PORTABLE FLUMES WITH ADJUSTABLE THROATS

Authors: Replogle, John; Wahlin, Brian

Submitted to: Proceedings ASCE North American Water and Environment Congress
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/27/1995
Publication Date: N/A
Citation: N/A

Interpretive Summary: A common perception by many irrigation water users is that flumes and weirs, devices that measure the rate of flow, significantly and harm- fully restrict flow because of the highly visible ponding upstream of the flume or weir. These perceptions cause opposition to flow measuring and thwart proper irrigation water management. In most instances, proper size selection and installation of the flow measuring device reduce or eliminat the physical effects of the problem but do not address the misperceptions. One such device (a vertically adjustable, long-throated flume) for canal flow measurement addresses these problems in field practice. We designed, tested, and verified that such flumes were practical and easy to use. They allow the minimum amount of ponding for all flow rates and not just the maximum, as is the case with non-adjustable styles. This provides sizing flexibility to meet the needs for a wide variety of field conditions. The reduction of ponding at nearly all flow rates for a particular flume size makes it more acceptable to the user. These devices are applicable to measuring flow rates in field ditches and lined and unlined canals. Canal operators, researchers, and farm irrigators dealing in water management and water management in canal systems, both large and small, should be active candidates for using these structures.

Technical Abstract: Vertically adjustable flumes for canal flow measurements address several problems in field practice. One involves the perception by some canal water users that flumes and weirs always significantly and harmfully restrict flow. These perceptions cause opposition to flow measurements and thwarts proper irrigation water management. The older Parshall flumes, commonly used in the past, require upstream ponding depths equal to about 40% of the head reading while long-throated flumes and the related broad-crested weirs required about 10 to 15%. The actual head drop through all flumes is usually greater than hydraulically necessary for all but the maximum design discharge. Because excess capacity is available at the low flows, it seldom affects the actual carrying capacity of the canal. However the highly obvious excessive ponding that results may be misunderstood as a significant restriction to the flow. The vertically adjustable, long-throated flumes can reduce ponding at nearly all flow rates for a particular flume size, thus reducing the amount of visible restriction. In small sizes, less than 1 m wide, and flowing less than about 25 to 30 cm deep, the ponding is only about 3 to 5 cm. The device is applicable to measuring flow rates in lined and unlined canals. It can serve as the shut-off structure when it is raised to its top-most position as well as in-line gate to measure and regulate the flow depth in canals.