Poachers Flooded Above the Rock Bridge

[AKuhlmann]

So I went to Poachers & OHA yesterday (with low expectations of much caving).

While I was expecting very high water I thought it might be worth reporting my findings in case it’s helpful to anyone. Attached below is the recent water levels at Rhydymywn.

So the river was flowing and lapping about 20cm below the OHA lid (which had fallen down the shaft so I did a quick rescue mission with a lookout). While I was down there as expected I could hear a roaring streamway which I didn’t dare go have a look at.

In Poachers through I was very surprised to find that it sumped all the way up to 1m below the base of the ladder pitch (basically the top of the small climb where the toy rat used to live). The surface water we could see was flowing with considerable speed too.

From what I could see (above & below ground) we were there at the peak of the flooding, but with the downstream Rhydymywn level being at 1.5m when we were there and 2 days earlier it had been 1.8m so it must have been briefly a bit higher.

Anyway it was news to me that Poachers flooded above the Rock Bridge anymore so if anyone has any insight on this I’d love to hear it

 

[Space Doubt Caver]

So I went to Poachers & OHA yesterday (with low expectations of much caving).

While I was expecting very high water I thought it might be worth reporting my findings in case it’s helpful to anyone. Attached below is the recent water levels at Rhydymywn.

In Poachers through I was very surprised to find that it sumped all the way up to 1m below the base of the ladder pitch (basically the top of the small climb where the toy rat used to live). The surface water we could see was flowing with considerable speed too.

From what I could see (above & below ground) we were there at the peak of the flooding, but with the downstream Rhydymywn level being at 1.5m when we were there and 2 days earlier it had been 1.8m so it must have been briefly a bit higher.

Anyway it was news to me that Poachers flooded above the Rock Bridge anymore so if anyone has any insight on this I’d love to hear it

Today we visited Poachers early this morning before going to a different location, and it was flooded right up by the entrance, so when you open the grate, and abseil in, and from where you go to go in the cave was flooded, so we exited and went somewhere else.
On Thursday some of my friends had been in there and it was quite dry, but yesterday Sat 28th it was flooded.

The trip to poachers was adequately cancelled.

 

[mikem]

The Alyn peaked at only 1.1m with 17mm & 23mm of rain at the nearest gauges, so not a huge amount:

Rainfall at Moel Y Crio

We publish the information about river levels so people living in flood risk areas are better informed and can decide what actions to take as the water levels change. Anglers and boaters will also be able to use this information to check the water levels before they set off.

rivers-and-seas.naturalresources.wales

 

[AKuhlmann]

Space Doubt - are the photos of the mined passage at the bottom of the pitch or the short section after you've stepped down below it with a way on to your left and right (and you go right)?

If the later is the case, then that would be in-line with the 1.8m reading I had in my original post - i.e. your experience was roughly ~0.7m less water.

To add to this - myself and others went to do OHA on Wednesday (25/09/24) and our advanced team discovered OHA was sumped at the wet crawl/duck with only a water level of 0.58.

[Picture from the Rydymwyn Level which is directly downstream of Cilcain/Pantymwyn bridge)

Having looked at the water levels for the last year it becomes clear we've had a very wet year and levels are yet to return to the normal of us having an actually Hesp Alyn (barren/dry Ayn).

My thoughts on this is that something must have happened in the Milwr or between Poachers/OHA and the Milwr. First after the 13/10/23 to cause the jump from 0 as the norm to 0.50 and a slight further deterioration between 12/05 and 02/06 to cause the new level to settle at 0.58 which appears to me the new normal, even with dry settled spells across August. Either that or United Utilities, who run the Milwr for Welsh Water (I believe) have changed something.

Rostam commented it could also be due to a series of perched sumps taking a long time to drain affecting the levels inside the caves.

The mystery continues

 

[Space Doubt Caver]

Space Doubt - are the photos of the mined passage at the bottom of the pitch or the short section after you've stepped down below it with a way on to your left and right (and you go right)?

If the later is the case, then that would be in-line with the 1.8m reading I had in my original post - i.e. your experience was roughly ~0.7m less water.

To add to this - myself and others went to do OHA on Wednesday (25/09/24) and our advanced team discovered OHA was sumped at the wet crawl/duck with only a water level of 0.58.

View attachment 20548
[Picture from the Rydymwyn Level which is directly downstream of Cilcain/Pantymwyn bridge)

Having looked at the water levels for the last year it becomes clear we've had a very wet year and levels are yet to return to the normal of us having an actually Hesp Alyn (barren/dry Ayn).

My thoughts on this is that something must have happened in the Milwr or between Poachers/OHA and the Milwr. First after the 13/10/23 to cause the jump from 0 as the norm to 0.50 and a slight further deterioration between 12/05 and 02/06 to cause the new level to settle at 0.58 which appears to me the new normal, even with dry settled spells across August. Either that or United Utilities, who run the Milwr for Welsh Water (I believe) have changed something.

Rostam commented it could also be due to a series of perched sumps taking a long time to drain affecting the levels inside the caves.

The mystery continues

I think your right something has changed dramatically, It's the first time I have ever seen poachers flooded and I think we need to be more observant of the water levels and how it is affecting the water levels of the caves in the area.
Seeing it flooded like that was very surprising,

I think what your saying about something happening between OHA and poachers and the Milwr tunnel is probably spot on, there has to be something choking the flow of water somewhere.

 

[mikem]

Presumably with the wet weather the tunnel hasn't been taking all the flow

From Wikipedia:
Flows in the River Alyn are significantly affected by mining, particularly the Milwr mine drainage tunnel which diverts a sizeable amount (23 million gallons of water per day.[1]) of the River Alyn out of its catchment and into the Dee estuary at Bagillt.[2]

References
edit
"Milwr Tunnel". Subterranea Britannica.
* Appleton, Peter (1989). "Limestones and Caves of North Wales". In Ford, Trevor D. (ed.). Limestones and Caves of Wales. Cambridge University Press. pp. 233–7. ISBN 0-521-32438-6.

This shows that the majority of time most years it has some water:

| National River Flow Archive

nrfa.ceh.ac.uk

 

[bigsafety]

On my way with my Freshers right now! Will send one of them down to let me know if I'll get wet feet.

 

[AKuhlmann]

Presumably with the wet weather the tunnel hasn't been taking all the flow

From Wikipedia:
Flows in the River Alyn are significantly affected by mining, particularly the Milwr mine drainage tunnel which diverts a sizeable amount (23 million gallons of water per day.[1]) of the River Alyn out of its catchment and into the Dee estuary at Bagillt.[2]

References
edit
"Milwr Tunnel". Subterranea Britannica.
* Appleton, Peter (1989). "Limestones and Caves of North Wales". In Ford, Trevor D. (ed.). Limestones and Caves of Wales. Cambridge University Press. pp. 233–7. ISBN 0-521-32438-6.

This shows that the majority of time most years it has some water:

| National River Flow Archive

nrfa.ceh.ac.uk

Often in wet spells the Tunnel doesn't take all the flow which is why the presence of the surface river can be used as a tell as to the conditions underground, but it seems to me that the Milwr is taking less of the flow than it used to. Unfortunately, there's no outflow data for the Milwr, that I can find, to help figure this out

 

[Space Doubt Caver]

Presumably with the wet weather the tunnel hasn't been taking all the flow

From Wikipedia:
Flows in the River Alyn are significantly affected by mining, particularly the Milwr mine drainage tunnel which diverts a sizeable amount (23 million gallons of water per day.[1]) of the River Alyn out of its catchment and into the Dee estuary at Bagillt.[2]

References
edit
"Milwr Tunnel". Subterranea Britannica.
* Appleton, Peter (1989). "Limestones and Caves of North Wales". In Ford, Trevor D. (ed.). Limestones and Caves of Wales. Cambridge University Press. pp. 233–7. ISBN 0-521-32438-6.

This shows that the majority of time most years it has some water:

| National River Flow Archive

nrfa.ceh.ac.uk

That's a great resource, saved it to my bookmarks, thank you

 

[mikem]

"The Milwr tunnel today disgorges an average flow of 23 million gallons per day, rising to 36 million in wet weather."

Milwr Tunnel – Subterranea Britannica

Subterranea Britannica is a society devoted to the study and investigation of man-made (including Nuclear Bunkers) and man-used underground places.

www.subbrit.org.uk

Although that sounds impressive it is only 1.2 and 1.9 cumecs respectively. On 6th November 2000 the Alyn ran at an approximated 43 cumecs, which is twice the volume of any other record (this page shows peak annual flows, whilst previous link was daily flows - it is also useful for converting any high river gauge / stage reading from metres into cumecs flow):

| National River Flow Archive

nrfa.ceh.ac.uk

It wouldn't take much for that small a water flow in the tunnel to be disrupted by a blockage and back up elsewhere - if the blockage then spilled, the flow could return to normal whilst higher levels remain flooded

 

[Ian Adams]

Wow.

I have never seen Poacher’s THAT full of water (or even known it to be) in the last 25 years.

The cave isn’t quite as “stable” as it might be believed. There has been a significant change to the lower series just a few years ago (perhaps just before COVID) where an entire floor collapsed which would have undoubtedly been due to waterflow. Right by that collapse is the internal waterfall that, still to this day, allows water to drop beneath its own catch pool and disappear through a tight rift into the unknown …

I think there is a good chance that, once the water has gone, an exploration will find another significant change.

Exciting times?

 

[Stones]

The water level in the Milwr has been pretty high all summer and only having a week or so of what I'd call normal summer levels.

Rostam commented it could also be due to a series of perched sumps taking a long time to drain affecting the levels inside the caves.

I'd agree with Rostam about a series of perched sumps. Couple of years we had a really dry summer, and the Milwr levels dropped really low, it took a really long time for any rain to affect the levels. This summer I've seen the levels rise in the tunnel by a couple of inch over a period of 4 hours

 

[mikem]

Couple of reports of falling rocks from 2021 and 2022 - another might have slowed the outflow

 

[Space Doubt Caver]

On my way with my Freshers right now! Will send one of them down to let me know if I'll get wet feet.

was it still flooded when you got there?

 

[Space Doubt Caver]

https://www.bbc.co.uk/news/articles...bCN_X9N12I-RvzsFLA_aem_K0uuJZtIFFIgow4LqrGbVA

https://www.facebook.com/reel/820248623517912

The whole area is badly flooded
October 1st 2024

 

[Space Doubt Caver]

 

[HardHat]

"The Milwr tunnel today disgorges an average flow of 23 million gallons per day, rising to 36 million in wet weather."

Milwr Tunnel – Subterranea Britannica

Subterranea Britannica is a society devoted to the study and investigation of man-made (including Nuclear Bunkers) and man-used underground places.

www.subbrit.org.uk

Although that sounds impressive it is only 1.2 and 1.9 cumecs respectively. On 6th November 2000 the Alyn ran at an approximated 43 cumecs, which is twice the volume of any other record (this page shows peak annual flows, whilst previous link was daily flows - it is also useful for converting any high river gauge / stage reading from metres into cumecs flow):

| National River Flow Archive

nrfa.ceh.ac.uk

It wouldn't take much for that small a water flow in the tunnel to be disrupted by a blockage and back up elsewhere - if the blockage then spilled, the flow could return to normal whilst higher levels remain flooded

spoke to some fellas in milwr before who told us of a big storm a few years ago where the water reached the roof. washed out all of their comms equipment and loads of other things left in the tunnels.

 

[Space Doubt Caver]

Hey all,

Glad to report that poachers is no longer flooded, the lower series seems to be draining as it used to, and as always, still super muddy 🤣🤣 after the recent flood, I'd say it's just as muddy as OHA 💯

So as long as the weather is good poachers is back to normal, just if you go in, remember it can flood 😁

Safe caving to all ❤️❤️❤️

 

[Space Doubt Caver]

Pictures by @UrbanEx2U