Rectangular Weirs

In Drainage and Utilities, a rectangular weir is characterized by two equations: suppressed and contracted.

Suppressed weirs prevent the contraction of the flow through the weir and hence the associated losses. These types of weirs are usually, but not solely, associated with broad crested weirs, and are defined by the following equation:

Q	=	flow (cfs, cms)
C	=	weir coefficient (US, SI forms)
L	=	length (ft, m)
H	=	head (ft, m)

Flow over a contracted weir does contract as it goes over the crest of the weir. These types of weirs are often associated with the sharp crested types of weirs, and are defined by the following equation:

Q	=	flow (cfs, cms)
C	=	weir coefficient (US, SI forms)
L	=	length (ft, m)
H	=	head (ft, m)

Note: For most rectangular weirs at ponds, C is usually 3.2 (US Customary units; for SI units, C is usually 1.8).