“Swales can change a dry garden into a lush oasis that doesn’t rely on your sweat to moisten it” Jenny Allen.
Do you live in a dry place? Do you need any more incentive to start planning for swales?
Swales are long, shallow ditches designed to trap water and allow it to soak into the soil, recharging it with moisture. They run along the contour of the land, usually on sloping ground where water would otherwise rush off, leaving the land dry and eroded. A series of swales can be positioned down a slope to distribute the water evenly.
Inside the swale can be gravel, grass, damp loving reeds and rushes or groundcovers holding the soil into place. Around them are the trees, an essential part of the swale system. They prevent erosion and keep the level of the water table in check, preventing the salt below from rising to the surface.
In time, trees will shade the swale and add leaf matter to it, improving its water holding capacity. And this is the other great thing about swales, not only are they virtually maintenance-free, but they improve with age. A mature swale system can reduce the water run-off by up to 85 per cent compared to bare soil, really drought proofing your land.
Sometimes, however, a swale can come to the rescue of a landscape with too much water… in the wrong place. That was the case on Anne and Greg’s suburban block in Canberra. For years, they put up with a sloping front yard which channelled water and dirt under their home every time it rained. “Not much was growing here” recalls Anne “Even the grass struggled to hang on”.
In 2006, some design work by Jennie Curtis led to a transformation resulting in a welcoming front yard with no more water run off problems. Instead, there is now a thriving native garden cut by a curvy swale, filled with attractive pebbles. “Jennie drew up plans for us” says Greg “then once we were all happy with it, a team of landscapers took less than a week to build it”.
Planning is key to successful swales as they have to be positioned in the right spot, along the contour and their beds need to be prepared to absorb water. If a clay soil is water repellent from having been dry too long, adding gypsum and organic matter will improve it.
More recently, volunteers from PermaBlitz ACT helped to dig and shape two small swales in the food forest at Roogulli. Careful planning of levels is the key to making the swales work well. Much discussion was had by the volunteers about whether the swale design would work, since the swales were much smaller than the textbook versions. The perfect test came with the first serious rain. Even though these swales are only about 100mm deep and less that 1m wide, they bring the water right across the food forest.
Another interesting feature of swales is that they can filter the water as they absorb it. Water can be directed to run into swales from water tanks, gutters, grey water systems or even roads and car parks. Swales use soil, microorganisms and plant matter to cleanse the water of pollutants, preventing them from contaminating the landscape. Many cities incorporate swales in their street design for filtering purposes.
So whether you are a farmer, a city dweller or a city planner, swales may just be what you need to make the most of the water you have, create an attractive landscape and clean the water in the process.