Sometimes active cross sections can produce strange shapes, like the example shown in the figure below (top). First, make sure the toe station and the movable bed limits are set to the same station. Second, the ARS-USDA BSTEM features often work best if HEC-RAS allows deposition outside the movable bed limits. In the Sediment Data Editor, go to the Options menu and select Bed Change Options. Then, under Deposition select the Allow Deposition Outside of the Movable Bed Limits option. This will constrain erosion to the movable bed limits (which will migrate with the toe if they have the same staring station) but will deposit any wetted node in the cross section. The model in the top figure was re-run in bottom figure with this option selected and produced more realistic results.
