South Wales Caves: Blog Post: Porth Yr Ogof - Diving and Data. By Christine Grosart, Project Manager. 25th June 2016

Porth Yr Ogof

An extremely busy year for both Rich and I meant that getting over to Porth this year was looking impossible, until I spotted a window of opportunity on a Saturday afternoon.

Of course, that means lining up the weather too and I kept a close eye on the Environment Agency River Levels Data website, which records the levels of the Mellte at regular intervals. Despite sporadic heavy showers, the water level in Tradesman's Entrance Station 3 was anecdotally low, the distance between the water surface and the top of the 'flat ledge' on the right being 64cm.

I decided to dive first and do the other data recordings at the other sites later. Kitting up in the car park, there were several mini buses of children going caving. I slid down to the water and to my horror, my go-pro 'pinged' from its string which had been tied to a bolt-snap and D-ring and vanished into the bubbling water.

Porth is notorious for eating dive gear, often dropped in the entrance and it is taken away by the fast flowing water, never to be seen again. I should have known better and put the go-pro in a pocket - but, furious with myself for not taking my own advice, continued with the dive in any case.

Standard photo of Tradesman's Entrance
Station 3

The flow in the entrance was moderate. I spotted 2 medium size trout which were pale in colour but not completely white, close to the first couple of tie-offs. I didn't have a helmet or helmet mounted lights, but used instead a Halcyon Focus hand held torch and back ups mounted on my harness.

As I approached the Secci disc, I stopped so that I didn't disturb the visibility ahead.

The line is tagged with red cable ties at 50cm intervals so I put the focus onto a fairly tight beam and could just about make out the secci markings from exactly 5m away, counting the tags as I moved forward.

The depth of the Secci was 2.9m and the water temp was recorded as 13 degrees C.

I noted some detritus starting to form on the face of the secci, despite it facing downstream.

I continued upstream, noting some larger, whiter trout and 3 bullheads, one of which was grubbing around in the silt.

River Levels data. Standard image of Station 6.

There was a thick layer of silt on the normally clean washed passage floor and the viz seemed gloomy to me, with lots of particles in suspension.

I then approached the 'Pot' which has been neatly re-lined by Max Fisher, with a rope protector in situ, doing it's job to stop the line fraying over the edge of the pot.

This seems the way forward as I don't see much value in damaging the cave further by putting in a bolt for this purpose.

The flow seemed to get a little stronger as I continued upstream, possibly due to recent bursts of rain which may have started to make their way into the cave. As I got to the cobble slope which surfaces in Upper Cave Water Chamber, I was shoved quite violently down the tube and decided to turn around - which took some doing - as the flow was definitely getting stronger.

Children on their caving trips

I had the usual low viz roller coaster ride home and once de-kitted in the car park, headed back into the cave to look for my Go-Pro which I luckily found just behind the water entry spot, pinned to a rock by the high flow.

It was already past 4pm so I elected not to dive again but instead visit the other stations to take standard photos of each station and water temperature readings where I could.
It's a pleasant job to wander down to Main entrance (station 4) and sit in the tranquility once the cavers have gone home. I spotted a small brown fish darting around in the entrance pool - and one welly boot!
It's a short walk down to the resurgence where I took a temperature reading with my D-Timer and also up to Top entrance where there were some really pretty wild flowers growing.
Back up the steps, a grey squirrel was busy running around the tree trunk.