July 30,1917 Evaporation from Water and Riuer -Bed Materials 227 



EVAPORATION FROM FLOWING WATER 



Early in July tank 26 was installed. This and No. 15 are of equal 

 depth and exposed water area. Installation was made so that the expo- 

 sure would be similar. They were located about 25 feet apart. A motor- 

 driven centrifugal pump kept the surface water of No. 26 flowing. No. 15 

 was motionless. Thermometers were placed in each tank. Owing to a 

 lack of means of preventing slopping, a surface velocity of 1.44 feet per 

 second was all that could be attained. 



Table VI gives the results of this investigation. These final figures 

 were arrived at after the application of a temperature correction. Data 

 for making this correction were obtained by the use of the special set 

 of tanks, No. 21, 23, 24, and 25. They are all of the same depth and 

 diameter. By the immersion of electric-light bulbs in them, a variation 

 of surface temperatures was obtained. The weekly data on this work 

 .are recorded in Table VI. Plate 36, B, shows one of these tanks. 



Table VI. — Relation between the amounts of evaporation from a tank of flowing water 

 and a tank of still water; tanks of equal exposed area, depth, and similar exposure. 

 Exposed water surface l.yy feet square; depth of tank 3 feet 



Date. 



Length of 

 run. 



Evapora- 

 tion from 

 tank 15, 

 still water. 



Evaporation 

 from tank 26, 

 flowing water. 

 Corrected for 

 temperature 

 increase. 



Surface 



velocity of 



flowing water. 



July 13. 



17- 

 18. 

 19. 

 20. 



21. 



23- 



29. 



Aug. I.. 



July 24... 



24-5- 

 25... 

 26... 

 Aug. 16. . . 

 17... 



Total a . 



Hours. 



12 



12 



12 

 12 

 12 

 12 



6K 



8>^ 



Inch. 

 o. 15 



. 22 

 . 16 

 • 04 

 . 24 

 •32 



•34 

 •25 

 . 12 



■ 13 

 . 21 



. 24 

 . 18 

 . 24 

 . 21 

 . II 

 .24 



3- 40 



Inch. 



O. 17 

 •23 

 ■ 19 

 .04 



.29 

 •32 

 .26 

 . 20 

 . 16 

 . 22 

 •32 

 •25 

 •30 

 .27 

 . 12 

 ■30 



Feet per sec. 



O. 68 



68 

 68 

 84 

 84 

 84 

 84 

 84 



3.86 



a Ratio, 52^'l-g^3:^^= 1.072 

 Still 3.40 



