HYDROLOGY OF NEW YORK 



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Cochituate and Mystic rivers have been deduced, it is believed, by 

 Mr Francis's formula for the Merriniac dam. As to the Desplaines 

 river, a discharge curve determined by current meter has, it is 

 believed, been applied. 1 The English streams cited, Lea, Wandle, 

 Thames, etc. have probably been gaged by a sharp-crested weir, 

 and the others mostly by the current meter and a rating table. 



Russell's formulas. Mr Thomas Russell 2 gives the following 

 formulas for the runoff of the Ohio, Upper Mississippi, and Upper 

 and Middle Missouri valleys, in terms of the annual rainfall. For 

 the Ohio river the formula is as follows : 



0=0.600+0.95 R— 0.90 R (0.975 e— 0.421 e 2 +0.G26 e 3 ). (27) 



For the Upper Mississippi it is : 



0=0.50+0.93 R— 0.88 R (1.131 e— 0.383 e 2 ). (28) 



For the Upper and Middle Missouri it is : 



0=0.12^-0.98 R— 0.93 R (0.91 e— 0.220 e : +0.009 e s ). (29) 



In these formulas R is the rainfall for the month in cubic miles; 

 e is the quantity of water required to saturate the air at any time, 

 equal to the difference between what the air contains and the 

 amount if it was saturated ; and O is the ( utflow or runoff. 



These formulas are interesting in the present connection, 

 because they recognize the fact that every stream must have its 

 own formula. The variation in runoff on the Ohio, Mississippi 

 and Missouri rivers will be observed on inspection of the formulas. 

 Like all formulas of this class they are subject to considerable 

 variation. In the month of October, 1881, the computed outflow 

 of the Missouri river was 4.9 culbic miles and the observed flow 

 Avas 1.6 cubic miles, a difference of 3.3 cubic miles. 



Relation between catchment area and maximum, minimum and 

 mean runoff. It is quite common for hydrologists to assume that 

 there is a relation between catchment area and maximum, mini- 

 mum and mean runoff, the general proposition being that mean 



lData Pertaining to Rainfall and Stream Flow, by Thomas T. Johnston: 

 Jour. Western Soc. Engrs., Vol. I, No. 3, June, 1896. 



2 Rainfall and River Outflow in the Mississippi Valley, by Thomas Rus- 

 sell: Ann. Rept. Chief Signal Officer for the year 1889, Part I, Appendix 14. 



