Cheshunt Flood Storage Reservoir Repair
Environment Agency
Government
Cheshunt Reservoir
Water structures
More than 170 years after its construction in 1837, the outfall structure of Cheshunt North Reservoir, located thirteen miles North West of London, was in a deteriorating condition. Some of the original mortar used in the masonry construction had been washed away over the years, leaving the structure weakened, and evidence of leakage had been observed. There were also concerns about other internal structural problems that were hidden from view. A succession of repairs over the years had not completely addressed the underlying problems, which meant a more long term sustainable solution was needed urgently.
Because it holds more than 25,000 cubic metres of water above the natural ground level, the reservoir is classified as a ‘large raised reservoir’ under the Reservoirs Act 1975. The client, the Environment Agency, as statutory undertaker of the Act, is required to protect public safety. The consequences of the reservoir being breached would include flood risk to nearby housing, contamination of the local water supply, and disruption to traffic on the nearby A10 trunk road.
In Spring 2010, Royal Haskoning was asked to carry out an initial structural inspection to determine the extent of the problem. Tei Ho, lead design engineer on the project, explains some of the interesting issues:
“Due to the age of the structure understanding how the reservoir had been built was challenging, as very little information existed. Original sets of drawings were created during different time periods and these differed slightly. While some of the nineteenth century designs were beautifully drawn, they were hard to understand, and some of the technical terms were different to those we use today. This meant we literally had to stitch the drawings together to understand the wider picture - it was like Crime Scene Investigation – Civil Engineering Special