Was “Arrollo” ever standard spelling for the modern word “arroyo” as in “stream”

I’m reading a Spanish translation of the lord of the rings which is now several decades old. The translator was a Spaniard I know that.

The exact phrasing is “Había un arrollo al pie de la loma”

That is perplexing because the previous page uses “arroyo” on the previous page to describe a river.

Is there some context as to why the translator would use both spellings? Did one spelling have a connotation?