Oxford Flood Alleviation Scheme - Updates since our last planning application

Closed 31 May 2021

Opened 17 May 2021

Overview

Updates since our last planning application

While we were changing our designs around the A423 to accommodate the proposed bridge replacement we also took the opportunity to review and update some other aspects of our scheme.

 

 

The progress is summarised below - please click on each item for more detail.

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In 2019 Oxfordshire County Council found that the A423 Kennington Railway Bridge (Southern by-pass), in the south of the scheme area needed to be replaced. The bridge is crucial to the Oxford Flood Alleviation Scheme as floodwater from the scheme needs to pass under it to re-join the River Thames.

Scheme route under A423 bridge.

The previous planning application for the Oxford Flood Alleviation Scheme had planned to construct 2 concrete culverts under the existing bridge to carry floodwater. Now that the bridge needs replacing we’ve used the opportunity to work together with the county council so that the replacement bridge will include our flood scheme. As part of the design of the replacement bridge, culverts will no longer be needed. Instead, the new bridge will be designed with open channels either side of the existing railway.

Oxfordshire County Council are responsible for the bridge and will be submitting a separate planning application for its replacement. We are working together to ensure disruption to residents, businesses and road users will be kept to a minimum during construction of both schemes.

 

 

We have produced a new hydraulic model to show how the water will flow around the A423 Kennington Bridge with these changes in place.

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The proposed replacement of the A423 bridge has changed where the new stream will pass underneath the A423. As the new stream now passes much closer to the railway, we also need to realign the channel through Kendall Copse to avoid tight bends for the water here. The new stream will now pass more centrally through the eastern part of Kendall Copse. This will improve river flows during floods, and retains some of the mature trees in the north east corner of Kendall Copse next to the railway line. It will keep the works further from the ancient culverts that were part of a medieval causeway under the Old Abingdon Road, removing the need to reinforce the bank next to these scheduled ancient monuments.

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We have made changes to improve traffic flow on Old Abingdon Road and Kennington Road whilst the scheme is being built. The new stream will need to pass under both these main roads. In our previous planning application we had planned to close each road for a period of time and divert traffic whilst the stream is excavated below the roads here. We model traffic flows to assess the effects of this and the modelling showed these road closures would lead to an increase in queuing traffic on the slip roads and the A34 at Hinksey Hill Interchange during peak times. This could have impacted road safety on the A34 which is unacceptable and wouldn’t have been permitted by Highways England who oversee road safety. We investigated other ways to manage the traffic but they also had impacts on the Hinksey Hill Interchange and the A34. To overcome this issue we have had to redesign our scheme to include a temporary road through the western side of Kendall Copse. This will allow 2 way traffic to keep flowing at all times whilst we build first one bridge and then the other.

This approach will benefit private road users and will also ensure that the existing bus routes that use Old Abingdon Road and Kennington Road will not have to be diverted.

In summer 2020 we undertook ground investigation work in order to complete our design for the temporary road.

Diagram showing location of temporary road

Once the construction period has finished and the temporary road removed, we will plant new trees in Kendall Copse. We will replant with native trees and where we’re unable to plant as many trees as before, we will compensate for this by planting trees in other locations locally. Although we will need to temporarily stop access to Kendall Copse during construction, we plan to provide public access to the newly planted Kendall Copse once we finish. We will also install an interpretation board to explain the history of the scheduled culverts which were part of a medieval causeway under the Old Abingdon Road.

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Our construction work in the south of the scheme area will now be managed from a temporary compound located in the western part of Kendall Copse. We will also need to use a small area of Redbridge Park & Ride for some specific tasks, such as drying out excavated material. As we no longer need to put culverts under the A423 bridge, we won’t be using Redbridge Park & Ride as our main base here and the size and time we’ll use it for has reduced since our last planning application.
 
The map below shows the intended locations of our 3 main construction compounds.
Location of main construction compounds

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When we designed the Oxford Flood Alleviation Scheme, we looked at moving the excavated material such as earth and gravel by rail. At the time of our previous planning application, the rail sidings were already in use, and we planned instead to move surplus material by road. Since then, local residents asked us to re-look at the rail option.

Changes to the construction date have provided an opportunity to use the rail sidings and we are now actively pursuing the option of moving some excavated material by rail. Our preference is to use rail. However as the construction date is still some time away, we cannot confirm with certainty that the sidings will be available for us to use. We are therefore submitting a separate planning application, alongside our main scheme application, for the movement of excavated material to the rail sidings, to be transported by rail.

The separate planning application will cover the additional land and changes required if we transport material by rail. This will include a haul road from our compound north of South Hinksey to the Hinksey Rail sidings. The planning permission for the rail element will only be implemented if the planning application for the main scheme is granted.

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Building the Oxford Flood Alleviation Scheme will reduce the likelihood of floods in built-up areas. Flooding increases carbon emissions due to direct damage and disruption, as well as the replacement and refurbishment of properties, vehicles and belongings. An Environment Agency research project has been looking at how flood schemes account for both carbon emitted as well as carbon avoided in the future as a result of reduced flood risks to properties. The purpose is to help projects consider the whole-life carbon balance of options alongside the need to reduce carbon emissions of our construction and maintenance as much as possible. This work is in its early stages but shows that by reducing flooding, the Oxford scheme will prevent the production of far more carbon emissions in the long term than are generated through its construction and maintenance.                             

We have also been reviewing how we can reduce our carbon footprint in constructing and maintaining the scheme as much as possible. This includes looking at the materials we are using and the way that we build the scheme, as well as the way we will look after it in the future.

The design of the scheme to create a stream with wetland habitat, with limited need for maintenance, fits with a lower carbon approach. Sustainable features include:

  • The scheme will create a natural looking stream, avoiding hard engineering where possible.
  • We are using earth embankments rather than building walls where space allows, which uses less carbon during construction.
  • Nothing in the scheme requires the operation of machinery which would produce emissions.
  • There are no permanent pumps or pipes to manage river floodwaters.  Manufacturing pumps and pipes is very energy intensive and they would also require regular maintenance and replacement.
  • Culverts for water to pass under roads have been minimised as far as possible, reducing the need for concrete and steel and reducing the need for maintenance and replacement in the future.
  • Vegetation planting will be low maintenance and incorporate species suited to our changing climate.
  • Sustainable or low carbon materials will be specified where possible. This will include lower carbon concrete as standard.            

Following the recent design changes to the scheme we have recalculated our carbon emissions. Our carbon forecast for the future operation and maintenance of the scheme after construction has reduced since our last planning application.  These updated figures will be presented in our planning application.

Most of our carbon emissions will be from machinery and vehicles needed to move material and from producing the concrete and steel we will use. We continue to explore ways to reduce the carbon generated through construction and maintenance, including how we might use current and future technology.

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The Environment Agency has formed a new collaboration with the environmental charity Earth Trust.

We are working with Earth Trust on our plan for the long term environmental and wellbeing benefits of the scheme. This partnership will help us make the most of this unique opportunity – ensuring the new landscape and habitats continue to enhance the local area for the lifetime of the scheme.

Once we have all the necessary approvals and are nearing construction of the scheme, we will appoint an environmental partner who will be responsible for looking after the wildlife and landscapes of the scheme area. They will continue our work to bring additional environmental enhancements, involve local people and interested groups and establish educational outreach and opportunities for scientific research. In this way the Environmental Vision will deliver a long term green legacy to the area.

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We have conducted wildlife surveys across the scheme area to ensure that we are avoiding and minimising disturbance to plants and animals as much as we possibly can. Many of the surveys that were carried out prior to submitting the planning application in 2018 have now been updated to ensure that we are assessing the likely impacts of the scheme using current data.

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One of our main environmental objectives is for the scheme to deliver a net gain in biodiversity. ‘Biodiversity net gain’ means leaving more good quality natural habitats and ecological features after a development is built than beforehand. We are ensuring the scheme’s features such as the new stream, ponds, wetland and floodplain meadow will leave the area with a greater variety of wildlife than before. This includes ensuring any unavoidable habitat loss while we build the scheme is more than compensated for by new habitats.

Since our previous planning application was submitted, Natural England has updated the way that biodiversity net gain should be calculated, with a further update due to be launched this summer. Since this is such a rapidly evolving and emerging field of work, we are continuing to liaise very closely with the ecologists at Oxfordshire County Council, Oxford City Council and the Vale of White Horse, as well as with Natural England, the local Wildlife Trust and other key environmental stakeholders to ensure that we are delivering a net gain in biodiversity. We will provide the most up to date information on our biodiversity improvements in our new planning application.

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Kennington Pond is in the Kennington Pools Local Wildlife Site at the southern end of the scheme. The pond is only connected to the river during floods, so water quality is generally good and it supports a range of freshwater plants and invertebrates. When we carry out work on the Hinksey Drain, just south of the A423, the size of Kennington Pond will be permanently reduced so we are planning to create a series of new ponds in the southern half of the scheme that will also only be connected to the river system during larger flood events. Following consultation with the Freshwater Habitats Trust, the size of one of these ponds has now been increased so that it better replicates the size and depth of Kennington Pond as it is now.

 

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Audiences

  • Recreational and commercial river users
  • Fishing clubs and representative associations
  • Members of the public with an interest in the river, the species and conservation
  • Businesses
  • Charities
  • Statutory organisations
  • NGOs
  • Members of the public
  • Elected representatives, including MPs
  • Local councils
  • Academics
  • Environment Agency customers
  • Environment Agency colleagues

Interests

  • Flood management
  • Habitats and wildlife