Water Harvesting and Storage
by Adrian Buckley, Permaculture Designer, B. of Community Design, Calgary, Canada
Good soil is nothing without water! Fortunately, there are simple and inexpensive methods available to us for capturing and storing rain water to meet our irrigation needs. It all starts from a firm understanding of how water flows on your property and designing to make the most use of it.
Water, Access, Structures
Permaculture design always starts with water, then access ways are planned, and finally, structures. So let’s talk about water first.
The best place to store water is in the soil. I have had conversations with several people about the role that beavers used to play in the landscape here in the Eastern Foothills region of Alberta (and wherever beavers live). Beavers have a peculiar behaviour; they build microdams used as their residence. When they build a dam on a watercourse, the dam provides an important function: it changes over-land water flow into under-land water flow. As industrial agriculture spread throughout Alberta, the habitat for the beaver was also wiped out. According to these reports, the landscape began to dry out in many places during this same period.
Beavers’ dams function to encourage stream and river water to seep into the ground around their dams, hydrating the ground and creating springlines in downhill regions. Once in the soil, water takes weeks, months, and even years to travel distances that would only takes days if flowing over the land. Plus, this water is fully protected from the Sun’s rays and evaporative forces. In dry climates, this means that water can be available to our plants during extended dry periods and drought. Watch the famous Greening The Desert project, managed by the Permaculture Research Institute for a really good example.
If we want to keep water at plants’ roots, we must capture water during rain events and store it in the soil, so that it stays on our site longer. While methods of doing so are many, an easy and commonly applied strategy is the swale.
Swales follow a similar pattern to the beaver: they change over-land water flow into under-land water flow. A swale is a level trench on contour, meaning that the bottom of the swale is exactly the same altitude all along its length. This is important because the function of the swale is to pacify and hold water, and not to transport water. Water enters the swale from over-land water during a rain event, over surfaces such as hard-packed ground, driveways, and from your roof’s downspout (roofs make excellent catchment surfaces). As it rains, the swale backfills and begins to seep into the soil.
Water is held long enough in the swale for it to seep into the soil below.
Soil excavated from the trench is mounded on the downhill side of the swale (when working with flat land, the soil can be mounded on both sides of the swale), which saves you from needing to buy soil as these mounds serve as your raised beds and planting surfaces. Soil quality is never much of a problem in the long run because your permaculture system will build the soil over time. You can speed this process up by employing a sheet mulch. The inside of the swale is filled with pea gravel and topped off with crushed gravel or some other kind of inexpensive pavement.
Your swales also function as your access paths. You walk on the gravel surface, compacting it into a stable path, and pick your fruit and vegetables. In permaculture design, function is more important than form. The materials and work invested in building the swale pays off both as a water harvesting and storage feature, but also as a pathway, saving you both resources and space.
Swales are not the only way of passively hydrating a landscape. Other effective methods exist, including keyline design. More on this in a future article!
- Keyline Swales – a Geoff Lawton/Darren Doherty Hybrid
- Use of Small Swales – a Case Study
- Life at Zaytuna – Swales in Landscape
- Tackling Urban Water Runoff in a Sydney Suburb