Harvesting rainwater to green our streets

An Alice Springs friend visiting Adelaide recently sent this photo which she captioned “Gutter dreaming” – her regret being the lost opportunities to green our town’s public spaces by harvesting rainwater.
This is relevant to the debate in Town Council this week about the pros and cons of concreting our street infrastructure, which has developed apace in recent years. Mayor Damien Ryan expressed his unhappiness at the prospect of another concrete roundabout, this time likely to be at the intersection of Undoolya Road and Sturt Terrace (see separate story). Council’s Director of Technical Services, Greg Buxton, defended the approach on the basis of deterioration to road surfaces caused by watering plantings.
But it doesn’t have to be like that, explains Mike Gillam, who on his commercial property in Hele Crescent uses an approved water-harvesting and retention system to cultivate a desert garden.
All rainfall onto the site, runoff from a nearby hill, shedding off buildings and discharging from rainwater tank overflows is retained on the site. In contrast conventional drainage systems discharge rainwater into gutters and drains on the street. With the exception of citrus trees, Mr Gillam’s flourishing gardens require no town water irrigation and that means no issues with salt. Most of the garden is  eight to 10 years old and it continues to grow, perhaps not as quickly as some gardens, on rain water alone. There were some failures in the early years and some trees that were proving too water-dependent were allowed to die.
The Alice Springs News Online asked Mr Gillam to explain what is going on in the Adelaide photo:-
 
Adelaide, and Salisbury Council in particular, is leading the way (Sydney is catching up). In some municipalities storm-water capture is not only watering the verges but with filtration and cleaning it is supplementing general water supply. In the photo we can see that runoff from the road, when it occurs, is collecting in the depression at ground level, giving the plantings a good soaking before any excess goes into an overflow, some kind of riser into the stormwater system. Some systems also use raised mesh grills to capture troublesome material like bark and large leaves and these would be periodically cleaned. It’s interesting to see that not only the significant depression in the foreground has been planted, but the tiny island in the background too, an indication of this enlightened council’s commitment to greening its streets.
The plantings would have been chosen carefully, hardy and decorative species that do not create a lot of leaf litter. This looks like a sedge – Lomandra species are often used in these situations. These favoured ‘architectural’ plants are associated with moist environments and in Central Australia there is a vast difference between a shady creek bank and an exposed roundabout surrounded by scorching concrete and bitumen.
When I planted a Lomandra on our block about eight years ago, I prepared the site by stacking several layers of old car tyres that had been split to create underground water-holding cells. The plant continues to benefit long after a rainfall event because its root system has tapped into underground lenses of water/moisture retained by the rubber tyres. Because it was an experimental planting, I chose an exposed position in full sun to see what would happen – the plant remains healthy but I would expect a more impressive plant with bigger leaves in a shadier environment. Without access to subsurface water my Lomandra would have perished in the first dry year.
In Alice Springs it may be necessary to water plants in the establishment phase but with certain plants, for example Sennas, planted at the right time and with careful preparation of soils you could get away with minimal watering and water harvesting devices could do the rest.
There are all sorts of materials and techniques available that allow retention of sub-surface moisture and myriad built surfaces in our town centre could be activated to harvest rainfall. Desert roundabouts, verges and public gardens are a reflection of our civic identity, pride and ingenuity or lack thereof – these public places should be seen as an opportunity to innovate. We would need a strategy to cope with drought years, and that may require more innovation. For instance we could extend/re-imagine the principle of temporary above ground watering systems, like the barrels that can be seen along the arterial roads in Alice [looked after by a contractor to the NT Government].
Roundabouts are ideally suited to rainwater harvesting: they can be landscaped as shallow bowls with runoff from the road draining into them through slots in the perimeter. Raised beds or terraces in the centre would improve drainage and create a variety of moisture zones to improve growing conditions and expand the options for desert plantings.
We could learn a great deal from the Adelaide experience while changing the mix of plants to better suit local conditions. There’s definitely a lesson for us in this photo and by striving for excellence in the design of our public spaces Alice Springs could quickly become the innovative desert town it wants to be, attracting attention around the world.