The Venturt Flume 
25 
found necessary, and this can best be accomplished by a false bot- 
tomed bucket or can, rigidly fixed to a long rod or wooden handle. 
Scales or gages attached to the inside surface of the flume foi 
determining the head are not sufficiently accurate for general 
purposes. 
Due to the nature of the law of flow through the Venturi 
flume, the accuracy increases as the difference in head inci eases, 
also the per cent of error in making the reading is decreased when 
the difference in head is great. Consequently, it is advisable, if the 
head is available, to operate the flume with the greatest difference 
in head possible. 
The application of the genei'al discharge formulas, as given 
for the Venturi flume, is not recommended for determining dis- 
charges for flumes having throat widths or depths beyond the 
limits of those shown in the diagrams; however, if these expres- 
sions are applied, the results will be only approximations. 
Concrete structures are recommended, but timber may be used 
if the structures are well braced to insure stability. 
The logarithmic discharge diagrams are used in exactly the 
same manner as an ordinary co-ordinate chart ; however, care must 
be used in picking off the values because of the fact that the inter- 
vals of equal value decrease as the quantities increase. ■ 
Changing the velocity or increasing the depth of water below 
the flume does not effect the utility of the device. All changes are 
automatically taken care of by the variation in the gage heights. 
