Overflow Gates

Overflow gates represent a gate in which the bottom of the gate opening moves up and down. Overflow gates can be completely open to the air at the top, or the top can be closed off. An example of an overflow gate is shown below in the figure below.
Example Overflow Gate

Overflow gates are generally modeled with the standard weir equation:

1)	$\begin{array}{l}\displaystyle Q=CLH^{3/2}\end{array}$

Symbol	Description	Units
$\begin{array}{l}C\end{array}$	Weir flow coefficient, typical values will range from 2.6 to 4.0 (1.6 to 2.2 for metric units) depending upon the shape of the spillway crest (i.e., broad crested, ogee shaped, or sharp crested). Most overflow spillways tend to be sharp crested, so a value of 3.2 (1.76 for metric units) is typical
$\begin{array}{l}L\end{array}$	Length of the spillway crest
$\begin{array}{l}H\end{array}$	Upstream energy head above the spillway crest

For overflow gates in which the Sharp Crested spillway crest shape is selected, the user has the option of using the standard weir equation, The Rehbock equation (Henderson, 1966), or the Kindsvater and Carter equation (1957).