HYDROLOGY OF NEW YORK 



453 



except for slight rises due to rainfall on September 7 and 8, and 

 September 15 and 18, until October 15, when the flow rose to a 

 little over 2000 cubic feet per second: At Rochester, on the other 

 hand, the effect of the heavy rainfall of August 29, was to so far 

 replenish the depleted ground water of the flats as, with the excep- 

 tion of a few days in the early part of October, when the flow 

 dropped to about 600 cubic feet per second, to keep the flow up to 

 about 800 cubic feet per second, for the balance of the year. 



The storage value of the Genesee river flats. In order to 

 further illustrate the great storage value of the flats, we may note 

 that the catchment area at Rochester is 2.3 times that at Mount 

 Morris; hence, for proportionate yields the flow at Rochester 

 should be 2.3 times that at Mount Morris. During August, 1893, 

 at a time of extreme dry weather, the flow at Rochester was 3.7 

 times that at Mount Morris, and after the extreme storm of 

 August 29, which replenished the ground water of the flats, the 

 flow at Rochester, during the entire replenishing period (Septem- 

 ber, October and November) was four times that at Mount Morris. 



A knowledge of this constant accession of large quantities of 

 water from the flats leads to another conclusion of great practical 

 importance, namely, that we may expect to realize at Rochester 

 the full value of all the water added from the storage at Mount 

 Morris; that is, an addition of, say, 700 cubic feet per second at 

 Mount Morris, in time of low water, will be likely to increase the 

 flow at Rochester 700 cubic feet per second more than it would 

 have been without such addition. 



In order to show more strikingly the value of the flats for such 

 storage, we will now compute the amount stored and held back 

 therein. 



Referring to Rafter and Baker's Sewage Disposal in the United 

 States, page 165, we find a tabulated statement of the per cent 

 of empty space in a number of soils, as follows : 



Per cent 



In Illinois prairie soil, the voids are 55.2 



In East Windsor, Connecticut, clay soil, the voids are. . . 48.3 



In coarse river sand, the voids are from 38 . 4 to 41.0 



In subsoils, the voids are from 34.6 to 42.6 



In blowing sands, the voids are 44.7 



