23/08/2018: Sink hole update. Well the good news is that it has not got any bigger. The bad news is that we do not know yet how we are going to fix it. The water running off the opposite mountain comes from the Dan Yr Ogof caving system and flows down a waterfall from a reservoir installed in Victorian times. This reservoir supplied water to the castle until a horse fell in it, back when it was a hospital. The hospital then decided to switch to mains water. The source of the water is not on castle land, and crosses under the main A4067 and then under our car park through a Victorian era stone culvert. Over time some stones have washed away from the side of the culvert, and water has washed a hole beside the culvert, creating a void. This void has led to a collapse of soil above it. The hole is not deep, but the void is 21 feet down.
There is a concern that further collapses could block up the culvert, preventing water flowing through it. This water would then run across the main A4067, flooding and eroding the road in wet conditions. The water would have to flow downhill, so away from the main castle courtyard but possibly into our Southern car park and thence into the Country Park below us. Our options since no one can fix the stone culvert from within the culvert (too small to barely crawl through) may be to line it with an internal pipe, known as slip-lining. Or we may need to dig down to the buried culvert (shifting many tons of soil and rock) to repair it from above. It cannot be repaired from within the culvert as it is too small.
The local caving club are sending some volunteers up the shaft of the culvert, with sonar equipment, so we can pinpoint where the void is. This is so when we dig down, if we do, we will be able to aim for the spot where the problem is. This survey is due to take place on 24/08/2018 if the rain lets off. We are not aware of any other weak areas in the culvert but will check for them and use sonar to detect any other voids. The majority of the main car park can be used but if we have to dig down, the whole car park will be closed while specialist engineering equipment digs down to reach the culvert, and a massive amount of soil and stone will end up piled in the car park until the hole is filled in again. We anticipate work will take 2 - 3 weeks if we have to go down this route. Ample parking is available in the main courtyard, the laybys, and in the adjacent Country Park car park.
We are hoping some financial contribution will come from Highways, who may wish to help prevent flooding across the main road.
02/09/2018: The sinkhole is now yesterday's news for the Country as a whole, but an ongoing issue for the world of Craig y Nos. It is proving to be more complicated than we anticipated. Volunteers from the Caving Club at Penwyllt enthusiastically crawled up the narrow and low underground Victoriana era stone culvert and using sonar equipment, helped us determine where the water from the culvert had washed away a void / cave underground. The hole was caused by constantly rushing water from the underground stream breaching the walls of the culvert. Running water is how many sinkholes are formed. The Victorian culvert carries water from the Dan yr Ogof caves, under our car park, exiting into to the Country Park and River Tawe.
The culvert failed because at some point a predecessor (hospital era most likely) punctured it when they channelled another pipe into the stone culvert. This weakened the finely stitched together stone walls of the culvert, leading to some stones falling out. Water was able to breach the side of the culvert and unknown to anyone, this water was swirling around in an ever widening whirlpool beside and outside the culvert. This eventually created a sizeable cave. The 'roof' of the cave then collapsed, creating our sinkhole.
Fortunately the collapse occurred outside the culvert itself, so water can still drain through the culvert. If it did not, it would have to traverse the main A4067 from the cascading waterfall on the mountain opposite. In winter the waterfall is an impressive torrent like the local Henrhyd Waterfalls but in summer it is a trickle. We are concerned the culvert could block up in the winter, and all this water, a raging river really, would then flood across the main A4067, affecting our southern (back) car park, and the riding stables’ outdoor arena. This could possibly lead to the closure of the A4067 due to water coursing across it. It is not clear whether we are entitled to support from Highways for repairing a culvert which crosses under the main A4067 but as the breach is under our back car park, we suspect any financial contribution is unlikely.
For a while we considered digging a 21 feet hole and shoring up the sides to repair the culvert ourselves, but after a lot of technical analysis and advice, realised this was beyond our skill level. So we are now inviting estimates from specialist contractors, (one in Bristol) to complete the repairs for us. Sadly this could cost anything from £20k to £50k, which means we need to sell a few more weddings! Nothing will be seen for this work, as it just a hole in the ground, a bit of a money pit, actually. Like a lot of the work at the castle, it goes on unseen, and nothing is seen for it. This work comes at the expense of cosmetic areas that customers do see. Making things safe is not something a visitor is aware of, but it is where the real money goes.
23/10/2018: The Sinkhole has grown larger now, following heavy rains. Rocks could be heard tumbling / rolling along deep down in the culvert, as more soil and rocks were washed down the culvert into the River Tawe. Our hole was thought to count as subsidence, and so be claimable under our Insurance with NFU. We were congratulating ourselves on having swapped from Ecclesiastical (who do not cover subsidence) a year earlier, to the NFU, who do cover subsidence.
The NFU appointed Loss Adjuster duly travelled all the way from Manchester, took one look at our now growing hole, and commented, "Don't know why they wasted my time sending me down here, this is not subsidence." "Why not?", we asked. Subsidence, he explained, is when a building subsides, and there is no building where the hole is, as it is a car park. As no building has subsided, it is not a subsidence claim. The only thing that fell into the hole was a car. So now it's back to the NFU to see what it is covered under, if not 'subsidence'. The odd £50,000 or so it is going to cost, is not something we can just magic up in a month or two, so the hole could be a feature for some more months yet, and it is now growing.