Note - Legacy Method Can Cause Strange Behavior
We added new volume to area change methods in HEC-RAS version 6.0 because the default method, inherited from HEC 6, used different methods to compute volume/area change for the active layer and the cross section nodes. This meant that the area and volume change did not always "match" and in extreme cases, HEC-RAS could compute a positive volume change (deposition) in the control volume but lower the cross section nodes (erosion) - or the opposite. We have left this method in the model for backward compatibility and it should remain default if the model was created in a previous version. But the other methods use the same algorithm for the active layer and the cross section change, and are recommended.