108 DIVISION OF WATER RESOURCES 



the periods of measurement, since the changes occurring in the head 

 are very slight. Therefore, either the inflow and deep percolation 

 would continue to be equal during the season, or else the inflow would 

 fall off because of the drying of shallow springs. The former would not 

 affect the results, and the latter would result in a constantly gaining 

 difference in the discharges at the time of daily maximum flow which 

 would not return to earlier values. An examination of Tables 35 and 36 

 shoAvs that the latter case did not occur, and that no combination of 

 deep percolation and inflow from shallow springs existed. 



If deep percolation existed it would be the same approximately 

 throughout the season, as has already been stated in the previous para- 

 graph. It is not conceivable that it would change from day to day, 

 since the temperature of the underflow does not vary appreciably. 

 Hence, if percolation did exist, it would prohibit the values of daily 

 differences in maximum discharges at the controls from ever reaching 

 a zero value. This is not the case, as a zero value was reached several 

 times in 1931, and in 1932 a value of 0.004 was reached on September 

 28, 0.003 on October 23, and zero on November 3. Hence, no deep 

 percolation could exist by itself. 



In case evaporation and transpiration are occurring at a time of 

 daily maximum discharges, the flow from the section will be less than 

 the flow into the section and the difference in maximum discharges will 

 have a positive value. The same effect also will be caused by the water 

 table's not being completely recharged from the stream by a time of 

 daily maximum discharges. It takes time for this recharge to take 

 place, and if the use by the vegetation has been high in the previous 

 day the water table will not be completely recharged during the night. 

 These two cases, either separately or together, account for the large 

 number of daj^s when there was a greater maximum discharge at the 

 middle control than at the lower control, as shown in Tables 35 and 36. 

 This difference in daily maximum discharges reached high values of 

 0.038 second-foot on August 26, 1931, after an excessively hot period, 

 and 0.050 second-foot on September 8, 1932, after a hot night during 

 which a hot wind was blowing doAvn the canyon. 



The growing seasons of 1931 and 1932 differed materially. During 

 1931 there were several summer rains accompanied by cloudy weather 

 at about the time of the rains. These conditions caused the use by the 

 vegetation to be less, on the average, this result being due not only 

 to the cloudy weather's preventing as much sunshine from reaching the 

 vegetation as would otherwise have occurred, but also to the fact that 

 the rain itself reduced use from the water table by the vegetation. 

 During 1932, no summer rains occurred and a greater amount of sun- 

 shine reached the vegetation, these conditions being more favorable to 

 a large use from the water table, which in turn is fed by the stream. 



An examination of Tables 35 and 36 shows that the values in 

 these tables during the two seasons reflect the different conditions of 

 the two seasons. In 1931 only a few days show any appreciably larger 

 daily maximum discharges at the middle control than at the lower 

 control, while in 1932 a great many of the days show daily maximum 

 discharges which are appreciably larger at the middle control than at 

 the lower control, because of tlie continued high use by the vegetation. 



