CHAPTER 9 - SUBMERGED ORIFICES

13. Radial Gate Checks Used for Measuring Device

Radial gates are widely used in canal check structures to control canal flows and water levels. By measuring upstream water level, downstream water level, and gate position, radial gate checks can also be used to compute flow. Computing flow at check structures prevents the additional cost and head loss from flow measurement devices such as flumes, weirs, or flow meters.

Radial gate flow is a type of variable-area orifice flow, which may be either free or submerged. However, accurate computation of radial gate flow requires complex analysis. Discharge under a radial gate is influenced by numerous parameters and structure dimensions. Figure 9-8 shows a typical radial gate with some of the variables that affect gate flow. The angle of the gate's bottom edge (gate lip) varies with the gate opening, Go, the pinion height, PH, and the gate's radius, r. Flow contraction is sensitive to the angle , the type of gate lip seal, and water levels.

 Figure 9-8 -- Diagram of radial gate showing calibration variables.

The general equation for flow through an undershot gate can be derived from the Bernoulli equation and expressed as:

where:

Q = discharge (gate flow)
Cd = coefficient of discharge
Go = vertical gate opening
B = gate width
g = gravitational constant