HYDROLOGY OF NEW YORK 



583 



of tlie stream below the storage point. Obviously the way to 

 do this is to plan for an outflow proportional to the catchment 

 area. In the present case we have a catchment area at Roches- 

 ter of 2365 square miles, and one of 1000 square miles above 

 Portage, or the area above Rochester is about 2^ times the area 

 above Portage. The minimum regulated flow at Rochester may 

 be made 2.365 times the assumed minimum flow at Portage. 



In the foregoing, the statement is made that the outflow 

 should be proportional to the catchment area. This is the theo- 

 retical view purely, and provided reservoirs can be constructed 

 at equally low cost in all parts of a catchment, it is the prefer- 

 able principle to follow. But this can seldom be done because 

 reservoirs will vary greatly in cost in different parts of a catch- 

 ment — they may run all the way from |15 to |20 per million 

 cubic feet stored to from |600 to f 1000 per million cubic feet. 

 This practical consideration will modify the theoretical con- 

 clusion. 



Assuming 680 cubic feet per second as the flow below which 

 the stream will never be allowed to fall at Rochester, we have 

 for a reservoir storing 7,500,000,000 cubic feet a corresponding 

 minimum outflow from the reservoir of 300 cubic feet per second, 

 or for a storage of 15.000,000,000 cubic feet an outflow of 457 

 cubic feet per second, the latter figure being arrived at by assum- 

 ing the maintenance of a minimum flow at Rochester of at least 

 1000 cubic feet per second. The computations of tables Nos. 

 <84 and 85 are carried out on this basis. The regulated flows 

 for the month of May are greater than for the other months. 

 They are also greatest during the months of canal navigation, 

 the addition being made in order to provide for the quantity of 

 water to be taken for the enlarged Erie canal, which quantity 

 has been fixed at 80 cubic feet per second for every month of 

 the navigation season except May, and at 177 cubic feet per 

 second for that month, the excess quantity for the -month of 

 May being required in order to provide for filling the canal at 

 the beginning of the month. 



Table No. 84 shows the effect on the flow of Genesee river from 

 June, 1894, to November, 1896, inclusive, as influenced by the 

 storage at Portage of 15,000,000,000 cubic feet of water, provided 



