Contraction and Expansion Loss Evaluation

Contraction and expansion losses in HEC-RAS are evaluated by the following equation:

1)	$\begin{array}{l}\displaystyle h_{ce}=C \displaystyle\left\lvert \frac{\alpha_1 V_1^2}{2g}- \frac{\alpha_2\ V_2^2}{2g} \right\rvert\end{array}$

Where: $\begin{array}{l}C\end{array}$ = the contraction or expansion coefficient

The program assumes that a contraction is occurring whenever the velocity head downstream is greater than the velocity head upstream. Likewise, when the velocity head upstream is greater than the velocity head downstream, the program assumes that a flow expansion is occurring. Typical C values can be found in "Basic Data Requirements."