Permaculture Earthworksby Douglas Barnes
We are fortunate to live in a climate that is relatively abundant in water. The disastrous drought of 2012, however, shows us that we can no longer afford to take water for granted. Globally, nearly half of all land is arid, with a further 25% threatened with desertification. That's the bad news.
I'm here to tell you the good news. I’m here to tell you about how, with a fraction of the time and energy we have spent degrading our environment, we can foster life and increase biodiversity. And we can do it profitably.
Let me jump right into the "how." The "how" is based on a few design strategies. One of those strategies is to hold onto the resources we have on site as long possible. In the case of water, we hold onto it in two ways. One is to put it through as many duties as possible before it is lost to us. The approach we are focusing on today, however, is to capture the water arriving on site, and take it over the longest, and slowest path practical.
Putting this approach into practice means starting at the highest elevation on a site and working downhill with the techniques I am about to highlight.
To hold water at the top of a site, we typically forest hilltops and ridges, along with steep slopes. Forests are very effective at capturing water with minimal runoff. They also have the added benefits of preventing erosion, and adding fertility to the top of a site where it can naturally flow downward. This is a strategy hit on by the Japanese in a traditional mountain region farming system they call Satoyama. Admittedly, this is not a form of earthworks, but it is so integral to water harvesting design that I would be remiss not to mention it.
Water harvesting earthworks have the goal of intercepting runoff water, and storing it. The simplest of the interception techniques involves patterned ripping of the soil with a subsoil plow, given the right soil conditions. With the plow, we cut narrow furrows into the ground just slightly off contour to capture runoff and gently direct it from wetter areas to drier ones. Originating in Australia, this technique has proven very effective there.
This type of interception technique is also really a storage technique as well. The ground is a fantastic place to store water. There it is largely free from evaporation while being available to plant and soil life.
Another common interception technique is the swale, which is a water harvesting ditch dug level on contour. It stops water flowing downhill, allowing it to sink into the ground.
This is a good point to address an argument that too often comes up around water harvesting. Sometimes you will hear a claim from downhill people that you are "stealing their water." Nothing could be further from the truth. They might see a temporary reduction in runoff onto their land as you hold onto more of your water, but, as you recharge the water table, the medium and long term effect will be to increase the local ground water. In many cases, ephemeral streams will start to have a more regular or even constant flow.
Both of these interception and infiltration techniques are inexpensive and cost effective to install.
Swales are also used in conjunction with earthen dams and ponds. The dams we are talking about are small reservoirs sealed with clay, not concrete structures. Both ponds and dams provide water for irrigation. They can also be put to productive use through aquaculture. While our climate does not support a very large variety of productive aquatic crops, warmer climates can produce prodigious quantities of edible and palatable plants. And even in our climate, water has a better feed conversion rate than terrestrial livestock. For instance, it generally takes 870 grams of feed to produce 100 grams of beef, or 190 g of feed to produce 100 g of chicken. The feed conversion rate for fish, however, is typically 120 g of feed to 100 g of fish.
Aquatic systems are also excellent producers of soil. Their periodic need for dredging yields a very valuable product that adds to site fertility.
In semi-arid and arid conditions, we sometimes employ a land imprinter - essentially a large, patterned drum which can break through desert hard pan and leave divots in the earth. Here debris, including seeds, will collect and moisture will concentrate during rains. This simple approach has proven effective in re-establishing grasslands.
Dug pits can work similarly to establish drought-hardy trees in semi arid conditions.
This has been a very rapid summary to give you a taste of some of the techniques we use. I'd like to leave you with a brief case study of the most dramatic work I have been involved in.
In 2009, I received an invitation to carry out a joint project with a local NGOin Andhra Pradesh, India. This region had traditionally had a dry tropical climate. In recent decades, however, it has grown increasingly arid at an accelerating pace.
When I finally arrived, I found the situation on the ground to be quite bleak. The vegetation is starting to give way to cacti and other desert xerophytes. The local village I worked in now has to draw water from a well over 1000 feet deep, the water from which is tainted with excessive amounts of naturally occurring fluoride.
Before leaving, I'd had it in mind to employ a number of techniques, including ripping the ground with a subsoiler, and building a dam. The soil conditions only lent themselves to swales, however.
I was given carte blanche over 7acres of arid hillside that a local mango farmer considered a write-off for everything except a seasonal crop of pigeon peas.
After crunching some formulas, we laid out contour lines on three levels, then excavated over 400 metres of swales, capable of holding over 1 million litres of water. Our host farmer was initially dismayed to see us chewing his land up, but started to get the gist of what we were doing. The night before we were to complete the project, a pre-monsoon storm hit, so when the rains hit, he took off on his motorbike, and headed to the site. He was delighted to see that all the water that would have washed down the hillside, and eventually out to sea, was now stored in the ground.
Before I left, I made what I thought was a bold prediction. I said that within 3 years time, there would be springs appearing at the bottom of the hill during the monsoon season. It turns out that my predictions were very conservative.
Six months after I left, I received a photo update of the site. In it, I saw that they had established mango seedlings, and they had managed to do it without drip irrigation - something very unusual even on flat sites in the area.
Tamarind trees on the opposite side of the valley had a very anemic crop, whereas a tamarind tree adjacent to the swales produced an unusually bountiful crop.
I'd made my bold predictions of springs appearing within 3 years. At the bottom of the site there had been a well with water 3 metres down while I was there. Now six months later, the well was full. Water is no longer an issue on the site. And what had been a meager pigeon pea field is now a lucrative mango polyculture.
The results were beyond my most optimistic expectations, and the cost of the immediate project was just $650 Canadian. This is really a prime example of how the cost, effort and time it takes to repair a site is far less than that required to destroy it in the first place. As soon as we pattern our actions in harmony with nature, the payoff is immediate.
These techniques have proven effective everywhere from arid desert to tropical rainforest. They help to rejuvenate drylands, and buffer against drought. We can expect increasingly erratic weather in our future, including severe drought. These water harvesting approaches can help us through the rough times to come, and they can replenish our water tables during the good years.