Segmented Weir Flow Equation

Simple Weir Flow Calculator
Irregular, Variable Depth Segmented Weir Flow Calculator

The equation for flow over a weir is

Q=Cw*L*H^1.5

where (in US units)

Q = flow in cfs
Cw = weir coefficient (about 2.5 to 3 for a broad-crested weir)
L = length of weir in feet
H = height of ponded water above lip of weir in feet

The equation for a sloped segment of an irregular weir is

Q=-Cw*(max(0,(H1-S*L))^2.5-max(0,H1)^2.5)/(2.5*S)

My online calculators for weirs are located at

http://www.hawsedc.com/engcalcs/Weir-Flow-Simple.php
http://www.hawsedc.com/engcalcs/Weir-Flow-Irregular.php

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