PORTABLE AND PERMANENT FLUMES FOR CHANNEL FLOW MEASUREMENT

Authors: Replogle, John; Wahlin, Brian

Submitted to: International Water and Irrigation Review
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: Many irrigation water users share a common perception that flow measuring devices (flumes and weirs) significantly and harmfully restrict flow because of the high visible ponding upstream of the flume. The perceptions cause opposition to flow measurements and thwart proper irrigation water management. In most instances, proper size selection and installation reduce or eliminate the physical effects of the problem but do necessarily address the misperceptions. We designed, tested and verified a modified, adjustable flume that addresses these problems in field practice and is practical and easy to use. They reduce to a minimum the amount of ponding for all flow rates. In the non-adjustable versions now in general use, only the maximum design flow rate enjoys minimum ponding. We also found that the flow discharge relationships can be accurately predicted with our previously developed mathematical model. 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 measurement in canal systems, both large and small, should be active candidates for using these structures.

Technical Abstract: Special flumes used for canal flow measurements that are designed with vertically adjustable control sections address several problems in field practice. One involves the perception by many canal water users that flumes and weirs significantly and harmfully restrict flow. These perceptions cause opposition to flow measurements and thwart proper irrigation water management. The older Parshall flumes require upstream ponding depths equal to about 40 percent of the head reading, while long-throated flumes and the related broad-crested weirs require about 10 to 15 percent. 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 an in-line gate to measure and regulate the flow depth in canals.