On checking 30 m is not accurate. I have read rail corridor is "15m from the outermost rail on either side" but it is clearly more than this in most places, 60 m or more. It does not alter conclusion for these tracks which are well outside rail corridor.

Yes. There is a sign on a gate that says "Rail Corridor" and "Authorised vehicles only" but the tracks are in Garrawarra State Conservation area not on the Rail Corridor which is only 30 m wide.

Two points:
1. I have stood there. It is definitely a cliff. It definitely makes sense to me.
2. There seems to be a lamentable tendency of some people to mistake Wiki guidelines as Gospel or some other divine authority. They are not. They are just what the name says, guidelines. The issue is what gets the message across accurately. Vague references to "issues for downstream data users" are unhelpful. If that is the best reason on offer please give a more helpful explanation.

It was definitely there on 17 Nov 14. It is mentioned in Wildwalks track notes and visible in Google maps (zoom in here: -33.491738, 151.225933). Maybe it had dried up when you visited.
Let's face it, it's a small pond. I gave it the generic name "Pond" so it would be more visible. Now changed to name=pond (intermittent)