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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:
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.
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.
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 there 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.
The future of the Leigh FSA reservoirs act works
August 2021 update
The Environment Agency is carrying out works to maintain the Leigh FSA. These works will ensure that we remain compliant with the Reservoirs Act 1975.
The works will involve stripping the top soil off the existing 1.5 kilometre main embankment, laying erosion protection matting. Then replacing the top soil on top of the embankment and reseeding with grass to further stabilise the surface.
Once these works are complete, the embankments will look the same as they always have.
These works will ensure the Leigh FSA continues to safely reduce flood risk to Tonbridge and Hildenborough and other downstream communities into the future.
During spring 2021 we carried out ground investigation works and vegetation clearance to enable access during construction. We also carried out ecological surveys to ensure that key flora and fauna were identified and protected from the works.
We set up our works compound at Lower Haysden overspill car park in early summer 2021. We then began works to the Leigh FSA embankment between the A21 bridge and southern tip of FSA on Lower Haysden Lane.
These works involve:
- Removing the topsoil from the top and downstream side of the embankment
- Carrying out works to raise the clay core in the centre of the embankment as this prevents water stored in the FSA from seeping through the embankment
- Laying erosion protection matting on the downstream side of the embankment
- Improving the drainage at the toe of the embankment so that water flows away more easily and enables better bank stability
Once these works are complete the topsoil will be re-laid on the top of the embankment and re-seeded with grass. This grass will help to strengthen the embankment.
On the downstream side of the embankment, we will re-seed directly onto the mat as it is permeable. We may need to fence off access to this area while the grass seed takes to ensure it establishes well.
A small diversion of the bridleway is in place while we are working in the area. The original bridleway will be re-opened once the works in this area are complete.
During autumn 2021 we will complete the works in the first working area. We will also lay a haul road on the existing mud lane for vehicle access to the next working area. This will be returned to its original condition at the end of the works.
We will move the working compound from Lower Haysden to Powdermill Lane, but we will retain site offices at Lower Haysden. Both car parks will open for normal use.
We will also carry out vegetation clearance at the next working area between the A21 and main Leigh control structure to allow access for works.
During spring and summer 2022 we will carry out works to the Leigh FSA embankment between the A21 and the main control structure at Leigh.
No works on the embankment will take place over autumn and winter 2022/23.
We will carry out vegetation clearance at the final working area. This is on the north side of the river between the control structure and Powdermill stream to allow access for works.
During spring and summer 2023 we will carry out works on the north side of the river between the control structure and Powdermill stream.
The Reservoirs Act works are expected to be complete in autumn 2023.
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.
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