“I got my first job at McDonalds at 14 years and nine months, and worked my way through uni thanks to the late night opening hours. Then once I had my Environmental Management degree I found a job digging holes building prison fences.” As odd as that sounds, doing time on the shovel was in hindsight a great move. “Among other things I learnt how to handle tools, drive machinery, read drawings & plans and pour concrete.”
But two of his former fellow students were now working for Natural Area and they wore him down with the argument that he could be using his brain doing what he’d actually studied. They won him over and it’s been eleven years since he joined them. Of course the team back then was smaller: now Dave as Operations Business Unit Manager has three regions to cover. In peak season this means a total crew in the field of around fifty trained staff. And while in the early days the service delivery centred on conservation planting and weed & erosion control, business has grown on several fronts.
Natural Area now offers a consultancy where the urban sprawl meets and interfaces with bushland, dealing with fire fuel load and other assessments. They still deliver projects involving weed control and revegetation, but now alongside environmental construction (creek faces, embankments, rock revetments) and on a larger scale. To get a sense: “We’re now putting in a million plants a year, which we produce in house.” As large as volumes like this can be, sometimes it’s the fun and games thrown up by a project that, once mastered, prove the most impressive. Like the challenges posed by one particular river promontory.
Across the Swan River from Perth’s iconic Kings Park, the south bank forms Heathcote Point. A heritage-listed former hospital is the focus of a cultural precinct, sitting high above the river. And until recently, there was a problem – erosion. Foot traffic from the river’s edge to the top of the bluff together with storm action and run off – all were having a negative impact. At some point it was likely that the footpath that wends it’s way around the point would start to fall in. It was Dave and his team’s task to take the coastal engineering brief and put it in place.
The project took over three months, and three weeks of that alone was spent placing the boulders to create a revetment. “Using a 14 tonne excavator with a specially modified rock grab we placed the boulders, (each one tested at the quarry for density and weight), to a laser level reference.” Along with meeting that reference point, each boulder was nested in via three points of contact and a sloping gradient was created on the revetment face facing the river.
“The next challenge was to hold up the rest of the embankment between the revetment and the footpath at the uppermost level. We needed to shape the hillside and reduce the gradient.”
The solution was to form terraces with super-treated pine along newly formed contours, held by 2.5 metre posts. “The posts wouldn’t be set in concrete, which is why they were to be positioned so deep; digging the hole was initially a problem. We tried a bobcat with a bucket on an extendable boom, using the bucket as a pile driver… but it didn’t work.” To appreciate why these particular holes were an issue, picture where they were being dug – on a serious gradient with no easy access. And then Jarred Pedro, the project manager came up with a nifty idea. “Pedro grew up on a farm down south and he’s really practical. He went off to a metal fabricator with some drawing he’d done at home of an extremely heavy steel cap. We then attached it to the rock breaking attachment on the existing excavator on site.” The result was an extreme-off-road pile driver. In other words, the excavator had to carve it’s own path along, and just above, the newly created revetment to position itself to drive in over 100 of the mega posts. “We progressively destroyed the caps but had two fabricated each time so we could keep pile driving.”
From this point on things were relatively straight-forward. With the posts in, the retainers were bolted into place. The soil was then levelled and compacted within the super-treated pine retaining walls. The coir mesh matting was laid and firmly stretched, bio-starch-pinned, and the edges tucked in. In went the mix of local plant species: “We kept them low to retain the views out over the river, including species like Banksia sessillis which is a food source for the endangered Carnaby’s black cockatoo.”
Conquering the trickier aspects of this particular project only added to the sense of a job well done. And there are a few other factors which have added to the glow. “The upper footpath had been surveyed every four metres to ensure there was no sinking, with inspections made every few weeks during construction.” With careful management of works on the embankment, there was no movement. Tick.
But the main achievement has been the effective addressing of erosion. The river may throw itself into a force during storms, people may run up and down the face of the bank, the wind may blow and the rain run-off course over and through the newly treated embankment planting, but the environmental engineering treatment Natural Area have put in place is holding its own.
Fixing the erosion issues at this particular point on the Swan River in WA was a complicated process. Here you can see the beginnings of the rock revetment going in along the excavated beach. Note too the serious gradient of the bluff immediately above: it was also given the erosion control treatment.
A practical solution was found for driving in the supports for the retaining walls, but getting access for the excavator with its one-of-a-kind pile-driver attachment wasn’t necessarily a breeze.
Here you can see hints – spot the post tops – of the engineering that’s gone in to modify and hold the new slope.
This is what it looked like freshly planted, and below, one year later just after a storm.