AVERACE MOMTHJf FLOW OF COLUMBIA RIVER AT 

 TRINIDAD FOR FIVE TEAR PERIODS 



AVERAGE MONTHLY AIR TEMPERATURE , NESPELEM . 

 FOR FIVE YEAR PERIODS 



AIR TEMPERATURE AND RjOW COMfORISONS BEFORE AND 

 AFTER CONSTFIUCTION OF GRAND COULEE DAM 



FIG. 39 



two periods of air temperatures. Flow 

 ccmparlsoQs were made using the U.S.O.S. 

 gaging station records for Trinidad, Wash- 

 ington, Just below Rock Island Dam. These 

 flow rates agree fairly closely excepting 

 for the spring months. The spring flood 

 of I9U8 caused the 1946-50 flow rate to be 

 greater than the 19314^-38 rate. 



Assuming then that the flow rates 

 for tbese periods are compeurable, a ccm- 

 peurison of water temperature at Rock Island 

 and air temperatures at Nespelem was made 

 for each month in the two five-year periods. 

 Each year, the water temperatures and air 

 temperatures were summed monthly in a 

 cumulative total, beginning with October 

 of the previous year. From these cumula- 

 tive monthly totals, the monthly difference 

 between water and air temperatures was 

 obtained for each yesir. The succeeding 

 monthly difference then, between these 

 monthly water and air taaperature differ- 

 ences was tabulated and averaged (plus or 

 minus) by the month for each five-year 

 period. Figure UO is a plot of these aver- 

 age monthly temperature diffeiences. It 

 shows a cooling effect on the Columbia 

 River from the Grand Coulee Dam construction 



FIG. 40 



FIG. 41 



66 



