Vyrnwy Dam Monitoring: Overcoming Extreme Environmental Challenges

Challenge

Located in mid-Wales, the historic Vyrnwy Dam, the first gravity dam built in Britain from mass-cut stone in the 1880s, presented unique monitoring challenges as part of meeting safety legislation.

With a dam over 140 years old, it is vitally important regular maintenance work should be carried out, to protect against catastrophic failure.

On this occasion, two critical monitoring systems had become compromised at the dam:

1. The pendulum monitoring device measuring dam displacement had failed due to a build-up of ochre blocking its optical sensors
2. The uplift pressure drain monitoring device stopped working due to ochre blocking pipe-work

Additionally, there was interest in monitoring over 80 uplift pressure well flows in the dam's adit - a narrow, wet, and difficult-to-access tunnel running through the dam's foundation.

Traditional monitoring methods would be prohibitively expensive, with the following extreme challenges presented to SOCOTEC’s Monitoring team:

• Confined space requiring specialist access equipment and rescue teams
• A 200m long tunnel: narrow, low, wet, and covered with slippery ochre deposits
• Equipment rapidly becoming covered with ochre when exposed to air
• Optical-based monitoring equipment failing quickly in these conditions