water temperatures (corrected for diurnal 

 variation) in the Yakiioa River between 

 Enterprise (near Richland) and Thorp (above 

 Ellensburg) for selected days of the year. 

 The irrigation season extends from March 

 to October with the heaviest water applica- 

 tions being from May through September. 

 Irrigation return flows enter the river 

 below Ellensburg and from below Yakima to 

 the river mouth. Most of the return flows 

 bring water into the river at a temperature 

 higher than the river temperature. The 

 water temperature increase, between Thorp 

 and Enterprise of 3.5* F. at the beginning 

 of the irrigation season in March, rises 

 to a 20° F. increase in August at the end 

 of the heavy irrigation season. Average 

 air temperatures at YaJcima are shown on the 

 figure for the date of sampling. These are 

 the average for the day proceeding tempera- 

 ture meeisurement , the day of measurement 

 and the day following. In December, March 

 and May, the water temperature around Yaki- 

 ma is higher than the air temperature. In 

 June, August and September, the water tem- 

 perature is lower than the air temperature 

 in the vicinity of Yakima. This illustrates 

 the effect of solar heating in the winter 

 and spring together with the entrance of 

 ground waters higher in temperature than 

 the air. These ground waters and the reser- 

 voirs have a cooling effect in the summer. 



Figure 32 shows the warmer water 

 discharge by Lake Wenatchee being cooled 

 below the outlet by the colder water of 

 the Chiwawa River and Nason Creek. The 

 only significant change in temperature be- 

 tween the headwaters and the outlet occurs 

 in the spring and autumn. In the spring 

 the water temperature increases about '4-'' 

 F. and in the autumn decreases about k" F. 

 between the headwaters and the outlet. 

 Air and water temperatures have about the 

 same relationship as on the Yakima River. 



The water temperature rise in the 

 Columbia Basin main irrigation canals be- 

 tween GrEind Coulee Dam and the Ik^ miles 

 of canals and reservoirs is shown in 

 figure 33. A temperature rise of Ik" F. 

 is noted for August I7, 1955. This is a 

 common rise on sunny days. The canal water 

 temperatures are very sensitive to air 

 temperatures when immediately below a large 

 reservoir. On June 29 and July 22, a tem- 

 perature decline beyond the PotholeG Reser- 

 voir is shown when nonnally the temperature 

 would rise. This decline is caused by less 



than average air temperatures on the 

 proceeding day and day of the observations. 

 The temperature decline beyond the Potholes 

 Reservoir in September shows how the reser- 

 voir water, warmed during the summer, is 

 cooled when it is released in a stream for 

 intimate contact with autumn air tempera- 

 tures. Rapid water temperature rises are 

 shown through the broad and shallow Equal- 

 izing and Potholes Reservoirs. Average 

 monthly air temperatures for the month of 

 observation are shown for Moses Leike weather 

 station, this being about the center of the 

 Ba^in. Water temperatures are higher than 

 air temperatures for each month excepting 

 June, indicating a high degree of solar ra- 

 diation absorption. 



WENATCHEE RIVER TEMPERATURES 

 AVERAGE MONTHLY. 1955-56 



CHELAN PUO THERHOCRAPH REC0R06 



-LJ \ LJ 



MILES ABOVE RIVER MOUTH 



FIG. 32 



NOFMAL RIVER WATER TEMPERATURE 

 CHANGES WITH DISTANCE 



A stream, during its nonnaJ. unhindered 

 flow, will usually experience a rise or fall 

 in water temperature as it progresses down- 

 stream. The magnitude of this temperature 

 change is related to the depth of flow, 

 quantity of flow, turbulence, season of the 



!^2 



