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After the engagement event in Spring 2021, it was clear to us that the greatest level of support was for the options that resulted in no changes to the water level. You shared with us concerns about any changes to existing water levels and highlighted the importance of the continued protection of properties from flooding.
We have carefully reviewed your feedback and have identified additional measures that could be incorporated into the options to mitigate the impacts of water level change. These measures aim to address the concerns raised whilst still managing the risk to flooding and seeking opportunities to enhance ecology.
Mitigation options that have been considered include measures to ensure continued flow into the Ember Loop, Old River Mole and Royal Mills side channels, and measures to reduce water level change in the main River Ember flood relief channel.
Each mitigation option has been assessed based on whether it would be technically viable to implement. We also carried out hydraulic flood risk modelling to determine the impact of potential mitigation measures.
For an option to be taken forward it must be shown to retain sufficient water levels when compared to the reduced water levels which would occurunder some of the options, whilstalso not increasing flood risk. Consideration has also been given to the funding likelihood, environmental impact and future maintenance of the mitigation options, as well as the potential construction risks, though further work on these aspects is required.
Molember Sluice
Upstream of Molember Sluice, rock ramp weirs were considered to mitigate a possible reduction in water level should the gates be removed. The construction of rock ramps were assessed to determine if they provide a viable alternative to the options already considered at this location, which include the replacement of gates, construction of a fixed crest weir, or gate removal at Molember Sluice.
The assessment found a 1.0m high rock ramp weir placed within the River Ember between Molember and the Summer Road footbridge, which increases water levels by 0.44m compared to an option which just removed the gates, would be a viable alternative in terms of flood risk and was taken forward for further investigation. It now included in the pink option.
A visualisation of what Molember could look like in the future.
Old Mole and Ember Loop channels
For the Old Mole and Ember Loop channels, options were assessed that could retain an adequate water depth in these channels, mitigating the water levels reduction in the River Ember channel that would result if the gates at Island Barn were removed.
These options included passive approaches such as weirs and channel reprofiling, and active pumping options at the Ember Loop channel. Although a solution which involved the reprofiling of the river bed was found to retain flows into the Old Mole channel, no viable option was found for the Ember Loop channel. This has led to the removal of the gates at Island Barn Sluice no longer being considered as viable. Option 6 of the shortlist presented in Spring 2021 has therefore been removed from the revised shortlist of options for the scheme that we are sharing with you now.
Viaduct Sluice
The area upstream of Viaduct Sluice, which includes the Royal Mills channel, was also evaluated. Options were analysed to see if they could provide a viable way to reduce the lowering in upstream water levels if the gates at Viaduct Sluice were to be removed. One of the mitigations considered was the introduction of rock ramp weirs within the main channel.
Visualisation of Viaduct Sluice
During the next stage of the project the revised shortlist of options and proposed mitigations will undergo an economic appraisal to determine the economically preferred option. This stage will consider the costs, benefits, and risks associated with each option. During the appraisal process we will consider how each option measures up to the objectives for the scheme and criteria for environmental, technical, maintenance, and carbon benefits.
Please find the complete mitigation report on the right hand side of this page. Should you require a more accessible version or a paper copy please contact us at fasproject.lowermole@environment-agency.gov.uk. We want to be as accessible as possible but also mindful of the environment, so please consider whether a paper copy is best option before you make your request.
After the engagement event in Spring 2021, it was clear to us that the greatest level of support was for the options that resulted in no changes to the water level. You shared with us concerns about any changes to existing water levels and highlighted the importance of the continued protection of properties from flooding.
We have carefully reviewed your feedback and have identified additional measures that could be incorporated into the options to mitigate the impacts of water level change. These measures aim to address the concerns raised whilst still managing the risk to flooding and seeking opportunities to enhance ecology.
Mitigation options that have been considered include measures to ensure continued flow into the Ember Loop, Old River Mole and Royal Mills side channels, and measures to reduce water level change in the main River Ember flood relief channel.
Each mitigation option has been assessed based on whether it would be technically viable to implement. We also carried out hydraulic flood risk modelling to determine the impact of potential mitigation measures.
For an option to be taken forward it must be shown to retain sufficient water levels when compared to the reduced water levels which would occurunder some of the options, whilstalso not increasing flood risk. Consideration has also been given to the funding likelihood, environmental impact and future maintenance of the mitigation options, as well as the potential construction risks, though further work on these aspects is required.
Molember Sluice
Upstream of Molember Sluice, rock ramp weirs were considered to mitigate a possible reduction in water level should the gates be removed. The construction of rock ramps were assessed to determine if they provide a viable alternative to the options already considered at this location, which include the replacement of gates, construction of a fixed crest weir, or gate removal at Molember Sluice.
The assessment found a 1.0m high rock ramp weir placed within the River Ember between Molember and the Summer Road footbridge, which increases water levels by 0.44m compared to an option which just removed the gates, would be a viable alternative in terms of flood risk and was taken forward for further investigation. It now included in the pink option.
A visualisation of what Molember could look like in the future.
Old Mole and Ember Loop channels
For the Old Mole and Ember Loop channels, options were assessed that could retain an adequate water depth in these channels, mitigating the water levels reduction in the River Ember channel that would result if the gates at Island Barn were removed.
These options included passive approaches such as weirs and channel reprofiling, and active pumping options at the Ember Loop channel. Although a solution which involved the reprofiling of the river bed was found to retain flows into the Old Mole channel, no viable option was found for the Ember Loop channel. This has led to the removal of the gates at Island Barn Sluice no longer being considered as viable. Option 6 of the shortlist presented in Spring 2021 has therefore been removed from the revised shortlist of options for the scheme that we are sharing with you now.
Viaduct Sluice
The area upstream of Viaduct Sluice, which includes the Royal Mills channel, was also evaluated. Options were analysed to see if they could provide a viable way to reduce the lowering in upstream water levels if the gates at Viaduct Sluice were to be removed. One of the mitigations considered was the introduction of rock ramp weirs within the main channel.
Visualisation of Viaduct Sluice
During the next stage of the project the revised shortlist of options and proposed mitigations will undergo an economic appraisal to determine the economically preferred option. This stage will consider the costs, benefits, and risks associated with each option. During the appraisal process we will consider how each option measures up to the objectives for the scheme and criteria for environmental, technical, maintenance, and carbon benefits.
Please find the complete mitigation report on the right hand side of this page. Should you require a more accessible version or a paper copy please contact us at fasproject.lowermole@environment-agency.gov.uk. We want to be as accessible as possible but also mindful of the environment, so please consider whether a paper copy is best option before you make your request.
A visualisation of what Molember could look like in the future.
Visualisation of Viaduct Sluice