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Wednesday, May 28, 2014

Kirstenbosch Botanical Garden's "Boomslang" Is Unleashed

The affectionately named “Boomslang” or Tree Canopy Walkway at Kirstenbosch National Botanical Garden is now open to the public and offers visitors an unusual and unique view from forest floor to treetops - yet another reason to visit the Garden. Below are some frequently asked questions that give an overview of this snake-like structure that runs through the treetops.  

Where is it? -  It's situated in the Arboretum (Enchanted Forest) which is nestled below the Protea Garden, above the Dell and above the Concert lawn.
How long is it? - It is 130m long and curves between the trees and through the branches.  It is roughly crescent-shaped and joins the forest floor in two different places within the arboretum.  Its highest point is 12m above the ground (approximately 3 stories).
Why was it built & What do you hope to achieve by it? -  We wanted to celebrate our Centenary (1913-2013) with a project that would be spectacular, unique and long-lasting.  This walkway, which had been on the backburner for many years, fit all the criteria and was a perfect way to mark the event in Kirstenbosch with something permanent.  It was built purely from bequest money which has been left to Kirstenbosch by 318839_num875358_600x600numerous donors, but predominantly Mary Mullins.  It is also a fantastic opportunity to take people into the treetops, a place with a unique ecology that is generally hard to get to.  From here people can experience the forest from high above the ground and also see birds and other animals that are generally hard to see otherwise.  One can experience tree dynamics - how the treetops move in the wind and how the crowns of the trees interact with one another.  The walkway then bursts through and above the canopy, giving you an impression of what it is like to be above the forest.  At this point, the walkway provides spectacular 360 degree vistas comprising Cape Town and the surrounding majestic mountain slopes.
What is it made of?  - It is made entirely of galvanized steel components which have been constructed offsite by Prokon Services's at their workshop in Blackheath.  Each component is 6m long and are painted with no less than 4 coats of the best quality paints available to prolong its life in the damp Kirstenbosch environment.  The handrails are made of a wood called Padauk, a sustainably harvested hardwood from West Africa; and decking consists of stained treated pine slats.  On site, the components were hoisted by a small crane, bolted together and mounted on top of long support columns, much like a giant mechano set.  A total of 19.6 tons of steel was used.  A total of of 5.3km of  8mm Ø round bar was used!
How long did it take? - Planning started seriously in late 2012.  Initial casting of the column foundations commenced in June 2013. Construction of the steel framework commenced offsite in August 2013, and the onsite construction commenced in November 2013.  Roughly a year since the first land survey was done.
What were the reasons for the delay in opening:  As with any first-time complex construction such as this, there were numerous unforeseen obstacles.  Fitting the giant pieces of the skeleton together proved more difficult than anticipated, especially within a building site as sensitive as the arboretum which is essentially a forest of tree trunks and branches.  Maneuvering a mobile crane within this space was a big challenge.   Both the painting and the carpentry were long and tedious jobs, all having to be conducted high above ground level.  The assembly and shaping of the magnificent handrails was an exceptionally complex and time-consuming process which had to match the curves and undulations of the walkway.  Each handrail consisted of about 15 slats of hard Padauk wood which had to be laminated together and molded and shaped to fit the steel railings.
Is there a cost to walk on it? - It's absolutely free to walk on.  A garden entry ticket is all that is required.
Opening/Closing times of the garden: September to March 08h00am -19h00pm, and from April to August 08h00-18h00 everyday
Is it Wheelchair accessible?:  Yes, it is.  The access to the arboretum, however, consists of steep paths and assistance is advisable.
Extra info about the arboretum:
Kirstenbosch's little-known arboretum is in the heart of the garden – nestled between famous parts of the garden, like the Protea garden, the Dell, Mathews Rockery and the Concert lawn, this relatively young part of the 100–year- old garden is where some of Southern Africa's remarkable tree flora are exhibited.
Kirstenbosch interpretation office Alice Notten, Kirstenbosch's first envisaged (in about 2005) some kind of elevated viewing deck, perhaps incorporating a walkway of some sort that would take visitors up into the tree canopies.  The Kirstenbosch Centenary rekindled interest in this project and so the boomslang was born in 2013.
The walkway encounters many interesting trees en route: some old 150 year old trees that predate the garden like Hard Pear - (Olinia ventosa) and Cape Saffron (Cassine peragua), the 100 year old Wild Banana (Strelitzia nicolai).  Other younger trees include White Stinkwood (Celtis africana), Cape Beech (Rapanea melanophloes), Coral Tree (Erythrina caffra), Myrtle Quince (Cryptocarya myrtifolia) and the Terblanz Beech from the protea family (Faurea macnaughtonii).
Technically speaking, this entire, elegantly designed bridge structure is a complex three dimensional truss, spanning 12 metres between columns.
Kirstenbosch is a very natural garden.  We were very aware that a large structure like this could become quite obtrusive if not carefully designed and built.  Utmost consideration was given to this by the architect with his objective to make the walkway as invisible in the landscape as possible.
Initially there were many critics, but all who have seen the bridge have given overwhelmingly positive reports.
Architect: Mark Thomas and Christopher Bisset of Mark Thomas Architects
Structural Engineers: Henry Fagan of Henry Fagan consulting engineers and Andrew Rich of Prokon Services.
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