Plans for a dam on the River Severn in Shropshire were today unveiled as part of a £30 million scheme to protect nearly 2,200 homes at serious risk of flooding downstream of Shrewsbury.

But more than 50 properties – including farms – in parts of rural west Shropshire would be in the enlarged flood plain and face more severe flooding if the scheme goes ahead.

Environment Agency chiefs hope to install a floodgate across the river beneath a bridge on Shrewsbury’s long-awaited £100 million North West Relief Road.

The dam could be ready by 2017, together with the controversial road, and would operate in a similar way to the Thames Barrier.

It could be closed in the event of a sudden rise in water levels and store excess water upstream, while lessening the severity of floods downstream.

Floodwater would then drain back into the river once flooding eases.

According to agency computer models, river levels would be up to a metre lower in Shrewsbury than they are now in the event of a “one in 50 years flooding event”.

River levels during a bad flood would drop about 80cm at Ironbridge, 26cm at Atcham Bridge and 9cm at Worcester. But villages like Montford Bridge, which lies within the proposed water storage area, could see water rise by more than a metre.

Details of the Severn Valley Flood Risk Management Scheme emerged at a special meeting called by National Farmers’ Union members at Walford, near Shrewsbury, yesterday.

Neil Baly, a farmer from near Montford Bridge, hit out at the plan and said he was “horrified”. He said: “I’m very worried. I’m going to lose half my farm.

“Has anyone considered the costs of compensation for loss of land? More houses will become uninsureable.”

Anthony Crowther, from the agency, told NFU members the scheme was “not a done deal” and would only be considered if deemed viable following consultation with landowners.

He said river levels at the dam could be 4.8m higher but get shallower upstream.

Speaking after the meeting, Paul Tullett, agency area manager, said the scheme is one of several the agency is mulling over as it prepares to tackle an increased risk of flooding in the next 50 to 100 years.