686 



ECONOMICAL ASPECTS 



the summation of them results in convenient units of day-second- 

 feet or a second-foot flowing for twenty-four hours (1.98 acre-feet) 

 as in Fig. 400. As the length of the ordinates shows the increase 

 or decrease of the twenty-four-hour flow, it will readily be seen 

 that the slope of the curve represents the rate of flow and that a 

 uniform flow is represented by a straight line as FG." 



40,000 



Oct. Nov. Deo. Jan. Feb. Mar. Apr. May June 



FIG. 400. Flow-summation Curve. 



The inclination of a tangent to the curve at any point indicates 

 the rate of flow at that particular time, and when the tangent is 

 parallel to the abscissas it illustrates that the flow at that time will 

 just balance the losses caused by evaporation, seepage, etc., while 

 a negative inclination of the curve shows that a loss from the 

 reservoir is taking place. 



" Assume, for example, that FG represents a regulated or 



