This question has a few parts:
1. Is it possible for a river to naturally form in the shape of a spiral?
2. If not, would an artificially-formed river, in the shape of a spiral, realistically maintain this shape?
3. If this is possible, what sort of a landscape would be necessary?
In the world that I'm building, a small group of people make use of magic to travel to a parallel universe and build a new society. The new planet that they land on has one circular land mass surrounded by water. I was imagining medieval or renaissance level technology for the world that they come from, but I'm open to changing this.
Unfortunately, I don't know very much about rivers, except that they flow downward, generally toward an ocean, so elevation is a huge factor. I guess my biggest concern is how this world's landscape would have to be shaped in order for a spiral river to exist. I'm especially interested in this because, for the purpose of the story, I want the world to appear as utopian as possible (i.e. minimal rough terrain, no crazy/jagged mountains, etc.).
Necessity of magic?
Even though magic exists in this world, I don't intend on it being widely used by the inhabitants, as it's almost impossible to wield. But, I'm wondering if the only way for my beloved spiral river to be formed and maintained is through the use of magic, and some fantastical hand waving. I haven't developed my magic system very much yet (as you can probably tell), and I'd like to get a sense of how much of my world can be formed 'naturally' before I decide what its magic needs to be capable of.
Any insights are greatly appreciated!