The Rhydymwyn Valley Works was built just before WW2 as a factory and storage area for mustard gas. Many of the original buildings have been demolished leaving just three large sheds, a few intermediate sized ones and a bunch of small ones.
When the works were being constructed one of the first jobs was to canalise the River Alyn, which meandered through the valley.
The river ended up in a channel along west side of the site, crossing over the southern end with some parts covered over (dashed red lines) as culverts.
A series of interconnected tunnels were dug in one side of the valley as storage, and the lower red line which loops off the main route seems to function as a drain for these tunnels.
The aim of this outing was to walk the channel and see what happens under the tunnels, since there doesn’t seem to be much information about this section - leaks in the tunnels were supposed to go into sumps not into the river.
This is in contrast to rest of site, which is very well documented with several report on here and loads of pictures, videos and history available online, see e.g.
https://www.rhydymwynvalleyhistory.co.uk/
https://www.subbrit.org.uk/sites/rhydymwyn-valley-works/
Rhydymwyn Valley is not in any way secret and is a nature reserve open to the public seven days a week although it seems you have to book online and join some society for official access.
There are also tours of the (empty) tunnels where they insist you wear silly clothes.
Most of the pictures were taken with a phone - for a few of the ‘underground’ ones I used the wife’s camera, an elderly Canon which I haven’t used for years and seem to have forgotten how to work.
Wading up the almost dry River Alyn from the south we arrive at the entrance gate, and splash happily along the shallow channel for a while…
…before arriving at the first short culvert, which had bats and swifts zipping through after insects.
Carrying on under another gate to the junction…
…heading left into the drainage section. There was a chilly breeze coming out of here, welcome on a hot evening, and numerous pipes in the ceiling dribbling cold water from above - hard to see what was up there through the pipes but definitely some sort of large spaces.
Looking back from where the drainage loop joins the main channel.
Heading back down the main channel it’s more or less straight with a narrow slot-like infall coming from the main site about half way down.
Turning round and carrying on north there’s another short section of boring concrete box culvert before the reaching the end.
About half way along I climbed out to have a quick unofficial look round the main site, since I hadn’t seen it before.
Just some nominal pics of big and small sheds here since it’s well documented elsewhere.
Cool enough in an empty-military-shed kind of way I suppose, but the history is what’s interesting here; there are handy tourist plaques saying what the various sheds were used for.
I did check a couple of the tunnel entrances but they were locked.
Heading back out along the old Denbigh-Mold railway which runs parallel to the river going south there is someone’s collection of old railway stuff.
The plaque is almost unreadable but says ‘Motor Rail & Tramcar Co. Bedford - England' with the locomotive type 'Simplex' in the centre, according to https://www.geograph.org.uk/photo/5085877 - see this page for more history on these old locos.
When the works were being constructed one of the first jobs was to canalise the River Alyn, which meandered through the valley.
The river ended up in a channel along west side of the site, crossing over the southern end with some parts covered over (dashed red lines) as culverts.
A series of interconnected tunnels were dug in one side of the valley as storage, and the lower red line which loops off the main route seems to function as a drain for these tunnels.
The aim of this outing was to walk the channel and see what happens under the tunnels, since there doesn’t seem to be much information about this section - leaks in the tunnels were supposed to go into sumps not into the river.
This is in contrast to rest of site, which is very well documented with several report on here and loads of pictures, videos and history available online, see e.g.
https://www.rhydymwynvalleyhistory.co.uk/
https://www.subbrit.org.uk/sites/rhydymwyn-valley-works/
Rhydymwyn Valley is not in any way secret and is a nature reserve open to the public seven days a week although it seems you have to book online and join some society for official access.
There are also tours of the (empty) tunnels where they insist you wear silly clothes.
Most of the pictures were taken with a phone - for a few of the ‘underground’ ones I used the wife’s camera, an elderly Canon which I haven’t used for years and seem to have forgotten how to work.
Wading up the almost dry River Alyn from the south we arrive at the entrance gate, and splash happily along the shallow channel for a while…
…before arriving at the first short culvert, which had bats and swifts zipping through after insects.
Carrying on under another gate to the junction…
…heading left into the drainage section. There was a chilly breeze coming out of here, welcome on a hot evening, and numerous pipes in the ceiling dribbling cold water from above - hard to see what was up there through the pipes but definitely some sort of large spaces.
Looking back from where the drainage loop joins the main channel.
Heading back down the main channel it’s more or less straight with a narrow slot-like infall coming from the main site about half way down.
Turning round and carrying on north there’s another short section of boring concrete box culvert before the reaching the end.
About half way along I climbed out to have a quick unofficial look round the main site, since I hadn’t seen it before.
Just some nominal pics of big and small sheds here since it’s well documented elsewhere.
Cool enough in an empty-military-shed kind of way I suppose, but the history is what’s interesting here; there are handy tourist plaques saying what the various sheds were used for.
I did check a couple of the tunnel entrances but they were locked.
Heading back out along the old Denbigh-Mold railway which runs parallel to the river going south there is someone’s collection of old railway stuff.
The plaque is almost unreadable but says ‘Motor Rail & Tramcar Co. Bedford - England' with the locomotive type 'Simplex' in the centre, according to https://www.geograph.org.uk/photo/5085877 - see this page for more history on these old locos.
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