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. 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!