Date published 18 March 2021
Two years after installation, the success of a flood alleviation scheme, designed to alleviate damage to local homes, community and roads from floodwater, is clear for everyone to see in Hagley, Worcestershire.
The ageing sewer network that drained the wastewater of 6,000 strong local community, towards the Severn Trent Water Milestone Drive Sewage Pumping Station, served the small town of Hagley on the Birmingham/Worcestershire boarder.
With increased urbanisation, growth and misconnections within the existing catchment, hydraulic pinch points on the foul sewer network subjected numerous clusters of low-lying properties across the village of Hagley to flooding during times of heavy rainfall.
Flow monitoring, hydraulic modelling and engagement with the active local Flood Group lead to the promotion of a £1.3m scheme to holistically solve the foul sewer flooding at 17 areas across the town.
NMCNomenca (now nmcn plc) were appointed as the principal designer and contractor, under the AMP6 framework agreement, working alongside Severn Trent to enable a solution, which avoided closing the A456 in Worcestershire, a significant 30-125MSA road and an important source of trade for Hagley high street.
The flood alleviation design philosophy of delivering the project entirely as a gravity solution and avoiding the A456 lead to two large network transfers in order to free up capacity in the main sewer flowing below the A456. The re-routed flow is now stored in large precast concrete attenuation tanks, in Hagley playing fields and Summervale Road, prior to being discharged through throttle pipes back to the neighbouring sub-catchment.
Flooding that used to be a regular occurrence on Newfield Road, Station Drive has been alleviated through a traditional concrete pipe sewer upsize to safely convey the wastewater away from the flooding properties, and respectively providing 165m ³ and 233m ³ of storage to ensure pass forward flows do not exceed downstream capacity.
NMCNomenca held extensive stakeholder meetings, including regularly attending the Monday evening Parish Council meetings, where the initial designs for the main storage tanks in Hagley Playing Fields came under scrutiny due to a planned expansion of their Community Centre.
Agreed locations for the attenuation tanks where met, to provide a future-proof solution that has satisfied the needs of both key stakeholders and the maintenance access needs of Severn Trent Water.
Careful phasing of the works across the village permitted NMCNomenca to have road closures running simultaneously, with three separate gangs working in different sections. Programme efficiencies lead to the successful completion of the project 4 months earlier than the Severn Trent Water completion date.
The sewer upgrade and attenuation tank scheme included the installation of 50 number 1500mm and 99 number 1800mm Marshalls Civils and Drainage water management precast concrete pipes, some of which were laid as a multi-tank system to improve the management of water, ensuring that flooding was no longer part of the day to day worries of the community. Using precast concrete pipe solutions minimised the volume of material being taken off-site as it could be reused as backfill. This led to a vast reduction in importing general fill material, reducing both disruption and the environmental impact of the project.
As part of their work within the community, NMCN invited the local fire and rescue team to practice a high risk confined space entry within the playing field tanks, which provided the local nursery with excitement and entertainment, with the arrival of large construction equipment and four fire engines.
The West Midlands Institute of Civils Engineers’ were so impressed with the scheme and project’s effective community engagement that they awarded the scheme their Communication Award. Judges were impressed that the Hagley community were informed of the project two years before work started and that stakeholder concerns were addressed and communicated with residents.
Two years after the project finished, you would never know that the large precast concrete attenuation tanks are keeping the flow running within the sewer network and not into people’s homes.
If you would like to see the installation of the precast attenuation solutions at Hagley please visit Hagley Flood Scheme – YouTube