Aygill Caverns - !WARNING!

[darklord]

!WARNING!

Erosion of the stream bank just downstream of the entrance to Aygill Caverns (near Bull Pot Farm) has drastically altered the local hydrology of Aygill, with serious consequences for access to the cave.

The gill has been steadily eating away at the bank for several years now, but without significant impact on access to the cave. This has all changed in the past two months.

On the 7th October during a resurvey trip the normal dry route to the Traverse Pitch was taken. At the bottom of the pitch a significant stream was found flowing from the upstream passage, which for many years has only contributed a trickle or small stream at best. The large stream was now flowing into the short low tube which leads to the second pitch and the main cave. The tube wasn't attempted, but would likely have been 'sporting' at the very least, and the pitch would have been a full-on cataract.

On the 18th November another trip was made to check on the water below the Traverse Pitch, as it was noticed that more of the surface stream appeared to be sinking than a month earlier. On this occasion the caver was stopped a mere 10 metres into the cave where a low crawl and short rift descend to a squeeze or wriggle through to an enlargement. This normally dry route was completely engulfed by a large stream issuing from the roof and falling down the rift to the squeeze. This would have been silly to attempt, and the squeeze would likely have offered a drowning experience.

On the 19th November, after 24+ hrs without rain, I returned to take another look at the situation.  The surface stream had subsided to a moderate-to-normal flow. Once again, 10m into the cave a large inlet was met and, although slightly less boisterous than the previous day, it effectively stopped any further investigation.  New cavities in the roof and wall suggest that the stream has loosened a lot of boulders which will have been washed down and most likely choked up against the squeeze at the bottom of the rift.

Effectively this situation closes the cave, either until a period of much drier weather, or until an efficient dam is built around the new sink.

* IT IS ADVISED NOT TO VISIT AYGILL CAVERNS UNTIL FURTHER NOTICE

(pic. shows inlet above rift/squeeze on 19/11/20 after 24+hrs without rain)

[CNCC]

Hi Darklord, thank you for posting this. We have added your warning to the CNCC website to see this circulated as widely as possible, as we know Aygill is a very popular trip that has seen increasing numbers of visitors in recent years. Please keep us updated if anything changes. If any support is needed for any restorative works please let us know.

[alanw]

We took a wander over to have a look this afternoon and took a few pictures.

Working upstream, there is a dig at SD 66291 81856, a possible sink at SD 66297 81849, Our Lady's Cave at SD 66333 81836, and directly opposite what looks to be the new sink: SD 66340 81838. Finally, the entrance to Aygill at SD66346 81843.

Any more heavy rainfall will further erode the steep bank behind the new sink, which is currently taking about half the flow.

Restricted to 6 attached images, only those of the sinks are here, at low resolution, all can be found at full resolution at https://www.rfvt.org.uk/aygill/. At least in Firefox, clicking on the image will scale it down to fit in the screen.

[darklord]

*UPDATE*

A temporary diversion dam has been built (thx. Andy Walsh/Bill Sherrington, RRCPC) to channel water past the new sink. In low flow conditions this does mostly bypass the new sink and stop the leakage into the cave. (see pic)

On Friday 4th December I made a quick trip into the cave to find only a small inlet entering where previously it had been a cataract. It was possible to scramble down the rift to the former 'pincer' squeeze.  This is no longer visible and is buried beneath the best part of a metre of compacted cobbles and gravel. THERE IS NO ACCESS BEYOND THIS POINT.

The rift where the inlet enters has been considerably modified and de-stabilised with boulders and large cobbles liable to further collapse down onto the new choke.

A plan is being made for a more permanent dam around the sink area, and if successful this will allow access to dig out the pincer choke and do remedial stabilising work on the inlet area and rift slope.  Both surface and internal work are considerable undertakings. Given we are heading into winter weather it is unlikely this work will be possible before spring.

* Please consider Aygill CLOSED UNTIL FURTHER NOTICE.

[Fulk]

What is the 'pincer squeeze'?

[Alex]

If I can get past the police, do you want a hand digging it out this weekend?

[MJenkinson]

Alex - if you PM me your email I can pass it on to those who are likely to be getting on with this.

[PeteHall]

Discussion on travel and other Covid rants have been moved here: https://ukcaving.com/board/index.php?topic=27292.msg333471

[darklord]

What is the 'pincer squeeze'?

It's a slot at the bottom of a rift about 10m into the cave - perhaps not technically a squeeze, depending on your size, but you have to get down on the floor and wriggle through feet first for a body's length to an enlargement.  Without proper dam work you will have half of Aygill surface beck crashing on your head at this point, likely with an unhappy outcome!

[darklord]

If I can get past the police, do you want a hand digging it out this weekend?

Thanks for the offer, Alex, but the whole project needs better weather and a comprehensive plan.  We're working on the latter but obviously winter is not the best time for working on it.

Digging the blockage out is one thing, but pretty pointless unless an effective surface dam/diversion has been built - else it will just wash in and fill again on the next flood.

[Fulk]

Thank you, darklord.