meaa nnrmnl flow of about ^7,000 c.f.s. at 

 Clarkston. The river and its tributaries 

 are regulated for power and the irrigation 

 of 2,800,000 acres throughout its IO60 miles 

 of flow. Temperatxire fluctviations of 3.5' 

 F. are shown in August and 1.^* F. in JUne. 

 These lower temperature variations are due 

 to the river's large size, great length, 

 many impoundments and the fact that it 

 receives a maximum of solar radiation which 

 brings its average sunmer water tonperature 

 to near the average air temperature. An 

 interesting feature of these Snedie River 

 diurnal water temperature plots is the "saw 

 tooth" effect at the time of maximum tem- 

 perature. This abrupt maximum temperature 

 rise to about 7:00 p.m. illustrates the 

 effect of unhindered solar radiation on the 

 river immediately above Riparia, Washington. 



Columbia River at Bonnevnie : The 

 dium€LL temperature variation at Bonneville 

 is very slight, even in the middle of August 

 where 0.7° F. is shown on figure 35. This 

 vau"iation is slight because of the river's 

 huge bulk, the dampening effect of the 

 Bonneville Reservoir and because the average 

 water and air temperatures are near one 

 another. 



It then compares these true daily average 

 temperatures with daily average temperatures 

 obtained by averaging; maximum and minimum 

 daily temperatures; 8:00 a.m. and U:00 p.m. 

 temperature; and midnight, 8:00 a.m. and 

 4:00 p.m. temperatures. These data show 

 that the average of the daily maximum and 

 minimum temperatures are within 0.5* F. of 

 the correct average; that the average of 

 the 8:00 a.m. and 14^:00 p.m. temperatures 

 can differ by as much as 2* F. from the cor- 

 rect average and; that the average of the 

 midnight, 8:00 a.m. and lt':00 p.m. tempera- 

 tures will vary by 0.5* F. from the true 

 average. 



It is suggested that when theimograph 

 records are tabulated, that the TngYjimnn and 

 minimum daily temperatures be recorded (as 

 is usually the case). It is further sug- 

 gested that when daily temperatures are 

 recorded from reading a theimometer, that 

 they be recorded for 8:00 a.m. and 4:00 p.m. 

 when the stream has a noimal daily tempera- 

 ture fluctuation (low about 6:00 a.m. and 

 high about 6:00 p.m.) and that when the 

 daily fluctuation is not normal (like on the 

 Yakima at Richland) that they be recorded 

 for 8:00 a.m. and 8:00 p.m. 



Columbia River at Rock Island : A 

 diurnal temperature variation of 1.7* F. is 

 shown for August. The temperature variation 

 is greater here than at downstream Bonne- 

 ville because the river flow is less, 

 because the Rock Island Reservoir provides 

 less dampening effect than the Bonneville 

 and because the average air temperature is 

 considerably higher than the average water 

 temperature . 



Nason Creek : This is a large creek 

 (flow not measured) which flows for about 

 20 miles through reaches shaded by both 

 timber and the mountains. It is tributary 

 to the headwaters of the Wenatchee River. 

 A diurnal water temperature variation of 7' 

 P. is shown for August. Due to the effects 

 of shading the maxlmimi temperature occurs 

 at 3:00 p.m. rather than in the nonnal late 

 afternoon or early evening. Minimum daily 

 temperature is at the usual 6:00 a.m. 



Deteimlnatlon of Average Daily 

 Water Temperatures 



Table 12 lists the average dedJ-y tem- 

 peratures computed from theimograph records 

 for the streams shown on figures 3^ and 35. 



The typical diurnal temperature curves 

 of figures 3*^ Bsudi 35 can be used to convert 

 any instantaneous temperature readings for 

 a similar stream to the average daily water 

 temperature. 



EFFECT OF EXISTING RESERVOIRS ON 

 DOWNSTREAM WATER TBgERATURES 



Impoundments will affect downstream 

 water temperatures depending upon: 



1. Volume of water Impounded. 



2. Average Impounded water depth. 



3. Surface area of impoundment. 



k. Depth at which water is withdrawn. 



5. Climatic conditions - wind and 

 amount of sunlight. 



6. Characteristics of upstream water 

 shed. 



7. Season of the year. 



60 



