By Martin Guthrie, Senior Partner Manager, Rezatec
If the Whaley Bridge / Toddbrook reservoir incident earlier this month in the North of England has taught us anything, it’s that it’s not just the catastrophic failure of a dam or reservoir that has high costs. Urgent, last-minute, remedial and/or preventative action does not come cheap either.
In the case of Whaley Bridge; 1,500 residents evacuated, an estimated 400 tons of aggregate used, an RAF Chinook helicopter working round the clock, 150 firefighters and 11 high-volume, 12-inch diameter pumps siphoning 7,000 litres of water a minute (later increased to 16 pumps), 40 soldiers from the Light Dragoons drafted in to help, and a promise from the new Prime Minister to do a “proper rebuild” of this “dodgy but stable” dam. Whatever the final tally of costs is deemed to be, it certainly seems inevitable that it will run to many, many millions.
Yet all this disruption and cost– or the risk of something much worse – might have been avoided.
Current legislation in the UK (covered in England by the Reservoirs Act 1975) specifies that each reservoir must be inspected every 10 years, or more often, where necessary. In practice this often means an annual inspection. These inspections are often visual – with accurate measurements only being done if there is a reason to think them necessary.
But these accurate measurements (whereby any movement of the surface of a dam wall or embankment can be measured to the millimetre) can spot underlying changes and/or possible weaknesses in the structure before they become visible – and potentially susceptible to severe weather.
Historically, making accurate measurements has been a specialised and sometimes manually difficult task. Also, annual inspections are fine – but extremes in the world’s weather are increasingly common – and certainly don’t wait for a year to pass before changing.
Rezatec, based near Harwell in Oxfordshire, is developing pioneering analysis techniques that can monitor dams and reservoirs for possible movement with millimetric accuracy using existing satellites in orbit with already-available data. The frequency of these measurements can be weekly, quarterly, or monthly as required – and can be done retrospectively as well, to see what movement has already happened over the last few years.
For example, you may recall the Brumadinho dam disaster in January this year in Brazil, where an iron-ore tailings dam failed catastrophically with the loss of at least 248 lives. The company that runs the dam, Vale SA, said at the time that it would take as much as 10% of its ore output offline in order to decommission 10 similar dams, costing it $1.3bn over 3 years. This in addition to the tragedy, the reputational cost and the consequential damages.
A preliminary retrospective analysis by Rezatec of the Brumadinho dam shows that its structure showed clear and measurable signs of movement for 9 or 10 months prior to its failure. In other words, it seems likely that its failure could have been prevented had remote monitoring been in place.
Rezatec will be carrying out a similar retrospective analysis of Whaley Dam in the coming weeks.
Watch this space…