688 ECONOMICAL ASPECTS 



vation will tax the reservoir capacity to its limit and settle the 

 question conclusively as to the maximum regulated flow obtain- 

 able." 



Having the mean daily discharges of a stream, it may also 

 be required to find how large a reservoir is required to obtain a 

 maximum regulated flow. This may also be obtained from Fig. 

 400. By drawing a line from B to D the maximum regulated 

 flow utilizing all the water is found, and the ordinate V 2 W rep- 

 resents the capacity of the reservoir in day-second-feet, which 

 would be required to effect this. 



The above method is suitable for determining the power pos- 

 sibilities of a given development when one or two power-houses 

 with accompanying reservoirs are involved. When a large num- 

 ber of related power-houses and reservoirs are involved, this 

 method of using the mass curve of discharge becomes very long 

 and tedious. Also, it is only approximate, giving as a result uni- 

 form flow of water, not uniform power, and it fails to take into 

 account regulative effect on the power output of the power-houses 

 situated on the upper sections of the watershed. To solve these 

 more intricate problems, a method of determination has been 

 proposed by Mr. L. A. Whitsit, and is described in the Engineering 

 News for September 11, 1913. 1 



The utilization of stored water so as to absolutely insure a 

 fixed minimum flow in all years, while, perhaps, best for streams 

 whose power is not developed up to the limit, leads to a very 

 uneconomical use of the reservoirs on streams which already are 

 highly developed as to power. As a condition of high ratio of 

 development exists on many streams where storage would be most 

 desirable and valuable, and as this condition will become more 

 and more pronounced on all power streams, it is apparent that the 

 subject of this basis of figuring the power benefits is of importance 

 in securing a proper view of the relation of water storage to water 

 development. 



The conditions may be such that when the method of regu- 

 lating for a minimum steady flow of water is applied, it has been 

 found, for example, that the storage capacity would have been 

 used to its full extent only once in ten years. During six of the 

 ten years it would not have been used at all, and during two years 



1 See also Engineering News, Aug. 24, 1916. 



