Portable and permanent flumes with adjustable throats

Abstract

The utility of developing vertically-adjustable flumes for canal flow measurement systems, is important to several problems in field practice. One involves the perception by some canal water users that flumes and weirs significantly and harmfully restrict flow. These perceptions, correct only sometimes, occur often enough to cause resistance to flow measurements and impedance to proper irrigation management. Parshall flumes and Cutthroat flumes require ponding depths upstream equal to about 40% of head reading while long-throated flumes and the related broad-crested weirs require only 10 to 15%. The actual head drop through all of these flumes is greater than hydraulically necessary for all but the maximum design discharge. The highly obvious excessive ponding is often misunderstood as a harmful restriction to flow. Also, the velocities at the low flows are reduced by this excessive ponding, which can aggravate sediment accumulation. The system described herein allows control of the ponding restriction from nearly zero to just enough restriction to gain measurement control of the flow at nearly all flow rates in the design range of a particular size. This reduces the amount of visible restriction. For a small structure size, with a control section less than 1 m wide and flowing under a head of less than about 25 to 30 cm, this restriction is about 10% to 15% of the head reading, or about 3 to 5 cm at maximum head. This maintains relatively high velocities in the approach channel for assisting sediment movement. The device is applicable to measuring flow rates in unlined and lined canals. The system described permits adjustment of the canal flow levels, reduces the perception of ponding, and minimizes the induced sediment problems.