Cipolletti (Trapezoidal) Weir Flow

Flow over a Cipolletti (trapezoidal) weir, whose 1H:4V side slopes make up the end-contraction loss, so it uses the full crest length with no deduction. Q = 3.367 x L x H^(3/2) (cfs, ft); a 3 ft crest at 0.5 ft head passes 3.57 cfs (1,603 gpm, 2.31 MGD). The common ditch/irrigation-turnout weir because the rating is simple and the length reads straight off the notch. Requires a ventilated, free-flow, sharp-crested weir; head measured ~4H upstream. USBR Water Measurement Manual; the operator of record governs.

Q = 3.367 x L x H^(3/2) (cfs, crest length L and head H in ft); 1 cfs = 448.831 GPM; MGD = GPM x 1440 / 1e6. Coefficient editable.

Per the USBR Water Measurement Manual (public domain) and King's Handbook of Hydraulics - the Cipolletti (trapezoidal, 1H:4V) sharp-crested weir discharge equation, by name.

Free at usbr.gov/tsc/techreferences/mands/wmm; the 3.367 Cipolletti coefficient is a fixed published constant and the user may override it with a site calibration.

Estimate. AHJ and licensed professional govern.

Field names used by the API: crest_length_ft, head_ft, flow_cfs, flow_gpm, flow_mgd

• Cipolletti discharge Q = 3.367 L H^(3/2) (cfs, ft); coefficient editableUSBR Water Measurement Manual / King's Handbook
• Contraction compensation 1H:4V side slopes cancel end-contraction, so the full crest length L is usedCipolletti weir geometry
• Weir condition fully-contracted, ventilated, sharp-crested, free flow; head ~4H upstreamUSBR Water Measurement Manual