Swales (Surveying & Installation)
Swales are simply ditches on contour (contour is a level line across the landscape), with the excavated soil from the ditch being placed downslope to form a berm. The purpose is to rehydrate landscapes, add texture and microclimates, and to be used as a tree growing system. You can also use swales to increase catchment for ponds.
Most landscapes can benefit from a swale system. There are some instances where it can be counterproductive or even dangerous. An extremely steep landscape with swales could cause mudslides. An extremely wet landscape probably doesn’t need them, although planting up in the berm can help the trees from getting wet feet.
When I am looking at a design, I want to see a contour map to figure out the possibility for pond and swale opportunities. For swales, I like to find the longest contour line first. Unless it is at the very bottom or top of the landscape, I will probably use this contour line for a swale. I am also looking to use the swales to make connections to ponds, or downspouts, or runoff.
There really is no right or wrong answer as to how many swales, how far apart they should be, how big they should be, or what you should put in the ditches. It is better to look at swales as a tree growing system and a way to rehydrate the land. Put in the type of swales that will best complete your goals for the site.
I have two different types of swales on my property. I have one system, where I filled the ditch with organic material. The thinking here is that the organic material will feed the trees on the downslope berm. I also have some of these swales feeding a drainpipe that feeds my pond. Then the overflow from my pond feeds on final very long swale. This swale is larger, but the ditch is not filled in. I did not have enough organic material to fill it, and I figured being at the bottom of the property, the soil is more fertile anyway. I have also used the swales as the basis for a food forest, by planting trees on the berms, but also planting downslope and upslope of the swale that will rehydrate that land making it suitable for tree growth. I prefer to fill the ditches with organic material for small swales, but I prefer the open swales in the video “Swales 2.0” for larger swales.
Once you’ve observed, planned, and mapped out your swales, you need to mark the contour lines. I’ve used and ‘A’ frame level and a laser level. If you don’t have a laser level, rent one, it’s worth it. I marked my lines with flags then painted with white turf marking paint. After, I pulled the flags up. Otherwise you destroy them with the excavator.
The next step is to line up your labor, tools, equipment, seeds, trees, and shrubs. I rented a mini-excavator with a 24 inch bucket. This was a good size for my 6 acre property, but if my land was wide open without obstacles, I would have gotten a bigger machine. It is necessary to plant your swales immediately following or even as you’re building the swale. If you don’t dominate the space with trees, shrubs, and complementary groundcovers, other plants that you may not want will take over.
I planted a wide variety of fruit and nut trees and shrubs, as well as a healthy dose of nitrogen fixers, pioneer species, nutrient accumulators, pollinator and predator insect attractors. Your ratio of nitrogen fixers to your productive species depends on what you are looking to accomplish and what type of climate you have. If you are in a desert climate, or the tropics, then you want lots of hearty nitrogen fixers, as many as 15-1. However, if you are in the temperate climate that gets steady rainfall, you can get away with as little as 1-1. It also depends on how much work you want to do. If you’re planning to bring in compost every year and tend to the trees carefully, you can put more productive species into your system, but if you want to put very little labor into your system, you might want to have a higher rate of nitrogen fixers in your system.
If planned well, a swale system is a simple earthworks system that can be implemented with a minimal amount of cost, but yield a tremendous amount of benefits.