To develop a continuous discharge rating relation for an orifice structure, it is necessary to handle flow situations in which the orifice opening is not fully submerged.

For circular orifices, Drainage and Utilities models partially submerged orifices by balancing specific energy across the culvert opening. This is implemented in the program by assuming a thin culvert (L = 0.002 ft). This approach makes friction conditions negligible. The inlet loss, Ke, is calibrated so that it matches the results of the orifice flow at the "just submerged" elevation.

Related Topics

• "Orifices"
• "Submerged Orifice Hydraulics"
• "Orifice Area Unsubmerged Hydraulics"
• "Orifice Orientation"