Case Study: The Green Tree Foundation Swales Project
Excerpt From The Permaculture Earthworks Handbook by Douglas Barnes
This is an excerpt from The Permaculture Earthworks Handbook by Douglas Barnes.
At the invitation of Gangi Setty, founder of the Green Tree Foundation, I was part of a project to implement water-harvesting earthworks in Talupula, Andra Pradesh, India. The project was more successful than predicted, and it serves as a good example of the potential that swales have for repairing damaged landscapes.
Technically, Andra Pradesh classifies as monsoon tropics. With climate change and the denuding of the landscape, the state is becoming semi-arid, with erratic and decreasing rainfall. The decreasing rainfall results in poorer agricultural harvests and greater abstraction and depletion of water tables as reliance on groundwater grows. The psychological effect of a browning landscape on the local population is quite devastating, and the hopelessness it engenders spills over to the economy, creating a vicious feedback loop.
The Green Tree Foundation, for its part, provides thousands of low- and no- cost trees for local farmers and residents in an effort to re-green the region. In addition to providing shade trees for roadways, they have supplied fruit-bearing trees for impoverished citizens, supported the local silk industry by supplying mulberry trees, and provided fruit- and fuel-producing trees for local farmers.
Before seeing the region, I had envisioned employing a variety of water-harvesting techniques. The conditions on the ground made swales the clear choice. Ripping (see the section “Ripping” below) the lateritic soils while dry—as it was when the project started—would have been extremely difficult and would have only chipped the earth into broken pieces. Wetting the soil would not help either, as the ground becomes quite plastic and self-seals. Building a dam would have required a reliable source of clay, which was not available. The lateritic soils are 8 meters (26 feet) deep or more in many places, and clay deposits are somewhat sporadic.
While swales were the obvious choice, we needed to know the volumes of rain that we might expect on site in order to size the swales correctly. Despite repeated requests over the years, the Green Tree Foundation was never able to obtain weather records from the government. As a result, we had to rely on local knowledge.
The site we selected belonged to Gangahadr, a local fruit farmer and long-time friend of Gangi Setty. The portion we were allotted for the project was a 7-acre section of hillside. While Gangahadr specializes in oranges, mangoes, and other fruits, on the hillslope he was able to grow only annual crops of pigeon peas because of the aridity of the site.
I started by mapping the site with GPS and observing the vegetation and erosion patterns to get an idea of how water was behaving on the site. After making some calculations, we designed the swale dimensions to be 4 meters (13 feet) across and 1 meter (3 feet, 4 inches) high to the spillway. The final plan would see four swales laid out on three contours. The runoff was estimated at 55 percent due to the lack of vegetation and aridity. We had a crew of engineers mark the contours on the site with a dumpy level they had on hand.
We were able to hire a local backhoe, which dug 400 meters (1,312 feet) of swales with a volume of over 1 million liters (264,172 US gallons) in three days’ time. We also had a crew of 10 local laborers to groom the site. As the soil is very hard in the dry season, they used steel pikes to break up the soil and groom the edges and mound of the swale.
The night before the final day of construction a pre-monsoon thunderstorm struck at 2 am. Being very excited to see what would happen, Gangahadr rushed to the site and watched in the rain as the swales captured and infiltrated the runoff. The rain also made grooming the swales much easier.
In the weeks after I left, the Green Tree Foundation planted pioneering trees and expanded the mango orchard to the hillside. What was truly remarkable was that they were able to establish the mango saplings without the aid of drip irrigation, which is something that isn’t normally tried, even on flat ground.
The expansion of the mango orchard means that more workers will be needed to tend and harvest the fruit. This provides employment and improves the local economy. The trees themselves also assist in water harvesting and in nutrient accumulation. And there have also been higher water levels in a downhill well since the swales were installed. Considering the cost of the earthworks was under US$570, the project was extremely successful.
No project is perfect, however, and there are always lessons to be learned. The sides of the swale were steeper than I had planned. The laborers did a great job of smoothing out the swales, but they were unable to reduce the slope of the swale mound. Fortunately, this did not result in significant erosion. Additionally, although the mango trees were established without additional irrigation, their growth was slow. The addition of biochar (pulverized charcoal) as a soil amendment would have helped to establish soil organic matter. This would not only provide the trees with greater nutrients but would have helped with the soil’s capacity to retain water. This approach was used traditionally in the Amazon and in Japan to assist in topsoil formation and is a feature of many permaculture sites today.