Orifice Design

The Orifice Design uses the methodology described in HEC-22 Manual. The orifice flow is determined as:

Q = C_o A_o (2 g H_o)^0.5

where:    Q = discharge, ft³/s (m³/s)
              C_o = orifice coefficient, unitless (0.40 - 0.60)
              A_o = area of orifice, ft² (m²)
              H_o = effective head on the orifice measured from the centroid of the opening, ft (m)
              g = gravitational acceleration, 32.2 ft/s² (9.81 m/s²)

This command designs an orifice structure and calculates its stage-discharge curve. Select Orifice Design from the Structure menu in the Hydrology Module to display the design dialog. Select the Section Type of the orifice, Circular or Rectangular. Enter the dimension for the orifice. In the Invert Elev box, type the absolute elevation at which the orifice will be attached to a reservoir. The attachment point is at the bottom of the orifice. In the Coefficient box, type a roughness coefficient for the orifice. The coefficient ranges from 0.4 to 0.6 (HEC-22). In the Number of Openings box, enter the number of orifices you want to combine.

In the Headwater and Tailwater boxes, type the absolute headwater surface elevation and tailwater surface elevation respectively. Click on the Calculate button, the maximum discharge and flow velocity through the orifice would be computed and displayed.

Click on the Stage-Discharge Result button to display the stage-discharge curve in the Stage-Discharge Result Dialog. This dialog allows you to write the stage-discharge data to a stage-discharge file(.STG), and draw the stage-discharge curve on the screen. From the Stage-Discharge Curve Draw Settings dialog , you can specify how to draw the curve. The Report button generates the orifice design report.

Orifice Design Dialog

Stage-Discharge Limits Dialog

Stage-Discharge Result Dialog

Orifice Design Report

Pulldown Menu Location: Structure > Orifice Design
Keyboard Command: orifice
Prerequisite: None