Another question. Is there a way to stop rivers from genning, while still having plains? I want the sweet plains for humans, but the rivers don't really fit in.
I haven't manipulated worldgen for rivers but I would suggest you should try
[RIVER_MINS:0:0]
as an advanced worldgen parameter. It certainly won't guarantee less rivers but what it will do is allow worlds with less rivers not to be rejected. (First value is pre-erosion minimum, second post-erosion.)
Turning the rainfall down, which you'll want anyway for deserts should reduce their number.
However importantly river start locations require an elevation of 300+, so limiting it to 299 should prevent any rivers from spawning. (Again haven't tested...) Please note that 300+ are mountains so, yeah, dwarfs...
Other less potent tweaks might include turning erosion cycle count down (rivers which exist are less major) and orthographic projection off (more consistent rainfall across world, so easier to control parameters).
Drainage may be problematic depending on what exactly is wanted. High drainage will reduce number of rivers but for deserts (sand) you will need low drainage, medium will give rocky wastelands and high badlands, that is when paired with low rainfall.
Finally, in my experience, humans have a thing for at least starting their civilizations adjacent to water. So if there are no rivers I would expect them to be starting by the coast. Though I certainly haven't ever dived into the code to see if this is explicitly stated or just one of those things that happens - repeatedly.