WHY WE SHOULD CONSIDER ALTERNATIVES TO THE OXFORD FLOOD ALLEVIATION SCHEME
Presentation to North Hinksey Parish Council Annual Meeting March 17 by Tim O’Hara
INTRODUCTION
When the impending planning application is made for the OFAS, the main element is still expected to be a 5km channel. This is actually a narrow channel within a much wider shallower second stage channel.
I’m going to explain why I don’t think this is the answer to Oxford’s flood problem, and why we should consider alternatives.
If you agree, then please express this view to the EA, and the planning authorities.
There are four main problems with OFAS
Firstly: failure to reflect environmental costs
The second stage (ie wide shallow part) of the 5km flood channel is why 400,000 m3 of soil needs to be excavated and 2000 trees need to be cut down.
But doing this will release substantial amounts of stored carbon into the atmosphere, in the face of commitments to reduce such emissions.
The loss of trees will work against the scheme because their presence helps reduce flooding.
We will lose 2 hectares of rare grassland in Hinksey Meadow: one of only a handful of remaining sites.
Moreover an expert believes the flood channel could damage the delicate ecology of the remaining grassland.
Secondly:failure to reflect social costs during the three year construction period.
Removing the excavated soil will require 29,200 lorry loads (assuming the use of largest lorries, and modest de-compaction ). These slow moving lorries can be expected to create congestion both en route to, and on the A34
Much of the flood channel is in well-used recreational areas (I.e. Hinksey Meadow and Electric Avenue), during construction its inevitable that access to these areas will be limited or removed altogether
Thirdly: Flood protection after 10 years .
The flood protection provided by OFAS is calculated by quantifying the damages from flooding that would be avoided as a result of the scheme, and over its 100 year payback period. These are then converted into a present day financial equivalent.
On this basis OFAS provides an extra £238 million of benefit compared to the current flood alleviation measures
The scheme will cost around an extra £150 million: but this only includes maintenance for 10 years. The EA expect other parties both to undertake and fund maintenance for 90 years.
Failure to maintain the channel will lead to a build up of vegetation. This will prevent flood water from being carried away, and so the purpose of the channel will be defeated.
Hence we may well have a similar flood risk as at present, but whilst incurring all the environmental, social, and extra financial costs.
Fourthly: Value for money
The EA calculate that OFAS will initially reduce the number of at risk dwellings as follows
(i) the number with a greater than 5% annual risk of flood will be fall from 562 to 14:
(ii) the number with an annual flood risk of between 1.33 and 5% will fall from 520 to 119.
Protection for Infrastructure is claimed, but the EA have not meaningfully quantified this.
Therefore, the financial, environmental, and social costs are mainly to reduce the risk of flooding for 946 dwellings
But the scheme is not just the channel. It also includes specific permanent flood defences for the high risk locations of Osney Island ( 267 dwellings) and South Hinksey.
So it seems probable that protection for many of the most at risk properties comes from these defences, and not the expensive flood channel.
These four disadvantages are rooted in two issues.
Firstly, OFAS replaces rather than augments the existing measures. For example by running the new channel under Willow Walk in place of the existing conduits.
Secondly, the second wider part of the flood channel is responsible for the vast majority of the costs of OFAS but seemingly provides minor benefit.
Overall: relative to the current FAM’s, OFAS has significant upfront environmental, social and financial costs. Yet the modest extra flood protection has no guarantees for 90 of its 100 year life.
This is a once in lifetime project: we should consider alternatives that don’t require the second stage channel, and/ or can work with the current measures.