79 



STREAM LOSSES BY EVAPORATION AND TRANSPIRATION 



The consumptive use of water by canyon-bottom vegetation is 

 taken as the difference between the flow at the upper and lower 

 controls of each section of creek bottom. Previous to the initial 

 work a survey of the rock outcrop in ravines entering the canyon 

 indicated that there was no side inflow into the stream. 



The characteristic curve of transpiration demand is similar 

 to the daily discharge curve of a flowing stream, although the 

 maximum and minimum points of the curve occur at different times 

 of day. Transpiration is at a maximum in the early afternoon and 

 at a minimum about sunrise. Stream flow, on the other hand, on 



clear days and with normal transpiration, has a maximum during 



* i 



midmorning and a minimum in late afternoon. Figure 9 shows a 

 curve of stream discharge at the middle control for the period 

 August 9 to 15, 1931. On the 9th, 10th, and 11th the days were 

 warm and discharge curves were normal in appearance. On the 12th 

 a light rain reduced transpiration and the effect was shown in a 



^ 0-5 



"5 0.4 

 o 

 « 

 n!! 0.3 



o 



il: 0.2 



0.1 

 0.0 



12 

 August 



FIGURE 9.-- Flow at middle Coldwater Canyon control. 



