#PARSHALL FLUME FREE#

To determine discharge through the flume under free flow condition, head is measured at upstream section (H a). Flow is submerged when the down-stream water elevation retards the rate of discharge. Discharge through the flume can occur under either free or submerged flow condition. Standard dimensions of Parshall flumes with discharge values are presented in Table 8.1 and 8.2, respectively. On the basis of the throat width, Parshall flumes have been classified into three main groups. Care must be taken while constructing the flumes exactly in accordance with structural dimensions. Parshall flumes are available in various sizes. The size ranges from 7.5 cm to several m in throat width. The size of flume is determined by the width of its throat. The flume consists a converging section with a level floor and walls converges towards the throat section, a throat section with a downward sloping floor and parallel walls, and a diverging section with an upward sloping floor and diverging walls towards the outlet. Parshall flumes are devices for the measurement of flow of water in open channels when depth of flow is less i.e., head drop is very small, the volume of flow is less and channel bed slope is less. Installation requires extremely careful work.įlow at the entrance must be evenly distributed, with little turbulence, to produce accurate measurements. Provides a reliable measurement in free flow and submerged flow conditions. The flow-rate in flumes is usually high enough to prevent sedimentation they are therefore self-cleaning. For large submergence, the tailwater height must be known and a different analysis method must be used.Enables measurement in a large range of flow. Equation 1 predicts the flow rate with reasonable accuracy, however, even for 50–80% submergence (calculated as H b/H a). A very high tailwater reduces the flow rate through the flume. Values of K are given in Table 1, although using a value of 4.0 is accurate for most purposes.Ībove a certain tailwater height, the Parshall flume no longer operates in the free-flow mode. Above 0.7, the true discharge is less than predicted by Eq. The discharge relationship for a Parshall flume is given for submergence ratios of H b/H a up to 0.7. This design eliminates any dead water region where debris and silt can accumulate (as are common with flattopped weirs). Following the critical section is a short length of supercritical flow followed by a hydraulic jump. The throat geometry in a Parshall flume has been designed to force the occurrence of critical flow at that point.

The length, width, and height of the flume are essentially predefined by the anticipated flow rate. The walls of the flume are vertical, but the floor of the throat section drops. The Parshall flume is constructed with a converging upstream section, a throat, and a diverging downstream section.

It performs well when head losses must be kept to a minimum and when there are high amounts of suspended solids. The Parshall flume is widely used for measuring open channel wastewater flows. Parshall Flume Flow Measurement Equations and Calculator Related Resources: calculators Parshall Flume Flow Measurement Equations and Calculator