HYDROLOGY OF NEW YORK 



449 



several feet — variously estimated at from three to five feet — 

 higher than the highest known preceding flood, and similar evi- 

 dence exists for points on the Genesee up as far as Wellsville. 

 This is not true, however, for the lower portion of the valley. 

 At Mount Morris the flood hight attained was about that of pre- 

 vious floods, but at Rochester the river showed a discharge of 

 only about 20,000 cubic feet per second against 36,000 to 40,000 

 or 42,000 cubic feet per second for the 1865 flood and the March, 

 1902, flood. The excessive precipitation, therefore, must have 

 been confined to the headwaters of the river. 



It must not be inferred that the maximum flood discharge at 

 Portage was less than 20,000 cubic feet per second, the discharge 

 at Rochester. On the contrary, there is good reason to believe 

 that the discharge at Portage with only 40 per cent of the catch- 

 ment area was very much in excess of that at Rochester, and the 

 reasons for this are: (1) the flood hight at Portage was from 

 three to five feet higher than during former extreme floods which 

 gave flood discharges of 40,000 cubic feet per second at Mount 

 Morris, which has only 7 per cent more catchment area; these 

 former floods must therefore have discharged not much less than 

 40,000 cubic feet per second at Portage; five feet, or even three 

 feet, added to the crest of these former floods indicate still greater 

 discharges and leave little doubt that the discharge at Portage 

 was nearly if not fully double that at Rochester; (2) an examina- 

 tion of the July flood at Rochester shows that the maximum stage 

 of water was reached at Rochester during the afternoon of July 

 8, while the maximum stage at Portage occurred during the 

 forenoon of July 6, indicating that the flood crest occupied 

 more than two days in passing from Portage to Rochester. When 

 we consider the topography of the valley between Mount Morris 

 and Rochester, this time consumed in transit must have been 

 accompanied by an elongation of the flood with a corresponding 

 diminution of the discharge per second. 



A careful study of the circumstances attending this flood of 

 July, 1902, in conjunction with the other maximum floods in the 

 Genesee, leads to the conclusion that the maximum flood at Roch- 

 ester has not yet occurred, and that by a combination of circum- 

 stances which do not seem at all improbable a maximum flood in 

 ^excess of 40,000 cubic feet per second may reasonably be expected. 



