Earthworks (10m 57s)
Earthworks are how we can catch, slow, soak and store water in the soil. The quote for this chapter is “soil putting, water going.” This was said by Sekar, the landowner of Magic House. I think this captures the essence of earthworks – moving earth to catch, slow, soak and store water.
Earthworks are large artificial embankments of soil. They often require heavy labor. But once you complete the earthworks, they provide back to you for many, many years.
For example, here in Auroville, a community called Sadhana Forest has been planting trees for 8-10 years. In this time, they raised the water table by 6 meters. So in a time where we often talk about falling water tables and water scarcity and things like this… what these people are doing is working, well.
Another story, at Kailash Akhara, a yoga community in Eastern Thailand, YJ was telling me this, the land was originally an old lychee forest. They dug swales about 10 years ago and since she has watched the land evolve – starting with grasses, legumes and wild flowers, these attracted dragonflies, birds and iguanas and snakes and mice. She’s watched the whole ecosystem evolve after basically providing a place to store water in the soil.
So when you first walk on to your site and you see, okay, here’s what we’re looking at, what are we looking for? First thing, just observe, observe the “natural order” of things, what the land is already calling for, where are the potential flood zones, what are the general contours of the land?
Many permaculture people like Geoff Lawton who do more broadscale work, talk about keyline design. The keyline is where the slope of a hill turns from concave to convex, at the nadir of a valley. So where it would normally go into the valley here. So you want to dig swales sloping a few degrees away from this line. This keeps land from eroding into the valley and spreads water out over the landscape.
There are a couple ways you can level things on the cheap: One is an A-frame, this is the most basic. It’s three pieces of wood in the shape of an A and a line hanging down with a weight on the end. Basically, you make these two points level, and then you mark a line right here. And that’s going to be the center. Anywhere you put these two points, you want that bob to hang straight down.
Another type of level is a water level. This is a clear hose, filled with water. Use it to determine difference in height or elevation at two points. There’s also a transit level or a laser level. These are two more technical devices. These are very accurate devices for finding level places.
And the last point on leveling I wanted to make: trust your eyes. For many small projects, the degree of precision usually isn’t terribly important. It’s more important to just keep moving forward before you lose patience in the project.
Now we’ll talk about some of the elements of earthworks. First, is okay, swales. I had never heard of this word or even the word earthworks before I learned about permaculture. Swales are trenches dug on a slope designed to prevent erosion and store water on the hill. It provides water storage for taproots to penetrate deep in the soil and better secure trees to the ground.
The sizes of swales range anywhere from 15cm-2m wide, 30cm-1m deep… There is a swale calculator online. From which you can take the amount of rainfall, the area above the swale, and the infiltration rate of the soil (the speed at which the soil absorbs water)… there’s a calculation online where you can determine a more calculated size of your swales.
On-contour swales. Totally flat, parallel with the elevation. So with on-contour swales, all of the water that falls on the hill will be stored on the hill.
Then you have off-contour swales, which are tilted 1-5º off-contour. Most of the water is going to soak into the soil, and then some runoff will run down the trench. In Thailand at Kailash Akhara, my buddy Ben and I were staying at a house with 10m of space on each side. There was a gentle incline of about 2 meters from back to front. We dug off-contour swales on either side of the house so the swales will store water in the soil and then channel excess water into a pond at the front of the house. Any overflow, runs off down the hill.
Behind the house, there are 4 ongs, 1000L cement water tanks. These catch rainwater from the roof to channel the overflow water into the trench system. So, most of the water that falls on this land, will make contact with cool, shaded soil or make its way into the pond.
Another type of swale is called “Net and Pan.” There’s a good image in the Designer’s Manual by Bill Mollison. The pan of net and pan is an arc you dig either above or below the tree. So from here, you can connect all of the pans together with diagonal trenches. This forms a net. You can also add mulch to the base of each pan, this creates shade which takes water a long time to seep into the soil and not evaporate. With the net and pan, most of the water that falls on the land will end up at the base of trees.
The next type of earthwork we can talk about is a bund. A bund is an inverted swale. So a swale is a depression and a bund is a ridge. Many places around Auroville have bunds. You can have a whole network of these things going through your site, outlining gardens and creating paths.
Another type of earthwork is a terrace. Terraces have been used for thousands of years, and are still being used today all over the world. A terrace is a series of steps made to create flat space on a sloped hill. When I was staying in Thailand at the Panya Project, a friend named Steve dug over 100’ of terraces by himself. He recommended each terrace to be about 1m wide, to allow room for a footpath and plenty of grow space. The height of each stair is determined by the slope of the land. He also said to keep the slope less than 18º – this angle will retain water and enable you to still walk on each terrace.
Ponds are useful structures for catching and storing rainwater or well water and they are a great environment for fish, frogs and tons of other plants, insects and animals. We will talk about ponds a few times throughout this course. Today we’ll talk about a few ways you can line a pond to hold water.
So the first method is clay. Many sources say you need at least 70% clay content in the soil to hold water. You can add organic material like cow manure, banana leaves or other available organic materials. Here are some pics of my buddy Prakash’s land, called Vanapa. They dug a hole with an excavator, lined the hole with cow manure and compost. I’m anxious to see how long this takes to hold water. Solid job. Over time the materials will form a thick, sticky, wet impermeable layer called gley. This is how many ponds naturally form.
Another way to line the pond naturally is to use pigs. Another well-known permaculture person is Sepp Holzer, he has this beautiful 40-acre piece of land in Austria which he used pigs to line the pond. For a few seasons, he put pigs in his ponds to roll around and use their bodies to compact the dirt.
I would say to first do several soil tests, and if you have a high enough clay content, over 70%, then go for it – through in some manure, more good clay, any other high-nitrogen gluey organic matter when broken down. Otherwise, there are a few other options:
When you think of clay on a spectrum, you have bentonite clay on one end and kaolin on the other. Kaolin is a soft, white clay used to make things like porcelain. Bentonite, on the other end, is impermeable to water once it becomes wet. The clay particles expand to keep water out. Manufacturers have designed liners which distribute this clay evenly throughout a plastic liners. This is a great way to line ponds. I think these are used mainly in industries where they need to contain some fluid. They also work great for ponds.
For example, at the Panya Project, a few years ago they dug a large reservoir at the highest elevation on the property. After the first rainy season, they learned there wasn’t enough clay in the soil to hold water. Some time later, another volunteer donated 4 rolls of these bentonite clay liners and stored them in a garage at the bottom of the hill. My buddy Cyril built this pulley to remove the liners from the garage and with about 20 people, we cut, rolled, transported and unrolled each piece of the liner in the pond. There were 16 pieces in total. We laid them out piece by piece. We overlapped each sheet by 30cm and packed 30cm of soil on top to create pressure and hold the liners together. Now the pond holds water.
Next we have plastic liners. This is probably the most abundant option.
You can find plastic liners in many hardware stores around the world. For larger ponds, look for heat guns and special tape to create seams. It’s good to have a shelf that is about 1 meter and you want each side to be about 30 cm. And on top, pack about a foot of dirt. And this will hold the liner down. Look for heat guns to create seams .
They use concrete rings a lot in Thailand and India. I like this method. Each ring is fairly cheap, you do stack the rings one time, and have them to use for a long time.
Ferrocement is another way to line a pond. Ferrocement is a metal rebar reinforced thin concrete wall. With ferrocement, you first form whatever shape you want using 3mm wire. Then wrap the wire with at least 2 layers of chicken mesh. Then mix sand and cement (1:3) and plaster the frame. There are many books on ferrocement and lots of diagrams online if you want to try it out.
Now we’ll talk a little bit about dams. For about every shape of earth, we have figured out a way to dam it. And we have also learned when you divert water using a dam, it affects below the dam. Every living thing that had water coming to it before, depended on that water and when we change the course of a stream it effects the entire ecosystem below it. I think the most important thing to remember is that a dam is something that catches and retains water and releases it on demand.
Okay, quick recap here:
- Earthworks are formations of dirt we use we catch, slow, store, and soak water in the soil.
- To do this, we can dig swales, terraces, bunds or ponds.
- If you want to build a pond, consider the different ways you can line the pond
Okay, so that’s generally the earthworks section. Thanks for your time.