How deep is OFD?

I know that this has been recently discussed, but I don't think that any clear and precise answer was given as to whether the 308 m "traditonal" figure is actually correct.

I was browsing through the Cambrian Cave Registry, as you do when it's raining, and noted that OFD1 entrance is at an elevation of 204 m and that Pwll Byfre is at 488 m. A difference of 284 m. I am aware that these points most certainly do not "bookend" the cave and so the depth must be somewhat more than that.

I then looked at OFD2.

According to the registry, on this page, Top Entrance is at an altitude of 1060 m. 

Like, wow, OFD is over 800 m deep. I never knew.

A good question Graham and the answer depends on who you ask.
It is my understanding that when the resurvey ran a new centre line through the main stream they discovered that they had rather carelessly lost about 100ft of elevation.  Brian Clipstone is perhaps the person to give the definitive response but I'm not sure he is on here.

I am reasonably certain that the true vertical range of OFD is around 30m less than claimed due to this legacy surveying error however I only have a conversation with Brian to support this.

The true vertical range is measured from somewhere in Nyth Bran series as this is the highest point and I assume somewhere in the sumps in OFD 1 as the lowest point (not sure where though).

Les' understanding is pretty good 

Maybe Brian can be pressed into a definitive statement, in the same way finishing production of a guide book or survey often leads to a breakthrough to make that 'new' document immediately obsolete!

graham said:

I then looked at OFD2.

According to the registry, on this page, Top Entrance is at an altitude of 1060 m. 

Click to expand...

Hmm...

There were reports a few years back that the Yorkshire lads had been seen stacking rocks around the entrance to GG to try to get their "deepest shaft" record back from Titan.

Don't tell me those South Wales boys have been doing the same thing?

graham said:

I then looked at OFD2.

According to the registry, on this page, Top Entrance is at an altitude of 1060 m. 

Like, wow, OFD is over 800 m deep. I never knew.

Click to expand...

Amazing, that's only 27m short of the summit of Snowdon!

Chris.

graham said:

According to the registry, on this page, Top Entrance is at an altitude of 1060 m. 

Like, wow, OFD is over 800 m deep. I never knew.

Click to expand...

Presumably that is supposed to be 1060 ft (i.e. 323m OD)

I'm not sure what unit the 1060 is meant to be. According to the OS maps, OFD2 entrance is at ~432m

According to  http://ukcaving.com/wiki/index.php/Ogof_Ffynnon_Ddu  OFD II Top Entrance is at 425 m...

The lowest altitude point in OFD is the bottom of Gothic passage sump.  According to the Welsh Sump Index it is 17 m below the level of the resurgence.