Dear Avalisha :
With our DTM Module in RMS / RiverCAD, you can draw in a channel improvement / channel modification in plan view, and the software will "cut" a new channel for you. You can define what the channel invert is along the river and it will maintain that invert using a "vertical curve". The channel improvement / channel modification alignment is drawn with a single polyline and the DTM Module will then "cut" a channel along that alignment.
If you have any additional questions or need any further information, please contact me again.
Sincerely,
Chris E. Maeder, M.S.
Senior Technical Engineer
chris.maeder@bossintl.com