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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.
(Score: 1, Touché) by Anonymous Coward on Wednesday August 07 2019, @05:46PM (3 children)
In meteorology rain is expressed in mm
(Score: 0) by Anonymous Coward on Wednesday August 07 2019, @09:20PM (2 children)
Ah, thank you for the response and answer. It was a serious question(for those who modded offtopic), if not phrased the best way. Yea, I'm the GP AC. I live in the Land of the Orange Man and am familiar with civilized units but not always standards. Around here, I've usually heard precipitation in fractional inches(rain but since it's rarely over 12 it doesn't reach the next unit) or feet, inches, and fractions(snow). I did live in England for a couple of years when I was very young, but do not recall forecasting nor reporting on the weather.
Now to wonder why meteorologists don't use increments. Oh well, off to duckduckgo and hope work's firewall won't stop me.
(Score: 0) by Anonymous Coward on Thursday August 08 2019, @02:15AM (1 child)
A mm is already a fairly small unit. To put it into perspective a tenth of our Yankee inch is approximately 2.54 inches. Plus, it conveys an idea of volume, as 1 mm over 1 square meter is 1 liter of rain.
FWIW, another reason why meteorologists use tenths of an inch is that it also gives us a sense of volume. One tenth of an inch on a square foot of surface is roughly a cup, which allows easy conversion to gallons. For example, 2 inches of rain on a 3000 square foot roof is 2*10*3000/16 (3750) gallons, which is pretty close to the actual measure of 3740 gallons.
(Score: 0) by Anonymous Coward on Thursday August 08 2019, @02:17AM
Ugh, I meant that first sentence to read "one tenth of our Yankee inch is approximately 2.54 mm."