Unreal Engine 4: River Tool w/ Terrain Snap

https://www.youtube.com/watch?v=POKsbXNdtuI

Allows you to drag out a river spline that will snap to the starting spline or to the underlying terrain. Will also create a spline for the river bed that's depth is configurable as well as a configurable water height. One you align the path as desired you can select the terrain that will need to conform the river and apply the spline data to it starting with the river guide then the river bed spline. The default settings for the falloff is what I've found to be a happy general starter. I hope this helps some.