80 



sudden rise of the stream surface. The 13th and l^th were cool 

 and cloudy, transpiration was low and there was little fluctuation. 

 The 15th was again warm, transpiration increased, and the stream 

 surface dropped. 



The daily loss of water from the stream in both upper and 

 lower sections of canyon bottom is shown in Tables 17 and 18. 

 These data are arranged to present also the average daily losses 

 for each section of canyon and the average loss per day per 1,000 

 feet of stream bed. There was considerable difference in losses 

 in the two growing seasons. In both years there was outflow at 

 the lower control, hence never a shortage of water for the trees. 

 The summer of 1931 had some light rain and cloudy weather, whereas 

 in 1932 the weather was clear. On the other hand, in 1931 temper- 

 atures were higher than during 1932, which would tend to offset 

 the effect of cloudy periods. On the whole, there seems to be no 

 reason why consumptive use should be greater in one season than in 

 another. 



It will be observed also that consumptive use by trees in 

 the upper stream section is less than in the lower section. This 

 cannot be accounted for by density of growth as there are more 

 trees per acre in the upper section. In the lower canyon, however, 

 alders account for 81.9 per cent of all trees and shrubs whereas 

 in the upper canyon they are 47.9 per cent of the total. In the 

 upper section there is an increase in California laurel from 4.1 

 per cent to 26.1 per cent. It appears probable that the fewer 

 alders in the upper section account for the smaller consumptive 

 use. 



The consumptive use by canyon-bottom trees and shrubs from 

 June to October commands attention. This is the period of maximum 

 use, not only by natural growth but by irrigated crops as well. 

 In estimating water supplies for irrigation a knowledge of the 

 effect of consumptive use of water by alders, willows, and other 

 stream-fed vegetation on depletion of stream flow is important to 

 engineers. The study shows a maximum use of 13.7 acre-inches per 



