Temperatures 



Table 1 lists the subsurface temperatures taken at various 

 stations along the lake. The instrument used for these determina- 

 tions was a Foxboro Portable Indicator manufactured by the Foxboro 

 Company of Foxboro, Massachusetts. Inspection of Figure 1, showing 

 temperature curves at three different stations, indicates that no 

 thermocline was present in Roosevelt Lake at the time of the ob- 

 servations. 



In Figures 2 and 3, temperature curves for days of maximtun 

 temperature gradient were plotted from data tsiken near Grand Coulee 

 Dam by the Bureau of Reclamation during the years 1943 to 1947. 

 During that period the maximum temperature gradient occurred in 

 August, just before surface cooling began. In 1946 and 1947 a 

 second maximum temperature gradient occurred in early spring before 

 the spring rvaioff (figia-e 3). In these years the oVserved gradients 

 were very slight, with the single exception of May 5, 1947 (Figure 3) 

 when temperatures between the five and ten foot depths were indicative 

 of a poorly developed thermocline. 



The reason for the absence of thermal stratification lies in the 

 ratio of inflow to storage capacity; although the lake can retain 

 10,000,000 acre-feet of water, the average annual flow of the river 

 is 80,000,000 acre-feet. Thus the reservoir could be refilled eight 

 times in one year by the flow of the river into it. 



Cheanioal Constituent* 



The following paragraphs set forth the results of chemical 

 analyses that were made at the mouths of the various streams flow- 

 ing into Roosevelt Lake. 



Determination of pH 



Table 2 includes all of the pH readings, which were made by 

 means of a standard colorimeter set. The pH of all waters tested 

 ranged between pH 7.2 and 8.2, well within the pH 6.3 and 8.5 range 

 considered readily tolerable by most fresh-'water fishes (if the 

 variations result from relatively small amounts of carbon dioxide 

 and carbonates as was true in RoxJsevelt Lake). 



