Ogof Hesp Alyn

Location
Grid Reference SJ 1920 6564

Altitude: 155m

Located about 1/2km downstream (north) from Cilcain bridge in the south bank of the river Alyn. An obvious covered shaft adjacent to the river, just opposite and downstream of the sewage treatment works.

Access
The shaft cover is unlocked. It is advisable to contact the North Wales Caving Club which has access agreements for the Alyn Valley caves.

Description
The majority of the cave lies below river level and is consequently very flood prone, particularly during winter when it can flood completely. During the summer, the cave is generally dry (although very muddy), apart from the canal and a couple of short sections. Hesp Alyn is Welsh for 'barren Alyn' and reflects the fact that the river is normally dry during summer months when drainage makes it's way underground.

All of the cave including the pitches (with water flowing upwards) were phreatically formed (the pitches formed by water flowing upwards). Water formerly resurged in the vicinity of the current entrance. Driving of the 10mile long Sea Level Tunnel (Milwr Tunnel) during the early part of the 20th century to drain the local lead mines lowered the local water table, draining Hesp Alyn.

The 7m entrance shaft should not be free climbed as there is a quantity of loose material about half way down. A low passage from the base of the shaft enters a large passage after about 100m. Walking passage leads to the low 10m long sand crawl which frequently fills with sand over winter, necessitating digging out in spring. A ladder climb upwards leads to a rift filled with deep water - The Canal which can be traversed by straddling. A 25m pitch, split by a ledge drops to the head of a second 8m pitch at the base of this a hole leads to a 5m pitch with a very slippy landing. Continuing down through the hole at the base of the slope the passage shortly arrives at the top of a pit. Descending this leads to a muddy climb back up the other side. The passage now slopes gently upwards to a 15m pitch which leads to the base of a climb up. At the top of this is Sump 1 which can be syphoned over a couple of days. Beyond Sump 1, Sump 2 is soon found which again can be syphoned. Several other pitches and climbs lead to the end of the cave, where part of the underground flow of the Alyn is encountered.

History
Disovered in 1973 by the North Wales Caving Club. A small patch of gravel just above the river was excavated to a depth of 7m to reach open passage. The entrance shaft has now been partly lined.