Define the Equations for a Contracted Rectangular Weir
If the rectangular weir is a contracted weir and the flow is restricted from passing freely through the weir opening, a reduction in Q is accounted for by reducing the weir length b:
beffective = bactual - 0.1(N)(H)
Q = 2/3 (C1) (bactual - 0.1(N)(H)) √2g (H)1.5 = Q = 3.33(L - 0.2H) H1.5