HYDROLOGY OF NEW YORK 



379 



by 10 feet 6 inches (or 4 per cent) for all depths less than 8 

 inches, while the length between wingwalls heretofore used was 

 substantially correct. It was also found that the dam crest is 

 not absolutely level because of settlement near the center pier, 

 and that the method of measuring the depth gave results about 

 0.30 inch too high. 



2) The flow in the old Croton aqueduct at the depth commonly 

 used before the new aqueduct was opened is less than previously 

 estimated by about 14,000,000 gallons per day, or 15 per cent. 

 These earlier estimates were based on using for the old Croton 

 aqueduct the same coefficient of flow found for the new, smooth 

 and clean Sudbury aqueduct, and not upon a gaging of the old 

 aqueduct itself. 



3) Gaged by the same observer with the same instrument, the 

 new Croton aqueduct is now delivering less water for a given 

 depth of How than when new. to the extent of about 40,000,000 

 gallons per day ; or, when the depth measured at the head of the 

 aqueduct is 11 feet, the shortage is about 15 per cent. 



4) An error was made five years ago in setting the gage by 

 which depths in the new aqueduct are read, so that it makes the 

 depth appear 2J inches too large; this cause alone contributes 

 about 0,000,000 gallons per day to the overestimate mentioned 

 above. 



5) The effect of storage drawn from Boyd's Corner and Middle 

 Branch reservoirs and the Croton lake in modifying the natural 

 flow had not been taken into account in these earlier estimates, 

 neither had due allowance been made for the controlled natural 

 ponds. 1 



Croton river is an average water yielder. The minimum yield 

 for a complete water year for the whole period 18G8-1899, in- 

 clusive, was in 1880, when from December to November, inclusive, 

 the total runoff was 13.71 inches. 



The Croton catchment contains thirty-one lakes and ponds, 

 many of which have been utilized as natural storage basins by 

 constructing dams at their outlets. The following tabulation 

 gives the entire natural and artificial storage, either actually 

 carried out or under construction in 1902, for the Croton catch- 

 ment area: 



l Freeman's report, pp. 121-123. 



