Overview

Project Overview

The Vale Brook river runs through the centre of Chesham. The river flows mostly underground in a series of buried tunnels (called culverts). Some sections of the culvert are now over 150 years old and they are in varying states of disrepair.

View culvert map here

The river is fed from groundwater and also the rainfall runoff from the roads via the highway drainage network.

There is a risk of flooding from the river if blockages within the culvert restrict the flow of water and cause it to back up and emerge through drains and inspection covers. From recent CCTV inspections, we've been able to see accumulations of debris and silt within the culvert, as well as the poor condition of the structure of the culvert in certain places.

The responsibility of maintaining the culvert and the flow of water through it, lies with the owner of the land above it, known as riparian owners. There are numerous riparian owners of the culvert through Chesham as it passes under the High Street so this project was established to investigate options to tackle this issue collectively, rather than relying on each individual owner doing maintenance independently.

In 2014 we completed some emergency works in Market Square to replace a section of culvert that was at imminent risk of collapsing. Over time, other sections of the culvert already in poor condition will continue to deteriorate which will increase the risk of flooding if debris accumulates or structures collapse.

We originally had over 1,500 different ideas as to how to repair or replace the culvert to address the risk of flooding. Most of these ideas have been ruled out because they were not technically viable, would be too costly, or would cause too much disruption to the town.

We have considered what would happen if nothing was done and this option is included in the project to act as a baseline to judge how effective the other options will be in comparison. This option would mean carrying out no maintenance and not acting upon the flood risk in Chesham. We have also considered carrying out minimal work. This option would involve heavy maintenance of the culvert sediment/material with periodic inspections to monitor changes to the culvert condition and potential for blockages.

Most flood risk management projects in England, including this one, require support from partners and stakeholders. This could be in the form of financial, technical and engagement support or contributions in kind, such as allowing access to land.

The Proposal

After producing a long list of options and then narrowing it down to a shortlist (which we consulted the public on in 2017), one option was chosen as the most viable economically and technically as a long term solution.

The proposal is to create a new river channel, mostly open channel, through Star Yard car park and then decommission and stabilise the existing culvert underneath the High Street. Although this option is extremely challenging and expensive, the benefits still outweigh the costs and is the only viable option for a long term solution. Carrying out repairs is a lot less expensive but that does not provide long term benefits.

Work on the project stalled in 2018 as the intention was to deliver this flood alleviation project alongside local authority proposals for regeneration of the town centre, which at that time were not confirmed. See the newsletter from 2018.

Since 2018, Buckinghamshire Council has become the unitary authority and there is fresh enthusiasm to tackle this flood risk issue. The project has not formally restarted but conversations between Environment Agency and Buckinghamshire Council have been ongoing for some time to try to manage the ongoing risk and to agree a way forward for the project. We hope to be able to restart the project soon, however, completion of any works would still be several years away. There is also a possibility that the project is no longer viable under current funding criteria and could eventually be closed with no alternative options to pursue.

Actions for Riparian Owners

If you own a building above the culvert, you have the right to carry out maintenance to that section of culvert you own. A Flood Risk Activity Permit must be granted from the Environment Agency before any maintenance takes place as the Vale Brook is designated a main river. Bearing in mind the longer term plan to potentially decommission the culvert, you would need to weigh up your own costs vs benefits of doing any work to the culvert.

We would advise occupiers of the buildings in High Street to ensure you have adequate insurance in place that would cover the costs of any damage to contents and loss of business caused by flooding. The Environment Agency is not responsible for the maintenance of the culvert so we are unable to reimburse any losses due to flood damage. We would also advise, where possible, to avoid storing valuables at ground level where they are more susceptible to flood damage.

Please check for any structural damage to your building such as cracks or subsidence. This could indicate a failure of the culvert beneath the building.

Please report any flooding to us 24/7 on 0800 807060, no matter how minor. It is important that we can investigate any flooding as soon as possible so we are reliant on residents and business owners to notify us when this occurs.

Emergency Planning

The Environment Agency has worked with Buckinghamshire Council, Bucks Fire and Rescue Service and Thames Valley Police to produce an incident response plan for flooding in the town centre. All emergency responders are aware of the situation with the culvert and the emergency planning that we've done will ensure a more coordinated response to any incident.

We will update this page when we have any new information to share.