WATER STORAGE 689 



only about one-half of the capacity would have been used. It is, 

 therefore, evident that capital if invested for use only once in ten 

 years must when it is used yield a very large return. Such a 

 method of management of a storage reservoir would call forth 

 just criticism when it was discovered that after money had been 

 spent for the auxiliary power during the low-water season, the stor- 

 age reservoir remains full of water. This has led the Water 

 Supply Commission of the State of New York to deduce a new 

 method of computation, which is based on an average rate of 

 release of stored waters, so that while the assurance of a certain 

 minimum flow would not be unduly sacrificed, the entire volume 

 of stored water could be used practically every year. This 

 method, which has been termed the " utility " method to dis- 

 tinguish it from the " insurance " method, has been based on a 

 knowledge of the conditions of the larger streams of the State, 

 where the developments can be run at full capacity up to about 

 60 per cent of the time reckoned over a long period of time, and it 

 assumes that there is always sufficient demand for power to 

 absorb any additions and render further development after 

 regulation as desirable as before. 



Figs. 401 and 402 represent graphically the results of an inves- 

 tigation for the regulation of the Genesee River by providing a 

 storage reservoir having a capacity of 13.5 billion cubic feet. 



The stream-flows are arranged according to magnitude, and 

 result in the curve marked " Natural Flow of River." Although 

 the vertical scale is given in horse-power, the power is propor- 

 tional to the stream-flow as long as the head is not affected, and 

 the curve would not be changed in any respect if stream-flow 

 instead of power were used. In order to plot the " Regulated 

 Flow " curve the mass curve, as previous^ explained, is used, and 

 the regulated flows are also arranged according to magnitude 

 and the values plotted as for the natural flow. 



The results were based on a " present " wheel installation of 

 29,200 horse-power, and by referring to diagram, Fig. 401, it will 

 be seen that one-fifth of all the water power with regulated 

 flow and present wheel capacity will be derived from the stored 

 water, shown by the vertically sectioned area. Without regula- 

 tion the present installation can be operated at its full capacity 

 for only 58 per cent of the time and diminishes to a minimum of 

 about 7500 horse-power. Similarly the amount of energy neces- 



