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Plan for 'mini-caverns' around island to unblock drainage pinch points

Plan for 'mini-caverns' around island to unblock drainage pinch points

Monday 21 November 2022

Plan for 'mini-caverns' around island to unblock drainage pinch points

Monday 21 November 2022


Smaller versions of the cavern under Fort Regent may have to be built around the island to deal with increasing amounts of rainwater and development.

The island’s drainage network is at capacity at certain ‘pinch points’ around the island, including Les Quennevais, Beaumont, Le Hocq and Five Oaks, and the Government is looking at options to deal with it.

One of those is to build new stormwater ‘attenuation’ tanks – which can store rainwater until it can be pumped to Bellozanne for treatment.

Speaking to Scrutiny recently, Infrastructure’s Group Director for Operations and Transport, Ellen Littlechild, said that smaller versions of the cavern, which can hold around 25,000 m3 of liquid waste, may have to be built around the island.

“We do have time to manage [capacity] before the system gets overloaded if we have money and the resources to support us to make that happen,” she said.

In most areas in Jersey, surface and foul water drains are separate, with the former flowing out to sea or into reservoirs, and the latter going to the Sewage Treatment Works in Bellozanne Valley.

Fort Regent Cavern

Pictured: The cavern under Fort Regent is designed to protect St. Helier from flooding.

However, in other places, notably Town, the two systems are combined, with everything flowing to the STW, which is in the last year of its life before a new one currently being built opens

In times of high rainfall and tides, the pipes and pumps of both networks can become overwhelmed. 

For some parts of Jersey, the cavern is used to store this water until the treatment works can cope. During periods of very high demand on the network, Infrastructure is also permitted to release foul water directly into the sea. 

Deputy Steve Luce, Chairman of the Environment, Housing and Infrastructure Panel, said: “If we take Five Oaks as an example, there are fields earmarked for development in the Island Plan and a masterplan being written.

“If an attenuation tank needs to be built there, you would expect it to be in place before houses start going up.”

He added: “The island is at capacity with all its waste streams at the moment – liquid, solid and contaminated – so we urgently need to address this. Thankfully, it does seem we have an Infrastructure Minister [Tom Binet] who is ready to tackle these difficult issues head on.”

At the panel hearing, Deputy Binet said he did not yet have the money to unblock the network pinch points but he would be seeking further funding in future Government Plans. 

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