Brougham Street Brick Arch Culvert

Investigation and design work in Westport to stabilise a damaged brick arch culvert, while creating safe access points and integrating a backflow prevention within the existing stormwater system.

Client: Buller District Council
Location: Westport, West Coast
Services: EnvironmentalGeotechnical engineeringSurveyingStructural engineeringCivil engineering
Status: Completed in 2025

The Brief

Several years ago, a collapse within the Brougham Street brick arch culvert (between Palmerston Street and the outfall) had caused the culvert to partially fill with cobbles and debris. The culvert backflowed in high river flows and flooded upstream properties and needed to be cleaned out to function effectively. To achieve this safely, an egress point was required at both ends of the culvert.

However, the outfall end of the brick arch culvert had sheared and was prone to collapse. The outfall was also located adjacent to a derelict, heritage wharf structure.

What We Did

The solution was to install a 1500 mm dia. access manhole in the riverbank that connected to the arch, replace a 12.5 m section of brick arch culvert with a 900 mm dia. outfall, and install a WaStop® backflow preventer to prevent backflow of stormwater into the town. This required us to remove the derelict wharf structure and rock armouring of the riverbank.

Innovation included a shear wall design that connected the 900 mm diameter outfall and manhole to the existing brick arch culvert. This was a bespoke design requiring careful consideration to ensure compatibility and constructability of the pipe and culvert.

Key deliverables

We provided environmental science contaminated soil sampling, testing interpretation and advice to the National Environmental Standards, civil and structural design, survey, and later construction monitoring. Specific deliverables included the detailed design package comprising the structural engineering design report and civil and structural design drawings.

Prior to the engagement on the Brougham Street Arch culvert work, our Civil Engineering Lead added value by providing the Buller District Council Project Manager with guidance on constructability, land ownership, KiwiRail permits, contamination testing, Heritage New Zealand concerns (wharf and culvert), and geotechnical and design considerations. This ensured a no-surprises project delivery.