Some of Britain’s rarest mammals had to be protected by Thames Water during water main upgrade work near Swindon.
Engineers came across a colony of water voles while carrying out the £13 million investment along the River Cole between Faringdon and Blunsdon.
Water voles are the UK’s fastest declining species of mammal, and are protected by law, so the team went to great lengths to avoid disturbing the rodents which live in bank side burrows up to five metres long.
Gareth Lavery, Thames Water ecologist, said: “The construction couldn’t continue without us encouraging the water voles to move. We made sure everything met the requirements of a special licence from Natural England, as well as following the strict guidelines in the Water Vole Mitigation Handbook.
“On top of that, the project had to guarantee there would be a net conservation gain for the water voles, and so the banks and stream will be reinstated and reseeded with a variety of marginal and bank side plant species once the work is complete.”
While laying the new pipe under the riverbed could be done away from the water itself, there was no choice but to construct an ‘outfall pipe’ on the banks. This pipe removes the water that has to be flushed through the new trunk main – at 640 litres a second – before it can start supplying drinking water.
This meant the voles had to be encouraged to move house before any work could start – and before the beginning of their breeding season.
To start with, the team removed vegetation from both banks to make the area unattractive to the water voles so they would move further up or down stream. Next, the area was left for just over a week to allow them to move and, finally, the burrows were searched and removed.
Now the water voles have moved, the outfall pipe will soon be put into action. To reduce the impact of pressurised water on the banks of the river, a temporary silt lagoon will be constructed close by, and discharging will take place via a temporary spillway on the river bank. The banks will eventually be reinstated and reseeded with a variety of vole-friendly plant species.