Lessons learned from reservoir discontinuances

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. 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 (HMG, 2011) will be touched upon, as complete removal of a reservoir is termed abandonment!