Cwm Dwr II - Sand Sump Extensions

We had had an encouraging days progress on the previous digging trip with a tantalising glimpse of open passage through the airspace above the partly drained sump. We returned with a little more knowledge of the site, digging gear, a second fire hose, video gear, photo gear and a set of surveying equipment all in anticipation of entering new or at least unsurveyed passage. We arrived on a fine Saturday morning and took a little persuading to break off tea drinking in the sunshine and head underground. Faffing over we went underground taking in a second fire hose to halve the time it would take to drain the sump. With a little video taken on the way we were soon set up and spent an hour clearing out rubbish and old digging gear from the cave. With the sump open, we bailed the last bit of water with buckets and then spent and hour clearing out the bottom of the sump. Eventually with a "Mark" sized bit of passage we could stick our heads through and take a glimpse of the passage ahead. Keith went through first and reached a large pool at the top of the slope. He gingerley dug a trench to drain the water back to the sump pool, where we bucketed out the water as it filled up. With the top pool drained as much as he could he popped up through a hole in a calcite floor. He then excitedly called us up to have a look.

Setting up the syphon in Sand Sump

The passage above was larger and started with a sand beach and a booming echo. This soon gave way to a calcite floor. We took off muddy oversuits and headed along the passage until we saw some tape around a small nest of cave pearls at the end of the passage. It was clear that someone had been here before and we had a look at two low side passages. Both were pushed a few body lengths to get too tight for even Keith to make progress. We then decided to call it a day and return to the cottages for hot food a tea.

A section of passage at the end of Sand Sump

We were joined by Mark and Chloe for an evening meal and then on the Sunday we entered the cave with some hand tools, photo gear, video gear and survey kit. We found that the sump pool had not refilled overnight - and encouraging sign. Jess and Brendan undertook a survey of the passage while the others looked at the digging possibilities. After a few hours video had been taken, and idea of a digging strategy had been formulated and a survey had been undertaken to the end of the main passage until Brendan ran out of lead in his pencil. At this point everyone was quite cold and so we exited the cave taking out kit as we went.

Rough survey of the Sand Sump extensions

Caves of the Cwm Dwr Quarry - based on survey © South Wales Caving Club 2015

As we left the cave we did a clean-up operation removing old digging tools, rotting wood cables and fertiliser sacks to leave the cave litter and tool free apart from a small amount of current equipment at the sump.

Clear out of old digging gear after the weekend

Some history of digging in Cwm Dwr II - courtesy of Tony Donovan

In around 1990 Malcolm Herbert, Hywel Jopling and Owain Harvey siphoned the sump at the top of the sand slope in Cwm Dwr 2 and it takes between 3 and 4 hours to drain. Owain was small enough to get through the siphoned sump which was tight and beyond there is some leads heading up dip which he thought looked interesting which could be enlarged. In 1994 Tony Donovan, Mike Booth, John Hale and Paul Roberts dug the trench in the floor with the intention of draining the sump completely which would allow digging without the need for siphoning the sump every trip, during one of the trips Paul Roberts from the Isca Caving Club wanted to have a look for himself as he was small enough to get through the tight bit in the siphoned sump being roughly the same size as Owain. On the first digging trip when the sump was siphoned John Hale was with Tony Donovan and he failed to get through the tight bit in the sump section, on the 2nd occasion Paul Roberts struggled and just got through and he looked at the leads, but detected no draught.

Present: Chloe Burney, Mark Burgess, Jess Burkey, Mark Burkey, Keith Edwards and Brendan Marris

Cwm Dwr II - The Wrong Dig!

Regular rain showers had kept the Brickworks Dig topped up with water, and with only enough people available for one days digging we had sought out an alternative site to work on, as most of our time would be spent dealing with the water at the Brickworks. We chose an old site in Cwm Dwr II, and after arranging permissions with the OFD Management Committee and Natural Resources Wales we were able to give this location some attention. There had once been a short sump in the entrance series to this cave - Helen's Horror which had to be syphoned to gain access, but this was removed some time ago and now is no more than a short wet crawl.

We entered the cave and rigged the 10m pitch down into Default Chamber. It is here that a slope leads up to a 20m long sandy passage that leads to the Sand Sump. The sand had previously been dug and only a small access crawl led through to what was once a body sized sump which had now silted up somewhat.

Keith in the sandy passage that approaches the Sand Sump

A view of the sump at the start of the dig with bucket for scale

To work the dig efficiently we removed the sand fill on the approach to the sump, clearing it from the sides and lowering the floor by 30-50cm. After a couple of hours and 40 buckets of spoil removed we had good access to the sump and we could now start draining it. Only a small part was visible of this perched reservoir, we expected to drain it fairly quickly, bailing it with buckets. After 100 buckets of water had been removed and the water level only dropping a few inches we decided on a Plan B. Brendan went back up the ladder and to Helen's Horror where a long firehose that was once used to syphon off the water could be found. This 40 metre heavy duty hose was brought back to the pitch and then lowered so it could be used to syphon the sump. At first we attempted to start the syphon by sucking on the pipe, but this failed, so Mark headed back up the ladder, the bottom end of the hose hauled up and the 10m head of water was used to fill the hose. Once the hose was full of water, it was dropped to the floor of the chamber where it began to syphon off the water immediately. The flow of water was directed to join the stream and then we returned to the sump. At this point most people went off to explore the cave while Mark and Brendan returned to the sump to monitor progress. It became clear that there was a large volume of water in the passage beyond as the water level very slowly fell. Rather than wait we continued to drop the floor of the approach to the sump. With everyone back at the dig over the next three hours we were able to clear about 40cm depth of sediment from the bottom of the passage over a 4 metre length, following the water as it slowly receded, until after three hours an airspace appeared. A short while later the hose broke the surface of the water and the syphon stopped. The passage is still too silted up to get through at the lowest point. At this point we had removed a further 60 buckets of spoil and were all exhausted and cold and so after all having a look through the airspace to the passage beyond we headed out of the cave knowing that on our next visit we would be in some interesting territory.

Keith at the sump at the end of the days dig

On our next visit we plan to set up the syphon again and drain as much water from the sump as possible. We will continue to remove the infill from the bottom of the sump to give easy access to the passage beyond, where we will be able to assess the future possibilities.

More information on Cwm Dwr II on this link.

Can anyone shed any light on who other than Hywel Jopling has previously dug at this site? During the day we talked to Hywel, but from his description of the dig we think that it must have been worked since his last involvement.

Present: SWCC Members - Mark Burkey, Keith Edwards and Brendan Marris + Chloe Burney, Mark Burgess and Ian Millward from Dudley CC.

Photos by Brendan Marris