Our Ref: Thames/Viano/GC
Date: 11 November 2009
Dear Ms Viano
FREEDOM OF INFORMATION REQUEST
Thank you for contacting me regarding dredging of the Thames and the flood alleviation scheme in Marlow in your email of the 13 October 2009.
From your email I have tried to identify the main topics of concern and have responded to them in turn.
Marlow Flood Alleviation Scheme (FAS) and Environment Agency Plans for Bisham
1) The Environment Agency has no plans to protect properties at risk on the Berkshire side.
Following the 2003 floods an extensive study was carried out covering the area from Hurley to Bourne End. This study assessed the risk and looked at potential options to reduce flooding in the area.
The options considered for Bisham met the minimum economic, environmental and technical criteria. However, when compared to other schemes from across the country the Bisham proposals did not rank highly enough to gain approval from DEFRA. The options in Bisham will remain on the National Priorities List and will be reviewed in the future.
2) Increased flood risk to communities on the facing bank.
A significant element of the Marlow Flood Alleviation scheme is a compensatory storage area off Lower Pound Lane. This storage area will ensure that any construction in the flood plain for flood defences is compensated for. As there is no reduction in the flood plain, the risk of flooding is not increased in other areas.
The Flood Risk Assessment (FRA), which forms part of the Planning Application for the scheme assesses all flooding issues including the compensatory flood storage and is attached for your information. The FRA along with the other planning application documents for the Marlow FAS are available on the Wycombe District Council website.
We believe we have presented the best option to reduce the risk of flooding in the Marlow area and have demonstrated that it will not increase flood risk to other communities through the FRA.
3) Are we counting The Compleat Angler Hotel, The National Sports centre and Longridge Sports centre each as 1 property?
In order to consistently assess flood alleviation schemes across the country we carry out project appraisals in line with the DEFRA Flood and Coastal Defence Project Appraisal Guidance (FCDPAG) and 'The Benefits of Flood and Coastal Risk Management: A manual of assessment techniques'. The guidance and manual identify how to calculate the economic losses caused by flooding in a 'do nothing' option and compares it against different 'do something' options. The difference between these is the benefits from carrying out the work.
The economic appraisal looks at individual properties and assesses damages based on its usage and expected flood levels versus property threshold levels. The flood damages and therefore the benefits of protecting a detached house are different from a terraced house and different again from a shop, hospital, hotel or sports centre.
Therefore, although we count these as individual properties there is a higher economic benefit from protecting them than a house or flat for example. This was part of the calculations in our bid to DEFRA for funding.
Dredging
4) You have allowed the Thames to be silted up after nearly 60years of regular dredging and maintenance. Why?
The dredging that was carried out on the Thames and was completed in the mid 1990 lowered the bed level by 30cm. Since then we have monitored the bed levels through the surveys that you have seen previously.
The surveys, which we have attached, show the river bed downstream of Marlow weir has lowered since 1999. During the period between 2003 and 2008 natural erosion of 185,282 cubic metres of material has taken place between Marlow weir and Cookham weir. This is an average erosion rate of 0.09m per year.
As there has been no increase in bed level and therefore no increase in flood risk we have no plans to recommence dredging at this location. We plan to survey this reach again in 2012/13.
We have permissive powers to carry out works on watercourses designated as main river. This means that should river bed levels rise in the future we will assess all the options available at that time. The options need to be cost effective and environmentally sound which may mean dredging is not the preferred way of managing the risk in the future.
5) Who authorised that the dredging/maintenance programme started in 1947 following the re-profiling of the River Thames be abandoned? On what grounds?
Following the completion in the mid 1990s of the dredging to lower the bed of the River Thames by 30cm studies were commissioned to look at the future justification of re-profiling works for Flood Risk Management purposes. These studies took into account the economic, technical and environmental legislation at that time. Based on the evidence from the studies it was decided that further re-profiling of the Thames could not be justified on economical or environmental grounds.
This reach will be surveyed again in 2012/13 and should river bed levels rise in the future we will assess all the options available at that time.
6) Confirm on what evidence you make the statement that “in our judgement sandbars do not increase the risk of flooding”
Thank you for the offer of an amended map. We are aware of the sandbar downstream of Marlow weir and our operations delivery team investigated whether it needs to be removed for navigational purposes. They concluded that there was no hazard to navigation.
In terms of flood risk, as I mentioned above, surveys show the river bed downstream of Marlow weir in general has lowered since 1999 and the capacity of the reach overall has increased. Therefore there is no justification for the removal of the sandbar.
A sandbar is a natural feature of a watercourse. Environmentally it provides the opportunity for marginal species to breed, and provides birds with a safe nesting area. In addition the increased movement of sediment caused by its removal could be more damaging to the watercourse through increased sediment suspension. This clouds the watercourse, and removes the stable bed.
7) Why spend millions of pounds of tax payers money on unproven flood alleviation schemes before undertaking prudent action like regular maintenance on ditches.
The Marlow scheme has developed over a number of years and has shown that it will provide a good level of flood alleviation for the residents of Marlow.
The responsibility for the maintenance of watercourses rests with the riparian owner, these are land owners and residents whose properties back onto a watercourse. Our “Living On The Edge - A Guide To The Rights and Responsibilities of Riverside Occupation” leaflet can be found on our website pages at:
The Environment Agency exercises its permissive powers to maintain watercourses on a risk based approach and the current maintenance programme reflects this approach.
8) Foul sewers and surface water drains are inadequate.
The responsibilities for foul sewers and surface water drainage rest with Thames Water and Local Authorities respectively who we work closely with.
The outputs from the Pitt Review clarifies responsibilities between the various organisations and DEFRA has made funds available for Local Authorities to carry out Surface Water Management Plans to enable them to better understand and tackle surface water flooding issues.
You also requested the transcript of a speech made by our Chairman, Lord Chris Smiths, to the Royal Academy of Engineering. I believe that you are referring to a speech our Chairman made to the Insurance Institute of London, a transcript of which I have attached. I have attached the report issued by the Royal Academy of Engineers referring to the likelihood of increased occurrences of tropical monsoon type weather. The two coincided and were pulled together in a Telegraph article which is also included.
I trust this response addresses the questions you raised, however please contact me if you require any further clarification on the details below.
Yours sincerely,
Doug Hill
Team Leader - Asset System Management
Thames Region - South East Area
01276 454513