The £15 million Banbury Flood Alleviation scheme will reduce the risk of fluvial flooding to 441 residential and 73 commercial properties within Banbury in the 1:200 year event (0.5% chance of flooding per annum).
Banbury flooded badly during Easter 1998 and again in the summer of 2007. More than 125 residential and 35 commercial properties were flooded in 1998, causing over £12.5 million of damage.
The flood alleviation scheme involves construction of a large upstream flood storage facility, together with carrying out on line improvements within three locations in Banbury.
The project is being carried out for the Environment Agency by Main Contractors Morrison Construction. Consultants are Black & Veatch.
The scheme’s main flood storage area is immediately upstream of the M40 with the on-line improvements being located at Wildmere Industrial Estate, Tramways Industrial Estate, and Moorfield Brook. The flood storage area will be capable of holding 3 million m3 of water in the 1:200 year event (equivalent to 1200 Olympic size swimming pools) and has taken over 150,000m3 of clay/earth to be construct.
The main site is arable farmland and, with the exception of the footprint of a new embankment constructed as part of the project, the land will continue to operate as arable farmland after completion of the scheme. The new earth embankment running alongside the Oxford Canal stops the floodwater from the storage area spilling into the canal. This is how the town primarily flooded in 1998.
The largest part of the embankment runs parallel with the M40 motorway. It’s maximum height is 4.5m with an overall average height of 2.5m and is approximately 3km in length. The embankment will be inspected regularly as it is classified as a dam structure. Three river diversions were required to allow the embankment to be safely built and the diverted rivers will be planted to become naturalistic sections of river once again with meanders and riverside trees.
A major element of the project has involved closure of the A361 Banbury – Daventry road for a number of months to raise the level of an a 850m long section road by 700mm (27ins) and install culverts to reduce the risk of the road flooding. This element of the works has included the decision to construct a new concrete saddle over the existing canal brick arch bridge located on the opposite side of the Oxford Canal – rather than install a temporary structure. The other main other challenge of the scheme is simply the 3km length of the site.
The main materials being used in the construction work are clay won from an adjacent field, and concrete for the project’s two main control structures, which are identical and incorporate a double baffle orifice that throttles the river during higher flows (some flow is allowed through at all times). There are no gates or moving parts within the control structures, the design for which was modelled at HR Wallingford.
Several large environmental areas are included in the works to create new valuable habitats, including wetland ponds and wildflower meadows. These should increase the number of birds, mammals and insects in these areas.
Trees and hedgerows that have been removed will be replaced and new woodland copses and hedgerows created to maintain the appearance of the valley.
The project is being funded by the Regional Flood Defence Committee via levy funding and external contributions from Cherwell District Council, Network Rail, Thames Water and Prodrive.
Work started on site in March 2011 and the scheme should be operational by Christmas 2011, with some finishing works to follow.
Galliford Try is one of the UK’s top ten contractors. From roads and bridges to renewable energy and water, the company’s vast experience and knowledge allows them to provide clients with infrastructure solutions across a range of sectors.
Most of the company’s work is delivered through frameworks and long-established collaborative relationships which significantly contribute to our strong long-term order book. Morrison Construction fully grasp the concept of genuine partnership to ensure delivery of innovative design and industry leading project management.
James tonks Tree Surgery
As an AA “Arboricultural Approved Contractor”. James Tonks Tree Surgery was invited to tender for tree surgery works on the proposed Banbury flood alleviation Scheme which was been carried out by Clifford Try and behalf of the Environment Agency.
We successfully tendered for the works, after several meetings with the contract managers of Galliford Try it was apparent that our success was not based on price but the professional approach we took. Understanding the Environments Agency protocols and the strict Health and safety requirements they felt we had exceeded their expectations. It was apparent that our previous experience working on environmentally sensitive sites such as SSSI for local authorities was the sort of expertise they were looking for.
We carried out all aspects of tree surgery operations over 3 areas around Banbury. All areas had their challenges from proximity to railway lines, power lines, poor ground conditions and many environmental considerations. The largest and most significant being the flood storage area which covered many Hectares of land alongside the M40 Motorway. We deployed 10 members of staff who simultaneously worked on different areas depending on the skill set and experience.
Due to the timing of works, nesting birds were a major concern. Planning ahead, we pre netted vast areas of hedgerows and trees. We knew it would be several weeks before we actually advanced up the site to carry out necessary works.
All arising produced had to be then stacked and re netted prior to chipping for biomass, this had to be done because no vehicular access had been created to allow us to get the biomass chipper in and extract the product. In all the works took nearly 2 months to complete, all arisings produced on site where recycled and transported to the power stations. The work we undertook was a physical challenge for all our employees as majority of work was done by hand, but it has been great to be part of such a large scheme and we have developed a very good working relationship with Galliford Try and the Environment Agency.