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England Dam at Risk of Collapse

Tuesday, August 6, 2019

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Heavy rain recently damaged the auxiliary spillways of a Derbyshire, England, dam, prompting an evacuation of the nearby town. Now, a helicopter has flown in bags of aggregate to keep the reservoir from collapsing, while questions about how well the structure has been maintained have been raised.

According to the BBC, around 1,500 residents were evacuated after the dam ruptured late last week. A few dozen have refused to leave, even with the warnings, however. The dam was built in 1831, and the auxiliary spillway is thought to have been added in 1969.

What Happened

The Guardian reports that an excess of water ran over the spillway above the town on Thursday (Aug. 1), and as a result, the spillway began to erode, also causing the concrete ballasts to move away. A Canal and River Trust employee tried to reduce water levels by opening valves, as well as clearing debris and continuing to track the valves, but there was too much overflow to account for, and the clay wall began to be washed away. Authorities were notified of the situation soon after.

Around that time, police, the Canal and River Trust and the Environment Agency have all said that there is a risk the dam could collapse. During the first few hours, only one pump was available. Others were brought in and a local civil engineering company built a temporary road to facilitate pump transport. Among tools used, 11 steel pipe hoses—each 500 feet long and 12 inches in diameter—were implemented to help tackle the water level.

“When I was over there it started to crack," said local resident Father Jamie Mcleod. "When it got worse I went over to the council and raised the alarm and said, 'We have to evacuate the village.’”

According to The Guardian, an RAF Chinook helicopter delivered 400 tons of aggregate—which largely consists of sand, gravel and stone—to help stem the flow of water into the reservoir. The same helicopter was also used to shore up the damaged face of the structure.

Dam Safety

A Whaley Bridge resident sent photographs—reportedly taken in 2016 and 2017—of the structure to the BBC, which showed concrete that had vegetation growing out of it. Roger Meredith, who previously worked as a construction engineer at the Tarbela dam in Pakistan, noted that he thought the signs of vegetation were not good: The vegetation’s “roots are going through the joint of the slabs or where the slabs are cracked.”

Meredith also added that there should be “water bars” between joints on concrete slabs in structures like this in order to help prevent water from passing through. No bars were reportedly visible in the photos of the collapsed spillway.

"When you look at the spillway the side kicks in, it's not straight. So you are increasing the amount of water trying to get down that side," Meredith said.

Moving Forward

The Toddbrook Reservoir has been drained of 5.7 meters of water over the past five days, putting it at 46% holding capacity currently. The capacity needs to be lowered to 25% before village residents can return to their homes. A spokesperson for the Canal and River Trust noted that “there are sufficient pumps on site to help mitigate against forecast rainfall.”

Reservoirs with a capacity of over 25,000 cubic meters above ground level located in England and Wales must comply with the Reservoirs Act, which includes having a supervising civil engineer and an inspecting civil engineer file annual safety reports. The Trust maintains that the Toddbrook Reservoir was “absolutely fine.” An independent inspection also takes place once every 10 years.

 "The last one was undertaken in November 2018 and signed off by the independent Panel Engineer and CRT Supervising Engineer in April 2019,” said the Trust.

"As you would appreciate, currently our focus is on managing the situation on site and drawing the water level down and [stabilizing] the dam."

The dam is now currently “relatively stable,” according to reports, though it may take years to get the dam back to full operation.

   

Tagged categories: Accidents; Health & Safety; Infrastructure; Locks and dams; NA; North America; Rehabilitation/Repair

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