HYDROLOGY OF NEW YORK 



447 



area in modifying the effect of an extreme flood, reference may be 

 made to fig. 35, in which, with time as abscissas and runoff as 

 ordinates, the runoff record of Genesee river for May 18-23, 1894, 

 has been plotted. The lower curve of that figure may be taken as 

 representing approximately the law of the runoff of any generally 

 distributed heavy rainfall on the catchment area of this stream. 

 In making this statement it is not overlooked that flood-flows at 

 other seasons of the year may differ somewhat in their movement 

 from that of May, 1894. Inasmuch as the rapidity and intensity 

 .of the runoff of any given stream depend largely upon the topog- 

 raph}, the statement may be made that the general law of move- 

 ment of floods in the Genesee river is indicated by the lower curve 

 of fig. 35. With this understanding we may assume any other run- 

 off and construct the approximate curve by drawing it generally 

 parallel to the curve of the actually observed case. In this way 

 the upper curve of fig. 35, representing the curve of a flood one 

 and one-half times greater than that of May, 1894, has been pro- 

 duced, slight irregularities of the lower curve having been neg- 

 lected in projecting the upper one. 



A flood-flow one and one-half times as great as that of May, 1894, 

 which culminated in a maximum of about 42,000 cubic feet per 

 second at 3.30 a. m. of May 21, gives a maximum of 63,000 cubic 

 feet per second, the movement of which would be, under the 

 assumptions, substantially as in the upper curve of fig. 35. As 

 to the probability of a maximum flood-flow of 63,000 cubic feet 

 per second on the upper Genesee catchment area, the case of the 

 neighboring Chemung river may be cited, where a flood-flow of 

 07.1 cubic feet per second per square mile occurred in June, 1898. 

 This figure applied to the. upper Genesee would give a possible 

 maximum runoff of 71,126 cubic feet per second. 



Flood of 1896. The flood of April, 1896, came very near reach- 

 ing the danger limit — so near, indeed, that it is now the opinion 

 of many thinking citizens of Rochester that the regulation 

 afforded by the proposed storage dam at Portage may not be 

 sufficient to fully protect the city from a repetition of the disaster 

 <»f 18G5. If the river were to again rise to the night attained in 

 that year, the damage would inevitably be several times greater 

 than occurred then. 



