In today’s blog post, I want to showcase the exact design process of creating a layout for a food forest with swales.
But before we start with the process, you have to understand one crucial thing about your site: the slope of the land.
You see, you can only install swales on gently to moderately sloped land (below 15% slope). Any steeper than this, you risk blowout from too much water buildup, overflow, and soil destabilization.
If your slope is steeper than 15%, you would have to use terraces, and they’ll act in a similar way to the swales in harvesting water on level ground.
Checking slopes across your property isn’t hard, and you can do it in 10 minutes with my Google Earth elevation profile hack outlined in this post. Once you determine that swales are indeed a viable option for your terrain, given your property’s slope gradient, you can proceed to the design process.
To give you an idea of how the layout of a food forest with swales looks like, here’s the final design.
What you’re looking at is a series of rows following the contours of the landscape, separated by approximately 15m (50 ft) distance, outlining a skeleton of the future food forest. This layout is ready to be “transferred” to the site itself, and then the on-site implementation can start.
Now let’s reverse engineer the steps required to get to the final ready-to-be-transferred-to-the-site design. We’ll use Google Earth for this and do it in 15 minutes, more or less.
STAGE A. Import a contour map into Google Earth
Swales are on-contour ditches, so to design them, we need a map that outlines the contours. Since we are using Google Earth for the design, we need Google Earth to show contours overlaid on top of its aerial/satellite view.
In case you already have this contour layer in Google Earth, you can skip this part, but if you don’t, I want to show you the easiest way you can do this.
STEP 1. Locate your property on the Contour Map Creator website
Now zoom in on your property, use the search bar, and then your mouse to center the map with your property in the middle.
Note: Don’t zoom in too much as you’re also trying to get the overall picture of the topography surrounding the property.
STEP 2. Draw a sampling area
Mark a rectangle by adding two pins onto the maps. Put one pin in the corner and the other in the opposite one.
STEP 3. Get a contour map
Now adjust the plot options, check the level interval option (1), and put in 5m/15ft (or less). This determines the resolution of your contour map; in this case, you’ll be getting a contour map with contours every 5m/15ft.
Click the ‘Get Data’ button under the sampling tab (2) – and voila, the app generates a contour map for you.
STEP 4. Import the contour map into Google Earth
Scroll down and press ‘Download KML file’.
Now locate that file in your download folder and open it in Google Earth. When you launch the application, it will automatically zoom in onto your property and you’ll have contour lines overlaid on top of the satellite photo background.
Note: If Google Earth doesn’t automatically take you to the area with contours, you might need to enable the newly imported ‘Contours’ kmz file in the sidebar under the Places bar.
STAGE B. Outline swales
Now with the contours visible on top of your landscape’s aerial view, you can proceed to design your on-contour ditches, a.k.a swales that will outline the layout of your future food forest.
STEP 4. Mark the first reference contour on your map – the initial swale
Zoom in to the area that you want to transform into a food forest and first mark what I call a ‘reference row’. This will be the initial swale that you’ll use as a starting point for your layout design.
It’s good practice that this first swale is at the highest point of the area of interest.
This is a very important principle of harvesting water, as this way you slow the flow as soon as possible. Otherwise, the flow might cause erosion before it gets to your swale further downslope.
Look at your map and try to find the longest contour line at the highest possible elevation.
Click the ‘Add path’ tool on the Google Earth toolbar (1) to draw a ‘swale line’ following or on top of the contour line (2).
Note: Where you begin and end your swale is entirely up to you. In most cases, the restrictions of the surrounding landscape (access, property boundary, fencing, etc.) will be your guide.
STEP 5. Decide on the distance between the swales
If you’re planning on having more than one swale, you’ll need to determine how far apart to make them. This will depend on your site goals and rainfall and runoff conditions, but the overarching rule of thumb is: the greater the runoff, the closer the swales should be spaced.
In general, it will be 5 – 20 m (15 – 65 feet). But again, the greater the runoff the closer the swales.
For example, on steep, overgrazed or disturbed land, you will be confronted with large volumes of fast-moving sediment-laden water in intense rainfalls so you should place your swales at close intervals.
On gentle slopes covered with thick native grass, the watershed can absorb more rainfall before significant runoff begins so you’ll need fewer, and more widely spaced swales.
STEP 6. Create the final layout of a food forest with swales
Now, based on the desired distance, mark the remaining swales, going down the slope from the initial swale.
(A) Click the ‘Ruler’ tool on the Google Earth toolbar (1) and switch to the line tab (2). Measure the desired distance to the next swale (3).
(B) Click the ‘Add path’ tool on the Google Earth toolbar (1) to draw a ‘swale line’ following or on top of the contour line (2).
Repeat measuring the distance (A) and drawing swale lines (B) until you outline everything.
Now you have a final food forest layout with swales.
Ok, so in 15 minutes or so you have something you can work with.
With this layout in your hands, you can now go to your site and crash test the map against the territory:
Save your work on the desktop app version of Google Earth, open the file on the smartphone version of the app, and visualize your layout as you walk around the site.
The layout won’t be perfectly accurate as the Contour Map Creator isn’t the most perfect tool for the job. Still, it will be good enough for you to start implementing and moving your project forward in real life (without having to invest a fortune into professional design software!!)
At the end of the day, all that matters is tangible results on the site as we don’t have time to waste. We need to establish our food forests, permaculture orchards, gardens, agroforestry crops and pastures, as soon as possible to ensure our food security and peace of mind.
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