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:
b_{effective} = b_{actual} - 0.1(N)(H)
Q = 2/3 (C_{1}) (b_{actual} - 0.1(N)(H)) √2g (H)^{1.5 }= Q = 3.33(L - 0.2H) H^{1.5}