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Calculate Required Length of Weir for Weir 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)
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Pre-development peak runoff rate (qpb - cfs or cms)
Water surface elevation at design volume (Es - ft or m)
Elevation of crest of weir (Ew - ft or m)
Weir coefficient (Cw)

Typical values for Cw (English Units):
Rectangular weir - sharp crested: Cw = 3.33
Rectangular weir - broad crested: Cw = 2.861
Cipoletti trapezoid: Cw = 3.367
Ogee spillway: Cw = 3.97
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Lw =

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