4 
Colorado Experiment Station 
possible at the expense of considerable loss in head or grade of the 
channel, and in many cases the installation of the standard weir is 
'imposslible on account of the lack of fall. This is especially true 
where large quantities are to be measured. Where the water carries 
considerable silt, there is a tendency to fill the weir basin with sedi- 
ment, which affects both the contractions and the velocity of ap- 
proach. The submerged orifice and weir are limited to practically 
the same requirements, in so far as contractions and velocity of ^ ap- 
proach are concerned, but permit of operation under conditions 
where a small loss of head is important. 
The rating flume, which is nothing more than a constant sec- 
tion through which the water passes, is the accepted standard for 
the measurement of the comparatively large flows. This method of 
measurement is subject to various effects, and is only rarely found 
to maintain a constant condition. Experience indicates that, in the 
majority of cases, the rating flume is wholly unreliable, due to the 
change of velocity of approach, silting conditions in the flume and 
the accumulation of vegetation in the channel, as well as along its 
banks. It is not uncommon to find the rating flume affected by 
check boards, placed in the channel below the flume, for the purpose 
of raising the water sufficiently to permit the irrigation of higTer 
lands. 
The Venturi flume has been developed to meet these various 
conditions ; however, it is not claimed that this device is accurate to 
the last degree, but under ordinary conditions it is believed to be 
very much more dependable than our present accepted methods. A 
number of these Venturi flumes have been installed and are in actual 
use, and it has been found that this new device possesses the follow- 
ing desirable features : * 
1 — It is moderately inexpensive and simple to construct. 
2 — It is simple in its operation. 
3 — It requires little maintenance. 
^ — It is free from working parts. 
5 — It is sufficiently accurate to meet practical needs. 
6 — It is unaffected by sand, silt or floating trash. 
7 — It requires but little loss of head in its operation. 
8 — It possesses a very wide range in its capacity of discharge. 
Altho the Venturi flume possesses many very desirable fea- 
tures, there still remain certain defects in the present design that 
work to its disadvantage. It is believed, however, with further 
"'(Journal of Agricultural Research, Vol, IX, No. 4, V. M. Cone) 
