52 W. & L. E. GURLEY, TROY, NEW YORK 



tin- mean velocit\. This coefficient varies from 78 to 98%, 

 depending on the depth and the velocity of the stream. The 

 deeper the stream and the greater the velocity, the greater the 

 coefficient. For average streams in moderate freshets, a co- 

 < ili< i.-nt of 90% should be used; in flood work, a coefficient of 

 f mm 90 to 95%; and for streams at ordinary stages, from 85 

 to 90%. 



Independent discharge measurements, as a rule, are of but 

 little value in hydraulic work unless they are taken at stages 

 \\hieh air known to be either extremely low or extremely high. 

 In ordinary work it is necessary to make a series of measure- 

 ments which, with daily gage heights of the flow of the stream, 

 make possible the computation of the total flow of the stream 

 and also its distribution. In connection with the individual 

 measurements, therefore, it is necessary to observe gage heights 

 and take full notes of the conditions under which the measure- 

 ments are made, in order to enable the construction of a station 

 rating curve and estimate the daily discharge. 



RECORDING THE DATA 



The observations should be noted at the time they are made 

 on properly prepared forms for discharge measurements, shown 

 on pages 54, 55 and 60. 



There should be shown in these notes: 

 In column 



1. The distance from the initial point of each vertical in 

 which soundings and velocity observations were made. The 

 distance between successive stations gives the width of the 

 partial area. The widths are written in column 11. 



2. The depth of water in the vertical at which the observa- 

 tion was made, as determined by the sounding. 



3. The depth from the surface down to that point in the 

 vertical at which the velocity observation was made. This item 

 is computed mentally in the field before making the velocity 

 observation, and will be two-tenths, six-tenths, eight-tenths, etc., 

 of the depth recorded in column 2, depending on the method 

 used in making the measurement. 



