Exit Loss Coefficient

Exit losses are computed as a coefficient times the change in velocity head from just inside the culvert, at the downstream end, to the cross section just downstream of the culvert. The equation for computing exit losses is as follows:

1)	$\begin{array}{l}\displaystyle \displaystyle h_{ex} = k_{ex} \left( \frac{a_{exV^2_{ex}}}{2g} - \frac{a_2V^2_2}{2g} \right)\end{array}$

Symbol	Description	Units
$\begin{array}{l}h_{ex}\end{array}$	Energy loss due to exit
$\begin{array}{l}k_{ex}\end{array}$	Exit loss coefficient
$\begin{array}{l}V_{ex}\end{array}$	Velocity inside of culvert at exit
$\begin{array}{l}V_2\end{array}$	Velocity outside of culvert at downstream cross section

For a sudden expansion of flow, such as in a typical culvert, the exit loss coefficient (kex) is normally set to 1.0 (FHWA, 1985). In general, exit loss coefficients can vary between 0.3 and 1.0. The exit loss coefficient should be reduced as the transition becomes less abrupt.