Lakes and void fills

Hello! seeing as WM is still living, today I purchased a new professional license! yay!

I am writing on the forum to ask a quick question, is there anyway of filling voids crated by noise or erosion to avoid voids that in real life would be filled by sediment or lakes?

Also is there a tutorial for using the new river tools? i find it looks amazing but I don’t see much information on-line about using it.