Tyne-Tees tunnel, Frosterley outlet
The Kielder transfer scheme was designed in the late 1960s and early 1970s to meet a rapidly growing demand for domestic and industrial water supply, particularly on Teesside. However, by the time the scheme was officially opened in 1982, growth in industrial demand had ceased and the requirement for the scheme was much diminished. 56 km downstream from the Kielder Dam, an 80m wide weir at Riding Mill on the Tyne feeds a pumped rising main (six pumps each of a nominal 1.05 cumec capacity) for 6.2 km to Letch House (in a 2m diameter steel pipe lined with 11mm of concrete) at 223m asl. Beyond this, the system is a gravitational tunnel, first to Airy Holm dam, which forms a head pond balancing input and output flows. The 31 km gravity tunnel was drilled predominantly through sandstones and mudstones, with a diameter of 2.91m with a minimum concrete lining of 200mm. The outlet portal above Frosterley (in this photograph) is at 180m asl, and to the Tees at Eggleston is at 177.75m asl. The maximum discharge capacity at Eggleston is 10.5 cumec, but here at Frosterley, only 2.0 cumec.
However, apart from some early testing and an annual freshet, to change the water in the tunnel, the scheme has never been used to put significant volumes of water into the Tees, but has been used much more often to support the Wear, particularly in the dry summers of 1984, 1989 to 1992, and 1994 (and possibly also more recently than the document from which these data are taken). The support is to ensure a minimum flow of 2.0 cumec below the major abstraction point at Lumley, 70 km downstream from here.