Kalbarri Skywalk

New Perspectives on an Ancient Place

Visitors to Western Australia’s Murchison River Gorge are able to connect with the landscape like never before, thanks to two cantilevered walkways fabricated from REDCOR^® weathering steel.

Overlooking the impressive Murchison River Gorge near Kalbarri, two new steel skywalks enable visitors to completely immerse themselves in the ancient landscape.

This new tourist attraction in Western Australia’s mid-west combines equal parts function and sculpture, and offers new vantage points from which to admire the sandstone river valley below.

About 600 kilometres north of Perth, the national park sits within Nanda country, and input from the local indigenous salt-water people played an important part in the design and delivery of this project. A new sign at the entrance proclaims the Nanda words for ‘sky’ and ‘to walk’: kaju yatka.

Accessible to all ages and abilities, the skywalk is the central showcase within a $13.2 million redevelopment at the National Park. In the 2019/20 financial year, the Kalbarri National Park attracted more than 200,000 visitors, a marked increase over the previous year.

Back in 2015, the Department of Biodiversity, Conservation and Attractions (DBCA) ‘Parks and Wildlife’ engaged Geraldton-based Eastman Poletti Sherwood Architects as principal designer for the planned tourism upgrade.

DBCA project manager Rory Chapple recalls meeting with architect Craig Poletti at the highest point on the cliff – the site of a previous lookout and where Skywalk 2 sits now – to envision a new attraction.

“Craig and I stood on the cliff edge together, mulling over how things might look there, and he was sketching,” Chapple says. “We were having issues with rough roads in the park – which required a 4WD to get anywhere – so we wanted to create a drawcard that would be seen as a tangible benefit in the national park.

From those initial discussions, client and architect determined that the innovative structures would be created using weathering steel, in keeping with the park’s management plan, which states: “The geology and landforms of the park provide a dramatic and scenic landscape. Any proposed recreation site, infrastructure or access developments in the park will require careful planning to minimise visual impacts since any visual impacts to the landscape become obvious in the predominantly low vegetation.”

During the design phase, BlueScope’s REDCOR^® weathering steel in grade WR350LOB was chosen for several key reasons. These included the remote location of the site, and a desire to minimise maintenance over its projected 100-year lifespan.

The brief called for a structure with a 100-year design life that would require low ongoing maintenance, and that blended into the surrounding natural landscape at the top of the gorge.

High-strength weathering steel from BlueScope – REDCOR^® – was deemed a perfect choice for the cantilevered box beams and decking outrigger joist/baluster elements, because its naturally forming patina provides long-term corrosion protection without additional protective coatings. In addition, the material’s rich colour mirrored the surrounding natural rock gorge face.

The massive box beams required extensive steel detailing because their tapered shape gives rise to varying dimensions and details along their length. “To prevent confusion between the connection requirements, each box beam splice was detailed in plan and section,” Poletti explains. “Typically, end-plate thicknesses and stiffeners were standardised across both Skywalk 1 and Skywalk 2. Additionally, only two bolt sizes were used in the main box beam connections.”

Steel was also an obvious choice to meet the extreme wind loadings for the site, which are equivalent to Region D cyclonic. The use of structural steel enabled the Skywalk to be prefabricated in segments in Perth and transported to site to be craned into place, where, as an environmentally considered building design, it blends harmoniously with the surrounding landscape.

The national park is located on an undulating sandplain plateau of white and yellow quartz sands with patchy outcrops of laterite, which contributes a reddish tinge to the iron and aluminium-rich soil. This particular plateau was uplifted during the Tertiary period – about 50 million years ago – and, since then, the Murchison River has carved the spectacular gorge, exposing Tumblagooda Sandstone along its length.

During installation, the largest crane used on the site – at 350 tonnes – was transported to site from Perth, along with smaller cranes that were brought in from Geraldton.

Part of its appeal is the fact that the spectacular skywalks are unique in Australia.

“One critical aspect was selecting connection elements that were compatible with the weathering steel,” says Paul Terpkos, engineer. “High-strength friction grip (HSFG) bolts to the main box beam splices were selected based on their similar chemical composition to the weathering steel plate - preventing the potential for galvanic corrosion - and closer bolt spacings were documented to prevent crevices forming between the connected plates.”

Since the new facilities opened, the response from visitors has been highly favourable, Chapple says. “It’s been really amazing. We’ve had a lot of people - in fact double the number of visitors over the previous 12 month period. And while COVID-19 has prevented international and interstate visitors, our local visitor numbers are up,” according to Chapple.

Chapple says that visitors are also moved by smaller elements within the precinct. “The link between architecture and landscape - the steel and the rock – creates a very earthy feeling for the site, and it’s obvious that the design team worked hard to integrate the architecture and the landscape,” Chapple explains.

The result is a place that makes it easy for visitors to feel at one with this ancient landscape, and that’s exactly what client and architect imagined when they stood on the cliff edge back in 2015.