Barnet Project
Background
Situated on Mill Corner in the London Borough of Barnet, is a privately-owned house that historically flooded on numerous occasions. Investigations showed the flooding was being caused by a damaged surface water drainage pipe that was directly underneath 1 Mill Corner.
The matter went to court and Barnet Council was ordered to provide a temporary and permanent solution. Public Sewer Services (PSS) were tasked with providing the permanent solution, which involved installing 230 metres of new surface water drainage pipework in May/June last year.
The solution
PSS ran a brand new 300 diameter pipe, from an existing buried manhole on the nearby Ashbury Lane, out on to a pond at Monken Mead Brook, which is approximately 300 metres away from the house.
An existing manhole was located around 15 metres away on Dury Road. PSS capped the northern branch from the manhole off and created a new outfall in the same position as the existing outfall, which was provided at the pond.
Trenches were dug down Ashbury Lane to enable the first section of pipe to be installed. The subsequent two sections ran through an established conservation area.
Transport and environmental benefits
The second section of pipe was installed by PSS in a tunnel that is underneath approximately 60 Tree Preservation Order-protected Oak, fruit and other mature trees. The final section ran through light woodland and grassland and was installed using open trench construction down to the outfall.
PSS carefully selected a route for the pipework that would cause minimum disruption to the trees and extensive local habitat. They steered clear of using traditional excavation methods to prevent damaging any of the surrounding vegetation. All trees of a stem diameter greater than 75mm, when measured at 1.5m above ground level, remained untouched.
Only two excavations were used, with PSS making sure they were of the smallest dimensions possible – 2 metres x 2 metres x 1 metre. They were deliberately installed away from any vegetation that was inhabited by local wildlife to avoid any disturbance. These two excavations alone were used as a launch and receiving pit for PSS’ directional drilling rig during the entire project.
Cost and productivity benefits
The work was carried out extremely efficiently by PSS, within the space of just two weeks. This was due to the fact PSS used no-dig Horizontal Directional Drilling (HDD) methodology. In comparison, using open cut methodology would have resulted in the work taking six weeks to complete.
Innovative concept
PSS’ approach to delivering this project was underpinned by innovation due to the fact they utilised trenchless techniques, wherever possible, in order to protect the local vegetation and habitat.
Customer benefits
The existing damaged surface water drainage pipe has been removed and replaced. Ultimately, Barnet Council and the local community have been provided with a permanent solution for diverting surface water flow away from 1 Mill Corner and preventing the area from flooding again due to historical drainage pipe issues.
Community benefits
Work was carried out with minimal disruption to the local community and surrounding woodland and wildlife habitat. Considerable care and attention was paid to making sure all of the protected trees remained intact and any wildlife was undisturbed by diverting the route of the pipework and using no-dig methods.
The fact the work was carried out so swiftly, within a fortnight, meant the impact on the local community was kept to an absolute minimum. What’s more, the risk of flooding at 1 Mill Corner and surrounding properties due to the old, damaged pipework no longer exists.