How to make flat river bed ?

[ttham]

I have this combination http://prntscr.com/f146ho
I'm trying to substruct river bed node from main terrain but its still taking in consideration terrain curvature http://prntscr.com/f147sx
how I can substruct it that bottom part was flat.
like that http://prntscr.com/f14a5b

[WFab]

I'm guessing the second combiner is set to "subtract". Move the slider all the way to the right for subtract and you'll get expected result.

[RiverDr]

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.