By Mary 'Klibs' Dralle, for Let's Talk Plants! December 2024.
Creating Small Scale Fish Scale Swales
This article was inspired after a group discussion on the use of swales in Africa. If it can work to re-green the deserts there, it can work here in America! While these are called Half Moons, the concept is a swale. So, let's talk Fish Scale Swales.
The result of Justdiggit's regreening project in Pembamoto village in Tanzania.
In Permaculture, a swale is one way to harvest rainwater. Swales are shallow trenches that run on contour with the land. They are level and collect water. Soil taken out of the trench is placed on the downhill side to create a berm. There is a saying, 'Slow it, Spread it, Sink it' when it comes to water. When the rain falls on the surface of the soil, the water runs along it and is collected in the swale thereby 'slowing it' down. It gives the water an area to 'spread' itself and slowly 'sink' into underground pockets that will supply plant roots through weeks and, in some plant species, months, without water.
As our rainy season is approaching, now is the time to see where there is room in your yard for a swale or two. This concept was alluded to in past articles, and this will be a bit of a deep dive. In some cases, there may be room for a lengthy swales over a long distance. Other times, there may not be much of an area to work with, and smaller Fish Scale Swales can be utilized.
Let's take a look at how to determine creating a Fish Scale Swale on your property. There may be an area with a slight incline that can be contoured with a shovel, and maybe a dig bar if soil is a bit compact, so that a fruit bearing tree can be planted with minimal water support.
Perhaps it would be good to have a fig tree. Figs are a tasty fruit that can be enjoyed off the tree or in sweet or savory recipes. Also, they can be dried and stored for future use. As Mediterranean natives, fig trees (Ficus carica) are well-suited to hot, dry environments and can survive with very little water. They thrive in full sunlight when planted in loamy, fertile, well-draining soil and are relatively low maintenance. All they require is a bit of compost, mulch, and some pruning. Perfect for Southern California gardens!
First, in that sunny spot, determine which way the water flows over the land.
It may be obvious if one side is far higher than the other. If need be, determine the slope with the help of a Bunyip or A-Frame water level.
Bunyip Water Level
Learn how to Make a Bunyip Water Level with Brad Lancaster Photo credit: SustainableWorld, https://www.youtube.com/watch?v=pRjNA0DZZb4
It is based on the principle that still water is level across its surface. Using capillary action inside a tube, the water flowing in a narrow space will become level in relation to the ground. If the tube has a bend in it, the water will seek level depending on the relationship to the soil at both ends. The measurements at the ends, can be used to determine slope, elevation relationships, and the placement of water-harvesting earthworks.
Water Level in a Bunyip Photo credit: Mary Dralle
Parts and tools needed to make a Simple Bunyip
Two 2-inch (5 cm) x 2-inch (5 cm) x 6 foot long (1.8 m) Stakes
Tape measure
Permanent Ink Marker
Approximately 30 feet (10m) or more of clear vinyl tubing, 3/8-inch (10 mm) ID is typically used
16 - 20 Insulated or Plastic Cable Staples
Hammer
2 to 3 gallons (9 liters) of water
Funnel to pour water into the tubing
Assembly of the Bunyip
Layout a stake and place the tape measure on top of it.
With the permanent ink marker, start at the top and mark off the units of measure in increments of 1. Repeat with second stake.
Starting at the top of one stake, secure the end of the clear vinyl tube with the staples using a hammer. Repeat at 1-foot (30 cm) intervals.
Repeat on second stake with opposite end of tubing.
Using the funnel, pour water into the tube, taking care to avoid creating air bubbles. The water should reach a level that is halfway up each stake.
Using the Bunyip
Stand with one stake of the Bunyip at one area and the other one in the location of interest. Take readings from the water levels on both stakes.
The water level will be the same in both tubes if the ground is level. i.e. Both Tubes read 36 inches (91.4 cm)
If one side of the water is higher than the other, the ground is sloped and can be determined by subtracting the measurements between the level marks on the stakes. For instance, if the water level on stake 1 is at 33 and 51 on stake 2, the difference would be an 18-inch gain in elevation. Conversely, if stake 1 is 51 and stake 2 is 33, there is an 18-inch drop in slope.
Calculate the percentage of slope as the change in slope, B, divided by the distance between the posts, A.
Measure the distance between both posts. This will require a tape measure. Let's say the distance is 5 feet, mark it as 'A'.
If the change in slope from above is 18 inches, marked as 'B".
For example,
Distance to ground = B = 18 Inches = 1.5 ft
Distance between Posts = A = 5 ft
Slope = B/A = 1.5 ft/5 ft = 0.3 = 30% Slope
Please note: If working alone, the Bunyip stakes can be cemented into buckets so that they can stand on their own. This is what I did and used an old tape measure instead of using a marker.
A-Frame Level
To check level over a shorter distance in order to dig a swale, an A-Frame level works well.
A-Frame Level Photo credit: Mary Dralle
Parts and tools needed to make an A-Frame Level
Two Wooden boards, 1 inch x 2 inch x 5 feet long
One Wooden board, 2 inch x 2 inch x 2 feet long
Three 3/8" x 2 1/2" Hex Bolts
Three 3/8" Wing Nuts
Five 3/8" Washers
One 6 in. Torpedo Level
Two #8 x 1-1/2-in Phillips-Drive Standard Sheet Metal Screws
Drill
3/8" Drill Bit
0.125" Drill Bit
Phillips head drill bit
Clamp(s)
Optional: A one-foot length of 1" PVC pipe and two more #8 x 1-1/2-in Phillips-Drive Standard Sheet Metal Screws
Assembling the A-Frame
Clamp two wooden boards together making sure they are square and parallel.
Measure down one inch from the top and center to drill a 3/8" hole.
Measure down 22 inches from the top and drill a second 3/8" hole that is centered.
Remove the clamp.
Use this bolt illustration to assemble the legs and cross brace.
Leg and Cross Brace Bolt Assembly Photo credit: Mary Dralle
Attaching the Level
Place the A-Frame on solid level ground.
Determine and mark the center of the cross brace, vertically and horizontally.
Center level on the front.
Drill a hole using the 0.125" drill and attach with one screw.
Make sure that all three bubbles are centered on the level and secure it with a clamp.
Drill second hole and use screw to secure level in place.
Optional: Secure the PVC pipe to the bottom of one leg with the two screws. This can be used to hold the landscape flags when marking long swales.
Using the A-Frame
Measure the distance between the A-Frame legs. Mark it down as 'A'.
Place the A-Frame perpendicular to the slope with one leg on the ground and the other pointing downhill.
Raise the downhill leg until all of the bubbles in the level are all centered.
Measure the distance from the bottom of the downhill leg straight down to the ground. Mark it down as 'B'.
To calculate the percentage of slope, divide the distance to the ground, B, by the distance between legs, A.
For example,
Distance to ground = B = 0.5 ft
Distance between legs = A = 5 ft
Slope - B/A - 0.5 ft /5 ft = 0.1 = 10% Slope
Swale Set Up
Once the slope into the area has been determined, it is time for set up. Typically, the swales are a 7 to 10 feet diameter LEVEL semicircles. Cross check the area with either the Bunyip or A-Frame level and adjust accordingly. The trench portion is dug on the 'higher upper' edge to a width of about 12 inches and depth of 8 to 12 inches. Soil is placed on the downhill side of a swale to create a berm. See Illustration below.
Fish Scale Swale Illustration - Photo credit: Mary Dralle
To prevent the swale from filling up with debris, or becoming a trip hazard, fill it with copious amounts of tree mulch. This creates bulk and allows water to percolate into the ground.
Now, it is time to plant fruit bearing plants. It can be either a tree or, one to two bushes, on the FRONT side of the berm. Do not plant in the trench portion of the swale. Planted this way, the roots will find their way down into the water supply. The main part of the plant(s) will be above the soil level and the roots will not develop “wet feet” when there is heavy rainfall.
When planned and carried out correctly, the plants will thrive in your garden. Should there be times of drought and the plants are showing signs of stress, 'extra' water may be added into the swale as support from time to time.
Here is to utilizing earthworks to grow more food in your garden with less water!
Until next time, keep those hands soiled.
Mary 'Klibs' Dralle
Certified Permaculture Designer, The Dancing Raven Ranch & Retreat Center
Chef, Cookin' with Klibs Presents the Chemistry of Cooking,
Labyrinth Coordinator/Builder, The Wander-Full Labyrinth Walkers
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