Flow measurement flume
Some varieties of flumes are used in measuring water flow of a larger channel. When used to measure the flow of water in open channels, a flume is defined as a specially shaped, fixed hydraulic structure that under free-flow conditions forces flow to accelerate in such a manner that the flow rate through the flume can be characterized by a level-to-flow relationship as applied to a single head (level) measurement within the flume. Acceleration is accomplished through a convergence of the sidewalls, a change in floor elevation, or a combination of the two.[4]
Flow measurement flumes typically consist of a converging section, a throat section, and a diverging section. Not all sections, however, need to be present. In the case of the Cutthroat flume, the converging section directly joins the diverging section, resulting in a throat section of no length (hence the term "Cutthroat"). Other flumes omit the diverging section (Montana, USGS Portable Parshall, and HS / H / HL flumes).[5]
Flumes offer distinct advantages over sharp-crested weirs:[4]
- For the same control width, the head loss for a flume is about one-fourth of that needed to operate a sharp-crested weir
- The velocity of approach is part of the calibration equations for flumes
- Unauthorized altering of the dimensions of constructed flumes is difficult (and therefore unlikely)
- Most flume styles readily allow for the passage of sedimentation and floating debris – reducing the time and effort associated with maintaining a flume installation
Styles of flow measurement flumes include: Cutthroat, HS / H / HL-type, Khafagi, Montana, RBC, Parshall, Palmer-Bowlus, Trapezoidal, and Venturi Flume.
Flow measurement flumes can be installed in earthen channels, concrete canals, below ground chambers, or factory integrated into Packaged Metering Manholes.[citation needed]