HYDROLOGY OF NEW YORK 



113 



is discharged into Cayuga lake without affecting Seneca river 

 below the mouth of Clyde river at all. It is undoubtedly due to this 

 fact that fall floods on Oswego river are almost entirely unknown. 



The evaporation of the Oswego river catchment area is exceed- 

 ingly large — about 28 inches — whence it results that the runoff 

 from a mean annual rainfall of from 3G to 37 inches does not 

 exceed about 9 or 10 inches. 1 



Computation of annual runoff. No general rule can be formu- 

 lated for computing annual runoff. The formulas of Mr Vermeule 

 are excellent formulas of the purely empirical class, applying 

 fairly well to many streams in the northeastern part of the United 

 States, but they do not apply at all to streams of the middle west 

 and far west. Nor do they apply to some streams in the north- 

 eastern section. Nevertheless, they take into account the ground 

 water, and are the most useful formulas thus far devised. It may 

 be mentioned that Mr Vermeule specially disclaims any inten- 

 tion of working out any formulas applying outside of the State of 

 New Jersey. His general formula is in the nature of a suggestion. 



Discrepancies in- computation of runoff. In computing the run 

 off of various streams small discrepancies will continually appear, 

 and when such do not exceed 1 to 2 inches they are outside the 

 limit of discussion. The question does not admit of such minute- 

 ness as to permit the discussion of small differences, although a 

 difference of 2 inches on several thousand square miles would be 

 much less serious than on the usual municipal catchment area 

 of from 20 to 100 square miles. The size of the catchment area 

 should, therefore, in this particular be taken into account. 



Moreover, the runoff of streams has thus far been almost uni- 

 versally over-estimated. Only a few were really down to the actual 

 fact. Probably in no department of professional work are there 

 more things to be taken into account than here. 



Actual gagings preferable to general studies. While on the gen- 

 eral subject of the computation of runoff the writer may repeat 



i The preceding chapter has been abstracted from the writer's report on 

 Special Water Supply Investigation to the Board of Engineers on Deep 

 Waterways. 



