Tackling Urban Water Runoff in a Sydney Suburb
Swales aren’t often found in backyards, and water systems are the backbone of a permaculture design, so the Permaculture Sydney North Gardening Team jumped at the opportunity to take on a swale project in a lush Turramurra backyard, just around the corner from the APC9 venue.
Turramurra has the highest rainfall in Sydney with averages of around 1300mm a year, and issues such as flooding and erosion are common in lower areas of the catchments. The traditional approach to urban storm water has been to treat it as a problem, and to our detriment our cities have largely been designed to collect and dispose of rainfall as quickly as possible. City watercourses are being battered by dramatic and damaging flow patterns that would not have existed before hard surfaces and drainage systems were put in place. We are also wasting a hell of a lot of water.
Local government often approaches the problem with end-of-pipe solutions such as preserving riparian vegetation and stabilising channels with weirs, logs or concrete ‘realignments’. Water sensitive urban design is starting to be considered by councils, but this usually focuses on public or industrial areas, and will often prescribe expensive engineering structures that are out of reach of most home owners.
The Permaculture approach is tackle the problem at its source by slowing the water down and putting it to good use, and keeping it on site as much as possible. Swales are a low cost way to recharge aquifers, grow food forests that are largely self watering, reduce erosion and water pollution, and restore downstream aquatic ecosystems to natural flow patterns.
The Turramurra project was a great example of what can be achieved with a group of permie enthusiasts and a few basic bits of equipment. The site had a gently sloping gradient and potential water inputs from a rainwater tank overflow and laundry greywater. The swales will enable the water and nutrients to be passively spread across the yard on contour to water the food forest, rather than straight down the hill and off the site.
The swales were pegged out on contour using high and low tech methods (for practice), including an A-frame with a spirit level on the cross bar, a long tube filled with water, and a dumpee level and staff.
The backyard is inaccessible to machinery, so the swales were dug by hand. As luck would have it, there was quite a bit of rain in the lead up to the big day, and the rich sandy loam was easy to shovel. It took 12 people around 3 hours to finish two 16m swales with troughs 20 cm deep and 1 metre wide. We put a 2m wide level sill in each swale to protect the banks from bursting under big downpours.
Luck was on our side again as we finished compacting the sills – a massive thunder storm erupted and the swales filled up almost to spilling level while we had lunch. Normally a big rain would be a disaster for a gardening team event – but this time it was brilliant because we saw once and for all that the swales were perfectly level. We also saw the massive amount of water that could be captured in swales – and this was without any input from the overflow or greywater. While some of the rain would have fallen directly into the trough, much of this volume would have been surface flows that would ordinarily have trickled over the compacted lawn and off the site.
We finished off the swale banks with lashings of green manure seeds, three bales of lucerne and young acacias spaced 1.5m apart. The acacias are nurse trees to fertilise and shelter the fruit trees as they are planted in to the system.
This project was completed in December 2008. These photos were taken on the day. I will be loading more photos of the system as it develops. For more information on this project or other Permaculture North activities, check out our website www.permaculturenorth.org.au, or contact the Gardening Team on: garden (at) permaculturenorth.org.au .