WATER liOSSES FROM WET AREAS 



63 



records at Santa Ana, i'rado, and San Bernardino. In other words, 

 95 per cent of the evaporation at a station is estimated to be the con- 

 sumptive use of water by aquatic growth in a natural swamp area in 

 tliat locality. Ilaviuir computed the estimated consumptive use in a 

 swamp, the percentage of computed swamp use to the observed tank 

 use, mav be determined. This was the method followed in compiling 

 Table 2i. 



TABLE 21 



ESTIMATED CONSUMPTIVE USE OF WATER BY TULES AND CAT-TAILS IN SWAMPS 

 BASED UPON TANK EXPERIMENTS, AND PERCENTAGE OF SWAMP USE 



TO TANK USE 



' The observed swamp consumptive use at Victorville is 95.2 per cent of the evaporation from the Weather Bureau 

 pan. This percentage multiplied by the evaporation at each station equals the computed swamp use for that locality. 



In the last column of the table there is a large difference in per- 

 centages. These are due in part to differences in density of gro^^i:h 

 in each tank. Disregarding small dift'erences in rates of transpira- 

 tion, which may exist in different varieties of aquatic growth, the total 

 use of water by adjacent tanks should correspond rather closely, pro- 

 vided that the dry weight of crop matter is nearly the same. Trans- 

 piration is nearly proportional to the transpiring area and is conse- 

 quently more where there is a heavy growth than where the growth is 

 light. Each tank used had different density of growth and a different 

 consumptive use. In Tank No. 22 cat-tails did not spread and produce 

 as thick a growth as is natural in .swamp areas, nor did they reach the 

 height of stems found in swamps. The same is true of round stem tules 

 in Tank No. 23. In both cases, the observed consumptive use is less 

 than that of triangular stem tules at Santa Ana or of round stem tules 

 at San Bernardino, and the percentage of computed swamp use to 

 observed tank use is much higher than the average for other tanks. 

 Likewise, consumptive use by tules at Prado is high and its relation 

 to swamp use is correspondingly low. 



The results of the tule tank experiments indicate the impractica- 

 bility of applying to field conditions records of tests made in isolated 

 tanks of tules grown apart from their natural environment. 



