Rhosydd is flooded to floor 9 level - as you've seen if you've walked in the #9 adit. Everyting to the Eastern side is in awful condition, or largely collapsed, whilst you can get a reasonable distance along floor 9 in the Eastern direction it won't take you anywhere.
On the Western side, the first flooded chamber you will come to is either 9A or 9B, sorry can't remember exactly. It's this one anyway:
[img]http://www.aditnow.co.uk/showimage?f=/community/Rhosydd-Slate-Mine-21-05-2006-Image-001/[/img]
Not crossed it, and if you did it wouldn't take you anywhere much, the Western workings on floor 9 only extend as far as 9D - see Barney's plan.
All the 'interesting' boating is actually in Croesor, and you'll have done a couple of fairly committing descents and bridge crossings to reach them - and from the Croesor side rather than Rhosydd*.
* Although there's nothing to stop anyone doing the CRTT in reverse the idea of ascending two longish pitches sonuds a lot harder than descending them...
my orders are to sit here and watch the world go by