top of page
© Copyright ~ 2020

Water was ever the problem.  Flintshire has been a vital centre of mining in Wales from the very earliest of times, famously of lead, but also coal, zinc and many other metals and minerals.  The Romans were active on Halkyn Mountain, Prestatyn and Meliden, mining the lead depths unaffected by flood water, likely smelting the ore at Pentre Ffwrndan in Flint and shipping it out to their imperial possessions from the recently discovered quay on the Dee Estuary.  Their mines are still there, many deepened and widened in the centuries that followed, but evident in the finds that still, at times are unearthed.


With the departure of the Romans in the early 5th century, the evidence of lead mining in the area that came to be known as Flintshire becomes scarce. However, by the 13th century farmers were beginning to take advantage of the lead that could still be found in plenty at the surface or at shallower depths, cutting trenches in the turf to reach the precious metal.  It’s hard not to see a correlation between the demand for lead and the immense castle building program initiated by Edward I in his conquest of North Wales in the last quarter of that century. Lead was as much a part of the agricultural year as harvest.  Farmers often left their families to tend the fields as they mined and transported the lead to Chester.  Such activity reached its peak in the late 16th century, when easily reached deposits were exhausted.  Flooding was becoming an increasing problem, reaching deeper levels ever more dangerous and difficult.


It is worth making the point, however, that there is a misconception that there was no solution to flooding until the advent of ‘fire engines’, the Newcomen steam engines of the later 17th, early 18th centuries.  Much of the issue was not so much the technology, but the cost effectiveness of mining the lead.  By the later years of the 16th century, and certainly by the early 17th century, the price of lead had increased substantially, and further exploitation of the Flintshire lodes became once again financially lucrative.  Deeper shafts were dug and the often expensively cut adits that drained them became cost effective.  But, the adits were not enough as the mines became deeper and deeper.  Flooding was always the problem, making it difficult to mine the lead and increasing the cost of gaining access to the deeper lodes.


Certainly, by the beginning of the 18th century, even the available technology was insufficient in clearing the mines of flood waters.  The London Lead Company had installed a ‘fire engine’ at their Trelogan mine by 1733, shipped up from London in order to drain their most valuable asset.  Further engines followed, but by the end of the 18th century, the financial viability of its great smelting works at Gadlys in Bagillt was over, and one of the greatest industrial concerns of its age came to an end.


Such was the state of affairs until the end of the 19th century when an amalgamation of mine companies, The Holywell Halkyn Mining and Tunnel Company, embarked on the hugely ambitious Milwr Tunnel project - an attempt to drive a drainage tunnel from sea level at Boot End at Bagillt into Halkyn Mountain.   Work began in July 1897 and, with some financial pauses enforced, did not stop until 1957, with the final extension into the Cathole Vein.  The aim was simple, if the project ambitious - to enable the working of rich seams of lead at depths which had previously denied them, largely through the crippling cost of implementing the technology that would allow the exploitation of the ore at those depths.


The Tunnel outflow at Dee Bank Quay at Bagillt.

The tunnel was begun at a point some 9ft below the high water mark, with self acting flood doors fitted to prevent flooding at high tide, and progressed steadily at a gradient of 1:1000.  The tunnel at this point was brick lined and cut initially through ubiquitous coal and shale, becoming unlined as it reached limestone just over a mile inland.  The tunnel continued to be cut until 1908, when the limit of the Company’s mining rights at that time were reached.  At this stage, the tunnel was draining 1.7 million gallons of water a day.


Objections to the extension of the tunnel were raised in Parliament, and by the people of Holywell, who worried for their water supply, including that which powered the industries of the Greenfield Valley and, of course, the holy flow of St Winefride’s Well.  However, work recommenced in 1913 after all objections were overcome, but the very worst fears of the people of Holywell were realised in January 1917 when at the intersection of the Pant Lode, a flooded cavern was breached, releasing 10000 gallons of water a minute into the existing tunnel, sweeping away the lines and working and causing considerable damage.  The full extent of the disaster was felt just 30 minutes later, when the flow that fed both the Greenfield Valley and St Winefride’s Well ran dry - the only time thus far known in its history.  The loss of the waters to the Greenfield Valley brought potential ruin to Holywell industry, as well as an existential crisis to the devout, the loss of the sacred waters to the Well and Shrine something more than a financial setback.  The waters were eventually restored to the Well and Valley from the the Holywell Boat Level, but it is worth pointing out that the original waters of St Winefride’s Well now flow into the estuary at Dee Bank Quay, which of course explains the origin of the Quay becoming known as, ‘The Holy’.


The Company was taken over in 1928 by the Halkyn District Mines Ltd and work continued in extending the length of the tunnel - the Olwyn Goch Shaft was reached in 1931.  A constant issue was the fluctuating price in lead ore, and a slump in prices caused a pause in extending the tunnel and a lay off in workers until 1939, when Pilkington Glass began using the tunnel to excavate high quality limestone - the side effect being the creation of huge limestone caverns.  Other caverns were discovered in the 1930s, including the utterly remarkable Powell’s Lode Cavern in 1931.  A natural chamber, some 130ft by 220ft, it contains a lake within it which is thought to be some 200ft deep.  It’s true depth is not known, since it was used to dump thousands of tons of spoil from the mine workings which has barely changed the water level.  It remains the highest natural underground chamber in Britain. During the Second World War, some of these caverns were used to store explosives.


Ore prices began to rise again in around 1948, and work on extending the tunnel began again - extending further south towards Loggerheads, discovering further lead rich lodes which gave work to many for another decade.  Between 1958-1964, limestone extraction was once again the dominant enterprise, since the quality of the stone was of the highest order, until the price of lead ore once again jumped.  The workforce, which reached a high point of 650 men, was in work until 1977, when mining on Halkyn Mountain came to an end.  The next ten years were ones of maintenance, until the Milwr Tunnel was finally closed in 1987.


The original site of the Olwyn Goch headgear on Halkyn Mountain - now at the Dolaucothi Goldmines in Pumsaint.

There is little now above ground to witness the workings below.  The headgear at Olwyn Goch was dismantled soon after its final closure and is now to be found at the National Trust’s Dolaucothi Goldmines at Pumsaint in Carmarthenshire, where they are displayed as part of a hard rock mining exhibition.  The gear and buildings were donated to the Trust by Flint based Courtaulds.  They remain the last known substantial remains of the lead mining industry in Flintshire.


The leases on the lead mines expired in 1991, the land returning to its owners, the Grosvenor Estate, the Estate which had first leased the mines to the London Lead Company at the end of the 17th century.  The Milwr Tunnel network was bought in 1992 by Welsh Water in order to supply water to industry in the area.  Today, access to the vast network of tunnels, which remain in good condition in the main, is possible only through the Grosvenor Caving Club, under strict conditions imposed by Welsh Water.


In all, the Milwr Tunnel runs from Bagillt on the Dee Estuary to Cathole on the Flintshire, Denbighshire border, some 10 miles to the south, but its network of mines, lodes and caves runs to over 60 miles. Today, it still discharges some 23 million gallons of water into the Dee Estuary every day, more after heavy rainfall.  Another example of Flintshire’s immense industrial heritage.

bottom of page