Weir / Flume Open-Channel Flow
Open-channel flow over a 90-degree V-notch or rectangular (Francis) weir in cfs, GPM, and MGD from the head over the crest and an editable weir coefficient.
Formula and source
90-degree V-notch: Q = 2.49*H^2.48. Rectangular Francis: Q = 3.33*(L-0.2H)*H^1.5 (contracted) or 3.33*L*H^1.5 (suppressed). 1 cfs = 448.831 GPM.
Per the USBR Water Measurement Manual (public domain) - V-notch and Francis rectangular-weir equations and Kindsvater-Carter / Francis coefficients, by name.
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