How to create a one-sided buffer for a polyline?

[No-Sass]

I'm looking to create a buffer area for one side of a polyline object. Specifically a river so its not a straight line. We've been able to create a buffer around the entire polyline object, but unsuccessful in being able to cleanly split and create a new object on the one side. Sample workflow attached. Thanks!

[BS_THE_ANALYST]

I think this is kinda working? @No-Sass  Check it out:

Initial line:

one sided buffer:

Regular buffer:

I