Lower Mole Flood Alleviation Scheme

Closes 31 Dec 2021

Opened 13 Dec 2018

Overview

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. 

Map of the existing Lower Mole Flood Alleviation Scheme

Map of existing Lower Mole Flood Alleviation Scheme

Come to our drop ins!

We need your thoughts on the short list of options that we are now considering for each of the main sluice structures including Viaduct, Island Barn, Molember, Zenith and Wilderness sluices.

Please come along to see the options and talk to our expert staff, we really want to hear your views and we value your input.

Your help now will ensure we have the best possible scheme for the environment, people and wildlife.

These drops ins are being held on:

1 June 2019 from 10am-4pm and 7 June 2019 from 10am-7pm 

at:

Imber Court,
Ember Lane,
East Molesley
KT8 0BT

Project Update - May 2019

Over the past few months we have developed our project appraisal for the scheme.

This appraisal established a range of options for the refurbishment of the scheme, and compared their economic viability (costs and benefits), technical feasibility (engineering difficulty) and environmental impacts. It also incorporated feedback we received from the public and other stakeholders.

Following our appraisal and using your feedback, we have developed our short list options which we will be sharing with you in June.

Your feedback from these drop ins will be considered as part of the decision making process for the preferred option.

Next steps

We hope to choose the preferred option by late summer 2019 and will consult on this later in the year.

We plan to update this webpage again at the end of May to share the drop in materials.

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:

FASProject.LowerMole@environment-agency.gov.uk

or write to:

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

For more information on how we will use and share your data, please see our Privacy Notice below and our Personal Information Charter.

Events

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  • Business and industry
  • Flood management
  • Coastal management
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