- 26th September 2017
- Posted by: Sophie Bunker
- Category: Projects
Ulverston is a market town on the South Lakeland peninsula in Cumbria. The town has suffered from 10 significant flood events since 1890, with 109 properties and businesses flooding in 2009.
The beck runs 1.5km through the town centre before passing through the railway embankment and into the floodplain. The beck has been significantly influenced by human activity: the channel has been artificially straightened, confined between masonry walls, and much now runs through culverts. In July 2015, JBA-Bentley began constructing the £6.1 million Town Beck Flood Alleviation Scheme.
Once complete (in late 2017) the work will protect 407 residential properties and 118 commercial businesses, including critical infrastructure, from a 1 in 100 year event.
Creating the culvert
The extensive culverting of the beck has taken place gradually over many years, with some sections originating in the early 1900s. As a result, the culvert has many forms of construction, shapes and sizes, making refurbishment work more complicated. It passes under numerous main roads within the town, and was in particularly poor condition in these locations. The road sections were generally rectangular and had been constructed with old rail track (beams) supporting a deck of thick stone slabs. It is virtually impossible to check the condition of this type of construction (which uses uncontrolled natural building materials), so the scheme’s original designers earmarked the soffits for replacement.
Unsurprisingly, given the urban setting, the roads contain many of the town’s major services. Replacing the culvert soffit would be very disruptive, a risk to health and safety and very costly. In a bid to avoid service clashes, the usual lining options (UV or thermal cured liners) were considered but ruled out due to the shape of the culvert and the need to maximise the flow.
Fortunately, since the original design work was completed, lining techniques had continued to develop. JBA Bentley proposed using Glass Reinforced Plastic (GRP) segmental lining units, which can now be formed to meet almost any size, shape or load requirement. This is achieved by simply adjusting the thickness of the unit walls. The product is built up by applying layers of GRP tape to a mould, and it has a very low hydraulic roughness that easily compensates for any reduction in cross section that it creates. JBA Bentley managed to show that the proposed lining system would not reduce capacity, but had enormous benefits.
The liners are rigid, and we used 3D laser scanning techniques and Revit models to ensure they fitted within the irregularly-shaped culvert and, where necessary, checked this using a plywood template.
This repair technique shortened the construction programme by 10 weeks and allowed JBA Bentley to repair the culvert beneath busy roads and residential properties with minimal disruption. JBA Bentley avoided closing roads, demolishing and rebuilding 3 homes and over £125,000 of major service diversions.
Jayne Kendall, Ulverston Town Clerk: “Ulverston Town Council has been working closely with the Town Beck FAS project team to make sure that they and ourselves are fully up to speed with the timescales and scope of the work, and the effects that the work has on the town. The relationship has been a true partnership approach, and has worked extremely well. The town council is extremely impressed with all of the team involved in this complex project and thanks them very much for their courtesy and efficiency.”
Want to know more?
For more information on this project contact Tony Moran, Technical Director at JBA Bentley. Why not find out more information on our engineering web pages or on the JBA Bentley website. You can also read more about this project on the UK Water Projects website.