Kris Croft: Waipoua Forest provides a unique sealing environment

Of all New Zealand’s kauri forests, none is more famous than Waipoua Forest on the west coast, just north of Dargaville. As the largest remaining tract of native forest in Northland, Waipoua is an ancient green world of towering trees and rare birds. The highway through the forest is memorable for the natural gateways created by huge kauri trees and the fringing of colourful ferns along the road’s edge.

This forest is the home of Tane Mahuta, the country’s largest kauri tree, which is approximately 2,000 years old and still growing. Nearly 18 metres to the first branch and 4.4 metres in diameter, Tane Mahuta is rightly called ‘The Lord of the Forest’. Another significant tree in Waipoua Forest is Te Matua Ngahere – ‘Father of the Forest’ – which is estimated to be between 2,500 and 3,000 years old.

Recently the Northland NOC team completed 23 kilometres of reseal on State Highway 12, the first time this section of road has been resealed in 24 years. All of the work was completed internally by Northland construction, sealing and traffic management crews with pavement repair assistance provided from Gisborne and East Coast.

The project was completed in stages from June 2019 to February 2020 consisting of:

Resealing 23 kilometres (87,000 m2) of road
Pavement Repairs
- eight digouts including first coat sealing (760 m2)
- 38 insitu stabilisation including first coat sealing (4,350 m2)
- 34 mill and fills (2,350 m2)

Work was completed according to the specific SOP with inductions for all Fulton Hogan staff and subcontractors completed by a Te Roroa Ecologist.

Kauri is part of New Zealand’s heritage, but kauri dieback is threatening their extinction. Spoil, vegetation, digout & milling material – all pavement & basecourse material is considered to be “soil” and was treated as infected with PTA. The soil was disposed of off-site by transporting it in trucks where the bins were double layered with 200um Polypropylene liners which were securely sealed and covered with waterproof tarpaulins. Once transported and disposed of the truck decks were checked then water blasted so they were totally soil-free and treated with a 2% SteriGENE solution.