Wave action along the Hundalee coastline was eroding the foreshore directly beside KiwiRail’s South Island mainline, threatening the track foundation. To address this, Bluemont Rock Bags™ and large Timaru Basalt boulders were installed together as a rail erosion control measure, securing the coastal margin and protecting the track corridor.
Project Snapshot
Location: Hundalee, South Island, New Zealand
Client: KiwiRail
Application: Coastal rail erosion protection
Total Material: 4t2W Bluemont Rock Bags™ and large Timaru Basalt rocks
Project Overview
KiwiRail’s east coast mainline connects Invercargill in the south to Picton in the north, running the full length of the South Island. Along much of this route, the track sits with little separation from the water’s edge, making rail erosion control a constant operational consideration. Hundalee is one of those locations where the coastline came close enough to the track to demand action.
The Challenge
Foreshore erosion at Hundalee had reached a point where the railway formation was directly at risk. Wave action was eroding the ground beside and beneath the track, and without intervention, the foundation could have been undermined – threatening both rail safety and service continuity on this key South Island corridor.
The Solution
The project team designed a layered rock protection solution to reinstate the culvert headwall and defend the rail corridor against ongoing wave energy. Large Timaru Basalt boulders form the lower layers, providing a heavy, stable base to handle direct wave impact. The design specified Bluemont Rock Bags™, also known as Kyowa Filter Units, for the upper section above the culvert headwall.
Installation
Bluemont Rock Bags™ were filled with rock sourced from Kaikoura while Timaru Basalt boulders were brought in by train. Two layers of Timaru Basalt formed the base, with Bluemont Rock Bags™ stacked above to complete the upper section. The flexible, contained form of the bags allowed them to conform to the structure and maintain stability against sustained wave action.
Results
The completed installation stabilised the Hundalee foreshore and significantly reduced the wave erosion risk to the railway formation. Bluemont Rock Bags™ provided effective armouring suited to the demands of this active coastal environment, delivering a durable rail erosion control outcome for KiwiRail’s east coast corridor.
Related Applications
Bluemont Rock Bags™ suit a range of erosion and scour protection challenges – from riverbank stabilisation and bridge scour protection to safeguarding transport infrastructure corridors exposed to wave action or flood conditions.
Contact us to discuss your erosion protection requirements. You can reach us on +64 9 872 2622 or email info@rockbags.nz for New Zealand-based projects.
