Lower Mole Flood Alleviation Scheme Information Page

Closes 31 Dec 2024

Opened 13 Dec 2018


The Lower Mole Flood Alleviation Scheme ('the Scheme') is reaching the end of its designed life. It needs refurbishing to maintain the standard of flood protection and to ensure it’s the best possible scheme for the environment, people and wildlife. 

Project update - July 2019

This update explains our current position on the planned refurbishment project for the Lower Mole Flood Alleviation Scheme. It aims to reassure you that all options for refurbishment remain open, and we have no commitment to:

  • Remove any of the sluices
  • Lower water levels
  • Commence any construction work.


The Lower Mole Flood Alleviation Scheme protects around 3,000 homes and businesses in the area from flooding.

The enlarged river channel provides additional capacity for the high flows in the river during periods of prolonged and heavy rainfall.

The sluice gates maintain water levels in normal conditions, but have to be opened when flows in the river are high.

The condition of the sluice gates is starting to deteriorate due to their age, and we need to take action to maintain the standard of flood protection for years to come.

We contacted you in January and March of this year outlining some of the background to the refurbishment project and what we are trying to achieve.

As part of the project, we shared a number of initial design concepts with residents at two public drop-in sessions in May and June. This was part of our early engagement with the community to share information.

Current position

Following feedback and concerns from the community, we are reviewing the initial design concepts, whilst continuing to assess the environmental, amenity and economic benefit of any new scheme.

This will take time and means that the original timescales for the project have now changed:

  • Selection of preferred option – this will no longer happen in late summer 2019
  • Share preferred option with community (and commence formal public consultation period) – this will no longer happen in late 2019
  • Construction starts – this will no longer happen in Spring 2020
    The above dates were presented at the public drop in sessions as provisional dates only, dependent on many factors. We apologise if this was not clear on our posters.

We cannot confirm yet what the new timescales for these stages of the project will be. However, it is important to note that this refurbishment project is in its early stages, and in order to take the project forward, partnership funding is required under government funding rules. We do not know how long this will take to secure but it can take some years.


In the meantime

Routine maintenance
Whilst we review the design concepts and seek opportunities for partnership funding, we will continue to maintain the existing structures to protect properties from flooding and maintain water levels.


We will shortly undertake a range of ecological surveys to gain a better understanding of the wildlife across the project area. Once we have done this, we will evaluate how refurbishment works will affect biodiversity along the river. We will look to maximise any benefits to wildlife in any refurbishment works.

We have heard how important the wildlife on the river is to residents and it is very important to us too. We would like to reassure you that the Environment Agency is committed to improving rivers for people and wildlife and we will seek every opportunity to achieve this.

Key points

  • Our priority is to sustain the current level of flood risk protection.
  • No decisions on how the scheme will be refurbished have yet been made and all concepts remain open for discussion.
  • No start or completion dates for the refurbishment have been decided however the start date is likely be in several years’ time.
  • Future decisions on the refurbishment will reflect the importance of water levels to residents.
  • We will share information with residents and stakeholders as the project progresses. The intention is for the conversation to remain open during the course of the project.
  • We are also investigating how to improve the biodiversity of the river and ecological surveys will begin in the autumn.

Whatever we propose, we want all interested groups to take the opportunity to have their say. We will continue to inform and engage with you during further stages of the project.

Map of the existing Lower Mole Flood Alleviation Scheme

Map of existing Lower Mole Flood Alleviation Scheme

We will shortly be providing further information via this website and a newsletter.

photo of molember sluiceMolember Sluice

Thank you!

Thank you to everyone who has sent us their comments and questions so far. Your feedback is essential to ensure the refurbishment is the best it can be for people, wildlife and the environment.

We have compiled your most common questions and answered them below.

Click the question to reveal our answer:

We are carrying out an appraisal to determine our options for the proposed works.
This appraisal establishes a range of options for the refurbishment of the scheme, and compares their economic viability (costs and benefits), technical feasibility (engineering difficulty) and environmental impacts to determine the best overall option. It also incorporates feedback we received from the public and other stakeholders.
As the scheme is funded using Government money, we are required to use the Flood and Coastal Erosion Risk Management Appraisal Guidance to carry out this assessment. This guidance sets out the steps that we need to follow throughout the project appraisal, which we must comply with in order to receive funding.
We start with a long list of options for the scheme, and try to narrow them down to a short list that has the best chance of attracting Government funding. As the project moves from the long list to the short list, the level of detail we have increases, allowing us to understand the pros and cons of each option more, and to rule out those which will not be viable for economic, technical or environmental reasons.
The appraisal process uses a range of information, for example, river modelling, costs, economic benefits, condition surveys of the assets along the Lower Mole, historical information, habitat surveys and feedback from stakeholders. This is used to understand both the opportunities and constraints present.
All of these are taken into account when making determining the preferred option for the scheme’s refurbishment.

One of the objectives of this project is to maintain the standard of protection against flooding that the scheme currently offers to households and businesses.

No. Maintaining the current standard of protection against flooding is an objective of this project and any option which proposes the removal of assets would be carefully assessed to ensure that flood risk is not increased as a result.

Currently, dredging is not planned to be carried out as part of this project.
We consider each location carefully and only carry out dredging where we know it will make a difference to the management of flood risk. Understanding where dredging will, and won’t, reduce flooding is the key.
Dredging has many short and long term environmental impacts such as the escape of silt plumes into the water, reducing water quality, or the removal of gravels from the river which is an important substrate on which fish spawn. In addition, this substrate helps to reduce channel erosion as it absorbs the energy of the river.
In the past, dredging was carried out periodically along the Lower Mole. However, regular surveys of the depth of silt in the river, highlighted that the accumulation of silt within the engineered channel was not significant, and was not reducing the ability of this channel to convey flood flows. Therefore dredging is not required and not the best use of our resources.

Floating pennywort is a fast growing invasive species of freshwater plant. It is well established in the south and east of England and is widespread in the channels that form the Lower Mole.
Floating pennywort grows in the margins of slow flowing watercourses and drains, forming dense mats of vegetation. These dense mats grow rapidly (up to 20cm per day) and can grow up to 15m out from the bank in one season. Due to the rapid growth of floating pennywort, it can quickly dominate a watercourse, restricting flows and pushing out native plant species. Oxygen levels in the water often become reduced and this can result in fish deaths. The plant also limits the movement of animals and boats, restricting the recreational use of the river.
The Lower Mole Flood Alleviation Scheme directs the majority of flood flows through the engineered channel. This is the river channel where Viaduct, Island Barn and Molember are located, called the River Ember.
We have a limited budget within our Environment Agency Area (Kent, South London and East Sussex) that is set aside for ongoing maintenance works, including the removal of pennywort. We prioritise this maintenance spend on areas at greatest flood risk. As the River Ember channel is essential for managing flood risk, our main focus on pennywort management is the Ember channel.
We work alongside the riparian owners along the River Mole and Imber Court Loop to raise awareness of and manage pennywort. During the past year a number of riparian owners along both of these areas of river have carried out work to remove pennywort. We will continue to engage with and work alongside riparian owners in the future to carry on the work that has been started to manage pennywort.
We have sprayed the pennywort in the past, though we favour its physical removal by hand pulling and offsite disposal as this is an effective way to reduce the strength of the plant. We have experimented with lowering the retained water levels within the river during frosty weather to expose a greater area of the pennywort plant to frost, which has been successful and we consider using this technique again in the future if necessary.

The original Lower Mole Flood Alleviation Scheme was designed to reduce the risk to flooding in the lower reaches of the River Mole catchment, following a significant flood event in September 1968. The River Mole has a history of flooding, though the September 1968 event is still considered to be the largest and most severe recorded flood event along the River Mole. It has been estimated that several thousand properties in the lower reaches of the River Mole were flooded during that event.
We then started to consider options to reduce the future risk of flooding along the lower reaches of the River Mole. These options included:
• creating flood storage areas in the middle area of the river catchment
• a tunnel scheme to carry water from the Hersham area to the River Thames
• a pump scheme that would move large volumes of water through the lower reaches of the River Mole
• widening and engineering of the river channel from Hersham down to the where the River Mole connected with the River Thames.
An engineering assessment was carried out to gain a better understanding of the magnitude of the flood that has occurred in September 1968, and to determine which of the proposed options could offer the best overall solution to reducing flood risk in the future. This assessment concluded that the scheme should offer protection against flooding if an event of similar magnitude to September 1968 was experienced again, due to the significant damage and disruption caused. The option that was taken forward for design, and ultimately construction, was the widening and engineering of the river.
A Public Inquiry was held in 1972 to discuss the planning application. As part of the proposed works, a Compulsory Purchase Order for areas of land, and a number of properties, was submitted for consideration. This land was needed to allow for the widening of the river channel. Objections from local residents, and others who would be affected, were made to the original proposal at the planning stage. The large scale nature of the scheme, the proposed changes to the existing river system and landscape, the loss of amenity, concerns over privacy and future access, were some of the concerns highlighted.
During the course of the Planning Inquiry, a number of recommendations and revisions were made to the proposed scheme in order to address the concerns and objections raised and to try and reduce the impact the works would have on the area. After consideration of all of the information, planning permission was granted for the Scheme in 1974.
The construction of the scheme took a number of years, with the works being completed during the 1980s. The scheme is now reaching the end of its design life and needs to be refurbished to maintain its standard of flood protection and to ensure it is the best scheme for the environment, people and wildlife.

To see our FAQs in full, please click the link at the bottom of this page.

Photo showing Lower Mole river downstream of Island Barn Sluice

Lower Mole downstream of Island Barn Sluice

Get in touch

If you have any questions or concerns, please do not hesitate to contact us at:


or write to:

Lower Mole Flood Alleviation Scheme, Environment Agency, Orchard House, Endeavour Park, London Road, Addington, West Malling, Kent, ME19 5SH.

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