Momentum

For a long culvert it is possible to include or exclude a contribution to the momentum equations at the outlet location. This contribution is estimated as the discharge multiplied by a velocity. Here the magnitude of the velocity is calculated as the discharge divided by the local total water depth. The direc­tion used for the two extent lines is the direction of the first and last segment of the transversal polyline. If the transversal polyline only contains one seg­ment (two points), the direction is determined as the direction perpendicular to the line given by the first and last point of the extent line.