- 26th April 2017
- Posted by: Joanne Woodhouse
- Category: Projects
The final part of Morpeth’s flood alleviation scheme completed in July this year. Work to construct Cotting Burn dam was the last piece of work on the multi-million pound joint Environment Agency and Northumberland County Council flood scheme. A drop-in event to thank residents for their patience throughout the construction took place on Friday 21 July.
Cotting Burn dam has been renamed “The Hargreaves Dam” in memory of RFCC Chairman Jon Hargreaves, who sadly passed away in October last year. The dam works alongside other flood protection measures to reduce flood risk to around 1,000 properties in Morpeth.
A coarse tree screen had to be installed on the river Wansbeck at Morpeth – a significant white clawed crayfish habitat in the North-East. This involved installing seven large tubular steel piles into the environmentally-sensitive river. Each tube weighed around 7.5 tonnes and was installed in a pre-drilled shaft through gravel, glacial till and boulders.
Substantial plant (cranes, drill rigs, and so on) was needed to work in the watercourse at restricted times to ensure that they were disturbing the river bed as little as possible.
The original scheme proposal was to have a piling rig travelling across the river moving from one pile to the next. This was significantly more expensive than working from a rig at ground level and had additional risk.
At tender stage, we proposed to construct a traditional stone temporary piling platform across the river, using concrete pipes to channel the flow or use specialist expensive piling kit that uses an installed pile to drive the next pile. This meant importing around 3,000 tons of clean aggregate to make a 1m deep platform, and would have taken around 4 weeks to install and remove or require expensive kit which had a long lead in time.
Our JBA Bentley project team devised an alternative solution using precast concrete Legato blocks placed directly onto the river bed, which minimised the load on the pipes. In addition, because the blocks could simply be placed and lifted, we disturbed the river bed as little as possible. We did not place the Legato blocks by the tree poles. We simply filled these voids and topped the surface with an imported aggregate.
‘Legato’ blocks, supplied by Elite Precast Concrete, are high-strength interlocking blocks designed for a huge variety of projects. We have also used them at the Foss Barrier to construct a temporary platform to lift M&E equipment above the potential flood zone.
Benefits of the Legato blocks included:
- reduced piling matt thickness
- reduced need for clean, imported stone
- speed and ease of construction
- fewer material deliveries to site
- Legato blocks can easily be re-used, minimising waste
- minimal disturbance to the river bed.
We estimate this approach reduced the programme by two weeks and saved around £34,000.
Want to know more?
You can contact Ben Darville, Designer, or Damian Ireland, Contracts Manager, at JBA Bentley for more information on this project. Andrew Gee from the Environment Agency was also involved with this project.
Our engineering web pages also have lots more information showing how we can help you with future projects.