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Calculate Required Diameter for (FHWA) Circular Orifice Outlet Control With Free Discharge:

(Note: All input Metric units are converted to English units for the equations below and then the output English units are converted back to Metric)
Pre-development peak runoff rate (qpb - cfs or cms)
Water surface elevation at design volume (Es - ft or m)
Elevation of centroid of orifice opening (Eo - ft or m)
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