The discontinuance of Boltby reservoir, North Yorkshire, UK

Boltby reservoir, North Yorkshire, UK, was completed in 1880 as a means of water supply to the local area. In June 2005 a flood event with a return period in excess of 1 in 10 000 years caused significant damage to the masonry-lined spillway structure. The reservoir had not been used for supply since 2003 and it was subsequently decided to discontinue the reservoir under section 13 of the Reservoirs Act 1975. The discontinuance work consisted of the excavation of a notch in the dam approximately 70 m wide at crest level. A new low-level overflow channel was constructed at the bottom of the notch such that the remaining dam impounds less than 25 000m³ of water. Construction work began in early October 2006 and the discontinuance phase of the scheme was completed in late February 2007. This paper describes the design and construction phase of the discontinuance project including the development of a detailed water level control and contingency plan and a large amount of environmental engineering works.