DIUEKAL WATER TEMPERATURE VARIATIOMS 



L€urge diurnal water temperature fluc- 

 tuations are found in the rivers east of the 

 Cascade Mountains because of the extremes 

 between daytime and night time air tempera- 

 ture. This daily fluctuation in air tem- 

 peratxire for eastern Washington (and other 

 eastern areas in the Columbia River Basin) 

 will vary from 20° to 50* F. in the simmer 

 while In western Washington^ the fluctuation 

 is front 10" to 30* F. These diurnal air 

 temperature fluctuations make individual 

 water temperature readings invalid insofar 

 as the average daily water temperature is 

 concerned unless this individual reading be 

 adjusted for the relationship between the 

 temperature reading at that time of day to 

 the average daily temperature. 



The streams studied herein eire all In 

 eastern Washington with the exception of 

 the Columbia River at Bonneville which is 

 influenced by east-of -the -mountain water 

 temperatures . 



Tabulated water temperature data that 

 are available for normal usage give the 

 maximum and minimum daily temperatures or 

 the temperatures taken at specific times 

 during the day, as for example, 8:00 a.m. 

 and 4:00 p.m., or at midnight, 8:00 a.m. 

 and If-: 00 p.m. What is the relationship 

 between these temperatures and the average 

 daily water temperature, or the relation- 

 ship of a temperature value taken at a 

 particuleo" hour to the average daily water 

 temperature ? 



The diurnal water temperature ranges 

 on a given stream at a given location are 

 dependent upon the following factors: 



1. Quantity of flow. 



2. Time of year. 



3. Dally temperature fluctuations 

 at location. 



U. Dally temperature fluctuations 

 upstream from location. 



5. Upstream impovindments . 



6. Upstream environment, such as 

 presence of irrigation return 

 waters, snow melt, shading frcm 

 trees and land masses, temperature 



of tributary stream and depth of 

 water flow. 



7. Flow time from critical upstream 

 conditions to station or location 

 in question. 



Table 11 lists the diurnal water 

 temperature variations by the month for 

 selected streams where maximum and m1n1m\mi 

 temperature data were available. Maximum 

 and minimum daily fluctuations for a given 

 month are shown. A study of this table 

 indicates the following general relation- 

 ships : 



1. The smaller the stream, the 

 greater is the tonperature fluc- 

 tuation. 



2. That significant tempeiuture 

 fluctuations are present in the 

 winter unless the streams are 

 covered with ice. 



3. That diurnal water teaperatvire 

 fluctuations are greatest when 

 there is the greatest difference 

 between the mean deaily air tem- 

 perature and water temperature. 



k. That the largest daily tempera- 

 ture variations are in August and 

 the least in December. 



Figures 3^* and 35 are plots of typical 

 diurnal water temperature fluctuations for 

 different environmental conditions cd streams 

 of widely varying flow characteristics. It 

 is evident frcm a study of these figures 

 that water temperatures taken at any random 

 hour of the day may vary widely from the 

 average dally temperature. It is also evi- 

 dent that no particular hour can be estab- 

 lished for a given stream at which time the 

 water temperature will be representative of 

 the daily average temperature. A discussion 

 of figures 3** and 35 follows. 



Chlwawa River : The Chiwawa is a cold 

 river, flowing 35 miles from the eastern 

 Cascade Mo\mtain slopes through forested 

 land to its confluence with the Wenatchee 

 River. It has a mean annuAi flow of about 

 460 c.f.s. The upper curve (fi«. 3''') is 

 typical for the susmter months ^ile the lotf- 

 er curve is typical for the spring and 

 autumn. There is very little diurnal varia- 

 tion in the winter months. During the sumner, 



55 



