I have a good workflow for making a river with a flat riverbed, but for both builds 3014 and 3015 it appears that the bed undulation capability is nonfunctional- or I am missing some unknown element to get it to work. Attached is a .tmd file that shows a simple straight river with a flat bed, including width variation. I do have the bed undulation curve plugged in and it is not working, so the bed is flat. If you unplug that thalweg undulation sinusoidal function, then you'll formally have a flat riverbed example you can use.
if you have any questions about this .tmd, let me know.
Regards.