![]() Where, Q is the discharge, C, n is the flume coefficients which vary with the size of the flume, and H is the measuring head. However in case of free flow conditions, the discharge is measured by the following formula: Generally, Parshall flumes are calibrated empirically in laboratory conditions before installing in the field. Dimensions and capacities of Parshall flume of various sizes (Letter, refer Fig. Free flow condition prevails if the submergence ratio (H b/H a) remains within 0.5, 0.6 and 0.7 for width of throat varying from 2.5 to 7.5 cm, 1.5 to 22.5 cm and 3.0 to 24.0 cm, respectively. However, downstream head (H b) is also measured for submerged flow condition. 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. The size of parshall flume are from 3 inch up to 48 inch depending on the requirement.Enables measurement in a large range of flow. A total of 22 standard sizes of Parshall flumes have been developed, covering flow ranges from 0.1416–92,890 L/s. The flumes are not patented and the discharge tables are not copyright protected. The design of the Parshall flume is standardized under ASTM D1941, ISO 9826:1992, and JIS B7553-1993. Some states specify the use of Parshall flumes, by law, for certain situations. Under free-flow conditions the depth of water at specified location upstream of the flume throat can be converted to a rate of flow. The Parshall flume accelerates flow through a contraction of both the parallel sidewalls and a drop in the floor at the flume throat. ![]() It is used to measure volumetric flow rate in industrial discharges, municipal sewer lines, and influent/effluent flows in wastewater treatment plants. The Parshall flume is a fixed hydraulic structure. The Parshall flume is an open channel flow metering device that was developed to measure the flow of surface waters and irrigation flows. ![]()
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