General information

Why was the Lower Mole Flood Alleviation Scheme built and why are these works being proposed?

The 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.

Work was 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 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 updated to maintain its standard of flood protection and to ensure it is the best scheme for the environment, people and wildlife.

Who owns the various flood control sluices?

The Environment Agency (as statutory successor to previous organisations) owns Molember sluice, Island Barn sluice, Viaduct sluice and Zenith sluice. Wilderness sluice and Royal Mills sluice are owned by third parties.

Why does the Environment Agency remove the vegetation along the walkways at Molember?

We manage the vegetation around Molember so we can clearly see the walls and walkway when inspecting the condition of these assets. We have a regular programme of asset inspection. We check for any possible defects and are able to keep a record of the condition of the current flood alleviation scheme. This allows us to plan for any maintenance works which may be required.

The walkways are accessible to the residents. Removing vegetation and keeping the walkways clear of moss, reduces the possibility of trips and slips during wet weather. This also helps our staff access these areas during the night to monitor water levels and operate the sluice during high flows.

We are happy to discuss whether there are any changes to our current ways of working which will allow a better balance between the operational needs of removing the vegetation, and the way that the scheme looks.

Why are there fences around the structures and along parts of the scheme?

A Public Safety Risk Assessment (PSRA) has previously been undertaken as parts of the scheme are located within a residential area, and many areas of the scheme and its structures are accessible to the public. This assessment determined that fencing was required in certain locations to protect the public from coming into contact with moveable parts on assets, such as sluices, and the edge of the river, which could be hazardous.

Fences have been raised from their original height at the request of residents as in some areas, illegal access and activity around the scheme was causing them a disturbance.

Can more be done to stop illegal fishing?

We have installed security fencing and placed signs along the scheme to deter illegal fishing on land under our ownership, and our staff will discourage this activity if we see this taking place. We seek to achieve the right balance between security and the way the scheme looks, as well as maintaining access to publicly accessible areas.

Unfortunately, our resources for tackling illegal fishing are limited, but we will continue to discourage illegal access for fishing by making the best use of the resources that we do have, and through the upkeep of appropriate fencing and signage.

What do the safety booms do and why are they there?

The safety booms were installed to safeguard canoeists and boat users from being swept into the sluices. There is a risk that people travelling on the river could be swept over the sluice structures or get into difficulties with the turbulent flows on the downstream side of the structures. A risk assessment carried out on similar structures on the River Medway following an incident where a river user was injured recommended that safety booms were installed on other sluices. The booms also prevent large debris from coming into contact with the sluices and either blocking or damaging them, especially during times of higher flows.

Are there any plans to install hydropower along the Lower Mole Scheme?

The potential use of hydropower along the Lower Mole Flood Alleviation Scheme has been discussed by residents before, however initial workings indicated it would not generate enough electricity to justify the investment. Hydropower generation requires strong river flows all year round, something this stretch of river cannot provide.

While the Environment Agency issues the required permits and regulates hydropower schemes, we do not fund or install them and strongly advise contact with a specialist when developing a proposed hydropower installation. We are supportive of sustainable hydropower schemes and we work closely with scheme developers to make sure their plans do not harm the environment or impact on flood risk.

Does the Environment Agency make changes to the water levels within the scheme during the year or does this occur naturally?

The majority of the changes in the water levels along the scheme happen following rainfall or longer spells of dry weather. We do reduce the level of the water if we are carrying out certain types of maintenance or survey work, for example, when we need to inspect parts of the sluices that are normally under water.

Since we started working on the Lower Mole, we have reduced the water level by 300mm at the start of the winter. This creates more volume within the river channel and helps to manage higher flows. We have also used the lowering of water levels over the winter season to help with the management of pennywort. This action has successfully helped to reduce the amount of pennywort regrowth along the Ember channel.

Will replacing or removing the gates affect the value of my house?

The Environment Agency is unable to advise on the effect on house prices as a result of any changes to the Scheme.

In recent years surface water flooding seems to have increased. How will the scheme deal with surface water flooding?

This scheme aims to ensure the standard of protection against flooding from the rivers is maintained, therefore is not specifically seeking to address flooding from surface water.

However, if gates are removed and water levels within the river are lowered on a permanent basis, surface water drainage would be able to discharge more freely into the river.

The responsibility for managing flood risk from surface water is held by the Lead Local Flood Authority which is Surrey County Council. We are sharing information about the proposals for the future of the scheme with Surrey County Council and will seek opportunities to work with others to achieve multiple benefits.

Would it be possible to inform people of when alterations to water levels are planned to take place?

We would be happy to let people know when we are planning to alter river levels. Please let us know if you would like to be kept informed. We would like to hear from you how best to communicate these messages.

What is riparian ownership and what are riparian owner's responsibilities?

A riparian owner is someone who has any watercourse within or adjacent to any boundary of their property. Where a watercourse is located between two or more property boundaries, each owner may be equally responsible. Riparian owners are responsible for maintaining the river bed and banks within their section of the watercourse. It is their duty to minimise pollution and prevent obstruction to the water flow.

Do you offer a flood warning service for this area?

Yes, we do. We operate a comprehensive free flood warning service. We would encourage householders and business owners to sign up for our flood warning service if they have not already done so. You can check if you are considered to be at risk to flooding by checking on Gov.uk using the link;

If you are located in an area at risk to flooding, you can sign up to get flood warnings by providing some contact details, the process is set out on the Gov.uk website;

https://www.gov.uk/sign-up-for-flood-warnings(External link)

We are not responsible for the third party content that can be accessed via the website hyperlinks.

Why was the Lower Mole Flood Alleviation Scheme built and why are these works being proposed?

The 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.

Work was 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 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 updated to maintain its standard of flood protection and to ensure it is the best scheme for the environment, people and wildlife.

Who owns the various flood control sluices?

The Environment Agency (as statutory successor to previous organisations) owns Molember sluice, Island Barn sluice, Viaduct sluice and Zenith sluice. Wilderness sluice and Royal Mills sluice are owned by third parties.

Why does the Environment Agency remove the vegetation along the walkways at Molember?

We manage the vegetation around Molember so we can clearly see the walls and walkway when inspecting the condition of these assets. We have a regular programme of asset inspection. We check for any possible defects and are able to keep a record of the condition of the current flood alleviation scheme. This allows us to plan for any maintenance works which may be required.

The walkways are accessible to the residents. Removing vegetation and keeping the walkways clear of moss, reduces the possibility of trips and slips during wet weather. This also helps our staff access these areas during the night to monitor water levels and operate the sluice during high flows.

We are happy to discuss whether there are any changes to our current ways of working which will allow a better balance between the operational needs of removing the vegetation, and the way that the scheme looks.

Why are there fences around the structures and along parts of the scheme?

A Public Safety Risk Assessment (PSRA) has previously been undertaken as parts of the scheme are located within a residential area, and many areas of the scheme and its structures are accessible to the public. This assessment determined that fencing was required in certain locations to protect the public from coming into contact with moveable parts on assets, such as sluices, and the edge of the river, which could be hazardous.

Fences have been raised from their original height at the request of residents as in some areas, illegal access and activity around the scheme was causing them a disturbance.

Can more be done to stop illegal fishing?

We have installed security fencing and placed signs along the scheme to deter illegal fishing on land under our ownership, and our staff will discourage this activity if we see this taking place. We seek to achieve the right balance between security and the way the scheme looks, as well as maintaining access to publicly accessible areas.

Unfortunately, our resources for tackling illegal fishing are limited, but we will continue to discourage illegal access for fishing by making the best use of the resources that we do have, and through the upkeep of appropriate fencing and signage.

What do the safety booms do and why are they there?

The safety booms were installed to safeguard canoeists and boat users from being swept into the sluices. There is a risk that people travelling on the river could be swept over the sluice structures or get into difficulties with the turbulent flows on the downstream side of the structures. A risk assessment carried out on similar structures on the River Medway following an incident where a river user was injured recommended that safety booms were installed on other sluices. The booms also prevent large debris from coming into contact with the sluices and either blocking or damaging them, especially during times of higher flows.

Are there any plans to install hydropower along the Lower Mole Scheme?

The potential use of hydropower along the Lower Mole Flood Alleviation Scheme has been discussed by residents before, however initial workings indicated it would not generate enough electricity to justify the investment. Hydropower generation requires strong river flows all year round, something this stretch of river cannot provide.

While the Environment Agency issues the required permits and regulates hydropower schemes, we do not fund or install them and strongly advise contact with a specialist when developing a proposed hydropower installation. We are supportive of sustainable hydropower schemes and we work closely with scheme developers to make sure their plans do not harm the environment or impact on flood risk.

Does the Environment Agency make changes to the water levels within the scheme during the year or does this occur naturally?

The majority of the changes in the water levels along the scheme happen following rainfall or longer spells of dry weather. We do reduce the level of the water if we are carrying out certain types of maintenance or survey work, for example, when we need to inspect parts of the sluices that are normally under water.

Since we started working on the Lower Mole, we have reduced the water level by 300mm at the start of the winter. This creates more volume within the river channel and helps to manage higher flows. We have also used the lowering of water levels over the winter season to help with the management of pennywort. This action has successfully helped to reduce the amount of pennywort regrowth along the Ember channel.

Will replacing or removing the gates affect the value of my house?

The Environment Agency is unable to advise on the effect on house prices as a result of any changes to the Scheme.

In recent years surface water flooding seems to have increased. How will the scheme deal with surface water flooding?

This scheme aims to ensure the standard of protection against flooding from the rivers is maintained, therefore is not specifically seeking to address flooding from surface water.

However, if gates are removed and water levels within the river are lowered on a permanent basis, surface water drainage would be able to discharge more freely into the river.

The responsibility for managing flood risk from surface water is held by the Lead Local Flood Authority which is Surrey County Council. We are sharing information about the proposals for the future of the scheme with Surrey County Council and will seek opportunities to work with others to achieve multiple benefits.

Would it be possible to inform people of when alterations to water levels are planned to take place?

We would be happy to let people know when we are planning to alter river levels. Please let us know if you would like to be kept informed. We would like to hear from you how best to communicate these messages.

What is riparian ownership and what are riparian owner's responsibilities?

A riparian owner is someone who has any watercourse within or adjacent to any boundary of their property. Where a watercourse is located between two or more property boundaries, each owner may be equally responsible. Riparian owners are responsible for maintaining the river bed and banks within their section of the watercourse. It is their duty to minimise pollution and prevent obstruction to the water flow.

Do you offer a flood warning service for this area?

Yes, we do. We operate a comprehensive free flood warning service. We would encourage householders and business owners to sign up for our flood warning service if they have not already done so. You can check if you are considered to be at risk to flooding by checking on Gov.uk using the link;

If you are located in an area at risk to flooding, you can sign up to get flood warnings by providing some contact details, the process is set out on the Gov.uk website;

https://www.gov.uk/sign-up-for-flood-warnings(External link)

We are not responsible for the third party content that can be accessed via the website hyperlinks.

Page last updated: 20 Jul 2023, 08:36 AM