Realigning Panner Direction?

Development Rendering
1

I’m making a spline-based river system, but I’m having trouble with the river surface material, specifically with panning the texture. It works fine lining up the straight-direction panning, but when I want to curve the river direction along the x/y axis, I’m having difficulty figuring out how to adjust the pan direction to match the direction that the river is turning.

Examples:

Correct

Incorrect

2

The best way is UV the river so that it’s straight in the UV map, it’ll look like it’s flowing along the river.

3

It’s straight in the UV, but the spline is duplicating the mesh and then skewing it to make the curve, which doesn’t angle the uvs in the new direction.