The Venturi Flume 
11 
section with reference to the g'Rge wells. If the current is flowing 
in the diverging section on the side of the observation wells, then the 
amount recorded will be more than the actual discharge; if the 
observations are taken on the opposite side from the current in the 
diverging section, then the reverse is true. Mean readings of 
simultaneous observations taken in four wells, as shown in Figure 
1, will, under ordinary conditions, give the true gage height. 
The derivation of the expression for computing the discharge 
through rectangular Venturi flumes is somewhat involved, and no 
attempt will be made to go into detail. As a general statement, it 
may be said that the basis of deduction is Bernoulli’s theorem, 
which results in the following for the theoretic discharge: 
Where jQ=discharge in second feet, 
W=width of throat in feet, 
Hb =head at the throat in feet, 
Ha =Head in converging section in feet, 
Hd = (Ha — Hb ) =difference in the two heads, 
C=constant. 
The value C, is really not a constant but varies with the 
width of the throat and also with the upper head, H a , and the dif- 
ference in head Hj. This variation is expressed by the following 
formula : 
which, when substituted for C in the theoretical equation, gives : 
Q=C W 
C=(0.9975--0.0175/F) + 
(i/^- 0.163//,^) 
Q= (0.9975 — 0.0175 w)-\ 
{Hd- 0-i« 
8 X _ _ 7 
The discharge diagrams. Figures 13, 14, 15, 16, 17 and 18 
appended to this report, are based upon calculated values as deter- 
mined by this expression. These curves are plotted on a logarith- 
