Flumes
FLUMES
Definition and Functions
Flumes
Flumes are used to carry irrigation water across gullies, ravines or other natural depressions. They are open canals made of wood (bamboo), metal or concrete which often need to be supported by pillars. Flumes are specially shaped, engineered structures used to measure the flow of water in open channels. Flumes are static in nature - having no moving parts - and develop a relationship between the water level in the flume and the flow rate by restricting the flow of water in various ways.
Types of Flumes
· Elevated flume - a structure used to convey irrigation water across and above natural depressions such as rivers or creeks
· Bench flume - usually a rectangular concrete trough supported on a bench excavated into a hillside and through which water flows into an adjoining canal
· SI-flume a combination siphon and flume that conveys water across a depression, drainage canal or stream usually from a higher to a lower opposite bank; usually a closed rectangular reinforced concrete conduit supported above by the ground columns or piers
History
1849-1888
Although Belanger and Bazin were fully aware of the existence of a unique relationship between the upstream sill-referenced head and the discharge over a weir with critical flow at the control section, their hydraulic theory was not used by irrigation engineers in their search for a discharge measuring flume.
1912
A second style of 'Venturi flume' was originated by the irrigation engineers, Harvey and Stoddard, both of the Punjab Irrigation Department.
1917
In Colorado, Cone laid the foundation for the U.S. practice of designing a style of flumes with a piezometer tap.
1928
Inglis reported on Crump's experiments on these 'standing wave flumes'. The head-discharge equation of the long-throated (standing wave) flume. This long-throated flume, became very popular for irrigation water measurement.
1931
Lindley described their flume as follows: 'By introducing a smooth hump on the bed, or smooth contractions of the sides of a regular channel, a dip in the water surface is produced equivalent to the head converted into increased velocity. Knowing the areas of the upstream and throat sections, and the amount of this dip, the discharge can be calculated'
1944
Mahbub and Gulhati report that, in 1944, about 12,500 of these open flumes were being used in canals in the Punjab alone.
Advantages
While having similar accuracy, flumes have distinct advantages over weirs, including:
· The ability to measure higher flow rates than a comparably sized weir
· Less head loss (1/4th that of a weir)
· More readily passes debris
· Wide range of styles and sizes
· Off-the-shelf availability
· Smaller installation footprint
· Less rigorous maintenance requirements
· Also, most flumes are resistant to changes or restrictions in the downstream hydraulics (submergence) - something not found with weirs.
· First, and most importantly, flumes are available in countless styles, which gives them a big advantage over other flow management devices.
· Minimal maintenance needs is another benefit of choosing a flume for flow management and measurement.
· T biggest strength of flumes is that they provide much more accurate readings than other devices you could choose. With a long-throat flume, for example, there are multiple points of measurement available, allowing your operators to choose the most accurate location. Assuming that they are sized and installed correctly, flumes provide the accurate flow readings that you need.
Disadvantages
· Cost is perhaps the biggest drawback of using a flume. These devices are typically more expensive than weir boxes, especially if you need a customized flume.
· Flumes can be difficult to install in some instances, although this isn’t always the case.
· Not accurate at low flow rates. It is therefore not entirely satisfactory for measuring widely fluctuating flow rates.