Part of Swansea Docks (nprn 580), King's Dock opened in 1909 for the export of anthracite. From the mid-1930s, around 6 million gallons of sea water per hour were drawn from King's Dock for cooling at the nearby Tir John Power Station (nprn 415587) and returned to the larger Queen's Dock (nprn 410503). The water was carried in two large concrete-lined tunnels, each about 3m in across and about 1km long, cut through solid rock at depths of up to 90m.
(Sources include "A Guide to the Industrial Archaeology of the Swansea Region", Association for Industrial Archaeology, 2nd Edition, 1989)
B.A.Malaws, RCAHMW, 25 October 2013.