WATER LOSSES FROM WET AREAS 



85 



the tank rims fully and tiile Tank No. 2 shows the higher rate of loss. 

 Thereafter, differences in losses from the two tule tanks may be 

 ascribed to a variation in the density of growth. By comparing the 

 losses from tnle Tanks Xos. 2 and 3, from Juno 1 to October 31, 1931, 

 it is found that the loss is 49.93 acre-inches per acre from the 2-foot 

 tank, and 55.08 acre-inches per acre from the 6-foot tank. For this 

 period, the loss from the 2-foot tank is 91 per cent of the loss from the 

 G-foot tank, as compared to Sleight's ratio of 117 per cent for free 

 water surfaces. The correlation of tank size is negative and diffci-ence 

 in use must be due to some other factor such as density of growth. 



Prior to the planting of tules in the tanks on January 29, 1931, 

 all three tanks were maintained with free water surfaces. The evapora- 

 tion in inches and rate of evaporation in inches per 30 days for the 

 Weather Bureau pan and Tanks Nos. 1, 2, and 3, and also the evapora- 

 tion from Tanks Xos. 1, 2, and 3, expressed as percentages of the evapo- 

 ration from the Weather Bureau pan for the period, December 5, 1930, 

 to January 29, 1931, are given in Table 29. During the period of these 



TABLE 29 



EVAPORATION FROM FREE WATER SURFACES IN THE WEATHER BUREAU 

 PAN AND TANKS NOS. 1, 2, AND 3 



December 5. 1930, to January 29, 1931 



Pan or tank 



Standard Weather Bureau pan (4 feet in diameter) 



Tank No. 1 (2 feet in diameter) located on bank near Weather Bureau 



pan 



Tank No. 2 (2 feet in diameter) located in swamp ._ 



Tank No. 3 (6 feet in diameter) located in swamp 



Total 



evaporation 



in inches 



4 20 



2.16 

 6 91 

 4.19 



Rate of 

 evaporation 



in inches 

 per 30 days 



2.29 



1.18 

 3.77 

 2.29 



Per cent of 



evaporation 



from standard 



Weather 



Bureau pan 



100 



51 

 165 

 100 



evaporation .studies from free water surfaces, the mean daily maximum 

 temperature was 65 degrees Fahrenheit, the mean daily minimum tem- 

 perature was 11.5 degrees Fahrenheit, and the total wind movement 

 was 1389 miles. The evaporation from the 6-foot tank (Tank No. 3), 

 located in the swamp, was practically the same as that from the Weather 

 Bureau pan (4 feet in diameter), the values being 4.19 and 4.20 inches, 

 respectively, while the loss from the 2-foot tank (Tank No. 2), located 

 in the swamp, was 165 per cent of that from the Weather Bureau pan. 

 The 2-foot tank (Tank No. 1), located on the bank near the evaporation 

 pan and set in the ground so that its rim was 1 incli above the sur- 

 rounding ground surface, lost 51 per cent as much as the Weather 

 Bureau pan. 



This demonstrates the effect of exi)osure and location on the rates 

 of loss from the different tanks. Tanks Nos. 2 and 3 were located in 

 the .swamp and the rising ground water from the swamp channel 

 flowed around them continuously. Tlie rising water in the swamp 

 carried .sufficient heat so that no ice formed on the water surface around 

 the two tanks, even though a minimum air temperature of zero degrees 

 Fahrenheit was recorded on December 23, 1930. The heat from this 

 swamp water was transmitted to the water in the tanks most effectively 



