The case of Havant Thicket reservoir in Hampshire highlights the consequences of climate change and population growth on the water-stressed region of the South East. The project, approved by both Havant Borough Council and East Hampshire Borough Council, is a joint effort by Portsmouth Water and Southern Water, and the result of regional water planning.
Though water from the 1.6km long and 0.8km wide reservoir would supply Portsmouth Water’s customers, the resource is ultimately designed to help Southern Water. Updates to its abstraction licences in 2019 restricting the amount of water it can take from the Rivers Test and Itchen – rare chalk stream habitats suffering from over-abstraction, combined with estimated population growth of 22% by 2045, have left the utility with a significant water supply deficit.
Once the reservoir is built, the water that previously supplied Portsmouth Water’s customers in the area will then supply those in the neighbouring area, with that effect mirrored across the region, explained Jim Barker, head of water resources at Portsmouth Water.
“There’s a series of piggy backs that will mean we have water available on our boundary. This shows the usefulness of sharing water across companies and taking a consistent view across the region on where water is available,” he said.
Some 13.67ha of ancient woodland will need to be destroyed to make way for the project, along with 7.18ha of priority lowland mixed deciduous woodland habitat, 1.21ha of purple moor-grass and rush pasture priority habitat and 3.7km of watercourses.
But the new water resource, which can supply 21 million litres a day, will protect the rivers Test and Itchen, and prevent the need for new infrastructure elsewhere, Barker said.
“If we don’t construct the reservoir, it would effectively mean a larger desalination plant [than that already planned for Fawley] would be needed, which would not be popular,” Barker said.
Planning officers deemed that this need, combined with plans to provide a minimum of 110ha of compensatory habitat off site, including 60ha of woodland, was enough to justify the loss of ancient woodland, which national planning policy allows only under “wholly exceptional reasons”, and with sufficient mitigation.
Compensation plans – drawn up with the Environment Agency and Natural England – also include creation of a wetland on site with water depths and vegetation designed to attract birds, and a visitor centre. Portsmouth Water will provide a £40,000 a year fund for community and environmental projects for 30 years from 2029, when the reservoir will become operational.
The Hampshire branch of the Campaign to Protect Rural England, while expressing concern about the loss of ancient woodland, noted the pressure on water resources in the South East, and that Southern Water only avoided the need to apply for drought permits in 2019 and 2020 due to rainfall.
“On balance we recognise that this is an important infrastructure project that will help to provide reliable water supplies … as well as providing some relief of stress on the Rivers Itchen and Test which could be considered assets more unique to Hampshire than this area of ancient woodland,” its submission to the planning application read.
Similarly, Havant Climate Alliance and Havant Friends of the Earth noted that the loss of ancient woodland was a “high price to pay”, but said the reservoir was justified to protect the two chalk streams.
However, Jack Taylor, lead campaigner for woods under threat at the Woodland Trust, believes that more could have been done to avoid the loss of ancient woodland, such using an alternative site, or developing two reservoirs either side of an area known as “the Avenue”, which contains many veteran trees.
More than 70 alternative locations were initially considered for the reservoir, according to the council’s planning document. Havant Thicket stood out as by far the best location for several reasons, according to Barker.
These include the clay underlying the site, which could be dug out and used to construct the reservoir walls and reduce the number of vehicles travelling to and from the site, and its proximity to the water sources the Havant and Bedhampton Springs, Barker said.
The company also considered building two reservoirs in order to save the Avenue, but that would not have provided enough water, he said.
“It's very sad that we have to fell some trees. We've adjusted the design of the reservoir to save as many trees as possible round the boundary, and we've been pushed very hard by the environmental regulators to make sure there’s really comprehensive mitigation plans in place. Overall, there will be a biodiversity benefit from this,” he said.
But for some the mitigation plans could never be enough. “Compensation is an act of making up for what's lost, but in our eyes, you can't make up the loss of something that's irreplaceable,” Taylor said.