Calibration of Portable Central Baffle Flumes for Measurement of Flow through Open Channels

Abstract

ABSTRACT newlineMeasurement of continuous flows in open channels is essential for optimal water use and proper scheduling for agriculture. The increasing stress and scarcity of water demands a device capable of registering discharge at the desired location and time in an open channel. Such a device will also be of great use even for the metering of water and subsequent billing. Typically, the flow measurements in open channels are performed using weirs or control flumes that establish a unique flow-depth relationship. newlineIn the present research, a particular type of control flume, referred to herein as the Central Baffle Flume (CBF), has been theoretically investigated. The flume consists of a streamlined body positioned axially in the open channel, contacting flow to create critical conditions. At first, a cylindrical object is placed at the center of the channel to achieve the required contraction. The stage-discharge relationship for the Cylindrical CBF is obtained by applying the concepts of dimensional analysis and self-similarity. The deduced form of the discharge equation is continuous and applicable for a contraction ratio range of 0.53 1 and channel side slope varying between 0.50 H:1 V to 2 H:1 V under free-flow conditions. The stage-discharge relationship for the Cylindrical CBF is characterised by absolute relative error, which was found to be less than 10 % when applied on the experimental data. newlineThe flow constriction is then achieved using a cone-shaped object by inserting it at the center of the channel. The change in geometry of the flume, after the insertion of the cone, has been studied and incorporated in the analytically derived discharge prediction model using the energy concept. A discharge correction factor is implemented to correct the unrealistic assumptions of uniform velocity distribution and streamline curvature. The discharge prediction model has been calibrated using the experimental data collected on rectangular and trapezoidal (1H:1V) channels. The calibrated discharge equation predicted disc