WATER LOSSES PRO:\r WET AREAS 25 



requirements of approximately 16 acres of citrus. For the upper 

 section, the loss in each mile wonld meet the irrigation requirements 

 of 11 acres of citrus. 



Evaporation from Free Water Surfaces 



The Bureau of Agricultural Engineering' has been keeping evapora- 

 tion records at several stations in southern California in cooperation 

 with the State Division of Water Resources, since 1928. Other agen- 

 cies also have been making observations. These agencies do not always 

 use the same type of evaporation pan and results from the different 

 types are not comparable. For this reason a cooperative, experimental 

 key station has been established at Baldwin Park for the purpose of 

 correlating the data being collected by the various organizations and 

 for determining factors that may be used to reduce the observations 

 on various types of evaporation pans to a comparable basis. This inves- 

 tigation is expected to continue for several years, until sufficient data 

 are available for the purpose. 



The Los iVngeles County Flood Control District, the 8an Gabriel 

 Valley Protective Association, the Pasadena Water Department, the 

 California State Division of Water Resources, and the United States 

 Geological Survey are cooperating with the Division of Irrigation, U. S. 

 Bureau of xVgricultural Engineering, in conducting this investigation. 

 Three types of evaporation pans have been installed at the station : 



1. Standard Weather Bureau pan, 4 feet in diameter by 10 inches 



deep, set upon a wooden platform above ground. 



2. U. S. Bureau of Agricultural Engineering type, 6 feet in diam- 



eter by 3 feet deep, set 2.75 feet in the ground. 



3. Los Angeles County Flood Control District type, 2 feet in 



diameter by 3 feet deep, set 2.75 feet in the ground. 



Records of evaporation from free water surfaces in pans and tanks, 

 collected by various agencies in southern California, are tabulated in 

 Chapter V. 



AVith few exceptions all records of evaporation are comparatively 

 recent, the majority being obtained since 1929. The oldest record 

 available, that at Pomona, was of short duration — from 1903 to 1905. 

 One record Avas begun at South Haiwee Reservoir, Inyo County, in 1924, 

 and one at Fairmont Reservoir in Antelope Valley in 1923 by the City 

 of Los Ajigeles. Both records are continuous to the present date. The 

 longest record available is at Chula Vista, San Diego County, main- 

 tained bv the U. S. Weather Bureau continuouslv since 1918. 



