temperature rise in May shows the effect 

 of the heavy runoff of melting snow water 

 encountering the warmer reservoir. The 

 temperature rise in August euid September 

 illustrates the effect of drawdown on the 

 reservoir which brings the upper layers of 

 warmer water into the more restricted area 

 at lower depths and thus produces a greater 

 depth of wanner water. 



Merwin: Impoundment commenced on May 

 13, 1931. This reservoir is iimnediately 

 below the Yale Dam and is somewhat larger, 

 but shallower, than the Yale Reservoir. It 

 has a length to width ratio of 23.3 which 

 will provide less short-circuiting through 

 the reservoir and more mixing than in the 

 shorter Yale Reservoir. The single set of 

 temperature data obtained in May appears to 

 be In error. In August and September, water 

 is discharged slightly colder than the res- 

 ervoir influent. During the other months, 

 the discharged water is warmer than the 

 influent . 



Yale -Merwin: Since these reservoirs 

 are close together, they are considered 

 herein as a single reservoir. Their com- 

 bined effect is to continually increase the 

 Lewis River water temperature from about 

 one to five degrees fahrenheit. During the 

 period of low-stream flow in September, the 

 water temperature increase is about three 

 degrees fahrenheit. 



Grand Coulee Equalizing: This is a 

 long eind shallow reservoir used to equalize 

 the flow of pumped water into the Columbia 

 Basin irrigation system. It has a length 

 to width ratio of I3.5. Data were available 

 only for the summer months. The effect of 

 solar heating on a shallow impoundment is 

 quite evident. During June and July, tem- 

 perature increases of over seven degrees 

 fahrenheit were observed. In August and 

 September, the inflowing water frcm Lake 

 Roosevelt had warmed sufficiently to reduce 

 this temperature increase to six and two 

 degrees respectively. 



Roosevelt: This is an exceptionally 

 long, deep, and large reservoir, having a 

 length to width ratio of I67 which will pro- 

 vide for some mixing of water in the reser- 

 voir euad reduce the anount of stratification. 

 Data were available for only the summer 

 months. In June and July, the re8er\''oir 

 reduces the Columbia River water tempera- 

 ture by about two degrees. In August, the 

 water level is feilling in the reservoir and 



the warmer upper layers are reaching the 

 turbine intsikes, producing no appreciable 

 temperature change between upstream and 

 downstream. In September, the warmer water 

 has reached the turbine intaJtes and the 

 average effect is to increase the Columbia 

 River temperature by 3.6" F. 



McNary: This is a relatively shallow, 

 run of the river impoundment, having a 

 length to width ratio of 6I. The Snake River 

 flows into the impoundment 32 miles above 

 the dam. This is the major tributary of the 

 Colimibia River and its temperature will 

 materially affect the reservoir temperature. 

 In the winter, the Snedce River is colder 

 than, and in the sunmer it is warmer than, 

 the Columbia River at Pasco. Since the 

 reservoir does not always provide complete 

 mixing, a slight temperature gradient is 

 usually noticeable across the reservoir at 

 McNary Dam. 



To evaluate the temperature change 

 through this reservoir, it was necessary to 

 compute the theoretical temperature of the 

 mixed flow of the Columbia suid Snake Rivers 

 below Pasco. This composite temperature was 

 then taken as the upstream temperature. Re- 

 ferring to table 13 it Is apparent that the 

 Impoundment produces a net cooling effect 

 (0.1*" - 1.5° F.) in the winter and spring 

 and a warming effect (0.1°- 0.5° F. ) on the 

 lower Columbia in the late summer and fall. 



Table ih shows the temperature changes 

 in the reservoirs based on their volume, 

 depth and area. These data will be used in 

 predicting future temperature changes in 

 the Columbia River. 



Table 13 shows that temperature 

 changes in reservoirs cannot be generalized, 

 such as, they waira the downstream water in 

 the winter and cool it In the summer. Each 

 reservoir behaves in accordance with its 

 own peculiar environment. 



Temperature stratification in 

 reservoirs : 



The temperature of the water down- 

 stream frcm an ImpoxindiMnt will vary accord- 

 ing to the depth frcm which the water is 

 withdrawn. A study of references (17), 

 (22), (U2) and (43) plxis University of Wash- 

 ington observations shows that of the 19 

 reservoirs observed, all but Lake Roosevelt 

 show markfe'! temperature stratification in 

 the spring, summer and fall and a lesser 



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