- 54 



FEB. MARCH APRIL 



MAY 



JUNE 



DEC. 



FIG. 38 



Water temperatiires for Late Roosevelt 

 in the year 1951 are shown in figure 38- 

 The Columbia River flow during 1951 was the 

 second highest flow on record for the Inter- 

 national Boundary gaging station. Even 

 though this high flow would provide extra- 

 ordinary flushing action, the temperature 

 gradients shown in figure 38 are similar to 

 those in reference (M^) and to data obtained 

 by the University. A maximum temperature 

 gradient of 4.5° C. is shown for August 

 with half of this temperature change occur- 

 ring in the upper 50 feet. Other than in 

 the summer, the temperature change from 

 surface to bottcm is very slight. 



Minlmvmi temperatures were in March 

 when the deepest water was the wannest, 

 this deep water being nearest to the tem- 

 perature of maximum density {k' C). Maxi- 

 mum surface temperatures were near the first 

 of September while the maximum temperature 

 for water withdrawal through the turbines 

 (at 260 ft. depth) was in the first part of 

 October when the reservoir was drawn down. 

 Isothennal conditions are shown at the end 



of January, May and October, when overturns 

 are possible. These isothennal conditions 

 eire a function of both atmospheric tempera- 

 ture changes and river inflow. 



Effect of Grand Coulee Dam on Columbia 

 River Temperatures at Rock Island : 



Water temperatures at Rock Island Dam 

 have been kept by the Puget Sound Power and 

 Light Company since 1933* These tempera- 

 tures were used for pre and post Grand 

 Coulee Dam construction comparisons. As 

 the water temperature is a function of air 

 temperature and flow rate in a given stream, 

 a five-year period (193^-3^) prior to con- 

 struction of Grand Coulee Dam and a five- 

 year period after construction (19'*6-50) 

 were chosen when the air tonperatures and 

 flow were similar. Figure 39 shows a com- 

 parison of these air temperatures and flow 

 for the two fire year periods. Air tempera- 

 ture were taken for Nespelom, Waishington as 

 this was the weather station that would moat 

 closely approximate upstream weather condi> 

 tlons. A close agreement is shown for the 



5^ 



