For validation purposes I've used a fairly simple straight concrete channel concrete structure (rectangular cross-section) for validation purposes. The channel is downward inclined under 0.14%, width 4m, length 1km and a manning coefficient of concrete (0.015) is used on surface and longitudinal lines. Boundary conditions inlet: Q = 27.2m3/s; outlet: Super-critical outflow. The mesh used is structured, cell size 0.25m.  The issue I am having is that results of Iber are not similar to theoretical values in water elevation that is settling in. It should level at 2.53m according to for example [https://www.eng.auburn.edu/~xzf0001/Handbook/Channels.html], while Iber is computing 1.82m at main channel section. What could've gone wrong here?