Raising the Lake Bank
28 June 2013
On 20th July 2007, it rained steadily all day, with over 4½ inches or 120mm falling in our area. There were serious floods and we were worried that the bank or bund (embankment) of our lake would fail and cause even more serious flooding downstream. Luckily, it did not, but that was probably because we had strengthened it in previous years as we were required to do under the terms of the Reservoirs Act 1975. I had doubted that some of the work was necessary as I had not been able to imagine so much rain in one day, but the provisions of the legislation proved to be correct.
The rainfall that day was almost certainly a one in 250 year event and exceeded the seasonal average by over 300%. It was an amazing, but slightly frightening sight to see the stream in the Park transformed into a river and to hear the roar of the water as it powered over the lake weir. I wished we had had a turbine to get some benefit, though it might not have survived the force.
As a result of more severe flooding elsewhere in the country, the Environment Agency decided the precautions taken before 2007 were not adequate, and we should prepare for the one in 1000 year eventuality. In our case, under a separate exercise supported by Natural England, we have replaced damaged stonework on the weir and made a new crest so that the water now overflows evenly across the whole of the top. We have also been required to raise the bank further, which is what Rob Shail, a local contractor, is doing in this image. The new soil was compacted by the mini-digger and covered with a netting material and grass seed. The idea is that the seed will grow, which it has been with the recent weather, and combine with the material to form a protective coat to stop erosion and even washing away in case of extreme conditions.
Rob did a very tidy job and we hope the work will pass the Environment Agency inspection. It has been approved by our consulting engineer, Mark Hayward of Fairhurst and the grass is growing well. I would be interested to see it all put to the one in 1000 year test, but I am not holding my breath.
James Hervey-Bathurst 21st June 2013