Risk of local property flooding

From the Planning Officer’s report to the West Area Planning Committee, December 2017:

“9.149. During the consultation process, reference has been made to the suggestion within the Factual and Interpretive Ground Investigation Report that the proposed drainage strategy will require the use of lime stabilisation to avoid damage to the paving within the car park expansion from changes to the clay layer below ground and that this needs to be given further consideration as part of any drainage proposals for the site. The concerns raised are that lime treatment is likely to have an impact on the permeability of soils below the car park, and therefore needs to be appropriately considered. 

The applicant has confirmed that the surface water drainage strategy has been designed as a tanked system which assumes no infiltration below the attenuation layer, with all storm water discharge from the site via a controlled outfall into Seacourt Stream. An impermeable membrane is included within the construction to prevent water saturating the clay. The underlying clay is of a low permeability whether lime stabilisation is employed or not, and it is envisaged that the attenuation will operate effectively in either scenario.” [emphasis added]

There is no mention in the Application of tanking, nor of an impermeable membrane. We have therefore not known of this till very recently and had no opportunity to comment. While there is little or no detail, the idea that the car park may be separated from the underlying groundwater table, as this implies, raises an extremely serious question. That is, where will the displaced groundwater go? This is a lot of water over such a large area. It is likely that it will cause a significant rise in groundwater levels around this low-lying site. This could cause (new) groundwater flooding within houses (and gardens) nearby. No decision should be taken until the details of  what is planned are made clear, appropriate calculations and modelling done, and presented as part of a further revised Flood Risk Assessment.

[By the same token, when it rains, water will be trapped within the tanking , draining only slowly – more pumping needed?]

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Our comments on Oxford Local Plan 2036

Oxford Local Plan 2036
“Oxford City Council is producing a new Local Plan for Oxford. The Local Plan is important because it will shape how Oxford develops.” (from the ‘Preferred Options’ document for the Plan, Oxford City Council). The Council called for comments and we wrote recently as follows:

We wish to submit the following comments in relation to the proposed Oxford Local Plan 2036. Our comments all relate to flood risk.

Overall we are satisfied that the City Council has adopted an appropriate strategic approach to development and flood risk in the city, with new development targeted towards areas least at risk from flooding. We welcome the recognition in the document that flooding is a significant risk for the city and that this needs to be managed.
 
On the specific sections relating to flooding in the Preferred Option, we would like to see reference to the need to actively maintain watercourses in the city so that they function freely during times of flooding. We’re surprised that the SFRA Decembrer 2016 makes no mention of the need for clearing of trash gates, and the removal of vegetation and fallen trees from streams and ditches. Riparian owners in the city need to be encouraged to maintain water courses.
 
On Option 38A we would prefer to see adoption of a policy which states that there will be no development of previously undeveloped land in flood zone 3b. As the SFRA notes, this is the position in the current Core Strategy and we see no argument for weakening this.The new plan does not designate greenfield sites in zone 3b for development.
We recognise that water compatible structures and essential infrastructure may, in exceptional circumstance, be permitted in zone 3b under the NPPF. But the Council’s recent attempts to argue that an extension to the Seacourt Park & Ride constituted ‘essential infrastructure’ caused the Oxford Flood Alliance considerable concern. While references to NPPF in the Council’s proposed Local Plan may appear to provide safeguards to the public, these are significantly weakened if the Council intends to ‘interpret’ NPPF along the lines argued for the P&R extension or similar. We believe the plan document needs to provide clarity on this.

 If Preferred Option 38A is adopted as proposed we wish to state for the record that we interpret this to mean that NPPF will be strictly applied. It is clear in Table 2 and 3 in this Guidance Note what ‘Water Compatible’ and ‘Essential Infrastructure’ mean. We are therefore interpreting the Council’s policy to mean what the NPPF guidance says it means. This does not include car parks.

In Option 56A we would like to see a reference to riparian owners responsibility to maintain water courses. Simply treating them as a design feature isn’t sufficient.

 

OFA Steering Group

Seacourt P&R extension proposal: potential risk to life

Liz Sawyer, who recently joined the OFA Steering Group, addressed Oxford City’s Full Council on 6 February 2017, about the potential risk to life posed by the proposed extension to Seacourt P&R.

There is also, as the photograph above shows so vividly, the potential for damage to the car park itself – and of course to vehicles. The Automobile Association’s ‘Flood Facts’ quoted in Liz’s address set out the risks of floodwaters very clearly.

Liz’s address can be downloaded here (pdf).

New flood advice website

Oxfordshire County Council, our Lead Local Flood Authority (LLFA), have just launched a new flood website which should be very useful, providing a single place where people can go for advice. The link is https://www.oxfordshirefloodtoolkit.com.

The Oxford Mail has an article on it http://www.oxfordmail.co.uk/news/14942940.FLOOD_victim_who_fortified_his_home_urges_others_to_use_new_council_online___39_toolkit__39_/

Storm Desmond, flooding and climate change

corporation road carlisleCorporation Road, Carlisle (Photo: North News)

There has been widespread and severe flooding in Lancashire and Cumbria due to unprecedentedly heavy rainfall in a short period from Storm Desmond. One feels for the people affected, many not for the first time.

‘The 405mm of rain that fell in Thirlmere in the 38 hours to 8am on Sunday marked a record amount of rain ever to fall in a 48-hour period while the 341.4mm recorded at Honister Pass on Saturday broke the highest rainfall record for any 24-hour period.’

‘Dame Julia Slingo, the Met Office’s chief scientist, said the “extraordinary” conditions were likely the result of climate change. Her comments were echoed by Liz Truss, the Environment Secretary, who told MPs: “Climate change is factored into all the modelling work the Environment Agency does but clearly in the light of this extreme weather we are going to have a look at that modelling and make sure it’s fit for purpose.” ‘http://www.telegraph.co.uk/news/weather/12038356/Floods-caught-ministers-by-surprise.html

‘Prof Hall [Professor Jim Hall, director of the Environmental Change Institute at the University of Oxford] said there was always a trade off between costs and risks. Nevertheless, he added that the latest floods “should be a trigger for a revaluation of protection standards”.’ http://www.ft.com/cms/s/0/57b91e9c-9cf1-11e5-8ce1-f6219b685d74.html#axzz3tiucxtde

There is more on the relation between flooding and climate change here http://www.belfasttelegraph.co.uk/news/uk/heavy-rain-and-flooding-fit-with-climate-change-predictions-34268682.html

Extreme weather events associated with climate change are already more common: we need to make sure the assumptions used in the modelling of the Oxford Flood Alleviation Scheme (Oxford FAS) sufficiently take into account the effects of climate change.

Natural flood management, climate change and Oxford: a symposium

Oxford Flood Alliance are hosting their Second Flood Symposium this week, in collaboration with the Environmental Change Institute, University of Oxford. The meeting is fully subscribed.

The topic is Natural flood management, climate change and Oxford.
We will publish a summary of the proceedings on this website.

MPs visit flooded areas

30 November 2012

Our MPs, Andrew Smith and Nicola Blackwood, have visited flooded areas to see the problems and how defences were working.

Oxford East MP Andrew Smith said: ‘The Environment Agency, City Council and Emergency Services have done a good job.  I saw for myself the effectiveness of the barrier by Hinksey Lake and the pumping operation in Vicarage Road, where we had 3 feet of water in 2007. The measures pressed for by the Oxford Flood Alliance and put in place have made a big difference; but it is all still on a knife-edge, and we must all keep up the pressure for more works to reduce the risks still further’.

Nicola Blackwood, MP for Oxford West and Abingdon, visited areas on the Botley Road and in South Hinksey before moving on  to Abingdon. She saw flood defences working well at Bullstake Close, Botley Road. In sharp contrast, in South Hinksey there was flooding of seven houses, with water which seems very likely to have been contaminated by overflowing sewers. Ms Blackwood is taking up this and other issues on behalf of residents.
Sewers and/or surface water systems appear to have been overloaded too in the Grandpont area, and parts at least of the Botley Road area. This is of great concern and demands urgent investigation and remedy.