conditions similar to those described by Harvey 

 and Cooper and were suspected to be the major 

 cause of supersaturation ; during periods of high 

 flow, large volumes of water plunge from spill- 

 ways at all the dams on the Columbia River into 

 various types of basins. 



OBSERVATIONS AT DAMS 



Samples analyzed at individual dams to deter- 

 mine the effect of turbines and spillways on dis- 

 solved nitrogen indicated that supersaturation in 

 the Cohmibia River is caused primarily by spill- 

 ways. This was clearly demonstrated during tests 

 at Bonneville Dam in March 1966 when the Corps 

 of Engineers spilled large volumes of water at a 

 time when spilling normally does not occur. Vari- 

 ables, such as spilling at upstream dams and rapid 

 temperature increases, were eliminated; the only 

 factor which remained that could create super- 

 saturation was the spilling of the water. The con- 

 centration of dissolved nitrogen at Bonneville Dam 

 before and during these spillway tests is shown in 

 figure 2. Two replicates of samples were taken be- 

 fore spill and three replicates after spill at each 

 location. Maximum variance in analysis at each 

 location before spill was 4 percent; after spill, 6 

 percent. Concentrations in the forebay and below 

 the turbines and spillway before the spill tests were 

 near normal saturation (98-102 percent). During 

 the spill tests, concentrations below the spill in- 

 creased to 125-percent saturation, whereas concen- 

 trations in the forebay and below the turbines 

 remained near 100 percent. 



Nitrogen levels at other dams (table 2) indicated 

 that each dam has different, characteristic effects 

 on nitrogen saturation. The spillways at Bonne- 

 ville, Grand Coulee, and Ice Harbor Dams in- 

 creased the concentration of nitrogen, but the 

 amount of the increase differed. By contrast, the 

 spillway at Priest Rapids decreased the concentra- 

 tion when the water was supersaturated above the 

 dam. Differences in the structural arrangement of 

 the dams, shape of the spillways, and depth of 

 tailwater are factors which could explain the 

 differences. 



EQUILIBRATION IN RESERVOIRS 



Sampling throughout the length of resei-voirs 

 above Chief Joseph and McNaiy Dams showed 

 that water supersaturated with dissolved nitrogen 



Table 2. — Average nitrogen concentrations (percentage 

 saturalion) in ike Columbia River of samples taken at 

 specific dams to determine effect of dams on water passing 

 through turbines and over spillways (spring 1966) 



- Forebay Tail- Forebay Tail- 

 Location and date above water above water Samples Spill 



spill below turbines below volume 



spill turbines 



Bonneville- Percent Percent PercerU Percent Number 100 cm. a. 



Mar. lOandll 102 125 94 98 8 28.3-42.6 



Ths Dalles' 



Feb. 27-Mar. 2 103 104 102 97 12 1-33.7 



Ice Harbor: , „ „ 



May 16 and 18 109 118 107 106 8 .6-0.8 



Priest Rapids: , „ „ , 



May26and31 131 114 121 --. 8 1.9-2.4 



Orand Coulee: 



Apr. 27 106 129 105 106 4 .7 



does not equilibrate during transit. In McNary 

 Reservoir on June 8, the saturation of nitrogen 

 that entered the reser\oir from the Columbia River 

 averaged 127 percent ; samples collected in the fore- 

 bay of McNai7 Dam on the same day averaged 127 

 percent. Evidently, hu'k of circulation and warm- 

 ing of the surface water in the foi-ebay tended to 

 maintain the saturation level. 



SEASONAL AND DAILY VARIATIONS IN 

 SATURATION OF DISSOLVED NITROGEN 



As expected, variations of dissolved nitrogen 

 concentrations from Grand Coulee Dam to the 

 estuary depended largely on the volume of water 

 released over the spillways. Nitrogen saturation in 

 February, March, and April of 1966 was below 110 

 percent except below dams where intermittent 

 spilling occurred. On February 9, when no dams 

 were spilling (table 3), all samples had saturation 

 below 105 {percent (fig. 3). The concentrations in 

 March were nearly the same except below the Bon- 

 neville spillway where spilling was minimal. Satu- 

 ration of dissolved nitrogen i-emained below 110 

 percent through April except in areas of spilling. 

 Streams began to rise in April, and spill releases 

 became regular at all dams by early May. Sur- 

 face concentrations of nitrogen were over 110 per- 

 cent at all stations except in the forebay of Grand 

 Coulee and The Dalles Dams. The highest concen- 

 tration in May (132 percent) was downstream 

 from the spillway at Bonneville Dam. Tempera- 

 ture on May 9 ranged from a low of 8.5° C. (47.3° 

 F.) in the forebay of Chief Joseph Dam to a high 

 of 15.3° C. (59.5° F.) in the forebay of Grand 

 Coulee Dam. 



U.S. FISH AND WILDLIFE SERVICE 



