62 DIVISION OF WATER RESOURCES 



occurs at approximately the time of highest air temperatures, although 

 such is not the case in this instance. 



Coastal Avinds continuing through several hours each day pass over 

 the Prado station and, in combination with high temperatures, are 

 responsible for a continued increase in both evaporation and transpira- 

 tion until 3 or 4 o'clock in the afternoon. This accounts for a larger 

 consumptive use than at other localities in the Santa Ana basin. 



Because of their exposure and abnormal conditions affecting 

 growth, use of water by tules grown in tanks was excessive. At Santa 

 Ana station, round stem tules used more water than did the triangular 

 stem tules or the cat-tails, their gro-\\i;h being greater in point of density 

 and height of stems. Their consumptive use frequently amounted to 

 more than 1| inches in depth per day and at one time averaged an inch 

 a day for a period of six weeks. Tules at the Prado station had a 

 higher consumptive use than did those of the same A-ariety at Santa 

 Ana, partly because of slight climatic differences, but also because 

 of differences in height and number of stems. The maximum daily 

 use at Prado was 3.6 acre-inches per acre on a day of high temperature 

 and wind movement. 



Intensive investigations near Victorsdlle, undertaken to determine 

 the proper adjustment factor to be used in reducing consumptive use 

 of water by tules groAvn in tanks to the actual amount used by swamps, 

 are discussed in the folloAAdng chapter. In this study, one 2-foot tank 

 containing tules Avas fully exposed to Avind and sunshine Avith a result- 

 ing large use of Avater. A large tank set in a protected area of a SAvamp 

 used a much smaller amount. Further investigation by the Bureau of 

 Agricultural Engineering in the Sacramento-San Joaquin delta indi- 

 cates a factor of 0.46 for cat-tails and tules for a 20-day period in 

 August, 1930. Reporting on this and other Avork, Charles H. Lee* has 

 adopted a tentative factor of 0.50 for making the reduction, admitting 

 that the value may be changed Avhen further data are available. By 

 applying the results of the Victorville investigation to the measured 

 losses from isolated tanks used in southern California, it is found that 

 the adjustment factor ranges in these experiments from 0.29 to 0.55 

 as shoAvn in Table 21. 



AYliile the relation betAveen the Avater requirement of a crop and 

 evaporation from a Avater surface during the groAving season is not 

 constant, month by month, it is the most practical means of making 

 comparisons of consumptive use, not only from year to j'ear, but between 

 localities having different rates of evaporation. For this purpose the 

 best records for comparison are those of standard Weather Bureau 

 eA^aporation pans, which are in more general use in investigational Avork 

 than pans of other sizes or depths. For the Victorville station, where 

 tules were grown in a swamp area, the percentage of consumptive use in 

 the swamp with reference to CA^aporation from the "Weather Bureau pan 

 is computed for an average year, the result being about 95 per cent. In 

 the average year the consumptive use for each month is taken as the 

 average of all records for that month. Neglecting other factors, such 

 as variety, density of groAvth, and seasonal variations in evaporation 

 and transpiration, this percentage has been applied to evaporation 



* BuUetin No. 28, Economic Aspects of a Salt AA'ater Barrier Below Confluence 

 of Sacramento and San Joaquin Rivers, Division of Water Resources, 1931. 



