Ruby Bay Slip - Tasman

01/03/2023

In August 2022, Civil Defence declared a State of Emergency in Nelson-Tasman as a five-day storm wreaked havoc in the region. 

A significant slip in Ruby Bay cast over 5000m3 of material across both lanes of Stafford Drive, a key access route for local residents, covering the former highway. 

The material, lack of stability of the cliff face and the potential safety risk for road users forced Stafford Drive to close. 

As a key connection between Māpua, Ruby Bay and Tasman Village, and part of a popular scenic route, Tasman District Council (TDC) needed to explore all options before permanently closing the route. 

The first step was to complete a geotechnical evaluation of the site.  Downer, as part of the Tasman Alliance, were able to offer our expertise in this area by using the expertise of Downer National Ground Engineering Lead, Julia Riding. 

“Tasman Alliance looked at the resources the wider Downer team had available and collaborated with me to provide a formal assessment and advice to the client,” Julia Riding said of her involvement. “Our collaborative, one-Downer approach enabled the client to have a direct relationship with the client as we met in person alongside Tasman Alliance, who provided practical construction advice, and enabled a prompt decision making process for Tasman District Council.”

Downer (DNZ) as part of the Tasman Alliance (TDC and DNZ collaborative delivery team) recommended three options to TDC, abandon the road and use an alternative route, undertake an intensive and costly solution by abandoning the road and changing the temporary alternative route to a permanent access, or remove the slip and open the road with a bolstered maintenance plan. 

TDC decided to implement the third recommendation, removing the slip material and opening the road, a cost-efficient option which, importantly, met the community’s needs.

After Julia's geotechnical assessment, in November 2022 TDC challenged Downer to reopen the road within six weeks - by Christmas. 

Although the slip had stopped moving, significant risks remained. Through simple controls, planned and implemented excellently, the Tasman Alliance achieved a 100% positive safety record despite the risks.

Safety wasn’t the only challenge the team faced, resources to complete the slip remedial work was limited, as many local contractors, Downer’s delivery partners, were allocated to storm recovery work nearby Whangamoa Hill on SH6. This, teamed with the proximity to Christmas, meant resources in the area neared an all-time low. 

Despite the challenges, Downer’s strong relationships saw Donaldson Civil and McDermott Earthworks commit as supply partners, providing key support to meeting the short time frame and creating a recipe for success. 

During the six weeks before Christmas, approximately 700m3 of slash, debris from trees which had fallen during the slip, and the 5000m3 of slip material were removed from Ruby Bay. 

About 1200 tonnes of rock was installed along the foreshore to prevent further erosion. Innovation, flexibility, and strong planning meant that this was delivered while the main works were underway, removing the need for another road closure post-Christmas and increasing value for TDC and the community. 

Thanks to our team’s hard work, Stafford Road successfully reopened on December 22, in line with the deadline. It was a welcome early Christmas gift for many locals.

Tasman District Council Road Maintenance Programme Leader Brian McManus was particularly impressed by the rapid delivery. 

“We set a very short time frame and the team jumped in and got it done. There were a lot of residents who were really happy that the road opened, it was an overwhelmingly positive response.”

Adverse weather could still impact Ruby Bay and Stafford Drive, which means safety controls will remain in place to protect the community, with regular maintenance and care from the Downer team. This maintenance and care ensured that there was no safety risk to the public during a heavy rain event in January 2023, when the road remained open and further slips remained at bay.