We have done what everybody has always thought to be impossible. In April 2013, we have sealed the large dam on top of our property. The dam holds 1.000.000 m³ of water and is now sealed with 3500 kg of bentonite clay liner. In this blog post, we will describe how we did it! Also see: http://youtu.be/gfyIY7whU9Y
Benefits of a large pond, as it relates to permaculture principles
A large pond provides many benefits to a permaculture site. It provides:
1) Water storage – to water food forest/garden/animals during dry season
2) A new ecosystem – A pond provides a habitat for fish, animals and plants. These plants and animals also enrich the water and provide more nutrients to the plants.
3) A charged water table – Holding rainwater uphill is good for the water table and it enables plants and trees to more easily take root.
How the installation utilized permaculture principles:
1) A few years ago, someone donated 4000kg of bentonite clay liner and stored them in the garage at Panya. The original plan was to pull the liners out and drag them up the hill using a small crane. We decided instead to build a pulley ourselves and manually pull out the liners and use the Panya truck to carry the liners up the hill. The human power utilized in this project illustrates how much can get accomplished when people work together.
2) To dig the shelf and trench at the top of the pond we rented an excavator instead of digging it by hand. We estimated the soil would take about 400 manhours, about 10 people digging for 40 days, or one machine 5 days to complete the job. We also wanted to get project completed before the rainy season. So we rented an excavator.
About $600 USD (20,000Baht) – 4 days excavator rental. This was the only cost of the project. The liners were donated a few years ago and human power in this case was free!
Initial pond area
Pond hole – The initial pond area was dug out in 2007 after the first PDC with Geoff Lawton. It was designed with a keyhole trench at the base of the downhill slope. This is to prevent the bottom slope of the dam from breaking under the weight of the water. The pond was also dug with two runoff points directed into swales. These points are about 50 centimeters below the top of the pond. This prevents erosion from under the liner in case the pond overflows.
Liner – The pond liner is a bentonite clay liner. This clay, wrapped in a synthetic mesh seal, expands when in contact with water. When the clay expands, it creates an impermeable seal. Using bentonite clay is a good solution for sealing a pond. The liners were a Bentonix BFG 5000 model at a value of a few thousand dollars. They liners were donated to Panya by a company from Singapore. The liners have been stored in the garage at Panya ever since they were donated. Each 40m roll weighs 1000kg (1 ton).
Digging the trench
We first measured the pond to a height that would allow us to use the most liner with the least waste. We measured the pond and spray painted lines where the top of the pond would be located. The next step was to hire a backhoe and dig a 30cm x 30cm trench with a 1m flat shelf.
Making a cut plan
We then made a cut plan for the liner. We knew we had 4 rolls of 40m x 4.85m liner. Or 160m long x 4.85m. We also knew since we were cutting the liner at the garage, we could only cut the liners 10m long. We made a few cut plans and ended up with this sketch.
We then assigned numbers to each piece and crossed them out as they were laid in place.
Making a pulley
To get the four 1-ton rolls out of the garage, we made two pulley blocks, each with two pulleys. We tied one pulley block to a tree out the front of the garage and tied one to the liner roll. Then we tied a line to the front of the truck, which ran through the pulley on the tree, then to the pulley on the roll, back to the tree, back to the roll, then back and tied directly to the tree. In theory, each two pulley’s reduced the amount of weight by half. So with four pulleys, we were only pulling 250kg instead of 1000kg.
Moving the liner
As mentioned, four 1000kg rolls of liner (40m each) were stored in the garage at Panya years ago. For each step of moving the liner, we utilized human power. We first used 10-12 people to roll the liner onto short perpendicular round pieces of wood in the garage. Then we hooked up the pulley to the roll and pulled it out of the garage. Then we used 10-12 people again to roll out the liner in the yard to be cut to a specific length. (accordingly to the cut plan). After we cut the liner in separate pieces, we rolled the liner up again and set it on the back of the truck. Then we drove to the top of the hill and unloaded it.
After we moved the pond liners, ten to twelve people picked it up again, carried it to the correct position according to the cut plan and rolled it out. Over the course of 1 week, the whole group lifted and set in place 3500kg of liner (we had half a roll left over to be used for other smaller pond projects). We overlapped each piece of liner by 30 cm. This is to prevent leakage between each piece of liner.
Refilling the trench
Once the liner was laid, we called the excavator to come back and place 30cm of dirt back on top of the liner. The compacted dirt will keep weight on the seal between liners once it rains and also to put some weight on top of the liner to keep it from sliding down the incline.
Once the pond fills up
After the rain fills the pond, we plan to:
- Plant a food forest surrounding the pond
- Plant water plants to protect the pond from evaporation
- Breed fish, frogs, birds and bees to fill in the new ecosystem
- Build additional water storage tanks (to store water for the food forest and animals in the dry season)
Thank you Brian, Cyril, Nick, Brecht, Greg, Pop, P’Om, Violaine, Toni, Maina, Steve, Kyle, Sandra, Jerry, Wouter, Ellen, Ben, Mei, David, Allan, Ann, Becky, Mariana, Beth, Erica, Ekaterina, Jo. You will all be forever remembered as the epic team that sealed the dam!