There are many types of open channel flow measuring devices available. Of these, flow measuring flumes are one of the most commonly used.
How a Flume Operates
Flumes are specially shaped, fixed hydraulic structures that under free-flow condtions force flow to accelerate in such a way that the flow may be characterized by a know relationship between the liquid level (head) at a single specified location and the flow rate. Acceleration is provided by converging the sidewalls, raising the bottom, or a combination of both.
Sections of a Flume
A flume normally consists of a three sections: a converging section, a throat section, and a diverging section. Examples of this configuration include: Parshall, Trapezoidal, Cutthroat, and RBC flumes - although technically the Cutthroat flume omits the throat section as it has no length in that style of flume.
Flumes range in size from the very small to the very large, with throat widths ranging from 1-inch [2.54 cm] to 50-feet [1,524 cm]. Measurable flows can range from 0.03 to 3,000 cubic feet per second (ft3 /s) [0.849 to 84,960 l/s].
Some flumes have calibrations available for submerged conditions where the critical depth has been nearly drowned by downstream backwater either purposely or by later increase of downstream flow resistance.
Advantages Over Weirs
Flume head loss is less than about one-fourth of that needed to operate a sharp-crested weir having the same control width. Another advantage compared to most standard weirs is that for a properly designed and installed flume, the velocity of approach is a part of the calibration equations. Unauthorized altering of the dimensions of constructed flumes to obtain an unfair share of water is difficult and, therefore, not likely. Unlike weirs, most flume styles allow for the ready passage of sedimentation and floating debris – reducing the time and effort associated with maintaing a flume.
- Stream gauging
- Irrigation studies
- Drainage studies
- Dam seepage monitoring
- Industrial pre-treatment discharges
- Sewage treatment plant flows
- Spring discharge
- Well pumping tests
- Mine drainage
- Tailwater runoff
- Flow splitting
Styles of Flumes
Openchannelflow offers a variety of flumes styles, allowing you to select a flume that best fits your particular site needs, including: Parshall, HS / H / HL, Trapezoidal, Cutthroat, Montana, and RBC. These flumes styles are standardized and non-proprietary. In some cases flume styles may be defined by industry, governmental, or international standards (i.e. TAPI, ASTM, ISO, JIS, etc.). Where industry / governmental / international standards do not exist, the flume style has been well documented in published research literature.
Flume Acccessories and Options
Select flumes styles are available in full and custom height (half or extended – in select sizes), nested (smaller flumes nested in larger flumes), and “magic bottoms” (replacement floors to correct installation deficiencies or raise the “zero” elevation of the flume).
Extended height flumes offer higher flow capacities than standard height flumes, but in a smaller footprint than a larger flume would occupy. The developmental literature for the Parshall flume leads Openchannelflow to note that the flow equations are believed to be accurate for extended height flumes, but are not guaranteed to be so.
Depending upon the type of flume, Openchannelflow offers several materials of construction, including:
- Fiberglass (standard)
- Galvanized steel
- Lexan (small sizes)
- PVC (small sizes)
- Stainless steel