Table 3. — Mean daily 



spill (S.) and. total floiv (T.), in 100 c.tn.s. (hundreds of oubic meters per second), at different 

 Columbia River dams, February-November 1966 



The. higliest nitrogen saturation during 1966 

 occurred in June. Concentrations ranged from 112 

 to 140 percent ; most of the samples were above 

 120 percent (fig. S). These values remained high 

 tlirough August between Grand Coulee and Priest 

 Rapids Dams. On July 11 and August 1, however, 

 the river equilibrated rapidly between Priest 

 Rapids and McNary Dams. Concentrations in the 

 forebays dropped from an average of 1152 percent 

 at Priest Rapids Dam to an average of 109 per- 

 cent at McNary Dam. Spilling at Bonneville Dam 

 tiien increased the saturation to above 120 percent 

 downstream from Bonneville. The rapid equilibra- 

 tion of gas content between Priest Rapids and 

 McNary Dams during July and August was jirob- 

 ably caused by the increased circulation of water 

 in the unimpounded river area below Priest 

 Rapids and the lower total flow and spill volumes 

 at Priest Rapids and Ice Harbor Dams (table 3). 



In September, Columbia River flows had de- 

 creased further and spilling had almost ceased at 

 all dams; tliis cjiange precipitated a marked reduc- 

 tion in the saturation of nitrogen at all stations — 

 only five samples were above 110 percent. Satura- 

 tion continued to decrease in October and was well 

 below 110 percent — ranging from 88.4 percent at 

 Rocky Reach Dam to 100.6 percent at Grand 

 Coulee Dam. Water temperatures in October 

 ranged from 16.1° to 18.6° C. (60.8-65.5° F.), and 

 the average temperature was about 1° C. lower 

 than in September. The lack of spilling and lower 

 water temperatures accounted for the decrease in 

 saturation from August to September. 



In the last survey during 1966, on November 7, 

 the saturation was not significantly different from 

 that in October 1966 (or November 1965). 



DIURNAL VARIATIONS 



During a 24-hour period (June 30 and July 1, 

 1966) of moderately high saturation in the forebay 

 of The Dalles Dam, nitrogen concentrations 

 varied only 0.6 p.p.m. from a maximum of 18.6 

 p.p.m. (114 percent saturation). Spill volumes at 

 The Dalles Dam were nearly constant for the 24- 

 hour period. 



SEASONAL VARIATIONS IN THE SNAKE RIVER 



Sami^les from the tailrace below the spillway of 

 Ice Harbor Dam in the Snake River (station 15) 

 indicated a seasonal variation in amount of nitro- 

 gen similar to that in the Columbia River; i.e., 

 normal saturation before spill releases increased 

 saturation as spill releases increased and de- 

 creased saturation as spill releases subsided. The 

 timing of the cycle differed from that in the 

 Columbia River, as spilling at Ice Harbor Dam 

 usually l^egan in late April, peaked about mid- 

 May, and ended by mid-June. Thus, the net effect 

 of the Snake River discharge on saturation in the 

 Columbia River was to increase the amount of 

 nitrogen in late April and May and decrease it in 

 June, July, and August. 



COMPARISION OF 1966 AND 1967 



Saturation of dissolved nitrogen in 1967 fol- 

 lowed the same general seasonal changes as in 

 1966. Values were normal in winter and early 

 spring before the dams began spilling, but rose as 

 spilling increased. Levels again were highest in 

 June and July when the largest volume of water 

 passed through the spillways. When spilling 

 ceased and cooling of the river began in Septem- 

 l)er and October, saturation decreased sharply 

 (fig. 4). 



SUPERSATURATION OF XITROGEN IN .COLUMBIA RIVER 



