Policy paper

Leigh flood storage area

Updated 19 December 2022

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History of flooding from the River Medway

Over the centuries, towns and villages have developed in the flood plain of the River Medway in Kent. As a result, flooding has always been a key risk.

Records show that a significant flood occurs in the catchment around every 15 years. Floods have been recorded in the:

  • 1920s
  • 1947
  • 1960
  • 1963
  • 1968
  • 1974
  • 1979
  • 2000/01
  • 2013/14
  • 2019/20

Flooding has a significant impact on communities; damage to property, disruption to businesses and upheaval to people’s lives. There is also the continued uncertainty of the threat of another flood.

Leigh flood storage area

In 1982, the Southern Water Authority completed the Leigh flood storage area (FSA). The FSA reduces the risk of flooding to around 1,200 homes and businesses in Tonbridge and Hildenborough. It works by storing the peak of a flood upstream and releasing it in a controlled manner once the peak has passed.

Image shows aerial view of site under construction in flat landscape of fields. A motorway runs diagonally across the right of the picture

Constructing the Leigh flood storage area control structure, 1980

The flood storage area sits between the villages of Leigh and Penshurst in Kent. When full, it covers approximately 278 hectares. It is formed of a 1.3 kilometre long, 5 metre high earth embankment across the Medway valley. The River Medway itself passes through 3 steel gates built into the embankment. These gates control the amount of water flowing downstream by either letting the river flow normally, or restricting the flow to hold water in the storage area.

The FSA is an ‘online’ storage reservoir, which means that the river is always flowing through it.

Image shows large expanse of water surrounded by trees in upper half of picture, with white water swirling through large concrete sluice gates in lower half of picture

The Leigh flood storage area in operation, February 2020

The Environment Agency is now responsible for maintaining and operating the Leigh FSA. We use it at the peak of a flood event, when river levels passing through the gates are at their highest. When there is exceptional rainfall there may still be some flooding downstream. But this will be much less than if the flood storage area were not there.

How it works – watch the animation

You can find out more about how the Leigh FSA works by watching our YouTube animation.

Leigh FSA reservoirs act works: December 2022 update

Between spring 2021 and December 2022, the Environment Agency carried out works to maintain the Leigh Flood Storage Area. These works were legally required under the Reservoirs Act 1975 to ensure the storage area continues to safely reduce flood risk to Tonbridge and Hildenborough into the future.

The works involved stripping the top soil off the existing 1.5 kilometre main embankment and laying erosion protection matting. The top soil was then replaced on top of the embankment and reseeded with grass to further stabilise the surface.

The works were expected to take 3 years but were completed a year early in, 2022. This has reduced the length of disruption to the local community and saved a lot of public money. Along with savings from reusing materials, finishing early has reduced the cost of the works from £10.1 million to £8.7 million - a saving of £1.4 million.

Completing early also saved a lot of carbon - at least 1,217 tonnes of carbon dioxide equivalent (CO2e) from a whole life estimation of 5,312 tonnes CO2e.

Tree roots removed from the embankment

Placing material on the downstream embankment, south of the railway line

Installing the Open Stone Asphalt protection on the downstream embankment, south of A21

Grass on reinforced embankment recovering after the hot summer. Once they recover, the embankments will look the same as they always have.

Leigh expansion and Hildenborough embankment scheme

Climate change will increase the risk of flooding in the coming years. To help manage this the Environment Agency is working with Kent County Council, Tonbridge and Malling Borough Council and the South East Local Enterprise Partnership. They will work on a project to increase the capacity of the Leigh FSA.

The Environment Agency is proposing to increase the maximum stored water level in the flood storage area. This is from 28.05 metres Above Ordnance Datum (AOD) to 28.60 metres AOD, and to build a new flood embankment in Hildenborough. This will reduce the risk of flooding to 230 more homes in Tonbridge and Hildenborough.

Due to the required timescales of completing the Reservoirs Act works, the expansion scheme is being delivered separately.

You can find out more about this project by viewing the Leigh expansion and Hildenborough embankment scheme webpage.

Contact

If you have any questions about the Environment Agency’s works at the Leigh FSA, please email the project team at LEHES@environment-agency.gov.uk

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