Policy paper

Leigh expansion and Hildenborough embankment scheme

Updated 24 December 2024

Background

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
• 2013 and 2014

The 1968 event caused significant flooding in Tonbridge and Hildenborough. The Leigh flood storage area (FSA) was built to reduce the risk of future flooding to approximately 1,200 homes and businesses.

It is likely that climate change will increase the risk of flooding in the coming years. The Environment Agency is working on a scheme to increase the capacity of the Leigh FSA. This will help reduce the risk of flooding to more local homes and businesses.

Proposed scheme

The Leigh expansion and Hildenborough embankment scheme will reduce the risk of flooding for more homes in the area.

It has 2 parts:

• increasing the capacity of the Leigh FSA
• constructing a new embankment to protect homes in Hildenborough

Currently, we can legally store water to a maximum level of 28.05 metres above ordnance datum (AOD). This is measured at the control structure.

Environment Agency investigations show that storing water to 28.6 metres AOD will reduce flood risk to over 1,400 homes in Tonbridge and Hildenborough. We will need 16.4 hectares of extra land to store to this level. This will increase the storage capacity by approximately 25% to over 7 million cubic metres.

Doing this needs permission from the Secretary of State for Environment, Food and Rural Affairs to increase the maximum stored water level.

Our application was approved by the Secretary of State in September 2021. This means we can increase the stored water level from 28.05 metres AOD to 28.6 metres AOD.

This approval meant we could start the Leigh expansion and Hildenborough embankment scheme.

Find out more about this decision and the scheme.

Investment and funding

We estimate the scheme will cost £24.8 million. We have secured funding from:

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

Expanding the reservoir is a big job which will take time. While the expansion scheme is being developed, we will carry out a programme of engineering works. This will keep the existing FSA fully operational and compliant with the relevant legislation.

These works will also feed into the design of the enlargement scheme.

Partnership

The scheme is being delivered in partnership with:

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

Autumn 2024 update

Leigh flood storage area expansion

In spring 2022, the Environment Agency appointed a contractor, VolkerStevin, to carry out the construction works on our behalf.

To expand the flood storage area we will need to replace the 3 gates at the Leigh FSA control structure.

Over recent months we installed the first set of new gates. This is the first time that a gate has been replaced in the structure’s 42-year life. Find out more about these works.

Due to their size, the gates had to be delivered in sections and welded together on site. Once assembled, each of them weighs around 12.5 tonnes. This is equivalent to the weight of a single-decker bus! 

The first new gate being installed at the Leigh flood storage area control structure (credit: project team)

We will also need to raise sections of the embankment. This year we have raised sections at Leigh pumping station and Cattle Arch bridge, near Leigh village. We are placing new topsoil along the final sections of embankment slopes where the last stages of work have been completed. 

The flood storage area remains fully operational throughout the construction works.

Hildenborough embankment

We have designed a scheme that reduces flood risk to as many homes as possible with as little impact on the local community as we can.

The scheme includes:

• a new embankment
• pumping station
• penstock structure on the Hawden Stream

It is designed to work with the Leigh flood storage area expansion and will further reduce flood risk to Hildenborough from the River Medway.

Tonbridge and Malling Borough Council approved our planning application in November 2022.

Indicative design of the Hildenborough embankment scheme (credit: project team)

Over the spring VolkerStevin cleared areas of vegetation in Hildenborough, before the bird nesting season started.   

Southern Water has been working to lay the new sewer pipe diversion to enable the main flood works. We have been working alongside them to install a temporary crossing over the stream. This allowed us to install sections of piling.  

Over the winter we will begin installing the new penstock chamber which will control the flow of water up and down the Hawden Stream.

You can find out more about how the Hildenborough aspect of the scheme will work by viewing our animation on YouTube:

Hildenborough embankment scheme.

Timeline

• June 2020 – application submitted to Defra to amend the River Medway (Flood Relief) Act 1976
• April to May 2021 – local enquiry held
• September 2021 – approval from the Secretary of State
• November 2022 – Hildenborough planning approval received
• spring 2022 - contract for construction work awarded
• autumn 2022 - pre-construction works started at Leigh FSA
• spring to summer 2023 – construction started at Leigh FSA
• spring 2024 – construction started at Hildenborough
• spring 2024 – Leigh FSA control structure gates started
• autumn 2024 – construct stream crossing for piling works and install sheet pile wall at Hildenborough 
• autumn / winter 2024 - install the new penstock chamber at Hildenborough 
• winter/spring 2025 - install new pumping station at Hildenborough 
• summer/autumn 2025 – install remaining gates at Leigh control structure 
• spring/summer 2025 – construct embankment at Hildenborough
• summer 2025 – finish Leigh FSA pumping station works
• end of 2025 – the scheme will be fully operational

Reservoirs Act work projects

In January 2021, the Environment Agency received planning permission to proceed with essential works required to the FSA under the Reservoirs Act 1975.

We started the work 2021 and expected to finish it in autumn 2023. We completed this a year earlier than expected, in autumn 2022.

The compound at the Leigh FSA control structure was transferred to support the works to expand the flood storage area

The footpaths are now open, though some fencing may remain in some areas to allow the grass seed to settle and grow. We will remove the fencing once the grass has grown enough for it to cope with foot traffic.

We are aware that some sections of footpath are a little muddy. We will monitor these and reseed with grass if needed.

Find out more about the Leigh Reservoirs Act works.

Medway catchment

The Leigh expansion and Hildenborough embankment scheme is part of the Medway Flood Action Plan. The action plan was developed by the Medway Flood Partnership.

It was established in January 2017 and brings together:

• local partners
• national agencies
• non-government organisations
• community representatives

The partnership focuses on reducing the risk of flooding from non-tidal rivers and surface water in the Medway catchment.

You can find out more on the River Medway Partnership website, and in the Medway Flood Partnership: objectives, members and action plan.

There are two other projects in the Medway catchment:

• Middle Medway property flood resilience scheme
• East Peckham property flood resilience scheme

More information

Find out more about the history of the Leigh FSA.

You can find out more about how the Leigh FSA works to reduce downstream flood risk in our YouTube animation. You can also search for Leigh Flood Storage Area.

You can ask our project team about the works or join our electronic distribution list for future updates by emailing us.

You can also follow us on Twitter: @envagencyse Hashtag: #LeighFSA; #HildenboroughFAS; #MedwayFAP