Clywedog Dam

Constructed between 1964 and 1967, Clywedog Dam in Wales is the tallest concrete buttress dam in the UK standing at an impressive 72m high and 231m long.

The reservoir incorporates Bwlch y Gle – a saddle dam – which was constructed to prevent flooding in the next valley after impounding. At full capacity, the reservoir contains 50,000 megalitres of water and plays a crucial role in managing the area’s increasing and varied demands for water, together with mitigating against flooding.

Summary of Works

Client: Severn Trent Water
Start Date: 2016
Completion Date: Ongoing
Monitoring System: Bespoke draw wire sensor, tipping bucket rain gauge, radar level sensor, thermocouple temperature sensors, automated pendulum, crackmeters, 3D (X,Y,Z) joint meters, pressure sensors, seismographs, vibrating wire piezometers, LoRaWan nodes, Calyx OMS™

A comprehensive manual monitoring system had been employed over the years to analyse the performance of both dams and ensure safe operation but, in 2015, Severn Trent Water (STW) commissioned an extensive 50-year review, which included an appraisal of the existing monitoring system. Two leading Inspecting Engineers from Atkins and Mott MacDonald oversaw the 50 Year Review and ITM Monitoring, now SOCOTEC Monitoring UK Ltd, was tasked with translating the findings of the review into a working monitoring system.

With the technological advancements of recent decades in mind, the Monitoring Design Plan detailed the required sensor types, an automated data acquisition system and data visualisation software, as well as additional deformation monitoring for the effects of Alkali Silica Reaction (ASR).

Robust passive sensors made from corrosion resistant materials with minimal parts and basic electronics were specified, to minimise the need for unplanned maintenance visits. For the ASR monitoring, an off-the-shelf solution wasn’t available, so ITM developed a bespoke draw wire sensor.

Challenges in the design of an automated monitoring system for Clywedog included the lack of mobile phone coverage, no provision of a telephone line or ADSL connection and a wide area distribution of a large number of sensors. With more than 150 sensors being installed across the site – some located on the Bwlch y Gle saddle dam approx. 1.69km from the main Clywedog dam – it was estimated that this would require more than 2km of cable. A cabled solution was quickly ruled out due to the logistical challenges, time and cost implications.

A wireless LoRaWan system was selected due to its transmission range of up to 15km from node to gateway, but also because of the encryption of the data before transfer, keeping it secure. The battery powered LoRaWan nodes also enable data collection across all sensor types with a single data acquisition network. Connection to the external servers is via a satellite link. Readings are taken every hour and all data is processed automatically using Calyx OMS™, ITM’s web-based data visualisation software, which enables greater insight into the asset’s performance 24/7.

Ian Hope, Severn Trent Water’s Dams and Reservoirs Manager, has been greatly encouraged by the successful delivery of the project.
The team were a pleasure to work with. By taking time to fully understand our needs, ITM Monitoring has developed and delivered a monitoring system fit for the 21st Century. This has given us increased confidence in the continued performance of both dams.