Table Ik. — Average monthly temperature changes through reservoirs - 

 area, volume, depth relationships; frcn table 13* 



Mar. 



May 



June 



July Aug. Sept. Nov. Dee. 



Yale - Merwin Reservoir 



1.9+ 1.1+ 4.1+ - 5.4+ 



1.9+ 1.1+ 4.2+ - 5.5+ 



1.0+ 0.6+ 2.2+ - 2,9+ 



7.9+ 6.2+ 2.1+ 



3.1+ 2.4+ 0.8+ 



14.5 ll.'»+ 3-S+ 



0.23- 0.01- 0.44+ 



0.27- 0.01- 0.51+ 



0.58- 0.03- I-09+ 



0.0 0.13+ 0.63+ 0.25+ 0.25- 

 0.0 0.03+ 0.13+ 0.05+ 0.05- 

 0.0 0.14+ 0.72+ 0.29+ 0.29- 



* Plus sign indicates temperature rise through reservoir; minus, temperature tall; - Indicates no data 

 available . 



stratification in the winter. The extent 

 of this stratification depends upon the 

 length of the reservoir, wind action on the 

 surface layers, amount of inflow and out- 

 flow and relative temperature of inflow to 

 reservoir temperatures. Wind is the prin- 

 cipal factor in mixing the summertime waim 

 surface layers into the reservoir body 

 since the rate of molecular diffusion is 

 low and because water has a high heat capa- 

 city. 



Figure 36 of Lake Merwin was prepared 

 from the unpublished data of Richard Smith 

 (22) and is corroborated by reference (17) 

 and University of Washington data. Yale 

 Reservoir shows a similar temperature 

 stratification. A pronounced warning from 

 Bolar radiation is quite evident in the 

 svmmier months with no marked thermocline. 

 Comparing the temperature at the turbine 

 intake with the upstream water temperature 

 indicates that the Merwin Reservoir, prior 

 to construction of the upstream Yale Reser- 

 voir, had a general warming effect on down- 

 stream waters in the winter and cooling 

 effect in the summer. After constructing 



Yale Reservoir, this was no longer true and 

 the combined effect of the two reservoirs 

 in series is to produce a year around wann- 

 ing of downstream water (table 13 )• 



Figure 37 was ^reTp&red from General 

 Electric Compemy data ^4^2) and from Fish 

 and Wildlife Service thennograph records at 

 Unatilla. The lack of stratification is 

 due to the shallow depth of the reservoir 

 and the short detention period for inflow- 

 ing water. Slight differences between 

 downstream water temperatures and the tem- 

 perature at the depth of the tvirbine intakes 

 (55 feet) is probably due to a difference 

 in the theimometer calibrations. 



A sharp thermocline is shown for 

 May 19, 1955. During this period, the 

 Columbia River and Snake River flows were 

 about equal and the warmer Snake River water 

 was contained in the upper layers of the 

 reservoir. By June 16, 1955, the Columbia 

 flow had more than doubled that of the Snake 

 and mixing occurred to destroy the tempera- 

 ture gradient. 



63 



