104 DIVISION OF WATER RESOURCES 



Plate XXVII I- A have the maximum rats of change in flow occurring 

 shortly after noon ; that is, there is a point of inflection on each dis- 

 charge curve between 12 noon and 1 p.m. However, an elemental 

 section of the stream passing the upper control at noon will not reach 

 the lower control until approximately 3 p.m. It will lose water continu- 

 ously as it passes down the channel to replenish the draft on the water 

 table caused by transpiration. The maximum rate of loss should occur 

 at approximately the same time at all points on the stream, but the effect 

 of the time taken for each elemental section to move down the canyon 

 is to displace the point of minimum flow to the right, as shown in the 

 graph. For this reason, the loss in flow curve for the middle control, 

 sho-s^ai in Plate XXVIII-A, is moved to the right 45 minutes, the time 

 taken for an elemental section of water to move from the middle to the 

 lower control. The curve of difference in flows, which is a measure of 

 the evaporation and transpiration between controls, rises rapidly to 

 a peak shortly after noon and then, as the water table is recharged, 

 it gradually falls and approaches zero before sunrise of the next day. 

 The position of the water table depends largely on the relation 

 of the rate of use from the water table by the vegetation to the rate 

 of recharge of the water table from the stream. The change in this 

 relation is the chief reason for such fluctuations in the ground water 

 as are shown on Plate XXVI, the water table reaching a maximum 

 level in the morning and a minimum in the afternoon. 



If the water table is completely recharged at the time of maximum 

 stream flow early in the morning, and there is no transpiration or 

 evaporation at that time, the total flow into the section must equal the 

 total flow from the section. The total flow into the section is the total 

 of the observed surface inflow and any underground inflow, as from 

 hidden springs. The total flow from the section is the total observed 

 surface outflow plus any underground seepage which leaves the section. 

 If there is neither any underground inflow nor any underground 

 seepage, it follows that in the stated case the observed inflow and the 

 observed outflow must be equal. 



As long as there is no inflow into a section between controls the 

 water table is supplied only from the stream, and therefore the water 

 table will never be higher than the water in the stream. From this 

 it follows that the stream wall never drain the water table and can 

 not gain in flow as it passes through a section where there is no under- 

 ground inflow. 



The daily maximum and minimum discharges at each of the con- 

 trols for the days of record are given in Tables 35 and 36. An exami- 

 nation of these tables shows that during all the period of record in 

 1931 and during the periods in 1932 from June 25 to July 26 and 

 from August 19 to November 3 the maximum daily discharge at the 

 lower control never exceeded by any significant amount the combined 

 discharges at the middle and branch controls. From this it follows 

 that there could be no underground inflow between these controls 

 during those periods, unless there was deep percolation as well. 



It is possible that a combination of underground inflow and deep 

 percolation might result in a daily difference of zero or thereabouts 

 in maximum discharges at the controls, but the deep percolation, if it 

 existed, would be approximately the same for different stages during 



