Tuesday, 28 September 2021

Drainage plan could ‘pollute water and worsen flooding’

Drainage plan could ‘pollute water and worsen flooding’

PLANS to drain floodwater from a new housing site in Shiplake into the River Thames at Henley should not go ahead, according to an environmental consultant.

HR Wallingford, which was hired by Henley Town Council to investigate the proposal by developer Taylor Wimpey, says this could pollute the water and worsen flooding on the main road into town.

It could also increase flooding on Mill Lane, off Reading Road, in Henley, which is already badly hit during heavy downpours and has been evacuated in the past.

Taylor Wimpey has consent for 95 homes at the former Thames Farm site off Reading Road, which it has rebranded as Regency Place.

Preliminary work started in 2019 but stopped when the company found the site was prone to developing sinkholes so draining surface run-off into the ground wasn’t possible.

It instead proposes compacting the ground and reinforcing it with grout injections, which would make it impermable so water must be drained elsewhere. This requires separate consent from South Oxfordshire District Council, the planning authority.

The developer, which has discussed this with Thames Water and the Environment Agency, wants to pump the excess along a culvert beneath Reading Road towards Henley.

It would then flow eastwards along a stream to the south of the Jubilee Park sports ground, which the town council owns, and across land south-east of Mill Lane before flowing into the River Thames at up to 8.5 litres per second.

HR Wallingford accepts this would have a minimal impact on the main river level, which sometimes swells in winter to flood the towpath at Mill and Marsh Meadows.

However, the rate and volume of water crossing Reading Road from the field at Harpsden Meadow, opposite Jubilee Park, could “significantly increase”.

This could worsen flooding at the sports ground, which is crossed by a dry stream that sometimes swells, forcing children’s football matches to be cancelled for safety reasons.

The report says it isn’t clear whether the grouting would worsen the impact as there are fears that it could displace an aquifer beneath the site which supplies Shiplake’s drinking water.

Taylor Wimpey says the grouting won’t go that deep but opponents say the water level varies throughout the year so there could be an impact at times.

Meanwhile, HR Wallingford says Taylor Wimpey failed to consider the impact on houses in Mill Lane because of a “significant modelling error”.

It says the developer’s consultant Enzygo incorrectly measured the impact of pumping water upstream of the weir at Marsh Lock when it is more likely to be pumped out downstream of it.

The company also warns of “significant water quality implications” because surface run-off would absorb pollutants from the ground on its way to the river.

Finally, it says pumping water off site is not environmentally sustainable so Taylor Wimpey should find a way of draining into the ground.

The town council will discuss the report at its next meeting on August 3 then make a recommendation to the district council.

Councillor Ken Arlett, a retired builder and vice-chairman of the town council’s planning committee, said Taylor Wimpey should build fewer homes to allow on-site drainage using soakaways and a “balancing pond” to store excess.

He said this was common practice and the owner of the neighbouring plot at Crossways, who was recently refused consent for 20 units, had reduced their proposal to 10 with a balancing pond.

Cllr Arlett said: “It’s very concerning that they didn’t take into account the impact on Mill Lane because there are a couple of streams going through that area which could all be contaminated.

“It’s pretty much a flood plain anyway — it doesn’t take a lot to flood and this will only add to it.

“As I’ve said before, Thames Farm needs to keep all its water on site. I’ve worked on similar projects and balancing ponds are effective.”

He added he would ask for the scheme to be decided by the district council’s planning committee and not by officers.

Taylor Wimpey said it would consider the report and continue working with the district council and Thames Water on the drainage plans.

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