Measurement and Division oe Water. 35 
corresponding to the depth at each end by the use of the tables. 
Multiply each of these quantities by the corresponding depth; sub¬ 
tract these two results and divide by the difference in the depths 
of the two ends, and take 2/5 of this quotient. The depths should 
be expressed in decimals of feet. 
pv 2 /Qi Eq Qo Ho \ 
^ 5 V H x — H 2 ) 
THE triangular WEIR or notch. 
A weir in the form of a triangular notch can be used in many 
cases to advantage. As the perimeter always bears the same ratio 
to the area the friction remains constant for different depths. This, 
notch does not seem to have been used practically. It, however, 
might be used to a greater extent for laterals from canals. For 
that reason table II., the first of this kind that I know of, is given 
for a right angled notch that will enable it to be used. 
The best form of notch would be a right angled notch with 
the corner downward. For a depth of one foot it will give a dis¬ 
charge of 2.5 cubic feet per second, which is as much or more than 
an ordinary lateral takes, and consequently may be used for that 
purpose. It is not applicable for large discharges. 
The equation for the flow through such an opening is: 
Q — 15 m Ty g h 5 ' 2 
where m is the coefficient of contraction, T the tangent of one-half 
the angle, G the acceleration of gravitation and H the depth. Giving 
M the value 0.592, the formula becomes: 
Q= 2 M Th 5 ' 2 
where Q is the discharge in cubic feet per second and the head 
on the notch is measured in feet. This should be measured at a 
point several feet upstream from the notch, the same as in the case 
of the weir. 
If the notch is a right angle notch we then have the equation 
of discharge: depths in feet. 
Q= 2 . 5 ! h 5 ' 2 
As this notch is especially adapted for small discharges it 
would be best adapted to conditions where the water is not over 
12 inches in depth. It is then convenient to be able to express 
the quantity in cubic feet per second, with the depth measured in 
inches. 
In this case the discharge in cubic feet per second would be: 
Q =.0051 h 5 ' 2 
where h is in inches. 
This notch should be placed to conform to the conditions of 
the weir, that is, it should be placed at right angles to the current; 
