Look deeper into the dam: detecting potential failure earlier?

Look deeper into the dam: detecting potential failure earlier?
01 October 2019

Reservoir inspections

The recent incident at Toddbrook Reservoir that caused the evacuation of the town of Whaley Bridge, Derbyshire is a pertinent example of the risks posed by our ageing reservoir infrastructure.  

Under the Reservoirs Act 1975, which provides regulations for the inspection of large raised reservoirs holding more than 25,000 m3 of water, dams such as the Toddbrook Reservoir require an annual inspection by a Supervising Engineer.  The Canal and Rivers Trust who own and maintain this reservoir more than adequately met this requirement, with bi-weekly checks on the dam’s condition conducted by their operatives and bi-annual inspections by a Supervising Engineer. Similar and stringent inspections occur for most if not all the 300+ embankment dams across the UK. Nonetheless, the dam failure at Whaley Bridge still occurred. 

Earth-filled reservoir construction

Toddbrook Reservoir opened in 1838 and like similar dams of its time is constructed with an earth-filled embankment and around a puddle clay core, impounding up to 1.29 million m3 of water that is used to feed the Peak Forest Canal. Following very heavy rainfall that caused the reservoir to overflow onto its auxiliary spillway, the spillway’s concrete slabs failed.  This failure exposed the earth embankment and core of the dam, making it vulnerable to erosion and resulting in a high risk to the dam’s integrity. Whaley Bridge was evacuated and the subsequent emergency drawdown of Toddbrook Reservoir pumped huge volumes of water into the River Goyt, resulting in increased flood risk to various towns downstream on the Goyt and some sensational headlines

The knock-on effects on peoples’ health and wellbeing, wider financial implications and the impacts on water quality and ecological habitats (especially on the Goyt) as a result of such an event can, as yet, only be surmised. The Whaley Bridge incident highlights the need to think more about how to detect potential risks to the integrity of embankment dams.  This is especially true of Victorian reservoirs that, whilst robustly designed, were not necessarily constructed to withstand the kind of extreme rainfall conditions we are now seeing almost 200 years later.

Early failure detection options and technology: the future 

The precise cause(s) of the near-failure of Toddbrook Reservoir are not yet known, however they occurred despite the dam’s stringent inspection regime.  Driven by high intensity rainfall events that are predicted to become more frequent in the future due to climate change, the Whaley Bridge incident means we need to rethink the monitoring of embankment dams to support earlier detection of potential risks that could result in reservoir failure, and ensure better protection of at-risk communities and environments.

The technology for monitoring dam integrity clearly exists and continues to be developed, but dam monitoring tends to lack the kind of monitoring installations used for legacy infrastructure in other sectors. For example, we have been supporting the energy industry through the integration of modern remote monitoring technologies and innovative, rapid early warning assessment to detect issues and implement associated management interventions.  These interventions support strategic asset resilience, reduce risk, lead to better investment planning and provide secondary, but no less important, benefits to the end user by reducing supply interruption. Organisations charged with the management of dams could benefit from a similar approach.

Traditional methods for monitoring embankment dams, such as piezometers, drainage flow monitors and turbidity sensors, could be combined with emerging methods using in-situ sensors to monitor electrical potential or temperature to detect specific locations of internal erosion or seepage. Satellite remote sensing is also providing new opportunities to monitor embankment dam stability that could be used in combination with in-situ sensors, providing a powerful, cost-effective approach to early failure detection that protects people, water resources, heritage infrastructure and the environment.  

Collecting these data remotely and in real-time can help to diagnose problems and target actions swiftly before another emergency like Whaley Bridge occurs.  The data collected and the approach to assessment needs to be relative to structural failure risks and potential impacts on people and the environment. Our experts have a wealth of knowledge and experience providing technical and data-led solutions to complex issues aimed at minimising environmental risk in its broadest sense by combining our water expertise, digital services, cutting-edge data analytics and early warning assessments.

For more information on how we can support you or to explore concepts contact gabriel.streich@ricardo.com