manawatu-highway-stormwater-design

Te Ahu a Turanga: Manawatū Tararua Highway is a complex, large-scale roading infrastructure project that will provide a key regional connection between Tararua and Manawatū. WSP have incorporated best practice stormwater design principles, design integration with iwi partners, and digital technology communication tools, to deliver stormwater solutions that tread lightly on the surrounding landscape. The proposed solution is a system of 40 culverts, 10 bridges, 12 wetlands, 5km of constructed streams, and 20km of open channels, along the 11.5km of new highway, which implement Te Ao Māori values and water-sensitive urban design practices.

The Solution

The Manawatū Gorge is a river valley that runs between the Ruahine and Tararua Ranges, in the southern region of the North Island. The stretch of State Highway 3 that passes through the Manawatū gorge provided an important east-west transport link between Hawke’s Bay and Wairarapa on the east of the ranges, and Horowhenua and Manawatū to the West, and has played an important role in regional development since its construction in 1872. The SH3 Manawatū Gorge route was permanently closed in 2017 due to frequent slips and ongoing geological movement.

Waka Kotahi have selected a 11.5km replacement route which is due to be completed in 2024. The road will also have a separated shared path for walkers and cyclists. The 4-lane highway will contain 10 bridge structures across tributaries of the Manawatu River and could involve significant environmental impacts. It is a challenging environment with a steep topography, high rainfall, existing flooding and erosion issues and the presence of numerous steep streams.

The Te Ahu a Turanga highway will restore a crucial link that supports the needs of communities, travellers and businesses across the North Island. By providing improved road safety and connection between Palmerston North and Woodville, it will support regional activities and development.

The Te Ahu a Turanga: Manawatū Tararua Highway project is an excellent opportunity to reconnect communities and deliver safe and resilient outcomes. By treading lightly, designing with iwi and incorporating Te Ao Māori values, the project has the potential to enhance the mauri in the area and be an exemplar project for environmental and cultural outcomes.

Facts

In the middle of the Manawatū Gorge lies a large red rock called Te Ahu a Turanga, which is considered tapu. Historically, Māori travelling along the river by canoe said a karakia when they passed this, the guardian of the Manawatū Gorge. It is said that even in the worst floods, Te Ahu a Turanga remains uncovered by water.