r the 
than the crest of the weir. If air has free access urn 
falling sheet it may be as high as the crest, without aJ 
the discharge; but if higher, the discharge is affect^^— 
form is objectionable. In such cases the discha^^^^ 
found approximately 
Let H = the depth or water over the wei^^H^ 
in feet;—the depth below the weir, jJjg«||^p.stream side, 
measured m stil water The latter sho^j^e the crest, both 
which IS formed below the weir andj^PffJy bg below the wave 
The discharge inay be found^«^asured in feet; 
mg that^ the water flows ove^pf^ppi-oximately by consider- 
though It came through an oj^^he weir for the depth, h, as 
pressure H h, and the height and under 
remmmng depth H ^ /^^pif^er portion of the stream for the 
I he discharge of ^^^or d, flows as over a weir, 
cording to the tables q 
I he discharore fl |pven with this bulletin or by the formula. 
or the opening height, h, may be coni¬ 
ng the velocity due to the head, d, in feet 
according to the Torricellian theorem, is 
4.4. The discharge through a foot length 
tion would then be 4.8 h i/~d, approximatelv. 
3 
o 
puted by determii 
per second, whid 
where g 
of the lower po 
That of the 
be, for a portj 
3-33 Hence, the total discharge would 
on of length L feet, 
This is no 
correctly 
dischar 
It 
a flur 
ditc 
Q = 3*33 L -|- 4.8 L// 
likely to vary by 5 per cent, if measurements are 
made. All dimensions are measured in feet; the 
& is given in cubic feet per second, 
s better to avoid the submerged weir, and instead use 
e placed in the ditch, of the same cross-section as the 
Ti, which should be rated at the different depths in the 
he manner as the measuring flumes near the heads of the 
anals in Colorado. The methods of the use of these will be 
described in a future bulletin. 
THE TRIANGULAR WEIR. 
The triangular notch or weir, proposed by James Thom¬ 
son, has been strongly recommended, as it has certain advan¬ 
tages due to the fact that the orifice preserves the same shape 
for all depths, and the ratio of the area to the weir peri¬ 
meter remains constant. The discharge depends onl}^ on the 
depth as well as the angle, instead of the width which is 
usually necessary also. The equation for the flowthrough such 
an opening maybe found without difficulty to be 
8 _ ^ 
O ="== 15 T d 'ig Jd 
where m is the coefficient of contraction, T the tangent of 
