/ 6 February 2014

A Tree-canopy walkway with a twist

Boomslang: The Walkway at  Kirstenbosch takes a sinuous route above the trees.
Boomslang: The Walkway at Kirstenbosch takes a sinuous route above the trees.


Although tree-canopy walkways are nothing new for botanical gardens, Mark Thomas and Henry Fagan's collaborative project has a uniquely South African twist. 

They've designed and built a 130m-long structure that mimics the sinuous skeletal frame of a boomslang and sits 11.5m above an indigenous arboretum in the Kirstenbosch National Botanical Gardens in Cape Town. 

Thomas, the architect responsible for the design, has been in the business for 28 years and has worked with great success both in South Africa and abroad. His interest in structural design is evident when he speaks of his love for creating "structural sculptures", works that fall well outside the traditional oeuvre of an architect. His work has been featured at Afrika Burn and he cites this nonconformist approach to design as imperative to the success of the "boomslang" tree-canopy walkway.

Thomas and structural engineer Fagan are quick to point out that this walkway is more than just a traditional boardwalk structure. Like the snake, it winds and dips. 

"It is, in essence, a highly sophisticated bridge," says Thomas. 

Structurally, the walkway functions as a unit. Every part is multifunctional in that it contributes both visually to its serpentine quality and structurally to the stability of the walkway.

Fagan attributes his ability to make the complex skeletal design a reality in part to the unique professional relationship the pair have built. Fagan's 40-year career has been recognised with a multitude of national and international awards. His portfolio includes the innovative swing bridge at the V&A Waterfront as well as the Cape Town Stadium. The creative partnership between the two stretches over 10 years and both parties agree that their work process for this project was unconventionally enmeshed.

"Normally an architect will come up with an idea and the engineer will have the job of making it concrete," Fagan says with a smile, mischievously adding that "architects aren't normally terribly practical". In this case, both parties contributed to the evolution of ideas from the outset.

Building a structure like this around the 430 trees in the arboretum meant that the environment dictated the nature of the structure in every respect. 

The pair agree that the sinuous footpaths in that part of the park naturally gave rise to the serpentine shape of the walkway. Even the decision to use steel was based on a desire to interfere as little as possible with the environment as steel structures require fewer support columns. 

Every tree in the arboretum was surveyed and drawn on a three-dimensional map indicating height and size of trunk so that Thomas could choose a path that least interferes with their future growth but ensures visitors get the best views. 

When asked what their proudest achievements in their respective illustrious careers are, both men answer that the "boomslang" walkway project ranks highest. Thomas adds: "This is a great honour. Kirstenbosch belongs to all of us. We simply can't mess this up."

The walkway is expected to open in March. Visit www. sanbi.org/gardens/kirstenbosch or call 021 799 8783 for information.