Policy paper

Leigh expansion and Hildenborough embankment scheme

Updated 16 January 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

December 2023 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.

We will need to raise sections of the embankment so that we can expand the flood storage area. This year we will raise a section at Cattle Arch bridge, near Leigh village. Over the summer of 2023, VolkerStevin has:

• cleared the vegetation at Cattle Arch Bridge to access the work area
• set up the site compound
• started construction of the temporary haul road which will be used to deliver the bank raising material to the site
• installed new kerbing at the top of the embankment and placed material to raise the embankment
• started building the new concrete retaining wall within the embankment at Leigh pumping station - this will help to reduce the impact of any waves when the reservoir is storing water

We will also need to replace the 3 gates at the Leigh FSA control structure so that we can expand the FSA and store water at the higher level. We will carry out this work over summer periods to make sure the structure can continue to operate over the higher-risk winter periods.

This year:

• we will assemble and test all the parts needed, ready for work to begin at the control structure in spring 2024

• we will start to construct temporary crane pads at the control structure

• our manufacturers will test the new winch system for the gates ready for further testing by the installation specialists

• we will finalise the design of the new gates and produce them

We will need to close the public footpath at Cattle Arch so we can carry out the works safely. This will take place from 29 August 2023 for the duration of the works.

We expect to complete the works and reopen the footpath in early 2024.

You can find out which footpaths will be closed on the Kent County Council website.

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.

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

Some works will be needed before we can build the scheme.

These include:

• Southern Water diverting an existing foul main around the new pumping station location - Southern Water have started these works near Hawden Lane, but they have been delayed due to the wet weather
• UK Power Networks upgrading the existing transformer for the new pumping station
• survey and ground investigation works using ground penetrating radar to map the location of services so that they can be avoided

VolkerStevin will start clearing vegetation in Hildenborough in early 2024, before the bird nesting season starts. We will start constructing the new flood embankment in spring 2024.

Next steps

Leigh FAS

• bank raising – we will continue work to create a small new embankment with hard standing for temporary pumps near Ensfield Road
• new culvert – we will build a new culvert to move water away from the railway and into the storage area during a flood event
• concrete wall – we will install a new concrete wall to reinforce the existing embankment at Leigh pumping station to help when flooding occurs
• eel pass – we will continue work on a new eel pass next to the existing control structure. This will allow elvers to swim past the barrier and migrate upstream
• temporary crane pads – we will carry out survey and ground investigation works so we can build the concrete pads

Hildenborough

• diversion works - Southern Water will start these in autumn 2023 ahead of the main embankment works
• vegetation clearance – this will begin in early 2024

Hildenborough engagement events – these will take place in winter 2024

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
• January 2024 – Leigh FSA Cattle Arch embankment works will finish
• spring 2024 – construction will start at Hildenborough
• spring 2024 – Leigh FSA control structure gates will start
• summer 2025 – Leigh FSA pumping station works will finish
• autumn 2025 – the full scheme will be finished

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 will remain ready to support the expansion works over the coming years.

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