Interesting article in the Independent today, "MI5: revealing areas at mercy of collapsing dams is a terror threat" 
http://www.independent.co.uk/environment/climate-change/mi5-revealing-areas-at-mercy-of-collapsing-dams-is-a-terror-threat-854325.html
Some extracts follow, basically if the damn had burst last year Sheffield would have had no electricity for "an indefinite period" and also the "main 42-inch gas main serving Sheffield" would have been taken out.
http://www.independent.co.uk/environment/climate-change/mi5-revealing-areas-at-mercy-of-collapsing-dams-is-a-terror-threat-854325.html Some extracts follow, basically if the damn had burst last year Sheffield would have had no electricity for "an indefinite period" and also the "main 42-inch gas main serving Sheffield" would have been taken out.
The scale of an alert at Ulley reservoir, near Rotherham, emerged for the first time at the publication of the independent review by Sir Michael Pitt into the lessons from the 2007 floods.
A major threat to infrastructure made the situation at the Ulley reservoir dam so critical. The dam came close to failure when water flowing down a spillway undermined its base. It was saved by emergency repairs after a midnight evacuation of 1,000 people and the closure of the M1.
The consequences of a collapse would have extended far beyond the immediate area. Waters from a breach would have knocked out the main electricity switching station in the Sheffield area for an indefinite period, perhaps leading to a breakdown in social cohesion. A dam flood would also have destroyed the main 42-inch gas main serving Sheffield, which would have created a hazard to aircraft from the gas escaping into the atmosphere. A five-mile aerial exclusion zone was imposed around the point where the main might have fractured. All this would have been in addition to hundreds of deaths caused by a wall of water driving down the valley below the dam if it burst.
Yet emergency services facing this crisis, Sir Michael said, had no maps of potential inundation to work from and had to work it out themselves. He added that because of climate change, flooding in Britain was itself likely to become a risk as great as terrorism or an influenza pandemic.
According to Cabinet Office and Environment Agency sources, the Water Act 2003 had specified that the maps should be made public, but this had not happened after MI5 objected.
A major threat to infrastructure made the situation at the Ulley reservoir dam so critical. The dam came close to failure when water flowing down a spillway undermined its base. It was saved by emergency repairs after a midnight evacuation of 1,000 people and the closure of the M1.
The consequences of a collapse would have extended far beyond the immediate area. Waters from a breach would have knocked out the main electricity switching station in the Sheffield area for an indefinite period, perhaps leading to a breakdown in social cohesion. A dam flood would also have destroyed the main 42-inch gas main serving Sheffield, which would have created a hazard to aircraft from the gas escaping into the atmosphere. A five-mile aerial exclusion zone was imposed around the point where the main might have fractured. All this would have been in addition to hundreds of deaths caused by a wall of water driving down the valley below the dam if it burst.
Yet emergency services facing this crisis, Sir Michael said, had no maps of potential inundation to work from and had to work it out themselves. He added that because of climate change, flooding in Britain was itself likely to become a risk as great as terrorism or an influenza pandemic.
According to Cabinet Office and Environment Agency sources, the Water Act 2003 had specified that the maps should be made public, but this had not happened after MI5 objected.
