Very occasionally, you can get a map where multiple rivers/streams/brooks meet in a small area. This can make it so that one of the rivers is in a gorge, and several other rivers then come over and dump into it as waterfalls.
To generate such a place, you'll want to set "Periodically erode extreme cliffs" to No, set the "Erosion Cycle Count" low, and increase the 2 "River Start Locations" parameters. That'll make it so that there are more big cliffs (so rivers that meet are more likely to be on radically different z-levels) and more rivers (so there are more rivers to meet, naturally).
For 40dx, there was a map which did have 3 or 4 minor rivers and streams and brooks falling into 1 major river where they could be put into a single playable map, though it was very big. I'll see if I can't dig it up. Even if you're playing 31.0x, you can still use the worldgen parameters as inspiration.
Edit: While it wasn't the one I was thinking of, I did find
this little place. Apparently, it has a 47-wide (!) major river that goes over a waterfall, and after its waterfall another river comes and joins with it (no waterfall on the minor river that I can see from the pics). Still, I would think that the 10-z-level, 47-tile-wide waterfall would be more than sufficient for most purposes.