Enchanted River Added At Last Minute?

I found out that the Enchanted River was not included in the early drafts of the Hobbit. It was added very shortly before publication and after it's one scene involving Bombur being knocked in (And shortly after knocked out) by a deer, it was barely mentioned and never appeared again. I'm going to get a copy of the The History Of The Hobbit, which will hopefully contain some more answers, but until then, I'm absolutely stymied. Theories? Thoughts? Answers?