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Jeremy Prentice >  |
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Guilfoyle’s Volcano Royal Botanic Gardens Melbourne, Australia Click images to enlarge |
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Since the late 1870s the RBG Melbourne has had a Volcano, not a geological one, but rather a water storage reservoir constructed in the form of a volcano cone, built by then Director William Guilfoyle. For some time there had been plans to reopen the Volcano to the public (it was left empty and locked away since the early 1980s) and finally in 2008 the project received the much needed funding and work commenced. With an overall planting theme of “Gardening for an Increasingly Dry Climate” (Melbourne’s projected future), the design is aimed at showcasing plants that perform well under such conditions. Not sounding very aquatic so far is it …? For a plan of the project, click here. |
 William Robert Guilfoyle |
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Fortunately, the central feature of the new design is the volcano cone itself (of course!) which holds around 1.3 million litres (343,424 gallons) of water – and bobbing around on the surface is a new addition to the Gardens: five round floating islands, planted up with aquatic and marginal plants. So, in mid 2008, the slopes of the volcano cone and surroundings were cleared so we could begin to ascertain whether it would still hold water and, if so, how much – you’ll note in the photos the cone itself is lined with bluestones, and all but the top twelve rows were part of the original 1880s construction. The Volcano was filled to test for leaks (with water pumped from our main Ornamental Lake), and over time it showed that, while the original construction was as good as ever, the top layers (laid in the 1970s) needed lifting and resealing. |
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It was then some time until the hard landscaping began, a period in which the design for the Volcano Islands (then known as Pods) changed dramatically, with thanks to a serendipitous connection made through our very own WGI Online Journal! The original concept had been to have islands below the water's surface and planted up with various Nymphaea hybrids. This would have been fairly straight forward except for the fact that we would be drawing water out of the Volcano for irrigation so the water level would then drop by as much as one metre (three feet) over the course of an evening and then topped up again). As you may well imagine, the engineering involved in keeping a submerged garden bed floating around 40cm (16”) below the surface and being able to adjust itself with the varying water column height became very cumbersome. It was about this time I was asked for some suggestions for the plant material (my first involvement with the project) and also happened to be reading Tamara Kilbane’s summary of her water gardening year in 2008 (WGI Online 4.1), in which she mentioned the use of some floating islands… fortuitous connection made! Tamara very willingly put me on to Bruce Kania’s company, Floating Islands International, and from there we made contact with Terry Wearmouth from New Zealand (the Asia-Pacific rep for FII). In the matter of a few weeks our logistical challenge of creating the original pod design had transformed into a prepackaged, lightweight, easy to install product with years of scientific support for its use in cleaning up water bodies AND providing an ornamental feature. A big thank you goes to Tamara for that connection, as it has made a huge difference for us. By mid October our islands were shipped over from New Zealand, prefabricated and ready to be bolted together, and within two days were installed and awaiting some choice grade H2O… |
| As these things run, it was a further three weeks before we could pump the water from our main lake system into the Volcano. During that time we installed our drip line reticulation system which draws from the bottom of the Volcano and disperses across the surfaces of all the islands, greatly enhancing the water treatment potential and helping prevent stratification within the water column. A real blessing was that over the weekend prior to pumping we had record rainfall of 50cm (20”) in 24 hours, so come planting Monday morning we had a good 50cm (20”) or so of water to wade around and plant into. |
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With many hands making light work, we had the islands planted within a day and securely bird-netted by the end of the next. By Wednesday the water was flowing in and the islands merrily drifted in the wind. In time we will remove the bird netting (three to six months), and see how the various plants have fared through the establishment phase. | |
| Ultimately the Volcano will be plumbed into and draw water from the greater water bodies of the Gardens – part of a grand scale water entrapment and reticulation scheme designed to harvest, store and treat more storm water from both within and around the Gardens, and a scheme which, pending funding, you will hear much more about – stay tuned for more developments on the Working Wetlands! |
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| Our species selection is below, listed from the largest to the smallest islands, with the species list reflecting planting from the outside in (i.e., shortest to tallest, edge to centre, at roughly 6 plants/m² [10.8 sq ft]). | ||
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Selleria radicans Chorizandra enodis Villarsia reniformis Alisma plantago-aquatica Baumea juncea |
Ranunculus inundatus Carex gaudichaudiana Philydrum lanuginosum Colocasia esculenta |
Isotoma fluviatilis Ficcinia nodosa Crinum pedunculatum |
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Triglochin striatum Isolepis marginata Eleocharis acuta Island 5 :: 12.8m² (138 sq ft) Marsilea drummondii Ranunculus amplus Meeboldiana scariosa Lythrum salicaria |
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Note 1: To cope with the changing water column height, and yet prevent the islands from bunching up on one side, we have used a pulley and leash system as roughly drawn here. The anchor cable has extra length to enable us to release it and draw the islands (via the "leash") to the edge for expected annual and ad hoc maintenance. |
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Note 2: We did an initial water test of the quality of our lake water when it was pumped in, which will be followed up in the future, to see how effective the treatment may be once the plants are established – (as taken from the surface, 11:50am 3/12/09):
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