Flood exercise today

The flood exercise mentioned in the last post, testing and demonstrating readiness to deploy defences, is under way today. In South Hinksey temporary barriers are being set up by the Environment Agency (EA). At Bullstake Close on the Botley Road the barriers there, which have been used before in a flood, will be erected; and fire crews are showing how the pipe which has been installed under the Botley Road can be used to deal with flood water and reduce the flooding of the road.

For South Hinksey this is a very reassuring demonstration of the ability to now defend the village from flooding. Such barriers have never been used here before.

Of course Oxford still needs a bigger, more permanent scheme – in the form of the Oxford Flood Alleviation Scheme. The OFA update in the previous post summarises the present position – the Scheme is under way, albeit delayed. In the meantime today’s activities show that we will not be without  protection in the interim.

Emma Howard-Boyd, Chair of the EA, and Sir James Bevan, Chief Executive, are in South Hinksey today to see what’s being done and meet the teams and there is no doubt that protecting Oxford in both the short and long term is being taken very seriously.

Our thanks to everyone who is working hard on behalf of the many local residents, businesses and other organisations affected by flooding.

OFA Update / OFAS & Flood Exercise

This update has recently been sent to those on our mailing list.

Dear OFA contact,

We last sent out an update in Oct 2019, just after the news about the problems with the A423 bridge (southern bypass) and likely delays to the Oxford Flood Alleviation Scheme (OFAS). OFA is still active and has been participating in meetings of the Sponsoring Group for the OFAS scheme and has also held separate meetings with the Environment Agency team about water course maintenance since our last update.

Despite the A423 issues, and the challenges presented by coronavirus, the OFAS scheme continues to progress. The EA and the County Council have agreed a collaborative approach to replacing the A423 bridge and constructing the OFAS scheme. This should save on costs for OFAS, and reduce the level of maintenance required in future.

The EA withdrew the original planning application earlier in the year and is currently revising this to incorporate the new A423 arrangements, and to update the documents on some other aspects of the scheme. Once these are resubmitted to the planning authority the public will have a fresh opportunity to comment on the plans. The EA is continuing to meet with objectors to the scheme with a view to trying to address outstanding areas of public concern.

Because OFAS is now expected to be delivered two years later than originally expected it is important that effective flood response procedures are in place in case a major flood event happens in the next few years. The EA, Fire Brigade and the local Council officials will be holding a practice response on 20 August to test aspects of current procedures. Because of coronavirus these will not involve the pubic.

The text of a recent update from the Environment Agency is pasted below which provides some additional information on OFAS and other matters,

OFA Steering Group

Oxford Scheme update

A423 bridge replacement

Oxfordshire County Council began the propping work on the A423 Kennington Railway Bridge in July.

Replacement of the A423 Bridge has provided an opportunity to design and build the bridge and the flood scheme together. This allows us to reduce disruption during construction and ensure the best use of public money. The updated design will use open channels instead of culverts to allow the flow of floodwater under the bridge. This will provide a better environment for wildlife and requires less maintenance.

The bridge is at the southern end of the scheme and during a flood, water would need to pass underneath it to re-join the River Thames. This capacity needs to be in place before the scheme is constructed to avoid increasing flood risk elsewhere. We also need to have all approvals, including planning permission and our Compulsory Purchase Order secured.

South Hinksey Archaeology

If you’ve been walking near South Hinksey, you may have spotted our contractors on site. We are carrying out archaeology surveys in a field near South Hinksey village to check whether the area is suitable for us to use as the main compound for when we construct the scheme. The archaeology surveys will determine whether there are any historical artefacts in the field. We want to ensure there’s no risk of us damaging any artefacts or remains. Once we have finished the investigations, we will remove our equipment from the site and reinstate the fields.

Kendall Copse Ground Investigations

To complement the new A423 bridge replacement, we are reviewing the design of the scheme around Kendall Copse, near Kennington.

From 10 August, we will be digging trial pits and drilling boreholes to understand the ground conditions beneath the site in order to finalise these designs.

Oxford Flood Incident Exercise

To ensure our flood protection plans are well-tested, the Oxford Flood Alleviation Scheme partners and emergency responders will be practicing their incident response plans on 20 August 2020.

The flood response exercise will consist of:

 •temporary flood barriers in South Hinksey and Bullstake Close

•pumps to remove flood water along Botley Road

Due to the current Government guidance on public gatherings, we won’t be able to invite members of the community to attend. We will be sharing updates on Twitter and Facebook as the exercise progresses. We will also share video footage of the temporary barriers and pumps so you can see our field teams in action.

Managing your flood risk

During the summer months, flood risk might be low on your list of priorities, but Environment Agency officers are thinking about it year-round. Throughout the year our operations staff carry out inspections and clear debris to keep main rivers moving. To report a blockage that could cause flooding call our 24 incident hotline: 0800 80 70 60.

You can also find out what maintenance is planned in your area: environment.data.gov.uk/asset-management/index.html

Stay prepared by signing up for flood alerts and preparing a flood plan: https://flood-warning-information.service.gov.uk

  

Want to know more?

If you have any questions or want to be added to our mailing list, please contact us at: OxfordScheme@environment-agency.gov.uk

Storm Dennis

Appalling floods in Wales (and elsewhere) https://www.bbc.co.uk/news

The Oxford Flood Alleviation Scheme is, unfortunately, delayed but is still as much needed as ever. In fact more so – as Earth continues to heat up the changing climate is producing more extreme weather and consequent severe flooding.

River levels above, and in and around, Oxford have already risen quite a bit since the storm’s rain over the weekend, and the next few days will see further rises in Oxford as the water makes its way downstream from the Cotswolds. It remains to be seen how big these rises are. You can follow local river levels and the flow rate upstream at Farmoor here.

Concern in the Oxford area

There is increasing concern today that water levels are high in the Oxford area, with a good deal more water still to come down to Oxford from the Cotswolds catchment. The area is presently (midday) on an EA Flood Alert (the lowest level of concern).

We’re seeing more flooding globally, Venice is badly hit at the moment – and the awful flooding in the north of England continues.

There is no doubt that the climate is changing. Oxford has always flooded but the change will make it more common and more severe. The immediate threat may recede now, let’s hope so, but it highlights again that it’s imperative that Oxford is better protected, not only for the many people directly affected but for the city itself to continue to function and thrive into the future.

The multi-partner Oxford Flood Alleviation Scheme is in process and all concerned are working hard to make it happen as soon as humanly possible. As we have said before, “it can’t come soon enough.”

 

 

Severe flooding in Yorkshire

Exceptional rainfall has caused widespread and serious flooding in the north of England. It seems pretty clear (from this, and many other events worldwide) that climate change is happening here and now https://www.bbc.co.uk/news/uk-england-50343977

Meanwhile in New South Wales a very different emergency, which again seems almost certain to be climate change related https://www.bbc.co.uk/news/world-australia-50341207

The list goes on.

Flood defences are sorely needed for Oxford’s river flooding, and more than ever now that we’re faced with more frequent extreme weather events. The Oxford Flood Alleviation Scheme is being developed to provide that defence.

 

 

A pipeline? (3)

There was an accompanying editorial in the Oxford Times of 26 January 2019.

At the moment the details of the pipeline proposal are not published. Here are some of the things we’d be interested to know about:

  • The OFAS scheme is designed to increase flood flow though Oxford by 38,000 litres per second. What is the volume of water the HOEG pump(s) will pump per second?
  • What size of pump is assumed for this job? How many?
  • Where would the pumps be located?
  • Will the pumps be secure against flooding themselves, and how would they be accessed for maintenance in a flood?
  • What provision is there for intrinsic pump failure?
  • If the pumps are electrically powered, how is the risk of failure of the electricity supply during a flood addressed. Would there be generators raised above any flood level with nearby fuel stores accessible during a flood?
  • What is the route, how would pipes be put underground, how would the many services in the ground be navigated?
  • Construction and disposal of spoil.
  • How is downstream risk to Kennington in particular, and possibly also Abingdon, addressed?
  • How were the costings were arrived at – what do they include?

[The suggestion of a second (albeit smaller) pipeline to Farmoor would be a very large project in itself and is so speculative and far removed from the present issue that we are not asking further about that.]

We wrote to the group concerned recently, on 25 January, asking if we may see their engineer’s plans and any other details; we look forward to their reply so we can better understand their proposal.

A pipeline? (2)

According to an article in the Oxford Times of 24 January 2019 the pipeline proposal has changed, so the pipeline would now involve  “a pumping station at Seacourt, under Botley Road and then along the Hinksey Plain to the Old Abingdon Road.”

That would mean that the start of the pipeline is (wisely) no longer proposed to be at Port Meadow, and that it ends at Redbridge rather than Sandford Lock.

The cost has risen from “around half the cost” [of the Oxford Food Alleviation Scheme presumably – HOEG press release of 18 January] – which would be about £75 million – to £100 million in the press report on 24 January.

More to follow.

A pipeline? (1)

The ‘Hinksey & Osney Environment Group’ issued a press release on 18 January 2019 which included:

“The group is also proposing an alternative scheme, drawn up by a local engineer, which will deliver all the flood alleviation benefits for around half the cost and for a greatly reduced environmental impact.
 
The alternative proposal involves a pumping station at Port Meadow that will divert flood water through an underground pipe to Sandford Lock.
 
The pipe would safely carry the flood water around areas currently at risk.
 
Other advantages of this proposal include:

  • Flood water can be pumped much faster than is possible when relying only on an open channel. This means Oxford would enjoy greater protection from flooding.
  • It uses proven technology and is guaranteed to work.
  • Using a second, smaller bore pipe, the pumping station can also be used to supply water to Farmoor reservoir.
  • An underground pipe would have no long-term environmental impact.
  • The destruction of local nature reserves, thousands of trees in the green belt and valuable flood meadows can all be prevented.”

This raised many questions and we were surprised that the proposal included a pumping station “at Port Meadow” – unlikely to be universally popular.

More to follow.

Answers to concerns

Some people have had concerns about the Oxford Flood Alleviation Scheme – the Environment Agency have recently made this response which we thought people might find of interest. (To avoid making it even longer we have not included the questions but the answers should make it clear enough what the questions are.)

Design of the scheme 

The scheme has been designed to be as natural as possible and respects and works with the existing natural floodplain. It is not a concrete channel. It is not an ‘on/off’ channel but a passive design which allows the natural floodplain to carry more water when needed. Most of the excavated area will be planted with vegetation and provide valuable new habitat for the area. It is designed to increase the capacity of the floodplain to carry more water.

The Oxford Flood Alleviation Scheme will not increase flood risk to properties downstream of Oxford. The scheme does not hold back water (like a flood storage scheme) nor does it speed up water (like a deep narrow channel could do). We conduct detailed modelling, which is always independently verified, and this shows the scheme will not increase flood risk to properties downstream of Oxford. In addition, the Vale of White Horse District Council also commissioned a completely independent review of downstream impact. This was published in December 2017 and confirmed that the scheme will not increase flood risk to downstream properties.

Willow Walk 

We will be removing the existing culverts and their metal railings, shown below and will install a new bridge in their place.

The existing Willow Walk track is already raised above Hinksey Meadow. The new bridge will continue from this track, just raised slightly higher, and will span 19 metres. The height of the deck of the bridge will be approximately 1.5 metres above the existing footpath. The bridge needs to be this size to allow flood water to pass underneath it.

We recognise the importance of Willow Walk as an historic route and a key east-west link for pedestrians and cyclists into Oxford City. Access will be needed for occasional maintenance vehicles. We have confirmed previously that there are no plans to turn Willow Walk into a road.

 Green Belt

If the scheme is approved we believe it will help to safeguard the Green Belt in this area as it will need to remain as a functioning flood alleviation scheme for at least the next 100 years. This will help to maintain and preserve the openness of this part of the Green Belt. The natural design for the scheme includes the creation of over 20 hectares of new habitat. The scheme aims to bring a long term green legacy to the area.

 Maintenance

The scheme will have a long term maintenance plan for the lifetime of the scheme, 100 years. This includes managing the vegetation in the area by grazing. The ‘second stage’ wider part of the channel has been designed to be grazed by cattle to create floodplain grazing marsh. Temporary fencing and removable barriers will allow the second stage channel area to be grazed. We will also create many wetland features within the second stage channel to maximise available habitat for wetland and aquatic species. The backwaters, scrapes and ponds will have a variety of depths, dimensions and gradients, to encourage diversity of wetland wildlife.

Existing streams

The new flood alleviation scheme does not divert water away from Seacourt, Bulstake and Hinksey Streams. The scheme lowers the existing natural floodplain so that in the event of high flows it can carry more water. In the Hinksey Meadow area, the existing Seacourt Stream will act as the first stage channel.

Managing excavated material

A Materials Management Plan has been submitted as part of the planning application. This plan explains the options we considered for both the management of the materials excavated as well as the options for transporting the material from the site. There are no plans to use North Hinksey Village to divert traffic or transport materials. We will construct a haul road specifically for construction traffic within the scheme area to reduce the need for lorries to drive on local roads to access different areas of the site. However, we will be removing a large amount of material which will need to remove from site. Lorries will leave the site via a new compound and access road at South Hinksey and join the A34. This will be our main compound and access point onto the road network.

The majority of the material being excavated will be alluvium, a silty clay. We will reuse this material in the proposed flood embankments where possible. Excavated gravel will be re-used in the scheme for environmental improvements and on the channel of the new river bed.

Most of the material leaving the site will be transported to old quarries and will be used to restore these sites. Once planning permission for the scheme has been granted we will be able to confirm which sites have the capacity and necessary permissions to receive the material.

Tree planting

To mitigate for the estimated 2,000 trees that will need to be felled during construction, we will be planting 4,325 trees. Approximately 15,000 smaller tree species, such as hawthorn, hazel and elder, will also be planted, along with many more native shrubs such as dogwood, goat willow, dog rose and wild privet. The tree-planting proposals result in more woodland within the scheme area after completion, than there currently is at present. These woodland areas will be managed for wildlife and include glades that are sown with wildflowers to encourage butterflies and other insects, as well as birds and foraging bats.

The replacement woodland trees will be saplings and it will be many years before they have the same ecological value as those being felled, so throughout the design process, our contractors, engineers and ecologists have worked together to minimise tree loss wherever possible. Once a contractor has been appointed we will work with them to further minimise losses of mature trees wherever possible. The contractor will also protect all retained trees and hedgerows within the scheme boundary by erecting stout fencing before materials or machinery are brought on site and before any work starts.

The Environment Agency is committed to the scheme bringing additional environmental benefits beyond reduced flood risk, and this includes our consideration for the trees and wildlife across the scheme area.

Dredging

Dredging the River Thames would not significantly reduce flood risk to Oxford. Even if we dredge all the channels that currently exist in Oxford, it would not reduce flooding from a major flood. In many cases, dredging isn’t the best long-term solution because rivers can quickly silt-up again. It can even increase flood risk downstream, alter the ecosystem, be environmentally damaging, costly and disruptive. Studies have indicated the River Thames would require frequent re-dredging as the natural tendency of all rivers after dredging is to deposit silt and return to their more natural dimensions. And it would not be a cheap option to dredge the River Thames.