HYDROLOGY OF NEW YORK 



375 



is about 4000 cubic feet per second. They are mostly of modern 

 types and have been tested at Holyoke. When the flashboards 

 are on, computations at Fort Edward have been made by the 

 Francis formula for sharp-crested weir, but when the flashboards 

 are off, the flow is computed by means of the East Indian engi- 

 neers' formula. 



In the winter of 1896-97 a flood spillway was cut in the rock 

 at the south end of the dam over which the water begins to flow 

 whenever it reaches the level of the crest of the flashboards. The 

 profile of this spillway is irregular and causes a good deal of 

 uncertainty in the calculated flows during high water. Indeed, 

 the uncertainty is so great that the writer has for a number of 

 years been unwilling to publish the record of this dam. He has, 

 however, finally reviewed it, recomputing a portion of the same, 

 and the figures are given for what they are worth. There is con- 

 siderable uncertainty in the high-water flows — perhaps as much 

 as 25 per cent. The entire low-water flow passes through the 

 water wheels, and there may be some uncertainty in this, although 

 not as great as in the flood flows. 



The summer flow of the Hudson river at Mechanicville and Fort 

 Edward is materially increased by the outgo from Indian river 

 dam, built in 1898. A record of the flow at Indian lake has been 

 kept since July, 1900. 



The geology of the Hudson river basin is complicated — from 

 its mouth to its extreme headwaters it crosses nearly every 

 formation appearing in the State of New York. 



Discharge measurements of Groton river. This stream serves 

 as the principal source of water supply for the City of New York, 

 Borough of Manhattan. The average daily consumption of water 

 in all the Boroughs of the City of New York was, in 1899 r 

 371,778,000 gallons, distributed as follows: 



Gallons. 



Manhattan 

 Bronx 

 Brooklyn . 

 Queens . . . 

 Kichmond 



230,000,000 

 21.000,000 



102,663,000 

 12.025,000 

 5.190,000 



The catchment area of the Croton river lies almost entirely 

 in New York, only a small portion being in Connecticut. It 



