Non-statutory reservoirs: a journey of discovery

The National Trust of the UK (England, Wales and Northern Ireland) owns some 200 reservoirs, of which 47 are statutory large raised reservoirs. Of the remainder, around 40 are thought to have volumes in the range 10 000–25 000 m³. The reservoirs were mostly built in the eighteenth, nineteenth or twentieth centuries, when construction methods were both varied and evolving. They have therefore never been fully assessed against modern dam engineering standards. The National Trust has endeavoured to identify and manage all its non-statutory reservoirs with a view to understanding the risk they pose, assessing investment requirements and their significance within the landscape and developing appropriate management and monitoring practices to ensure dam safety. With the likely change in threshold for registration with the regulator on the horizon, the trust has reviewed its non-statutory reservoir assessments and collected a number of common challenges and themes that appear regularly across its portfolio. These range from working within complex heritage designations and tree and vegetation management to better understanding of the resilience of reservoirs in small catchments. This paper aims to share some of this knowledge and raise some questions about potential future regulation and management of reservoirs.