92 



NEW YORK STATE MUSEUM 



Increase of runoff ivith increase of rainfall. In making allow- 

 ance for difference in rainfall, it should be remembered (1) that 

 in many catchment areas the annual runoff is in nearly constant 

 relation to the precipitation; and (2) that such relation will be 

 more marked when the excess rainfall above a certain minimum 

 annual depth is taken into account. This subject will not be 

 pursued at length any farther than to point out that in the 

 Genesee catchment an average of 10.5 inches runs off in the stor- 

 age period; 1.7 inches in the growing period, and 2.0 inches in 

 the replenishing period. In the Hudson catchment, an average of 

 16.10 inches runs off in the storage period; 3.45 inches in the 

 growing period, and 3.72 inches in the replenishing. In the Cro- 

 ton catchment, an average of 16.83 inches runs off in the storage 

 period ; 2.57 inches in the growing period, and 3.42 inches in the 

 replenishing. These figures, it may be again stated, are the 

 means — the maximum and minimum runoffs can be determined 

 by examining the tables. 



Broadly, the proposition is that a given increase in rainfall 

 above the amounts required to produce the foregoing figures will 

 be -followed by something like a similar increase in runoff. Such 

 increase, however, is not very definite, although the broad state- 

 ment is true that it bears a relation to the rainfall. 



The following will illustrate the essential truth of this proposi- 

 tion : 



, Inches \ 





Rainfall 



Runoff 



Genesee river. 









40.3 



14.20 





31.0 



6.67 



Difference 



9.3 



7.53 





47.79 



19.38 





40.30 



14.20 



Difference 



7.49 



5.18 



Comparing the maximum year with the mi 



nimum, we have: 



1894 



47.79 



19.38 



1895 ■<Pe«r-M>*>*niMt 



31.00 

 16.79 



6.67 

 12.71 





