Apr. a$, 1917 
The Venturi Flume 
119 
The Venturi flume with rectangular cross section is especially simple to 
build of any material suitable for use in water, and will probably be the 
most popular type. Its practical minimum throat width is 1 foot, and 
the largest one thus far constructed has a throat width of 7 feet. 
A general formula for the discharge through rectangular Venturi flumes 
has not been worked out, because calibrations have not been made on 
flumes large enough to warrant a formula of general application. Dis¬ 
charge curves are given in figures 2, 3, and 4 for throat widths of 1,1^, 
and 2 feet. 
TRAPEZOIDAL VENTURI FLUME WITH SIDE SLOPES OF TO 1 
Although no trapezoidal Venturi flumes with side slopes of i^to 1 
have been constructed, there is no reason apparent why their behavior 
would not be similar to that of rectangular cross-sectional type. The side 
slopes of 1 yi to 1 will fit the majority of canal banks, and the resulting 
cross section will accommodate a greater range of discharges than the 
rectangular flumes. Therefore it is believed that, for the larger canals, 
the more satisfactory type of Venturi flume will have a trapezoidal cross 
section with side slopes of 1% to 1. It will fit nicely with concrete lining 
of canals. This form does not call for warped surfaces, because the 
slopes are taken normal to the axial line of the flume, which is in a plane 
normal to the side of the throat section but is not normal to the side of the 
converging and diverging sections. The general plans for this type are 
given in figure 6, but no discharge curves are available at this time. It 
is expected that calibrations will be made from structures as they are 
installed under actual field conditions. 
V-NOTCH VENTURI FLUME 
There has been a demand for many years for a device to measure small 
flows of water where the permissible loss of head is small, or where sand 
and silt is carried by the water. After repeated unsuccessful attempts 
had been made to arrange a modification of an orifice or weir to meet 
these conditions, it was decided to ascertain what combination could be 
made of the Venturi flume and the triangular-notch weir. The result 
was the V-notch Venturi flume shown in figures 7 and 8. The side 
slopes of ^ to 1, in a plane normal to the axis of the flume, give a cross- 
sectional area of the throat section for different depths of water, which 
allows a good range of discharge from extreme high to low heads. This 
form is applicable under conditions of head commonly found in small 
ditches to flows of from 0.1 to 2 or 3 second-feet. 
Discharges through V-notch Venturi flumes are given in graphic form 
in figure 5, and those computed from the formula are given in Table II. 
