Challenging coastal erosion and few retreat options means armouring is required to extend the security and life of this highway
Katiki Beach adjoins State Highway 1, sandwiching it between rail corridor and coastal cliffs with 20-metre drops. With difficult detour options, this ‘lifeline route’ is crucial to the local economy.
We helped the New Zealand Transport Agency with data collection, risk management, improved road safety and resilience, and protection of this route.
From 2008 to 2014 we surveyed coastal regression and found that, on average, the cliffs retreat almost one metre closer to the road every 10 years. By 2015 we understood the area well, allowing us to compare sites; we triaged the beach length and identified 30 sites needing protection. We also worked with the Department of Conservation and the Historic Places Trust, organisations protecting the beach’s nesting penguins and Moeraki Boulders. Work began in August 2016.
Where erosion put the highway directly at risk, we installed rock protection at the foot of the cliffs up to 3.5 metres above sea level, and at one site we reinstated the failed slope with geogrid-reinforced earth, protected with rock armouring. LIDAR (Light Detection and Ranging) survey data gave us accurate regression modelling and provided a detailed surface for design, giving us confidence in the work required, accurate quantities, and cost control.
Completing protection of four locations by mid-2018, we were invited to offer to design protection works for a further round of at-risk areas on this retreating coast.
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