In my Last blog 8 Rainwater harvesting methods for large and small-scale agriculture, I introduced Swales in the checklist. Each of those eight methods of rainwater harvesting works, you just have to find which will work best for your purposes and your land. In this Blog post, I’m going in-depth into Swales. I am going to take you knee deep in the trenches of swales. I will go over types of swales, how to build a swale and, when other methods may be better designed for your site than a swale.
Types of Swales
There will be three types of swales mentioned: On contour swale, water-transporting swales (or diversion ditches) and, soil conservation swales (a modified form of diversion ditch).
On Contour Swales
An On contour swale is a Permaculture rainwater harvesting design that keeps everything on a level. When the water is on a level than rainwater will all be absorbed evenly. If you do not make the swale contour than the water would flow to one side or the other, and preventing this flow is what makes the water become passive rather than destructive, as is the case with water draining en masse and quickly in one direction.
Water-transporting Swales (or diversion ditches)
Water transportation swales are designed to move water safely without causing erosion, as opposed to infiltrating it. Water transporting swales drop in one direction at the rate of 1 %(many times the drop is 1% but you would need to verify the drop percentage in your field). A 1% drop is sufficient to allow water to flow efficiently toward a storage point or drainage—at the same time, it is slow enough to allow sediment carried in the runoff to drop out of suspension and collect in the ditch bottom (in heavy rains a great deal of soil can be deposited).
Soil Conservation Swales (a modified form of diversion ditch)
9 Steps To Build A On Contour Swale
- The first step is to plan your swale site. You want your swale site to be slightly up-hill from your concerned area. Take some stakes and run a line between them for the length of your swale. The Swale must be dug on contour and, have the bottom to be level.
- Attach the line to the stakes. By doing this you can tell if the land is at the same elevation when using a line level water or laser level. Your swale may be diagonal across your slope, just stagger your swales so that runoff can’t get by.
- Pound in stakes once you’ve found the contour for your swale. A good swale width is wide enough for you to get in and dig.
- Dig a trench. All the loose dirt goes on the downhill side of the swale, heaped up into what is called a “berm”. Which holds back the rainwater that fills up the swale.
- Make sure the bottom of your trench is flat and level.
- Begin filling your swale with Gravel or to stimulate the natural compost like starting with leaves.
- Add the bulk material such as rotting wood.
- Add final materials such as straw.
- Dig more swales and plant your beams!
There are directions with images to follow if you go to Wiki How To Dig Swales
When to build a Swale
One reason to build a swale is to take a destructive path of rainwater that’s causing erosion. This will cause the rainwater to change the path so it can allocate the nutrients, silt, and organic matter. Swales are also perfect for those of us wanting to build no-dig garden beds, as digging the (swale) paths provides the necessary topsoil. Additionally, a swale is best used in reforestation of degraded, mostly-bare, arid or semi-arid hillsides, to direct water to trees. A great tool to use in calculating a swale is the calculator. (This is just a tool that gives an idea. please verify the calculations with Permaculture Consultant or your Design Manual.)
When Not to Swale.
Should I swale that? This Image is a great reference if you’re asking yourself if a swale is appropriate. The image breaks down by slope, soil, hydrology, management, ecosystems and available resources. The original image is from Ben Falk of Whole System Design, I modified the image to bring more details. A swale may not work in every location, each individual site, every climate or every situation. They are just one method of rainwater harvesting systems out of many. A swale without trees can possibly be even more damaging than a destructive flow of water. In my experience as a permaculturist and, as a farmer I have had experiences where a swale was the right design to use and a time where I had to tear it down and start over. If you have any doubts that a swale is appropriate a Permaculture Consultant or your Permaculture Design Manual.
Stay Tuned… Next Monday’s Blog Post will be on Rainwater Barrel Systems