HYDROLOGY OF NEW YORK 



327 



is employed. Gagings are also sometimes made by the use of 

 floats, but so far as New York streams are concerned, the results 

 would be so unsatisfactory as to render this method undesirable. 

 It has also been attempted to gage the flow of the Mohawk river 

 by velocity and slope measurements, but thus far the results are 

 not satisfactory. 



The method of gaging streams by the use of the current meter 

 has some advocates who consider it superior to any other. Prob- 

 ably the reason for such an opinion is that tests of a current 

 meter in uniform masonry or concrete channels, where the condi- 

 tions are the most favorable possible to obtain, have shown fairly 

 accurate results ; but in a shallow stream, flowing over a boulder 

 bed, the conditions are so different as to make rational compari- 

 son impossible. The current meter is indeed only really useful 

 when the following conditions obtain: 



1) A smooth, uniform channel for a considerable distance on 

 either side of the point selected. 



2) Considerable depth at the point selected and for several 

 hundred feet to either side. 



3) Smooth bottom of either fine sand, hard earth or very fine 

 gravel. 



4) That the current be positive and of some little velocity 

 throughout the whole section. 



New York streams as a whole do not, except rarely, answer to 

 these conditions. They are usually shallow, rapid flowing in 

 places, and frequently encumbered with boulders. Current meter 

 observation may be at times from 100 per cent to 200 per cent in 

 error. Broadly, we may say therefore that where a good dam 

 exists on a stream the gagings should preferably be first of all 

 made at this point. Or, if there is money available, a special 

 weir may be erected. Failing in either of these the current meter 

 is a proper instrument, with due understanding of the limita- 

 tions indicated in the foregoing. 



Streams discussed hi this report. It is impossible to give in the 

 following discussion the measurements of all the streams now 

 being gaged in the State of NewyYork, and accordingly a number 

 of the more important have been selected for which the records 

 will be given. The detail of the balance may be obtained from the 



