Milwr Tunnel

The Milwr Tunnel is a mine drainage adit running some 10 miles from the hamlet of Cadole near Loggerheads, Denbighshire to Bagillt on the Dee Estuary in North Wales. It was originally built to drain the lead mines beneath Halkyn Mountain, which were plagued with flooding in their lower levels, but enabled the exploitation of new lodes and was variously used for the extraction of lead, zinc and limestone during its working history. It is part of a network of mines, lodes and natural cave systems – the Halkyn United Mines – that extends for up to 100 kilometres, the longest in the United Kingdom.

It forms part of the mine drainage system that is responsible for draining Ogof Hesp Alyn and leaving much of the River Alyn between Loggerheads and Rhydymwyn dry during summer months.

The first phase of the tunnel was driven by the Holywell-Halkyn Mining and Tunnel Company, a consortium of local mines, under the supervision of engineer Nathaniel R. Griffith of Wrexham. The Company was formed in 1896, its Secretary and Manager being John Philip Jones, and its directors listed as the Hon. C. T. Parker, H. A. Cope, J. B. Feilding, T. Snape, John Brock, Henry Taylor, and Eustace Carey. The mines involved hoped that the construction of the tunnel, by allowing them to work rich seams of ore at depth without incurring high pumping costs, would enable them to meet their low-cost international competition head-on.

Tunnelling was commenced in July 1897 at Boot End, Bagillt, from a point 9 feet below high water mark on the Dee foreshore, where self-acting flood doors were fitted. It was driven at a gradient of 1:1000, initially brick lined where it passed through coal measures and shale, and unlined after the first 1.5 miles where it passed through chert and limestone, successively reaching the Pen-yr-Hwylfa, Dolphin, Drill, Coronation and Caeau veins; a branch tunnel accessed the Old Milwr vein. In 1908 driving stopped 2 miles from the portal at Caeau Mine, the limit of the company's mineral rights, at which time the tunnel was draining some 1.7 million gallons of water per day through the drainage channel cut in its floor.

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