Technical Notes: A Portable Electronic Indicator for Head Measurement with Long-throated Flumes

Abstract

Measuring the height of water in portable long-throated flumes equipped with a stilling well in the sub-critical flow area is somewhat ambiguous. The developers of the flume (Bos et al., 1984) leave the decision of the method of determining the head up to the user. A common method of measuring the head uses a mounted point gauge located in the stilling well. During field use problems of accuracy, repeatability, and ease of reading the head measurement device are evident with this method. To solve these problems, a portable electronic device was developed that is capable of measuring the head in flumes equipped with a stilling well (fig. 1). This device triggers an audible signal when the indicator rod touches the water in the stilling well, allowing measurement of the head without seeing the water surface, which is at or below the ground level. It also eliminates the need for a head measuring device mounted on the flume, which can be difficult to read and easy to damage. In laboratory and field tests the electronic device has proven to be accurate, mechanically reliable, with repeatable results between different users, and easy to use. The electronic device has been used in a wide variety of field conditions with no reported malfunctions. A linear regression analysis of laboratory flow rates measured using the electronic device results in a R2 of 0.995, a y-intercept of 0.022, and a slope of 0.991 (fig. 2) when plotted versus the known flow rates.