The Dwyryd estuary is a quiet place, a long, long way away from any crowded city. It’s somewhere to watch the sea and the wild life. Where can you find it? It’s just south of Porthmadoc or, to put it another way, just up from Harlech on the Cambrian Coast. An internet entry describes it as ‘hauntingly beautiful, spoilt, some say, by the National Grid pylons’ which stride across from bank to bank.
In its quietness it is constantly changing. The River Dwyryd brings silt from the hills above the Vale of Ffestiniog, and slowly, over the years, the course of the river moves around the estuary. One of the offending National Grid pylons is immersed in the water, but this was not always the case. Built in the 1960s, along with a huge swathe of national energy infrastructure, it was originally on dry(ish) land and remained that way until about three years ago.
But, hang on, in the whole of this long and wordy paragraph there has not been one mention of a railway. And, after all, this is meant to be a railway engineering magazine!
Well, for once, this is not a story about track or trains or signalling. Just as a diversion we are looking this month at an industry that has an uncanny similarity to our own. An industry that has ageing infrastructure, that has emergencies and which responds rapidly to ensure that what it is carrying – in this case rather a lot of volts instead of trains – is transported safely and reliably. So, in this article we are looking at the plight of the marooned pylon and how its seemingly rapid demise prompted the maintenance teams of National Grid into action to safeguard the public. There is a railway involved, so read on!
On the move
The Grid has a programme of works and inspections just like the railways. Theirs is more seasonal though. Through the spring and summer, teams work through their schedule of tasks making sure that they keep their specialist skills up to date. In the winter there’s plenty to keep them occupied with all that the Welsh weather throws at them.
In between the seasons are the autumn inspections and surveys. National Grid uses LSTC Ltd to carry out detailed route surveys and it was during one of these routine inspections that pylon 4ZC30 was found to be leaning. On closer inspection, it was apparent that the seawater of the estuary had either done for the piled foundations or the bolted connections or both. In any event, the pylon was on the move.
This is not a small structure. At 60 metres high and with a base measuring 18 metres this is a major piece of kit. Coupled with this is the fact that it carries 6 cables at 400KV each along with a leased line to Scottish Power at 132KV. This is nationally strategic power transmission and not something to fool with. It forms a vital part of the electricity transmission network in North Wales.
And a railway
Ivan Lea (team leader) and Martin Sankey (overhead line engineer), both based at the Wolverhampton office, took the call. It looked likely that the tower was going to be lost. An emergency conference was held with head office designers and power distribution experts. There was no alternative. The route had to be severed – or, in railway parlance, there had to be an emergency possession of the line. Electrical supplies were diverted and the area around the site isolated (in a process similar to railway working).
This was not the end of the matter. Beneath the power lines runs the Cambrian Coast railway and a minor road. The rail service through to Pwllheli was severed with trains terminating at Harlech, so there were no trains to Criccieth or Porthmadog. It may seem a sleepy backwater, but these trains are well filled, especially with students and school children. They were destined to be transported by road – the long way round as the minor road over the Briwet bridge (of which more later) was closed too. The hitherto almost unknown station at Llandecwyn became the focus of attention.
Forces to balance
If a railway line has to be cut, then that’s exactly what happens. It’s pretty crude. A large spanner or a burner does the trick generally. But Ivan and Martin have their lines suspended between 10 and 30 metres above ground level and it’s certainly not just a matter of chopping them down. There are forces to balance in the rest of the route. Dismantling sequences are a design process just as much as any new construction.
As the calculations were being performed for taking the cables down, there was plenty of other activity that had to be considered. The ailing pylon was surrounded by water, the pylons on either side, whilst notionally on dry land, were practically inaccessible for heavy plant. The structure to the west was in the middle of an environmentally sensitive SSSI (site of special scientific interest), so special measures were taken to avoid permanent disturbance. The structure to the east was the ‘wrong’ side of the Cambrian coast railway.
Just like the railways, National Grid has special powers for gaining access, but these are meant to be used for a limited time only while a true emergency exists. Thereafter it’s down to negotiation and diplomacy to enable all the plant and equipment to reach the sites. No formal roads existed and so use was made of the ‘trackway’ system of temporary metal roadways. As the designers came up with their method of working it was obvious that just about every winch in the north of England would be needed to lower all the cables simultaneously. Along with the winches came maintenance gangs drawn from Newcastle, Manchester, Wolverhampton and Leeds. Llandecwn was becoming crowded.
Access to the eastern tower was over a railway level crossing that had to be widened and manned throughout the project. As Martin says, one of the differences between the railway and power industries is the choice of colour scheme for high visibility clothing. National Grid turned up bedecked in yellow with white helmets. So it was all change for access to Network Rail territory with the railway’s favoured orange and blue.
As the days passed, a decision was taken to ease the block on rail movements. Trains were allowed to pass beneath the affected cables with a temporary speed restriction and constant monitoring of the crippled tower. That, at least, eased the transport difficulties for the local scholars, but trains had to stop running after dark.
With preparations complete, the cables across the estuary and the railway were lowered on Sunday 13 October. After a very long day and with darkness approaching, everything was dragged clear of the track in readiness for being cut up. The central tower had been successfully isolated and the initiative now passes to National Grid’s Capital Construction teams and their Energy Alliance Partners (familiar term!) – Babcock and Amec. Ivan’s teams have resumed their pre-winter checks and maintenance and, for a while, at least, this part of Llandecwn is relatively quiet. The skyline is radically changed. There are no graceful curves of cabling strung from tower to tower. Instead there are structures that look a little forlorn, bereft of purpose.
And what happened next?
But there is a final twist to this saga of the Dwyryd estuary. Close to the power line, the Cambrian coast railway crosses the estuary on the Brewit bridge (Pont Brewitt), a grade II listed timber structure with a narrow roadway clinging to its side. In part of a £20 million project, Gwynedd Council and Network Rail are replacing the bridge with a new railway bridge accommodating a widened roadway free of weight restrictions.
Soon after the power line problem was solved, the old railway/road bridge decided that it too would settle into the mud. Constant precautionary monitoring had revealed that the bridge had sunk 50mm and so, yet again, the line to Pwllheli has been shut. For a station that few have heard of, Llandecwn is achieving a level of national notoriety.
Report by Grahame Taylor