Normal Depth of Flow in the Culvert

Normal depth is the depth at which uniform flow will occur in an open channel. In other words, for a uniform channel of infinite length, carrying a constant flow rate, flow in the channel would be at a constant depth at all points along the channel, and this would be the normal depth.

Normal depth often represents a good approximation of the actual depth of flow within a channel segment. The program computes normal depth using an iterative approach to arrive at a value, which satisfies Manning's equation:

1)	$\begin{array}{l}\displaystyle \displaystyle Q= \frac{1.486}{n} AR^{2/3}S^{1/2}_f\end{array}$

Symbol	Description	Untis
$\begin{array}{l}Q\end{array}$	flow rate in the channel	cfs
$\begin{array}{l}n\end{array}$	Manning's roughness coefficient
$\begin{array}{l}A\end{array}$	area of flow	square feet
$\begin{array}{l}R\end{array}$	hydraulic radius	feet
$\begin{array}{l}S_f\end{array}$	slope of energy grade line	feet per foot

If the normal depth is greater than the culvert rise (from invert to top of the culvert), the program sets the normal depth equal to the culvert rise.