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Redundant reservoirs, whether they are subject to the provisions of reservoir legislation or not, have an ongoing maintenance requirement that places a burden on reservoir owners. Reservoirs upstream of communities also pose a risk to life. For these reasons, reservoir owners often consider discontinuing redundant assets; however, reservoirs can deliver amenity value for local communities as well as contributing to a desirable environmental habitat. Careful consideration should therefore be given to balancing the advantages and disadvantages when deciding whether to discontinue a reservoir. This paper will draw on case studies of five Scottish Water reservoir sites where the merits of discontinuance have been assessed. Two have been retained; and three have been discontinued. The key influences and lessons learned will be presented including identifying and mitigating environmental aspects; the findings from public consultations; the approach to whole life cost estimates; the benefits or otherwise of carrying ground investigations; the approach to dealing with sediment issues; the approach to managing flood risk during removal of the reservoir; and the approach to managing downstream flood risk following removal of the reservoir. The peculiarities of the Reservoirs (Scotland) Act 2011 will be touched on, as complete removal of a reservoir is termed abandonment!

Loch Drunkie is retained by two earth dams built in 1859. The outlet pipe is a 24 in dia. cast iron pipe through the highest part of the east dam with downstream control only. Although no record drawings exist, it is considered that the pipe is laid directly within the foundation or embankment fill and the presence of any concrete surround is unlikely. The pipe is over 160 years old and, due to the valve arrangement, is always subject to internal pressure from the reservoir. The east dam was inaccessible with no vehicular access to within 500 m. In the 2014 Statutory Report, a recommendation in the interest of safety was made to ascertain the condition of the outlet pipe and carry out any works deemed to be required to reduce any potential threats posed to the safety of the dam. This paper describes the series of investigations and subsequent pipe lining works that were carried out at the reservoir. Due to concerns regarding the integrity of the pipe, all investigations and pipe lining works had to be carried out with the reservoir at top water level to ensure the internal pressure to the pipe was maintained throughout.