In September 2013 a large landslip closed State Highway 6 on the West Coast between Haast and Makarora.
The slip left over 40,000 cubic metres of rock and debris on the highway, initially closing the highway for 11 days. The road was re-opened, from 8.30am to 4pm each day but only a single lane was available at the slip site. The road was closed outside these hours due to a risk of slips. Some 14 months of remedial work was required to stabilise the site and reinstate two lanes.
The most complex rock fall protection system in Australasia was installed at the slip site to enable restoration of full access through Haast Pass. Each of the three rock fall protection fences built on the slip face is capable of stopping a boulder weighing up to 16 tonnes (the size of a small car) travelling down the hillside at a speed in excess of 90km/h.
The total cost of managing access and remediating the Diana Falls through the installation of rock fall protection measures was $8m.
State Highway 6 is the only route linking the West Coast to the regions further south and as a result of the closure, journeys required a detour through Arthurs Pass. The journey from Haast to Wanaka, normally 142km, became a 950km journey as a result of the closure. This has created significant inconvenience and additional costs for residents and businesses on the West Coast.
The West Coast regional economy is heavily dependent on tourism, contributing approximately 10% of regional GDP (the second highest in the country). Because of the lack of alternatives and long detours, any closure on State Highway 6 is likely to have a disproportionately high impact on the local economy as tourists choose to take alternative routes between Queenstown and Christchurch.
Because events on this route can have significant social and economic impacts, mitigations have been put in place through improvements or enhancements to build in a higher level of resilience into the network.
This case study demonstrates the difficulty of managing the network during extreme events in remote areas with limited communication networks and few users on the roads. In these situations it can take a long time to confirm the location and scale of network closures, and to pass that information on to network users.
