53 



protected swamp areas. They are often found directly exposed to 

 sun and wind in narrow ribbons along stream channels and drainage 

 ditches where exposure is nearly similar to that in isolated 

 tanks. Under such conditions it is reasonable to expect that 

 consumptive use of water is somewhat less than from exposed tanks, 

 but considerably more than from larger swamps. 



Midway between Santa Ana and San Bernardino, consumptive 

 use of water by tules was ascertained in connection with a study 

 by the United States Geological Survey of the flow of the Santa 

 Ana River. As the station was isolated and daily visits were not 

 practicable, recording devices were attached to both tule tank 

 and Weather Bureau evaporation pan. From the records, hourly 

 rates of consumptive use and evaporation were obtained. Samples 

 of these are plotted in Figure 6, showing also air and water tem- 

 peratures. 



t. u: 



•2 j; .10 



August 



FIGURE 6.-- Hourly rate of use of water by tules, evaporation 

 from standard Weather Bureau pan, and air and water tempera- 

 tures, at Prado station. 



There were periods during the early morning hours when the 

 loss of water was too small to be recorded and evaporation or 

 transpiration during these hours is shown as zero. Characteristic 

 of both evaporation and transpiration is the daily increase or 



