was stabilised along 30m of its length by freezing over a period of three months, using 175 brine tubes cooled to . A tunnel was excavated through the frozen ground to just wider than the two long preformed concrete box sections, which were jacked through as the excavation proceeded. This created a wide by high concrete culvert which can be seen from the Bath Road Bridge. The channel also had to be taken through Black Potts Viaduct, a series of 13 brick arches carrying the Waterloo to Windsor railway line over the Thames flood plain. Protective concrete and blue brick barriers were built around the older brickwork to preserve the viaduct's structural integrity, as well as to control gates to adjust the amount of water rejoining the Thames immediately downstream. The channel involved complex civil engineering to deal with utility conduits, roads and railways, as well as ecological and social issues, entailing compulsory purchases, community lectures and consultations and a public enquiry. For example at Manor Farm a weir was constructed. Conception to fruition took about 20 years. Water is admitted to the river through sluice gates at the upstream end of the channel near Taplow. This is normally controlled by measurements of the water levels below Boulters Lock and the estimated flow of the Thames at the Datchet gauging station near Windsor. The first serious test of the new structure occurred during the flooding of early January 2003, and revealed a number of defects in the design. With both the Boulters Lock levels and the Datchet flow indicating that the channel was needed, the Taplow sluices were opened briefly on 1 January, but were then shut again until 4 January, by which time the Boulters Lock levels were above the target levels, and the flow at Datchet was some 320 cubic metres per second, 140 cubic metres per second above the recommended flow. A subsequent investigation revealed that the Environment Agency had known there were defects in the channel since November 2002, and this had been a major factor in not operating it correctly. When flood water was admitted to the channel, the flows were well short of its designed maximum flow capacity, and yet there was significant erosion of the banks in several places. There was considerable erosion at the Taplow Sluice, due to the lack of a stilling basin; embankments at Marsh Lane were badly damaged; the