Horwich Town Centre Flood Alleviation Scheme
Overview
Horwich has suffered from repeated flooding caused by rapid rain run off the West Pennine Moors into the Pearl Brook. The aim of the scheme was to reduce flood risk to Horwich Town Centre from Pearl Brook during extreme storm events and protect over 200 houses from flooding. Eric Wright Civil Engineering were awarded this scheme through Lot 4 of the Bolton Highways Framework Contract.
In general, the work consisted of:
- newly constructed flow control chamber on Pearl Brook within Old Station Park. Existing sections of earth embankment were altered and new sections constructed to form a new attenuation basin all lined with a geosynthetic clay liner. Recycled 6F5 material was imported and used to make up shortfalls in site material to complete the earthworks elements
- Other new ancillary structures within Old Station Park included inlet and outlet headwalls, a “self closing flood barrier” and associated retaining walls
- The existing highway drainage in the vicinity of Winter Hey Lane/Chorley New Road were upgraded with the introduction of new rider drains and replacement/new gullies
- Additional installation of new play area including minor earthworks, edgings, sub-base and surfacing with binder course macadam
- Recreation of MUGA area including removal of existing fencing, preparation and resurfacing.
Drainage works were carried out in the centre of Horwich as part of the works. These were facilitated with localised road closures which EWCE allocated sufficient resource to ensure roads were opened timely. There were significant services encountered with EWCE employing vacuum excavation techniques to avoid service damage.
Working around live watercourse: The work in Pearl Brook involved construction of a concrete flow control chamber with associated masonry walling. The existing inlet headwall to Pearl Brook culvert was raised with masonry walling. Prior to commencement and with input from EWCE into the methodology, the client procured permanent and temporary permissions from the Environment Agency. A flume pipe was employed and scaffolding access placed to protect the live watercourse. Care was taken at every stage to avoid contamination of the watercourse from concrete, cement and fuels.
Invasive species: Himalayan Balsam was identified along the banks of Pearl Brook. This was carefully removed by hand and bagged. The resultant waste was disposed off-site by a specialist.
All trees were retained.
The majority of material removed from site was taken to Ruttle and recycled by processing.
Imported fill material was recycled 6F5 crushed brick and concrete hardcore.
Mixed waste skips were supplied by Kenny Waste and over 90% was processed and recycled.
Solar panels were used to power our site cabins.
Key Challenges
There were some challenges with securing the large extent of the site and fences had to be reinstated at times. However, generally there was little incidence of unauthorised access, vandalism or attempted theft. A remotely monitored security system was employed which proved a worthwhile deterrent.
The local community were pleased that the area would remain a park with improved footpaths, a relocated and improved children’s play area along with a new MUGA space.
There may have been initial reservation from the local community, but the long term benefits in terms of flood risk alleviation had been clearly communicated by Bolton Council.
Added Value
Eric Wright Civil Engineering proposed a change to the basin drainage by replacing the smaller filter pipes with a drainage membrane. This improved programme and cost.
Over 6,000 sq m of material excavated with only 2,500 sent to landfill. We re-used approximately 3,500 sq m to form the storage basin embankments.
At pre-construction, it was estimated that approximately 2,400 sq m of topsoil was to be imported. We re-used mostly topsoil generated on site therefore reducing the need for import by 60%.
In keeping with the town’s railway heritage, a set of rail buffer stops uncovered during construction have been incorporated into the re-modelled park.
Client Feedback
It was a pleasure working with the EWG team on the project, and Ruttles too! Hopefully, our next scheme together isn't too far away.”