A report commissioned by the Government found that intermittent maintenance was one of the key factors which led to the partial collapse of the Toddbrook reservoir’s spillway at the end of July last year, as reported in Ground Engineering Magazine.
A period of heavy rainfall caused overtopping of the crest of the earth embankment dam, leading to the evacuation of over 1,500 residents from nearby Whaley Bridge, with some unable to return to their homes for six days.
Whilst the UK has an excellent dam and reservoir safety record, incidents like the one at Toddbrook raise questions about what more could be done to ensure the continued safety of all dams and reservoirs in England and Wales. In this blog, Nick Slater – monitoring services director at SOCOTEC Monitoring – considers the role monitoring could play in this, from regular scheduled maintenance of legacy instrumentation, to installing the latest technological innovations in monitoring.
A brief history of dam and reservoir monitoring
For nearly 40 years, SOCOTEC Monitoring has provided bespoke monitoring systems for water-retaining structures and waste impoundments throughout the UK. In many cases, the SOCOTEC Monitoring team – many of whom are still with us today - were involved in the installation of the original instrumentation during construction of these dams, and continue to maintain it today.
Given this history, the SOCOTEC Monitoring team has unrivalled knowledge and expertise in the delivery of monitoring services for these kinds of assets, and we understand the unique challenges which come with working in these environments, from servicing legacy instrumentation through to installing the latest wireless data acquisition technologies.
Traditionally, instrumentation was installed in dams to monitor the asset during construction, to ensure that the design was performing as expected during filling and the first few years after commissioning. The instrumentation used to do this included mercury manometers, most of which have now been stripped out and replaced with electronic equipment, and hydraulic piezometers.
In 1975, the Reservoirs Act came into force and, during the late 1980s, the number of dams being constructed in the UK dropped. At this point, the focus for SOCOTEC Monitoring changed from monitoring during construction to the ongoing monitoring of dams, as the Reservoirs Act mandates that if an asset has instruments installed, they must be maintained.
In our experience, since privatisation of water-retaining structures, many dam and reservoir owners only carry out an adequate level of monitoring to satisfy the inspectors, maintain their certification and abide by the Reservoirs Act. At SOCOTEC Monitoring, we believe that maintaining instrumentation and using the latest technologies to monitor a dam’s behaviour should be more than just a tick box exercise, as there are many other benefits to understanding asset performance.
Why monitor dams and reservoirs?
Many of the dams and reservoirs still operational today were built over 200 years ago, to no recognisable engineering standards. These assets are experiencing impacts from climate change, such as excessive rainfall, putting them under increasing pressure and making them challenging to manage, potentially leaving them vulnerable to failure.
A report released by the Environment Agency, entitled ‘Delivering benefits through evidence: lessons from historical dam incidents’ states that “the number of casualties arising from a breached dam can be greater than from most other kinds of technological disaster.” Most reservoirs have a low probability/high consequence risk and, fortunately, there hasn’t been a dam failure which has caused a loss of life in the UK since 1925. However, monitoring the performance of these ageing assets is critical, as the consequences of a failure are too catastrophic to risk.
Whilst the importance of monitoring the performance of dams is widely accepted, the Reservoirs Act only goes as far to stipulate that any existing instrumentation should be maintained. What this legislation does not do is impose a duty of care to the point that reservoir and dam owners are required to have instrumentation installed if it is not already in situ. Rather, installation of new instrumentation tends to be reactive, in response to a specific issue having been identified.
Recent developments in software, sensor and communication technologies have reduced costs and consequently increased the opportunity for reservoir and dam owners to monitor assets remotely. And, the introduction of innovative new, low cost technologies such as PRIME – which combines state-of-the-art geophysical ground imaging technology with innovative data telemetry and web portal access – even allows asset owners to 'see inside' vulnerable earthworks.
Automated data acquisition provides many advantages to a dam monitoring campaign, but the importance of engineers taking manual readings and observing on site changes cannot be overlooked. By taking a more proactive approach to monitoring, and introducing automated systems alongside a planned schedule of maintenance of existing manual instrumentation to ensure their reliable ongoing functioning, dam and reservoir managers and engineers can:
- Access reliable data about the asset’s performance 24/7, with reduced inaccuracies attributable to user error
- Retrieve data easily from remote or inaccessible locations
- Detect any changes in behaviour, spot defects and take corrective action before they become problematic and costly
- Access better insight to support infrastructure maintenance and retirement planning and ensure budget is directed to the most required areas
- Reduce the number of personnel required to visit the site to collect and evaluate data, which reduces labour costs and risk
- Reduce the need for lone workers on site, improving health and safety
- Minimise carbon footprint, with fewer site visits required
- Optimise the ongoing performance of assets
- Have increased confidence in the continued functioning of dams and reservoirs throughout their lifecycle
Clywedog: a case in point
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.
A comprehensive manual monitoring system had been employed over the years to ensure safe operation but, in 2015, Severn Trent Water commissioned an extensive 50-year review, which included an appraisal of the existing monitoring system.
SOCOTEC Monitoring installed an automated monitoring system, which features a range of robust passive sensors made from corrosion resistant materials with minimal parts and basic electronics - to minimise the need for unplanned maintenance visits - an automated data acquisition system and data visualisation software, as well as additional deformation monitoring for the effects of Alkali Silica Reaction (ASR). For the ASR monitoring, an off-the-shelf solution wasn’t available, so SOCOTEC Monitoring developed a bespoke draw wire sensor.
This monitoring system has helped Severn Trent Water understand their asset’s behaviour and provided increased confidence in the continued performance of both dams. The full case study can be read here.
Want to know how monitoring can help you to ensure the reliable functioning of your earthworks asset long into the future? For more information about SOCOTEC Monitoring’s specialist services for dams and reservoirs, download our brochure or get in touch to speak to a member of our team about your requirements.
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