How to Make a Swale
August 1, 2017
When heavy rains hit a large plot of land, it can have more impact than just annoying puddles. Large water flows can case erosion on sloped surfaces, affect the water quality of many nearby bodies of water and eventually can cause significant changes in your soil moisture levels. This is where swales come in. A Swale (a contour bund) is a ditch or a hollow place in your land. This swale can be utilized to filter water through your soil, as opposed to having a drainage ditch to move water quickly from your property. If you are going to have an immense amount of water flood your property, you may as well have it work to your advantage. This method has been used for years by farmers and homesteaders alike. The following steps are how you can implement this technique in your own home or of a client’s home.
Step 1: Outline Your Swale with an A-Frame
This is the first and most important step because an “A” frame helps indicate whether your swale is on contour - level with the slope of the land. It is recommended to use 5-foot and 8-foot boards so you have plenty of length without the weight, but the size will ultimately depend on the length of your swale.
First you need to measure your contour lines. Take two 8 foot piece of lumber to make an upside down V. Make a cross brace about a foot above the ground. Make sure that the distance between the ground and your first cross brace is exactly the same distance on both sides. You might want to add additional cross brace up higher to make it easier to carry. Attach a bubble level on the bottom cross brace.
Next, move your “A” frame to stand in the location where you want the swale to end. Mark your contour lines across your slope horizontally with a flag. Once you have a one foot mark, adjust the feet until you have achieved a perfect level. Mark both sides with flags. Move the A Frame to the other side of the second flag. Again, move your “A” frame feet until you receive a perfect level. Continue this with the rest of the swales. This can also be done with a laser level if you have access to one. You can connect the flags with paint to make excavating easier.
Step 2: Dig It Out!
Estimate the amount of water that runs over your property by taking the average feet of rain per year multiplied by square feet. This will determine the number of swales and depth of each swale that you will need. Using whatever tools you have available – dig a ditch to meet your water demands – be sure to place the removed soil downslope of your swale. Use this soil to create a berm but take the rocks out and place in a separate pile for a different use. Use you’re A frame to level your ditch lines so they configure to the slope of the land. Again, as you find rocks, place them to the side.
Swales will need drainage components to compensate for heavy rains. Identify how many drainage points will be needed to displace a 10 or 30 year rain. Cut drainage areas into slopes that are higher than the rest of your property to let gravity aid in the drainage. Be careful that the drainage point isn’t too severe because it can cause erosion. If you have the option, draining to anther downslope swale or a small pond is ideal. Use your rocks along the water catchment and hydrations sides of your swales.
Step 3: Observe, Test and Maintain Your Swale
Now that your swale is done, you may want to test the holding by filling up the swale with your hose. For larger land, you will want to wait for the next major rain. Afterwards, use your “A” frame and a pickaxes to make small adjustments. Soon you will find vegetation that facilitates soil infiltration best for your land.
For the full length article, detailed instructions and informational videos please visit www.grit.com/farm-and-garden/landscaping/using-swales-for-water-control-zspz1706zcwil