HEC-RAS allows complex cross sections. USDA-ARS BSTEM idealized cross sections in a couple of important ways. HEC added logic to adapt BSTEM to complex cross sections but some cross sections shapes still tend to be unstable. In particular, avoid "bank depressions" (see figure below) if possible. Cross section node elevations should increase from the toe to the edge of the bank.
The model can become unstable when a soil layer boundary crosses the cross section more than once. Therefore, if the cross section includes an important bank depression, make sure that the soil layer does not pass through it.
