Oxford Flood Alleviation Scheme - Frequently Asked Questions

Closed 31 May 2021

Opened 17 May 2021

Overview

Thank you to everyone that submitted questions to our online survey.  We are compiling these into groups by topic, listed below. Where we received similar questions we have combined these. We are also producing a video with members of the project team answering some of the questions on a range of topics that you have asked, which will be uploaded here.

We hope you found this opportunity to submit questions of clarification about the scheme useful.

Once we submit our new planning application in late 2021, Oxfordshire County Council will consult the public as part of the formal planning process on the proposed scheme.

If you would like to get in touch or request to be added to our newsletter distribution list, please contact us at OxfordScheme@environment-agency.gov.uk.

Click on a topic below to be taken to that section.

Trees

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We will remove trees only where we absolutely have to in order for the new stream and lowered floodplain to be created to reduce flood risk. We expect to need to remove around 2000 trees.
While designing the scheme, engineers, contractors, landscape architects and ecologists have worked together to minimise tree loss. We will also seek to further minimise tree loss when we are building the scheme. If it becomes clear that the contractor can work around trees that have been identified for felling without damaging them then they will be retained. An Environmental Clerk of Works will be on site and work alongside the contractor to make sure that these further opportunities are identified and taken wherever possible.
We will be planting over 4000 trees and ensuring an overall improvement in woodland quality after the scheme is in place.
For more information please see the section on 'Trees and hedgerows' on Page 2 - Environmental features of the scheme.

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We will plant saplings (young trees), which have a much better chance of establishing than replanting with older trees. As it will be many years before the new trees have the same ecological value as some of the older trees being felled, we've ensured our planting proposals account for this. The number of new trees planted will greatly exceed the number being felled, and the way these new trees will be planted and managed will lead to higher quality woodland habitat in the area after the scheme is in place than before.
As well as over 4000 trees we will plant many thousands of native shrubs and smaller-growing trees, such as hawthorn, hazel and elder, dogwood, goat willow, dog rose and wild privet. We will also be planting new hedgerow. The woodland areas will be managed for wildlife through traditional techniques such as coppicing which allows light to reach the woodland floor and encourages a diverse ground flora. The woodland areas will also include glades that are sown with wildflowers to encourage butterflies and other insects, as well as birds and foraging bats. This is in contrast to the majority of the existing woodland where the unmanaged, single age mature trees support only sparse shade-tolerant ground flora.
We calculate the biodiversity of woodland habitat before and after the proposed scheme is in place, and are ensuring we leave an overall improvement, known as 'biodiversity net gain'. In addition to improved woodland habitat, the scheme will also increase biodiversity of other valuable habitats, such as the creation of new wetland that will attract further new species.

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We will ensure the woodland habitat continues to improve over time and that newly-planted trees which do not survive are replaced where needed. We will submit a Habitat Creation and Management Plan with our planning application. This will set out the short, medium and long-term landscape management objectives, activities and responsibilities for the scheme.
The new habitats, including trees and woodland, will be planted and initially maintained by a landscape contractor. Once the scheme nears construction we will tender for an environmental partner who will continue to maintain the habitats and landscape of the scheme after the landscape contractor has ensured initial establishment. The environmental partner will ensure that not only are the newly planted trees and woodland area properly maintained, but that they continue to be enhanced further into the future. We are dedicated to ensuring the scheme area improves the environment in the long term.
We have recently formed a collaboration with environmental charity Earth Trust who are helping plan the long term environmental benefits of the scheme.

Grassland

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Our modelling has demonstrated that we need to lower the ground in order to create enough space for more floodwater to move through the fields. By lowering areas of the floodplain we will reduce flood risk to homes, businesses, roads, rail, and other vital infrastructure. In Hinksey Meadow, we need to lower the ground on the western edge of the meadow, next to the Seacourt Stream. We will keep the lowered ground here narrower and route it to avoid the rare grassland as much as possible. The extra space this creates will allow more floodwater to pass through and under the new bridge, which replaces the existing flood culverts under Willow Walk.
For more information please see the section on Grassland and floodplain meadow on Page 2 - Environmental features of the scheme.

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We have carefully considered how best to preserve the grassland found in Hinksey Meadow, which is a species-rich flood meadow that includes rare grass species such as snake's head fritillary. We appointed the Floodplain Meadows Partnership (FMP) of the Open University, as national experts in this type of grassland (known as MG4), to provide independent expert advice on how best to preserve the meadow and provide replacement meadow where some loss is unavoidable.
The area of MG4 grassland that will need to be removed to build the scheme has been kept to an absolute minimum. The 2 hectares of MG4 that needs to be removed will be carefully lifted by a specialist contractor and taken to a pre-prepared site with similar soil and groundwater levels. The new site will be managed as hay meadow, and the flowers, plants and insects in the transplanted turf will be monitored so that we can assess how well they are faring in their new home. We will make every effort to ensure the survival of the translocated MG4. However since there are no records of this operation having been carried out successfully to date, we will also create a large new area of MG4 floodplain meadow close by. Our aim is to leave the area with an overall increase in this valuable grassland, even if the transplantation itself is not fully successful. Our mitigation plan is explained further in the Grassland and floodplain meadow section on Page 2 - Environmental features of the scheme.

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We have considered how to maintain groundwater levels in Hinksey Meadow to help protect the rare MG4 grassland here. We will maintain existing water levels in the Seacourt Stream and Bulstake Stream under both low flow and average year conditions. This will maintain corresponding groundwater levels in Hinksey Meadow at or above existing levels. In the Bulstake Stream we will put in a series of gravel riffles (raised gravel areas along the stream bed) to help achieve this.
For more information please see the section on Grassland and floodplain meadow on Page 2 - Environmental features of the scheme.

Recreation and public access

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Some areas of the new stream and wetland will be accessible. Other areas will be prioritised for wildlife and access to these may be restricted.

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We are building new bridges in the scheme area to ensure access is maintained over the new stream and wetland from North Hinksey. Please visit Page 2 - Background and Benefits > What is the scheme design for more details.

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While the scheme has not been designed for swimming or kayaking, the new stream will be accessible to small boats, canoes and kayaks.

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We will be creating a new track along much of the scheme to allow access for maintenance. A proportion of the track will be made into a permissive path that the public are allowed to use for walking or cycling, except when maintenance or other activities would conflict with this. We are also building new bridges in the scheme area to ensure access is maintained over the new stream and wetland.
Visit Page 2 - What is the scheme design for more details.
Bridges in the scheme area

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The concrete track known as the Electric Road (because it covers underground electric cables) runs from Osney Mead Industrial Estate to the Devil’s Backbone at South Hinksey. While we build the scheme our contractor will be working on or close to the track in some areas, but it will not be closed. Once the scheme is constructed, access will remain as it is currently.

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The scheme maintenance track is in addition to the electric road.

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We do not own the electric road and we have no plans to tarmac it as part of our construction works.

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Willow Walk is a designated bridleway and will remain so once the scheme is in place. Horses can also cross the scheme at the Devil's Backbone, which while not designated a bridleway is suitable for horses.

Scheme design

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Drawings of the scheme will be available as part of our planning application. If you would like to see anything specific, please email us at OxfordScheme@environment-agency.gov.uk.

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The only new in-stream structure is one which controls the flow in the Eastwyck Ditch, which prevents water from flowing the wrong way at different water levels.
The scheme doesn't involve new weirs, lock gates or sluices to direct flood water into the scheme. During high water levels, floodwater on the fields north of Oxford is drawn into the lowered area of ground by the Seacourt Park and Ride. This forms the start of the Oxford Flood Alleviation Scheme which allows more floodwater to move through the floodplain rather than built up areas. The benefit of this design is that it is passive, and doesn't need to be actively turned on or off during floods using lock or sluice gates. You can find out more on Page 2 - How the scheme works.

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We have met with the Hinksey & Osney Environment Group (HOEG) on several occasions over the past few years to discuss their ideas, and we continue to look into some of their suggestions.

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Our scheme is designed to work with the natural floodplain. The Environment Agency designs passive flood alleviation schemes where possible. Passive schemes don’t need to be actively turned on or off during floods. They don’t have as many mechanical elements which might need fuel or have the potential to fail and need replacement, and need fewer operational staff to maintain the scheme in the long term. The Oxford Flood Alleviation Scheme provides a sustainable, long term solution for Oxford.

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The Oxford Flood Risk Management Strategy considered over 100 combinations of options to reduce Oxford's flood risk. As a result of the huge quantities of storage required and the costs involved, the Oxford Flood Risk Management Strategy concluded that an upstream storage area would not be a viable standalone option for reducing flood risk to the city.
Creating a new upstream storage area would not be an effective way to reduce flood risk to Oxford on its own. Because flood water can stay in Oxford for days or weeks, an effective upstream storage area, on its own, would need to store approximately 50 million mᵌ of water in the existing floodplain of the River Thames. This is equivalent to an area the size of Oxford 1 metre deep in water.

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The new stream will carry flowing water all of the time, including during the summer months. The scheme is made up partly of existing streams and new sections of stream alongside the lowered floodplain. You can find out more on Page 2 - How the scheme works.

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Our scheme relies on existing culverts underneath the railway. Constructing a new culvert under the railway would be very costly and extremely disruptive and is not needed for the scheme to function.

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There are no plans to compulsorily purchase the North Hinksey Lane allotments or any part of them.

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Dredging is an important part of maintenance but would not work to protect Oxford from a major flood. Even if we dredge all the rivers and streams in Oxford, it would not significantly reduce flooding from a major flood. Deepening channels around Oxford simply will not work, as excavating below the groundwater level would mean any extra space created simply fills with water. As there is barely any fall in land height over the 5km from Botley Road to Kennington, water will sit and silt will redeposit.
If done in the wrong place, dredging can damage the environment and increase flood risk downstream.The natural tendency of all rivers after dredging is to deposit silt and return to their more natural dimensions. This means dredging is inefficient and would need constant repetition. Each repetition causes further environmental damage without ever allowing full recovery. Frequent re-dredging would also be disruptive and expensive.

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Sustainable drainage does not form part of our scheme. We are creating ponds in the scheme area for wildlife. If you want to find out when SUDs are used you can contact enquires@environment-agency.gov.uk.

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Climate change is expected to cause more frequent and more severe floods. In the face of increasing flood risk due to climate change, the scheme will provide a long term solution to help manage flooding in Oxford for the next 100 years.

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The scheme will re-join the River Thames at Kennington, just downstream of the A423 ring road bridge. You can find a map of the scheme on Page 2 - What is the scheme design?

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The scheme is designed to work with the natural floodplain, by creating more space for floodwater away from built-up areas. We will construct flood walls and earth embankment in a small number of locations where properties would still otherwise flood. Constructing these defences without the extra space for floodwater in the lowered floodplain would risk transferring flood risk to other communities.

Flood modelling and flood risk

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We use detailed computer modelling to design flood alleviation schemes and check they will work. We first create a baseline model of river flows that recreates water levels and flows using current and historic data and the dimensions of the rivers and streams. These are the models used to create flood risk maps (flood-warning-information.service.gov.uk/long-term-flood-risk). These models are calibrated using known previous floods, such as the records from the 2007 floods, to make sure that they reflect reality.
Using this model, different design options are then explored to work out the best way to reduce flooding. This is then translated into a ‘detailed design model’, built by design consultants and which undergoes independent expert review. Modelling continues to inform and refine the final details of the scheme design.
We also look at what has worked elsewhere. Similar schemes have been built to reduce flood risk by providing more space for water, for example https://qwag.org.uk/river-quaggy/flooging.

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We have ensured the scheme will not increase flood risk to properties downstream. We work to reduce flood risk, not to transfer it from one community to another.
The scheme will not hold back water (like a flood storage scheme) nor will it speed up water (like a deep narrow channel could do). We use detailed modelling, which is always independently verified, to design the scheme. This shows the scheme will not increase flood risk to properties downstream of Oxford.
As well as our own detailed modelling, our approach has been independently confirmed by the Vale of White Horse District Council.

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The model itself requires specialist software to use. We can share the outputs of our modelling in the form of flood maps or our Flood Risk Assessment. If you would like this or any other details, please email us at OxfordScheme@environment-agency.gov.uk.

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Flood risk to properties in Kennington (or any other location) will not increase due to the scheme.

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The scheme will reduce flood risk to all properties in Oxford currently at risk of flooding from the River Thames. On opening the scheme, the vast majority of these will be protected in a major flood with a 1% chance of happening in any year. This size of flood was last seen in Oxford in 1947. However, not all properties will experience the same level of flood reduction as this depends on where they are located in the current floodplain and their threshold level (the point at which floodwater will start to enter a property).

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Once the scheme is in place, all properties currently at risk of flooding from the River Thames on Abingdon Road will see their flood risk reduced. The scheme is designed to cope with major floods of a scale last experienced in 1947. This is far bigger in size than any of the floods Oxford has experienced in recent decades.

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All properties in Oxford currently at risk of flooding from the River Thames will see their flood risk reduced when the scheme is in place. We have not designed the scheme to prioritise any area above another.

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In major floods water will still use the wider existing floodplain which is mostly farmland and flood meadow. In fact this is an integral part of our overall solution. The scheme is designed to work with the natural floodplain.
The scheme does not increase flood risk to any properties. We conducted a Flood Risk Assessment (FRA) which demonstrates that there is no increased flood risk to properties as a result of the scheme.

Process and timescales

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Before we can start construction of the Oxford Flood Alleviation Scheme, we need to have all approvals in place, including planning permission and our compulsory purchase order to access the land needed for the scheme. To bring the scheme to Oxford as quickly as possible we value the support of local communities through these processes. The planning consultation by Oxfordshire County Council will be open to the public later this year. Once all approvals are in place, the scheme will then take 3-4 years to build. We will update the public as soon as we have more details on timeframes and construction.

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The purpose of our current engagement is to update members of the public on progress since we had to withdraw our planning application in March 2020, because Oxfordshire County Council discovered that the A423 bridge needed replacing. The main design of the scheme is the same as we submitted in that planning application, which we had already held public consultations on.
Once we submit our new planning application in late 2021, Oxfordshire County Council will consult the public as part of the formal planning application process on the proposed scheme.
We are inviting the public to submit questions about the update until the end of May, which we will respond to via our online Frequently Asked Questions. Beyond the survey period the website will remain live and any questions can still be emailed to us at OxfordScheme@environment-agency.gov.uk.

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We have used extensive computer modelling to ensure the scheme will work for Oxford. The concept of a new stream with lowered floodplain alongside has been used effectively in other flood schemes.

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We issue regular newsletters which are sent to local and regional media outlets. The scheme has been covered in the Oxford Mail, BBC Radio Oxford and BBC Oxford webpage.
In addition we regularly include articles in several local newsletters including the South Hinksey Echo and the Sprout newsletter which covers Botley and North Hinksey.
If you would like to sign up for our scheme newsletters please email oxfordscheme@environment-agency.gov.uk to ask to be added to our mailing list.

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More maps and plans of the scheme will be available as part of our planning application, which will be submitted later in 2021.

Costs

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The scheme is expected to cost around £150 million and is fully funded.

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The Oxford Flood Risk Management Strategy looked at over 100 combinations of options to reduce the risk of flooding in Oxford. These ranged from non-structural measures such as flood warnings, to natural flood management measures, to full engineering interventions such as raised flood defences. The options were identified through consultation with specialists, flood action groups and local residents. The current scheme was found to be the most effective and economically viable scheme for Oxford.
The Environment Agency is in the early stages of developing the Thames Valley Flood Scheme to manage flood risk across the wider Thames Valley, for more information visit their webpage and respond to their consultation.

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The scheme is fully funded by over £88 million of central government money and the remainder from partnership and third party contributions.

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In the 2020 budget, the government committed to doubling expenditure on Flood and Coastal Erosion Risk Management (FCERM) to £5.2 billion between 2021 and 2027 (HM Treasury, 2020). The Oxford Flood Alleviation Scheme is one of the key flagship schemes within our programme and the funding is secure.

Construction

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We will be constructing a temporary road through the western side of Kendall Copse near Kennington. This will allow 2 way traffic to keep flowing at all times on Old Abingdon Road and Kennington Road during construction. Please see Scheme updates - New temporary road for more details.

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The railway sidings are already operational. As part of our Environmental Impact Assessment, we will consider the impacts of the new haul road to the railway sidings and the changes that need to be made to the sidings. This will cover air quality and noise.
One of the requirements of planning will be a construction management plan that will cover these issues. Find out more detail on this on Page 2 - How will the scheme be built.

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We will reuse as much of the excavated material such as earth and gravel as we can on site, for example in earth embankments and environmental features. Most of the material leaving the site will be transported to old quarries that have planning permission for restoration. Once planning permission for the scheme has been granted we will be able to confirm which sites have the capacity to receive the material.

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We plan to remove some of the excavated material such as earth and gravel by rail, but this depends on a separate planning application being successful and commercial agreements with the operator of Hinksey sidings.
Find out more about our plans on Page 3 - Potential transport of material by rail.

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We will re-use much of the excavated material on site, for example in earth embankments and environmental features, and we’ll retain some topsoil to help vegetation recover after construction. We will still need to transport around 365,000m³ of material out of the area. We cannot leave it in the floodplain, so it will be moved off site to be used for landscape restoration in previously excavated quarries.
The majority of the excavated soil will be removed from site by lorry on to the A34 near South Hinksey. We are also investigating removing some material by rail, but this depends on a separate planning application and commercial agreements with the operator of Hinksey sidings. The number of lorry movements will depend on how much material can be taken by rail. The details of material management and lorry movements will be in the Material Management Plan and Transport Assessment of our planning application.
Find out more about our plans here on Page 2 - How will the scheme be built?

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The A423 bridge is owned by Oxfordshire County Council. You can find out about their plans here: www.oxfordshire.gov.uk/residents/roads-and-transport/roadworks/future-transport-projects/a423-kennington-bridge-works.

Long term management and legacy

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Our partnership with Earth Trust will help us plan the long term maintenance of the new landscape and habitats, ensuring the scheme provides a green legacy for the local area.
Earth Trust will develop an overarching strategy for how the scheme will benefit the environment over its lifetime. This strategy will include a habitats plan, environmental management and work with local communities. We will work collaboratively with Earth Trust for the coming years, to establish a plan for longer term engagement with scheme neighbouring landowners, communities and stakeholders to support our environmental objectives.

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The new stream will carry flowing water all of the time and because the stream meanders and is not over-widened the amount of water flowing through will keep sediments moving through natural river-processes.
Most of the space for floodwater is created by the lowered floodplain. Watch our video on how the scheme works here.

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One of the ambitions of our Environmental Vision is to connect people with the scheme. This will especially benefit local primary school children to have such a location within walking distance of their school and homes. We'll be working with the environmental charity Earth Trust on these plans to provide access and opportunities for education.
For more information please see Page 2 - Environmental features of the scheme.

Previous page: Scheme updates

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