OF AN OPEN CHANNEL BY GANGUILLET AND KUTTER’S FORMULA. 
A=k’b:, 
(5) [p= 
The equation (4) gives Q in terms of the bottom breadth b. Hence, 
b is determinate when Q is given, and plotting Q as abscissa and b as 
ordinate, we get a graphic representation of the equation (4), giving 
~ 
b for a given Q. This b multiplied by 2k’ is equal to the depth d. 
Thus the eross section is determined for a given discharge. 
When once the curves (4) are plotted on paper for several values of 
0, J and n, they may be used thereafter and the laborious calculations 
involving the repeated application of Ganguillet and Kutter’s Formula 
may be practically avoided, while the Formula acts as the basis of these 
curves. 
Moreover, by the aid of these curves, the variations in Q due 
to that of n, @ or J may be traced. Conversely, the variations in the 
elements n, @ or J for a constant discharge may also be put in evid- 
ence. For intermediate values of n, # or J other than those adopted 
below, the bottom breadth may be determined by a graphical interpolation, 
To meet the various requirements occurring in practice, I have cal- 
culated the following sixty sets of curves for values of 
G30, 40°; 60° and 90°: 
| 1 t 
I= 309 > 500 ° 1000 ° 3000 
and 
5000 ’ 
n—0'020 for rough rubble in cement, stone pitching, 
n=—=0,025 for rivers and canals in perfect order, free from 
stones or weeds, stone pitching in bad condition, 
n—0030 for rivers and canals in good order. 
Plates I, If, III and IV show these curves plotted for constant 
values of 9 ==30°, 45°, 60° and 90° respectively. 
In these plates, the scales for depths d (—2k’ b) are given along with 
the scales for bottom breadths b, so that b and d for a given Q may be read 
off at once. Logarithmic scales are used for Q. Q is in cubie feet per 
second and b & d in feet. These may be taken as cubic shaku (FR) 
per second and shaku (NR) resp., without sensible error. 
