Aerial view at sunrise of the completed He Ara Kotahi cycle and walkway bridge over the Manawatu River, looking NE towards Palmerston North CBD and suburbs.
Included as part of the nine-kilometre long He Ara Kotahi (1) cycleway and pathway project, is a new bridge over the Manawatu River. By Richard Silcock.
South-west of Palmerston North city, this distinctive 192-metre long, steel and concrete bridge and cycle/pathway provides access to the southern side of the river and is a direct route to/from the Linton Military Camp, Massey University, the Crown Research Institute and local residential housing.
The bridge and cycle/pathway concept design was initially provided by WSP Opus, however, Rotorua based Concrete Structures (NZ) civil division, which provided the winning bridge construction tender, opted for an
alternative structure designed by Holmes Consulting that resembles a fallen karaka tree lying across the river.
An unusual feature of this four-span, 4.5-metre-wide bridge is the nine-metre-wide viewing bulge in the centre. This provides a vantage point from both sides of the bridge for pedestrians to view the river 10 metres below, the surrounding countryside and views of the Tararua Ranges.
The contract was awarded in October 2017, construction began last year and was completed in May this year.
Civil manager for Concrete Structures, John Pohlen, says the $11 million, three-pier, single column bridge was constructed over 11 months, however the entire project, including the pathways and hard landscaping took 16 months.
“Piling work for the bridge was carried out by Richardson Drilling, our sub-contractors, to a depth of 22.5 metres into the riverbed and compact gravels beneath the water table,” says John.
“Eighty percent of the bridge is constructed of steel, including the high grade stainless steel safety rails and curved, painted rib features on either side that represent the curvature of a tree trunk. Two hundred and thirty tonnes of grade-350 weathering steel was used for the fabricated bridge beams which were manufactured by Eastbridge in Napier and trucked to the site.
“A temporary river-shingle causeway was created by dozers and excavators to allow two 100-tonne crawler cranes to lift the bridge beams into position, which were then bolted together using around 1200 bolts.
“The 130 cubic metres of precast concrete for the decking came from our Hastings facility where we have a manufacturing plant.
“Laying the concrete deck took us a day to pour and we worked from the centre of the bridge out to each end simultaneously. It was then cured with water pumped from the river over a period of seven days, with our teams working 24-hour shifts,” says John.
Another feature of the bridge is the Maori inspired and designed embedded patterns on the deck. These signify the bark of the tree, the koru patterns – the people, and the pods – the karaka berries. These patterns were created using a coating of calcium bauxite and are black and burnt orange in colour.
To minimise glare on sunny days the concrete on the northern side of the bridge has also been treated with a black oxide additive.
The 100-tonne concrete abutments did not require piles, but are embedded into an engineered fill overlaying the natural gravel.
John says the biggest challenge was the environmental concerns of working over and above the swirling river which is prone to rapid increases in both flow and water-level and in a matter of a few hours can rise several metres.
“We were able to get hourly reports from the regional council of these increases, particularly following heavy rainfall in the headwaters,” he says. “This allowed us to take the necessary safety precautions and move our people and machinery away.”
Suspended beneath the deck and hidden from view behind the steel beam facades are utility ducts which carry power, telephone and broadband cabling.
The main earthworks, services and scour protection rockery at either end of the bridge were carried out by Stringfellows Civil Contracting of Palmerston North. The hard landscaping, concrete walls and specific design features were completed by Concrete Structures and sub-contractors provided the lawn areas, pathways, gardens and LED lighting.
Over 30 people were involved in the construction, with all of the sub-contractors Palmerston North based.
There are four other shorter bridges along the cycle/pathway, one of which, the Kahuterawa Bridge, is a 45-metre long swing bridge.
Following a powhiri by local Rangitane iwi, the He Ara Kotahi Bridge and pathway was officially opened by the Associate Minister for Transport, Julie-Anne Genter and the Mayor of Palmerston North, Grant Smith, on June 7 at a ceremony that involved the cutting of an iconic flax harakehe (woven flax ribbon) made by iwi to signify their connection with the river and the historical significance of native karaka, totara and flax that once grew in abundance around the area.(2)
The Minister said that the project was a part of the Government’s programme to foster people to walk and cycle around and beyond their cities and for it to be a part of their transport options.
The Mayor paid tribute to all those involved in the project and said: “The bridge will provide a safe, convenient and scenic route for bikers and walkers that will connect our green and blue spaces, our heritage areas and embrace the river as a feature of our city.”
Following the opening, a group of school children from a nearby school, and Army recruits on a training run, were the first to use the bridge and within days of the bridge opening 12,213 people had walked over it.
Funding ($18.4 million) for the entire project was provided by NZTA (from the urban cycleways programme and the Land Transport fund), Palmerston North City Council and PowerCo.
ALL PHOTOS SUPPLIED BY CONCRETE SOLUTIONS (NZ) LTD.
(1) He Ara Kotahi translates as ‘a pathway that brings people together’.
(2) Up until the late 1880s there were some 20 Maori pa sites along the Manawatu River, which was a major source of freshwater and food and provided canoe access to the upper reaches. Flax for rope making and export was centred on parts of the Manawatu and Horowhenua between the 1860s and 1920s with large swampy areas devoted to cultivation. (Refer Contractor July 2019 – A reminder of days past.)