Rotherham council was this week considering whether to demolish a dam which almost collapsed last month following torrential rain.
Long-term risk to the area around the Ulley dam, which suffered near catastrophic embankment scour two weeks ago, has prompted engineers to seriously consider permanently draining the 14ha reservoir.Emergency repairs successfully prevented the dam collapse.But Andy Shaw, community delivery manager atStreetpride, Rotherham's civils and infrastructure division, said options to repair or abandon the dam were still being assessed.'A downside of losing the reservoir would be losing an important sailing, fishing and recreation site,' said Shaw.Pumping continues at the reservoir to control the water level, at a cost of £30,000 a week.Arup associate director Peter Kelham, who advised Rotherham council during the emergency, said: 'The dam must be re-inspected by an All Reservoirs panel engineer, who will assess the dam, its capacity and category.'Before the recent crisis, the reservoir held 582,000m3 of water and was rated as category C, meaning it presented a negligible risk to human life, but some risk to property, according to the All Reservoirs panel engineers.It could now be upgraded to a category B structure which means that fewer than 10 lives could be at risk if it fails, but that there could be extensive property damage.This would have important consequences for the reservoir, as Rotherham council would have to mitigate the increased perceived risk.Investigations by the panel engineer will include boreholes into the dam's puddle clay core, and examination of valve shafts, outlet pipes and tunnels in the dam wall.The panel engineer will then make recommendations. 'The problem is that the reservoir is a liability. There is no guarantee that any repairs will be totally effective,' said Kelham.Shaw said that a range of solutions were under investigation, including modifications to keep the water level down.'We could introduce a V-notch in the dam wall, or put a tunnel through to prevent it being a reservoir.'Final decisions will not be made until September, but in the meantime, the council must decide whether to keep the pumps or lower the water level.