Horticulturist Tim Edmondson designs subterranean river system for Coombs block

In a suburb not known for its green canopy, the Dickersons have grown a climate-friendly oasis in just a few years, through the installation of a block water harvesting system.

Enlisting the expertise of horticulturalist Tim Edmondson, water runoff travels through trenches into a below-ground system lined with geotextiles, river rocks and sand, mimicking a natural river bed.

Mr Edmondson said the garden harvested almost all the water that fell on the property, compared with the 70 per cent a typical Canberra block would lose.

"The whole thing's at 400 millimetres below finish level and then it's another 300 to 400 millimetres deep, so tree roots can get in," he said.

"During the hottest part of the day when they're most needing water, they can access moisture for transpiration and continue growing."

He said the system helped control plants through limiting growth factors: temperature, light and moisture.

"As we move from low temperatures in winter into summer when the temperature picks up, suddenly the availability of moisture in the ground for plant growth drops," Mr Edmondson said.

"So you've got this huge spell in summer with good light, good temperature but no water.

"By making readily available water, you're pushing potential growth up into the top percentage rather than down in the bottom third."

The Dickersons approached Mr Edmondson after seeing the success of the water harvesting system he built at Orana Steiner School, following the 2004 bushfires.

Mr Edmondson received the The Australian Institute of Horticulture's horticulturist of the year award in 2010 for the project, with students planting trees which now cool the school yard.

He said 10 years since they planted, trees in the zoned harvesting system area were around one metre round, while drip-watered trees were still small enough to reach his hands around.

Since the success at Orana, water harvesting has been adopted at Watson and Downer micro-forests.

Mr Edmondson said while there were a few critical points in designing a home harvesting system like the Dickersons, it was not out of reach for someone with some soil hydrology know-how.

"You want to be precise, but it's not that complex," he said.

According to the Coombs case study, the benefit of the system is not just rapid garden growth but the natural cooling the thick foliage provides.

With new suburbs sprouting in the Mologolo Valley and fake lawn rolled out with increased frequently, Mr Edmondson said newer suburbs were at risk of becoming heat traps.

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Coombs homeowner Luke Dickerson said the cooling effect of their now six-metre trees was significant.

"We can certainly enjoy our deck in the shade of the tree in the late afternoon, whereas in the past we would've been roasted alive," he said.

Having incorporated solar-passive principals into the house, including double-glazed windows and facing the main windows north, Mr Dickerson said the inside temperature was regulated, too.

With an estimated additional 8000 people in Canberra each year, Mr Edmondson said learning from nature regarding energy production solutions was key.

"The more we can emulate that, then the better life we're going to have," he said.

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