Protect your land from erosion with backyard swale construction and a system of swales, ditches, and catchment systems, such as ponds, to better hydrate your soil.
When water flows across your acreage, its speed and route — especially during heavy rains — affects erosion of sloped surfaces, the water quality of nearby ponds, creeks, and streams, and, ultimately, your soil moisture levels. Swales, also called contour bunds, are ditches that catch and slowly filtrate water through your soil as compared to drainage ditches, which quickly move water from your property. Swales aren’t new or overly complicated, and today a growing number of farmers, homesteaders, and ranchers in regions with heavy rains, long droughts, and dropping aquifers are taking advantage of this land management technique.
Step 1: Outline Your Swale with an A-Frame
The humble A-frame is the most important tool for building or maintaining swales, because it indicates whether your swale is on contour, or level, with the slope of your land. The size of your A-frame will depend on the length of your swale, but 5-foot boards and 8-foot boards will provide a length of run without adding too much weight.
To assemble an A-frame, find two 1-by-4s or 2-by-4s, a couple scrap pieces of lumber for the horizontals, two bubble levels, and a plumb bob, if you wish. Drill and bolt the boards together to form the legs of your triangle and then attach the horizontals far enough down the legs to be comfortable for your height and the conditions that you’re working in. Measure the length of legs beneath the horizontals and make sure that they are equal. Finally, attach the levels to the horizontals. If you are adding a plumb bob, attach the string to the tip of the A so that it hangs down the center of the frame on level ground.
Once you have your A-frame, simply stand it in the location where you would like for your swale to end, find contour between the two points, and then mark points outside of the legs with flags. Move the A-frame so that the flag is outside of the leg, find a contour and mark the next point. You’ll continue in this fashion until you’ve marked the length of your swale.
Video by Phil Williams, Permaculture PA
If you have access to a laser level, this will greatly speed up your swale building process.
Video by Phil Williams, Permaculture PA
Step 2: Dig It Out!
With some quick arithmetic, you can estimate the amount of water that runs over your property (average feet of rain per year multiplied by square feet) to determine the number of swales and depth of each swale that will be needed to capture and distribute that amount of water.
Whether you use pickaxes, a bulldozer, a walk-behind tractor, or an excavator, dig a ditch that meets your water demands, placing the removed soil downslope of your swale, forming a berm. As you build the berm, place rocks into a separate pile for later use. Next, go down the length of your ditch and use your A-frame to level your ditch lines to the slope of the land. Again, as you find rocks, place them into the separate rock pile.
Video by Phil Williams, Permaculture PA
All swales will need a drainage component to their design for heavy rains, so identify the number of drainage points that will be necessary to displace a 10- or 30-year rain and cut those drainage areas to a slope that is higher than the rest of your property to promote drainage, but not so severe that it risks erosion. If you have a large enough property, this drainage section can connect to another downslope swale or it can lead to an existing pond or spillway.
Finally, if you’ve been collecting your rocks, you can spread them along the water catchment and hydration sides of your swale.
Step 3: Observe, Test, and Maintain Your Swale
To test the holding capacity and drainage of smaller instillations, you can stretch a hose up to the new swale and fill it up. On larger installations, you’ll need to wait until your first big rainstorm. Chances are that after the first couple of rains, you’ll want to bring your A-frame and pickaxe out to make minor adjustments, but the hard work should be done.
To control the vegetation that will grow in the soil depression and on the sides and top of the downslope berm of your swale, use mechanical vegetation removal tools, such as a string trimmer and brushcutter. In cases where trees have grown into the depression, a chainsaw may be required.
With careful observation, you will identify an optimal vegetation height that facilitates soil infiltration, while allowing plenty of water flow in the drainage areas. Many land managers plant trees and deep-rooted bushes in the berm, as they will help hold soil in place and can provide habitat and food for you and wildlife. Once you’ve built your swale and berm, regular observation of soil moisture levels and water flow will indicate where improvements can be made to your design.
