Lower Mole Flood Alleviation Scheme Information Page

Closed 31 Dec 2023

Opened 13 Dec 2018


Update June 2023

We have a new website for all the latest information on the Lower Mole Flood Alleviation Scheme at Lower Mole Flood Alleviation Scheme | Engage Environment Agency (engagementhq.com). Please note that we will no longer be updating this site.

Update - February 2022 update 

We are writing to update you on work we are carrying out on the Lower Mole. In our November 2021 update newsletter, we mentioned that our project team were working through a number of potential mitigations that address concerns raised by the local community about some aspects of the scheme. This includes investigations into measures that limit the reduction in water level along the main channel, and measures to ensure continued flows into the Old Mole and Ember Loop. These works are continuing and once completed we will notify all stakeholders and members of the local community.

There was also concern expressed last year that any options taken forward that would reduce water levels would impact the quality of the river water.

To build upon the work we have already carried out to investigate these concerns, we have just started to build a water quality model of the river. This model will be focussed on the reach of river both up and downstream of Esher Wastewater Treatment Works, so it is possible to understand any impacts of a reduced water level on the quality of water in the river.

As part of the water quality modelling, we have recently started to install some water quality monitoring stations along the river. We are also in conversation with Thames Water, who own and operate Esher Works, to understand what information they can share to help with our model.

These monitoring stations will collect a range of water quality data, including dissolved oxygen and temperature, on a real time basis. This data will be used in the water quality model to firstly understand the baseline, or present-day conditions, and then to aid understanding of how potential changes in water level may affect the water quality within the river.

We expect the installation of the monitoring stations to be completed during February. The water quality model will be built during the spring, and initial results from the modelling should be available during the summer.

As a result of this monitoring along with other mitigation work which is currently ongoing, we do not expect now to announce a preferred option until later in the year. We will of course continue to send updates on the work we are doing, and we will be engaging further with the community as this scheme develops.

November 2021

Please see a copy of our Lower Mole newsletter which details our maintenance work over the next few months.

You will also find an update on our Lower Mole Flood Alleviation Scheme where you will see that we have delayed announcement of a preferred option until next year. Our project team are currently very busy looking at mitigation options in response to the feedback received from the public earlier in the year and want to allow for the extra time required to do this as thoroughly as possible.

August 2021

We are pleased to announce that the report into our spring engagement exercise has been published and can be downloaded here.

We would like to thank everyone who contributed to our online engagement between 8 February and 1 April 2021.

We received over 5,250 unique visitors to our interactive website during our 8 week engagement with the community.  Through our online platform we were able to reach a larger number of the community than we have done during previous face to face engagement, resulting in a significant amount of feedback. The feedback we have received has enabled us to gain a thorough understanding of the community’s positions, interests, needs and expectations.

Our engagement report has six main sections:

  • Executive summary: This provides you with the key information detailed in the report.  Click here to read the Exec Summary.
  • Introduction: This section provides the context behind our spring 2021 engagement with the community and details our engagement aims.
  • How we engaged with the community: We have provided an overview of our online engagement, and detailed how many visitors we received and how visitors interacted with our website.
  • What we discovered: We have summarised the feedback from our survey and included the top 10 themes.
  • Summary and conclusions: We have provided a summary of the feedback we received and have drawn conclusions from this.
  • What are the next steps: We have detailed how we are using the feedback in our refinement of the options, provided details of the decision making process and provided a timeline of the programme going forwards.

We are currently further developing the options by taking into account the feedback gained from the consultation and seeking to mitigate changes in water levels whilst maintaining flood protection. This will include assessing the additional cost of the mitigation measures and the benefits they provide.

In order for the project to reach the detailed design and then the construction phase, further work which includes gaining staged approval for funding, is required. We have shown the main stages in the programme going forwards below.

As always please contact us via our inbox FASProject.LowerMole@environment-agency.gov.uk if you have any questions.

June 2021 

We continue to review feedback from the online presentation of our updated options earlier in the year and we expect to publish the report on your comments at the end of July.

During the 8 week engagement exercise our website received 5,400 hits made by 5,250 unique visitors. We received over 300 survey submissions, 375 quick poll submissions, and over 250 questions.  You also provided us with 75 contributions to our ideas board and over 20 ideas were placed on our interactive map.

Through our ongoing review of your feedback we have noted particular themes of support, interest, ideas and areas of concern.  For example, there was support for maintaining water levels and the standard of flood protection.  Themes of interest included, preserving the environment and securing recreational use. Popular ideas from the ideas board and interactive map included improvements to access along the Lower Mole, the introduction of beavers and replacing the sluice gates with a hydroelectricity scheme. We will be looking at the feasibility of implementing the ideas you submitted in more detail as the scheme progresses.

From your survey responses we have noted that many respondents have raised concerns regarding the impact of lower water levels and this correlates with the feedback we received from our 2019 engagement. However, your responses have helped us to understand these concerns in more detail, and to determine what refinements to our options we should consider. Of note were concerns that the river could run dry, and with lower water levels, a general sentiment that this would lead to a loss of recreational opportunities and reduction in local biodiversity. Other themes that have come from our analysis are concerns over the visual impact of lowering water levels, concerns over safety, sewage effluent in the river, property values and security.

Whilst we continue to review your feedback, we are also exploring additional works that we can add into our refined options analysis. These additional works would help mitigate some of the concerns you have raised. For example, exploring measures that would ensure continued flow into the Ember Loop and Old River Mole, and measures to reduce water level change in the main River Ember flood relief channel.  Such measures would help to limit the visual impact of lowered water levels, help retain recreation opportunities and protect biodiversity if such an option was taken forward. We are also continuing to engage with Thames Water to enhance our understanding of the impact of treated effluent in the Lower Mole from the different options.

After we publish our report on your comments at the end of July, we will be sharing more information about our mitigation options with stakeholders later in the summer.

April 2021 Update

Thank you to everyone who commented on our updated options during February, March and April of this year. We have received just under 1,000 comments from our survey, website questions section and email inbox, and we are looking at every single one. We will publish and share the report which will summarise all feedback received later this year.

Following a recent public engagement exercise this page has now been updated to share all of the information recently made available via our interactive website which was live between Wednesday 03 February and Thursday 01 April 2021. We produced the website because pandemic restrictions prevented us meeting with the community face to face. Whilst this project is in the early stages we wanted to share as much information as possible so the community could comment and help shape decisions made in the future. This information is contained below along with all of the questions, ideas, comments and feedback received from the local community.

Please view our welcome video here


The Lower Mole Flood Alleviation Scheme (FAS) 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 scheme itself refers to the section of the River Mole as it makes its way northwards from Hersham up to the River Thames. This also includes the River Ember; the engineered channel created when the flood scheme was constructed during the 1980s, and the side channels at Royal Mills and the Ember Loop.

Why it was built

The original Lower Mole FAS was designed to reduce the risk of 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.

Planning permission for the scheme was granted in 1974. The construction of the scheme took several years, with the works being completed during the 1980s.

How it operates

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.

Why it needs updating

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.

What are the Options?

As the scheme is now approaching the end of its design life it needs to be updated so that it maintains the same standard of flood protection whilst ensuring it is the best scheme for the environment, people and wildlife.

There are six main water level control structures (sluice gates) and we need to make decisions on their future. It is vital that we talk about the area as a whole system because whatever we do in one location will potentially have an impact on another.

There are many factors that we need to take into account when looking at each option in turn:

Environmental impacts, Carbon footprint, Impact on water levels, Cost, How it can be delivered, Expected design life, Long term maintenance requirements

We have developed four options where significant changes would be made to update the current scheme. There are two further options, one to do nothing and the second being to do the minimum. It should be noted that the ‘Do nothing’ option is a requirement of the appraisal guidance in order to set a baseline to compare the other options against. Therefore whilst this option costs nothing as a project, the costs of repairing any damage caused if the assets were to fail in the future would be very high.

Comparison Table

The table below allows you to compare the options in terms of whole life cash cost, water levels, carbon and environmental benefits for each option. To learn more about the symbols please click here

For a brief summary and overview of each option please click here.

For a more detailed analysis of the options and the appraisal process please see the Information sheets available below.

Options full table

Understanding the Appraisal process

Water Level along the River Mole presentation.

Join the Conversation

During the 8 weeks that our interactive website was live we received a large number of contributions from members of the community. There were numerous ways people could get involved; submit a question, propose ideas, use the interactive map or complete the survey. The Lower Mole FAS project team are now going through all of the feedback received and this will be shared with all respondents and published here. Over the coming months, we will be developing our options to incorporate all of the feedback received.


The following document contains all of the questions received along with the responses from the project team.

Questions and Answers Document

Supporting documents: 


We asked members of the community to tell us their ideas about potential opportunities and improvements that could be incorporated into the scheme such as opening up an access paths, providing information boards about local wildlife and making the watercourse more accessible. We received a number of ideas which can be found here:

Ideas document

Interactive Map

We asked for comments, observations and ideas relating to specific locations along the scheme directly onto our interactive map which can be seen below:

Interactive Map

For more information on our 'work so far' and 'improving the environment' click here. 

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.


  • Anyone from any background


  • Business and industry
  • Flood management
  • Coastal management
  • Fishing and boating
  • Water resources