168 DIVISION OF WATER RESOURCES 



inflow" and ''measured outflow" g'ives the quantity of water con- 

 sumed in the area of natural losses. Tlie inflow has been plotted for 

 every da.y b,y use of the three methods on these plates. ]\Iost of the 

 apparent irregularities during Aug'ust and September, 1931, were 

 due to surface run-off from rainfall, which could not be evaluated. The 

 true relation holds only when all tlie water comes from subsurface 

 sources. 



Relation of natural losses to evaporation. 



In order to make the data computed in Table 3 applicable else- 

 where on the Santa Ana River, the natural losses over the area were 

 determined as a function of evaporation. The resvilts are given in 

 Table 4, in which the natural losses for each 5-day period have been 

 converted into acre-feet. The average loss in feet over the whole area 

 was computed by dividing the losses in acre-feet by the area in acres. 

 This average was compared with the evaporation from a standard 

 "Weather Bureau pan at Prado for the same periods, expressed in feet, 

 and the ratio computed. This ratio gives the losses as a percentage 

 of evaporation. For example, for the period July 1-5, 1931, the 

 natural losses amounted to 0.109 foot, or 61 per cent of the evaporation 

 from a standard Weather Bureau pan for the same period. The means 

 of these percentages were computed for the three months in both 1931 

 and 1932. They were 68 per cent for 1931 and 64 per cent for 1932. 

 The average for the two seasons was 66 per cent. These ratios do not, 

 however, apply w^here the natural losses are compared to evaporation 

 from a reservoir or other relatively large free water surface. By using 

 the coefficient of 1.427 determined by Rohwer ■'' for the correction of 

 the standard pan record, the natural losses for 1931 and 1932 are found 

 to be nearly equal to the evaporation from a reservoir or other large 

 free water surface. 



Natural losses and inflow between Riverside Narrows and the 

 Prado gaging station. 



Between the gaging stations at Riverside Narrows and Prado there 

 is 4040 acres of land subject to substantial natural losses. By means of 

 the coefficient determined in the preceding tables, the natural losses 

 within this area were computed and converted into acre-feet for each 

 5-day period from January to November, 1932. The results of these 

 computations are expressed graphically on Plate XI. 



A check on the computations for inflow for the area above the 

 Prado gaging station was made by using the data collected at The 

 Atchison, Topeka and Santa Fe Railway Bridge for the period May to 

 November. The area of natural losses above this station is 3580 acres. 

 With the coefficient of 66 per cent the natural losses were computed 

 from the evaporation pan record at Prado. The addition of these 

 losses to the flow at the railway bridge gaging station gave the total 

 inflow for the area between Riverside Narrows and the railway bridge. 

 These results have been plotted on the graph in the form of a dotted 

 line. 



The 2| miles of river channel between The Atchison, Topeka and 

 Santa Fe Railway Bridge and the Prado gaging stations is cut through 



" Rohwer, Carl, Evaporation from free water surfaces : U. S. Dept. Agri., Bull. 

 271, 1932. 



