Section 2. FLUMES
1. INTRODUCTION. A flume in an open or closed conduit is similar to a
venturi in a fully charged pipeline. The channel is constructed to cause a
decrease in pressure and an increase in velocity. A common characteristic of
flumes is the formation of a standing wave close to the outlet of the
constricted section which is why they are sometimes called standing wave
flumes. There is no "standard" flume; each is individually designed.
1.1 Meter Designs. The Parshall flume and the Palmer-Bowlus flume are two
designs currently in common use.
2. OPERATING PRINCIPLES. In flumes, the measuring section can be designed
with a contraction of the sidewalls, by a raised section, or hump, of the
channel bed, or by a combination of both contraction and hump. These changes
cause a measurable difference in head pressure between the converging section
and the throat. The difference in these pressures is used to calculate flow
rate. .. .
2.1 Parshall Flume.
The Parshall flume is a measuring flume that is
well-adapted to use
in irrigation canals and ditches. This flume consists of
an entrance section
with converging walls and level floor, a throat section
with parallel walls
and a downstream sloping floor, and an outlet section with
diverging walls and
rising floor (Figure-7-4). The crest is the line where