Ramsay Bay, Hinchinbrook Island

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Key Facts

• Logistically complex boardwalk in a remote island National Park with a very narrow construction corridor minimizing the ecological footprint
• Materials and construction activities, including waste removal, could not introduce any potential contaminants to the site
• Robust/durable, prefabricated sections were taken in by helicopter and barge and installed by two Queensland Parks and Wildlife Services (QPWS) rangers

Project Data

Location: Ramsay Bay, Hinchinbrook Island, Qld

Year completed: 27th of May 2008

OVERVIEW

Hinchinbrook Island is renowned as one of the world’s most outstanding island National Parks. Small areas of the island have been opened for visitor access in limited numbers. The main access to Hinchinbrook Island is by water taxi from Cardwell to Missionary Bay. From there, visitors access Ramsay Bay and the Thorsborne Trail by way of the Ramsay Bay Boardwalk which takes visitors through mangroves to the sand spit at the back of the Ramsay Bay beach. This makes the Ramsay Bay boardwalk a key piece of infrastructure in the context of this very important National Park. 

This project comprised the replacement of the old worn out timber boardwalk with a new structure, and the installation of a new floating pontoon and gangway and supporting marine piles at the Missionary Bay end of the boardwalk. The main objective in replacing the boardwalk was to find a system that could tie in aesthetically with the natural environment, be constructed without causing any environmental damage, and outlast the previous boardwalk. The project budget was $450,000.

PLANNING AND MANAGEMENT

The biggest challenge in the construction of this project was the logistics of working in what is a relatively remote island National Park, while staying within a very narrow construction corridor so as to minimize the ecological footprint of the project. This required careful planning and careful consideration during the design.

In order to achieve this, most of the materials were pre-cut to size, with the design typically based on components that were able to be man-handled by two men. All of the materials for the project were then packaged into bundles suitable for lifting by helicopter (1500 kg maximum). They were then loaded onto a 30m barge at Port Hinchinbrook Marina, Cardwell, and shipped to Ramsay Bay where they were unloaded by helicopter onto the sand spit behind the mangroves at the back of the existing boardwalk. This exercise was completed in a 3 hour period.

The existing boardwalk was demolished progressively as the new boardwalk was built, with temporary gangway support in between. All waste materials and construction rubbish, including the entire old boardwalk had to be removed from the island. This was achieved by ferrying bundles to the barge by helicopter and then barging the waste and rubbish back to Cardwell via Port Hinchinbrook Marina.

SITE

This remote project site is located in the northeast corner of Hinchinbrook Island.  The site extends along a narrow corridor through well-established mangrove vegetation, from a water taxi landing point in a Missionary Bay tributary to the sand spit at the back of the Ramsay Bay beach.  As much of the walkway is located above very soft mangrove mud, the original boardwalk was used where possible to limit activities in the mud.

As the site is located within an important National Park, strict controls were implemented to minimise any disruption to the surrounding environment.  This included specifying materials and construction activities which did not introduce any potential contaminants.  All waste material also had to be carefully removed from the site.

The remote nature of the site, and requirement to minimise any environmental impacts, meant there was no opportunity to utilise construction machinery other than compact hand held equipment.  This meant that all material needed to be prefabricated in sections which could be physically manoeuvred and installed by two Queensland Parks and Wildlife Services (QPWS) rangers.

DESIGN

The replacement boardwalk required a solution that was robust and durable, yet easy to build in a challenging remote environment. The final product employs stainless steel tube piles, driven by a hand held pneumatic hammer using the existing walkway as a work platform, with a hardwood timber boardwalk over.

The stainless steel and timber boardwalk merges well with the aluminium and timber gangway to the new floating pontoon, and allowed enough flexibility in construction that the route could be altered to avoid any removal of mangroves, or to cater for tolerance in the positioning of the marine piles supporting the floating pontoon. The Hinchinbrook Boardwalk has met all of the project requirements, and the system is set to be rolled out across more of FNQ’s national parks, and possibly right across Queensland.

MATERIALS

Material selection was driven by the site and construction constraints.  Materials required a durability sufficient to withstand the harsh marine environment.  This was particularly important as the remoteness of the site meant that regular inspection and maintenance would not occur.  Materials also needed to be light so that they could be safely manoeuvred and installed by two QPWS rangers without the aid of any machinery.  This also meant that the piles, which extend up to 10 m in length, would each need to incorporate numerous splice connections.

The final design employs grade 316 stainless steel piled foundations and fixtures, and a hardwood timber boardwalk structure.  Stainless steel was selected because of its resistance to the high chloride marine and mangrove environment.  Splice connections could also be welded on site during installation.  Employing a timber boardwalk with an appropriate durability grade also allowed elements to be easily adjusted on site.  This introduced the necessary construction tolerance for this project where it was challenging to design, document and prefabricate to exact tolerances. 

Timber is a renewable resource which complements the surrounding mangrove environment.  Selecting timber for the boardwalk therefore allowed a sustainable material solution to be achieved, which was appropriate for this infrastructure which is located in a National Park.

OWNERS/USERS STATEMENT

“The Hinchinbrook Boardwalk is a unique piece of infrastructure to Hinchinbrook Island National Park as it provides the only opportunity to access this otherwise unreachable mangrove.  It allows users to sustainably observe and research the mangrove ecosystem, including the bird and marine wildlife.

The boardwalk is also located at the northern end of the Thorsborne Trail hiking track, making the eastern side of Hinchinbrook Island much more accessible.”

PROJECT TEAM

Base building architect/ designer: Arup & DNPRSR

Structural engineer: Arup

Services engineer: (mechanical electrical, hydraulic, fire): Arup

Project manager: DNPRSR

Other consultants: The Jetty Specialist – designer and supplier of jetty pontoon, gangway and marine piles

Builder: DNPRSR

Other main contractors: The Jetty Specialist – designer and supplier of jetty pontoon and marine piles