State of the existing bridge
The Opawa River Bridge was designed in 1912 and opened in 1917. It is located on State Highway 1 between Picton and Blenheim on the northern edge of Blenheim. The bridge is a Heritage NZ Category 1 heritage place, indicating a place of outstanding significance. It is also a legacy structure, being the first of its kind (concrete bowstring) constructed in New Zealand.
The Opawa Bridge is 170m long and carries 9,800 vehicles per day, 9% of these being heavy vehicles. The bridge is located north of Blenheim across the Ōpaoa River, which forms a natural geographic boundary between the urban and the rural agricultural activities on the lower Wairau River Plain. As the bridge is on the northern urban fringe of Blenheim, it is an important gateway to Blenheim.
As part of our investigation, we identified two problems with the State Highway 1 Opawa Bridge and the traffic flow over it:
Problem one: The bridge is too narrow
At 5.49m wide between kerbs, the bridge does not meet today’s requirements, particularly for heavy commercial vehicles.
When large vehicles cross the bridge, they become a hazard, particularly if they cross the centre line. Many opposing vehicles must slow down or stop because they cannot pass, causing frequent delays and uncertain travel times.
Also, long traffic flows trail behind large freight trucks that travel along State Highway 1 heading to or departing from the interisland ferries. This adds to congestion on the bridge, making journey times unreliable.
Problem two: The bridge has poor structural resilience
The bridge’s structure would not be adequately able to withstand a significant earthquake. Its structure could be affected as a result of shaking or liquefaction that could cause the bridge piers, or the entire structure, to collapse. Also, the bridge is vulnerable to significant flooding events as floodwater could undermine the bridge’s central pier and cause partial bridge collapse.
Given the importance of the bridge to the transport network, we need to ensure we can keep this route open.
Why the road and bridge are strategically important
The Opawa Bridge is integral to the state highway network and the interisland ferries. It is also a vital freight link between the North and South Island via the Port of Picton, which is why the Government included investigating its replacement in the Accelerated Regional Roading Programme.
The bridge spans 170m and carries 9,800 vehicles/day. It serves many functions in the region today, though it has changed little over its 100-year life. It:
- is a protected heritage item under the Wairau / Awatere Resource Management Plan
- is listed as a category 1 historic place by Heritage New Zealand
- is an important local gateway to Blenheim
- carries a considerable amount of inter-regional traffic. This is because Marlborough is an export-focussed producer of primary products
- is a key cycle route with plans underway to extend an off-road cycle path that serves as a transport corridor for local access between Spring Creek and Blenheim. This is something the Marlborough District Council, the Transport Agency, and Government (through its urban cycleway fund) are investing in.
We appreciate that the road and bridge are integral to the larger Picton to Christchurch state highway network. Some people have expressed an interest in building a bypass route to the east. This is a separate issue. We need to replace the Opawa Bridge now in order to address its identified problems, particularly as the majority of its current users will continue to use it to access central Blenheim from the north.