The Environment Agency (EA) has been given the green light to progress its plans for a £21.5 million scheme to further strengthen flood protection for over 1,200 homes and businesses in Tonbridge and Hildenborough by increasing the maximum stored water level in the Leigh flood storage area.

Communities in Tonbridge and Hildenborough are at risk of flooding from the River Medway. Flooding occurred in these areas in 1960, 1963, 1968, 1974, 2001 and 2013/14 – with significant flooding in Tonbridge and Hildenborough in 1968. The Leigh flood storage area (FSA) was built to reduce the risk of future flooding to approximately 1,200 homes and businesses.

In response to the growing threat that climate change will increase the risk of flooding in the coming years, the EA has been working on a scheme to increase the capacity of the Leigh FSA.

To reduce the risk of flooding for more homes in the area, the scheme will increase the storage capacity of the existing Leigh FSA. Works will also include the construction of an embankment in Hildenborough.

The flood storage area is operated by three storage gates to store the highest flows and control the flow of the river to reduce flood risk to properties downstream.

Currently the Environment Agency can legally store water to a maximum level of 28.05 metres above ordnance datum (AOD), as measured at the control structure. Investigations have shown that storing water to 28.6 metres AOD will reduce flood risk to over 1,400 homes in Tonbridge and Hildenborough. Storing to this level will need 16.4 hectares of extra land but will increase the storage capacity by 24% to over 7 million cubic metres.

Increasing the maximum stored water level required permission from the Secretary of State for Environment, Food and Rural Affairs –. at the end of September 2021 the Minister approved the EA’s application to increase the maximum stored water level within the Leigh Flood Storage Area from 28.05 metres AOD to 28.6 metres AOD.

The Secretary of State confirmed that a compelling case in the public interest was made and approved the application to increase the level without modification or conditions.

Estimated cost of the scheme to expand the reservoir is £21.5 million – the funding has been secured from and from the following three local organisations who will deliver the scheme in partnership with the EA:

• Kent County Council
• Tonbridge and Malling Borough Council
• South East Local Enterprise Partnership

While the expansion scheme is being developed, the Agency will invest in a programme of engineering works which will keep the existing FSA fully operational and compliant with the relevant legislation.

Next steps

The EA is currently preparing the planning application for the Hildenborough aspect of the scheme and expects to submit this to the planning authority in December 2021.

The Environment Agency expects to appoint contractors in spring 2022 with the works currently programmed to begin at the FSA in summer 2022.

The works will involve lifting the top soil of the existing 1.5 kilometre main embankment and laying reinforcing materials. The reinforced layer will be covered with a layer of soil then sown with grass to further stabilise the surface.

The full scheme is due to be complete in autumn 2024. This is a year later than originally planned due to the time required for the public inquiry.

The construction programme for this part of the scheme is dependent on the planning decision. An update on the programme will be provided if and when planning permission is received.