columbia on October 12, 



Patently, the formation and lifting of the Willamette River oxygen 

 block is not a function of water flows exclusively for such factors as 

 hours of sunshine, water temperature and turbidity, and the seasonal 

 variations in pollution loading also play important roles. Generally 

 speaking, however, water flows would be a — 'if not the — dominant 

 factor. 



The station at Sellwood Bridge has been selected as a reference 

 point to illustrate the formation and lifting of the block. River 

 flow data supplied by the Portland District Office, Corps of Engineers, 

 and dissolved oxygen concentrations are plotted in Figure 1. These data 



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