Results can be very sensitive to groundwater. Two particular groundwater errors that can create model problems:
Never specify a starting or static groundwater table that is higher than the bank edge.
Groundwater elevations far below the channel water surface elevation will prevent the bank from failing. The USDA-ARS BSTEM applies a hydrostatic assumption, computing suction according to a hydrostatic gradient from the groundwater elevation. Therefore, in ephemeral streams or situations where the groundwater table is unknown, estimate the groundwater elevation or put it at an average surface water elevation banks should fail.