Improving the environment on the Lower Mole

We know from our conversations with you that the wildlife and environment around the scheme is highly valued by the community. The initial design of the scheme built in the 1980s was focused on providing protection to properties from flooding, without much consideration for the impact on wildlife. This resulted in the creation of a deeper and wider artificial channel to accommodate high flows. The current water level control structures impound water within this channel, causing the river to back up and creating a static, lake-like appearance for stretches up to 14.7 km in length.

It is important to note that a meaningful increase in biodiversity for this project is only possible where we reduce or remove impoundments, the amount of water backed up behind a structure. In doing so we would create a healthier meandering gravel river within the existing channel.

Opportunities to enhance the environment

Options that maintain current water levels through the retention of water level control structures, including the 'do nothing' and 'do minimum' options, will preserve the habitats with their current low level of biodiversity. There will be limited scope for improvement, although fish passes will be added to the structures to enable fish migration upstream. However, the passes may not be 100% effective for all fish, particularly smaller species, and natural river processes will still be prevented.

Examples of rock ramps


Some of the options aim to reduce impoundment along the river, which will lead to a more natural flow and allow us to restore habitats in the river, ultimately increasing biodiversity. The implementation of these options will cause the channel to begin meandering within its existing footprint.

Reducing or removing the impoundments will allow naturalised flows to strip away years of fine sediment from the centre of the river and reveal more gravels. The fine sediment will be re-deposited to form new vegetated berms along the margins. There will be a mixture of wide, shallow gravelly areas (riffles) where the babbling water is oxygenated, and deeper, slower-flowing pools. For more information about impoundments please visit our combined 'water quality, levels and understanding impoundments page'.

Large reedy margins can establish along the river, with plants species such as branched bur reed and yellow flag iris. These will provide nesting sites for birds, such as reed warblers, ducks, coots and swans. These could provide places for herons to hunt, and mammals such as otters to lie up during the day.

Aquatic plants in the river will provide food and shelter for a wide variety of birds, fish and insects, such as dragonflies and damselflies, and plenty of opportunity for kingfishers to feed.

The reconnected river and varied depths will provide habitats for fish to migrate both upstream and downstream, providing opportunities for spawning, feeding, and shelter. The shallows will be suitable for fry, while deeper water areas will cater to mature fish.

Biodiversity Net Gain

We are committed to providing a Biodiversity Net Gain (BNG) through our projects as part of the Government’s ambition to improve our environment.For this scheme, we would like to deliver a BNG for local wildlife and will use the Department for Environment, Food and Rural Affairs Biodiversity Metric to help demonstrate improvements where we can achieve these.

We want to make environmental enhancements where we can. Together with reducing impoundments and planting reeds in the river channels, we are also looking at what we can do with surrounding land near to the structures. Here are some further examples of what we could do to achieve better BNG:

  • Increase the range of flowering plants along the river to help pollinators. We would do this by reducing the number of times we cut the grassland along the river banks

  • Planting more trees or hedgerows to provide future nesting areas for birds and other wildlife 

  • Working with landowners to create new habitat features such as ponds or ditches close to the river 

  • Working in partnership with Surrey County Council and Elmbridge Borough Council to create new habitats or improve management on land close to the scheme. This will help us to wider benefits to people and wildlife in the wider Lower Mole community 

Assessing and understanding the environmental impacts

We have conducted the following surveys to ensure we have a good baseline of the existing habitats and wildlife found along the River Mole:

  • River corridor surveys

  • River condition assessments

  • Protected species surveys

  • Invertebrate and fish survey

We have carried out initial assessments of the potential impacts on the environment, that enables us to identify both the positive and negative impacts of a scheme. This process also enables us to determine the measures that we can take to avoid or minimise any negative impacts.

We know from our conversations with you that the wildlife and environment around the scheme is highly valued by the community. The initial design of the scheme built in the 1980s was focused on providing protection to properties from flooding, without much consideration for the impact on wildlife. This resulted in the creation of a deeper and wider artificial channel to accommodate high flows. The current water level control structures impound water within this channel, causing the river to back up and creating a static, lake-like appearance for stretches up to 14.7 km in length.

It is important to note that a meaningful increase in biodiversity for this project is only possible where we reduce or remove impoundments, the amount of water backed up behind a structure. In doing so we would create a healthier meandering gravel river within the existing channel.

Opportunities to enhance the environment

Options that maintain current water levels through the retention of water level control structures, including the 'do nothing' and 'do minimum' options, will preserve the habitats with their current low level of biodiversity. There will be limited scope for improvement, although fish passes will be added to the structures to enable fish migration upstream. However, the passes may not be 100% effective for all fish, particularly smaller species, and natural river processes will still be prevented.

Examples of rock ramps


Some of the options aim to reduce impoundment along the river, which will lead to a more natural flow and allow us to restore habitats in the river, ultimately increasing biodiversity. The implementation of these options will cause the channel to begin meandering within its existing footprint.

Reducing or removing the impoundments will allow naturalised flows to strip away years of fine sediment from the centre of the river and reveal more gravels. The fine sediment will be re-deposited to form new vegetated berms along the margins. There will be a mixture of wide, shallow gravelly areas (riffles) where the babbling water is oxygenated, and deeper, slower-flowing pools. For more information about impoundments please visit our combined 'water quality, levels and understanding impoundments page'.

Large reedy margins can establish along the river, with plants species such as branched bur reed and yellow flag iris. These will provide nesting sites for birds, such as reed warblers, ducks, coots and swans. These could provide places for herons to hunt, and mammals such as otters to lie up during the day.

Aquatic plants in the river will provide food and shelter for a wide variety of birds, fish and insects, such as dragonflies and damselflies, and plenty of opportunity for kingfishers to feed.

The reconnected river and varied depths will provide habitats for fish to migrate both upstream and downstream, providing opportunities for spawning, feeding, and shelter. The shallows will be suitable for fry, while deeper water areas will cater to mature fish.

Biodiversity Net Gain

We are committed to providing a Biodiversity Net Gain (BNG) through our projects as part of the Government’s ambition to improve our environment.For this scheme, we would like to deliver a BNG for local wildlife and will use the Department for Environment, Food and Rural Affairs Biodiversity Metric to help demonstrate improvements where we can achieve these.

We want to make environmental enhancements where we can. Together with reducing impoundments and planting reeds in the river channels, we are also looking at what we can do with surrounding land near to the structures. Here are some further examples of what we could do to achieve better BNG:

  • Increase the range of flowering plants along the river to help pollinators. We would do this by reducing the number of times we cut the grassland along the river banks

  • Planting more trees or hedgerows to provide future nesting areas for birds and other wildlife 

  • Working with landowners to create new habitat features such as ponds or ditches close to the river 

  • Working in partnership with Surrey County Council and Elmbridge Borough Council to create new habitats or improve management on land close to the scheme. This will help us to wider benefits to people and wildlife in the wider Lower Mole community 

Assessing and understanding the environmental impacts

We have conducted the following surveys to ensure we have a good baseline of the existing habitats and wildlife found along the River Mole:

  • River corridor surveys

  • River condition assessments

  • Protected species surveys

  • Invertebrate and fish survey

We have carried out initial assessments of the potential impacts on the environment, that enables us to identify both the positive and negative impacts of a scheme. This process also enables us to determine the measures that we can take to avoid or minimise any negative impacts.

Page last updated: 15 Aug 2024, 09:03 AM