Hi, I'm the same person, now with an account. 

On OsmAnd, which sources from OpenStreetMap, it describes it as "natural", and renders it using the same icon as the Niagara Falls. 

On Google Street View, it looks like some sort of decorative water structure with water falling down a large slope. 

I personally can't find a better description than waterway=waterfall, and I don't think there is a way to categorize them. Maybe just create a description?