Lower Mole Flood Alleviation Scheme revised shortlisted options

Overview

The Lower Mole Flood Alleviation Scheme protects around 1,300 homes and businesses in the area from flooding. It 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. Construction of the scheme took several years and was completed in the 1980s.

The Scheme covers the stretch of the River Mole from Hersham up to the River Thames. This also includes the River Ember, an engineered channel created as part of the flood scheme, along with side channels at Royal Mills and the Ember Loop. The enlarged river channel provides additional capacity for high flows in the river during periods of prolonged and heavy rainfall. The sluice gates regulate water levels under normal circumstances but are opened during times of high river flows to allow water to pass to the Thames as quickly as possible.

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. There are six main sluice gates and we need to make decisions on their future.

A Map showing the Rivers Mole and Ember, black line, and where the six main sluice gates, bright green dots, are located along the rivers to form the Lower Mole Flood Alleviation Scheme. Source: Environment Agency.

Why your views matter

In 2019, we engaged with stakeholders and the community on our initial options and heard your views around proposed changes to existing water levels. As a result of that feedback, we ran sessions with the community on how the scheme currently works and how we operate the sluice gates. Following this, we began work to better understand the dynamics of the river in more detail to help inform further investigations and designs. This work included bathymetric surveys, biodiversity net gain reviews, bat surveys, fish and invertebrates surveys.

In 2021, we shared a short list of options with the community. This was only carried out through online engagement due to Covid 19 restrictions. Using this feedback, we carried out additional work that included further modelling and several studies carried out by our engineers. This modelling work was key in ensuring that the updated designs would not increase flood risk. After completing all this work, we have created a revised shortlist of options.

For all flood risk management schemes, we follow funding rules set by the Government. We can attract funding for schemes through Grant in Aid (GiA) and other sources. For this Scheme the costs of all the options exceed the maximum amount of funding we can attract through GiA. This means that additional funding would need to come from external sources. This could come from Local Authorities, partners, businesses and the community. All of the options identified as part of the appraisal work will require additional partnership funding to deliver them.

We consider the cost and benefits of each option, using the decision rules set out in the appraisal guidance. We have also reassessed the changes in water levels, environmental benefits, cost, carbon footprint and maintenance implications, for each option.

Following the process, we have identified the national economically preferred option. Delivery of Options Red, Blue and Pink will require a greater proportion of additional funding. You can find more detail about the national economically preferred option on the whole scheme, funding and rating the options page and in the Government appraisal guidance links below.

Your views on the Options Red, Blue, Pink and Orange are vital throughout the consultation period to help us make the final decision. The full shortlist includes Option Yellow ‘Do nothing' which is a requirement of the appraisal process to allow for the comparison of options. This helps us understand what the impact would be, if we did not deliver the project. Option Yellow is non-viable as it would lead to an unacceptable increase in flood risk if the gates at the main structures were not opened when river flows are high.

Option Purple ‘Do Minimum’ is also included in the full shortlist. This offers the same outcomes for the river in terms of water levels as Option Red, but at greater cost and in a less sustainable way with a higher carbon footprint. Therefore, although Option Purple is a viable option to maintain the current level of flood risk protection it is not considered an option we would seek to progress as the preferred option for the scheme.

This work over the last 5 years has been vital in helping us understand what is important to the communities of the River Mole and Ember. We thank you in advance for giving us your views. We will continue to listen to your feedback to help refine the direction of the project and future designs. Please share this with others in your community, so we may hear their views as well. Please click the online consultation link below to begin.

What happens next

Thank you for your views. We will now review them and update the Lower Mole community.