Torrential rain in the Midlands and North of England that saw half a month’s rain fall in one day caused such volumes of water to pass through the spillway of the Toddbrook Reservoir dam, above the town of Whaley Bridge in Derbyshire, that the protective concrete facing was damaged – badly enough to put the dam at risk of a full collapse.
Were the dam to fail this would be the first dam breech in the UK since 1925, when the Llyn Eigiau dam burst when its foundations failed in Wales, and its floodwaters overtopped the Coedty reservoir dam downstream, causing it to also fail and flood the valley at the cost of 16 lives. With emergency work underway and more rain forecast, this is still a very real possibility for the Whaley Bridge dam.
The dam above Whaley Bridge is an earthfill or embankment dam built in the 1830s using a mix of soil and gravel. The massive volume of water cascading down through the hills of Derbyshire’s Peak District from the heavy rain meant the floodwaters increased the reservoir water level up to the dam’s crest and onto the concrete spillway. Most dams are equipped with these concrete structures for the safe and controlled release of excessive flood water downstream.
But in Whaley Bridge the concrete spillway has collapsed under the torrent of high-speed waters, leaving a substantial hole across about a fifth of the face of the spillway. In fact, the current concrete spillway was installed at Whaley Bridge in around 1969 after it suffered similar damage in the winter of 1964.