Divination is already a function of the Druidcraft forum.
Dowsing is not a form of divination. It's an art and study all its own. Dowsing doesn't predict the future - it can show what is, now, not what will happen. It is very useful for this. Dowsing can easily be discussed in the Druidcraft forum, or in a sub-forum, or in a separate forum, depending on the level of interest.
When, for example, someone dowses to find out the gender of an unborn child, that's not predicting a future outcome - it's answering what is already the gender of the child. Thus, it's not a predictor, and therefore, not divination even tho some put it there.
Divination shows what is now, and uses current patterns to predict likely outcomes.
Tarot and runes are valuable ways to discover current patterns in one's life - and likely outcomes of those patterns. It doesn't predict the future, just shows probable outcomes if current patterns continue. We always have free will which allows us to conscously change patterns in our life. Self knowledge is IMO the main purpose of divination, so that we can make informed choices in our lives.
Astrology isn't really divination either - it is similar to divination methods as it also works with current patterns in one's life, based on placement of the stars, and thus can outline the likely ongoing results in one's life.