Warwick Rowell
Chinampas are a very old food production system from central and south America. They can take either of two forms, and we have tried both:
- Floating islands on which food crops are grown;
- Constructed interlocking fingers of land and water.
We initially constructed two small (35m x 20m), fairly shallow, rectangular dams, and lined them with clay. We then bulldozed reasonable soil back out into the rectangle, so that the deeper parts looked like a comb structure. The fingers of land poking out into the water are used to grow vegetables and other food plants, and because they are “in” the dam, and water is available through capillary action, the plants never suffer water stress, and so production possibilities are increased. We are currently examining this relationship quite carefully; it seems that our original estimates of the height of water required were too generous; with the water level in the dam section about 1m below the surface of the planted areas, the ground is moist to within 20cms of the soil. This means we may adjust the overflow pipes, and make them much shorter than they were previously.
The overflow pipes feed back to a 10,000,000 dam adjacent to the two chinampas, with a windmill pumping from the large dam into the chinampas to maintain a constant water level in the summer, and the overflow pipe ensuring winter levels are maintained.
The floating form of chinampas was practised by the Incas. They bundled enough reeds together to support the weight of soil and plants that grew well in the humidity of the pond, enjoyed the extra light reflected from the water surfaces, and didn’t suffer from mountain frosts, due to the high humidity around them. After some very small trials in Shenton Park before we came down to Dunsborough, we are now working on a larger, modern version of this floating system, with 90mm UPVC pipe, and a mesh to support a growing medium. Once we have that worked out, we will undertake various trials. The first will be with a rich soil, and then vegetable seeds and seedlings. The next will be with native rushes on the supporting mesh. These will be tethered to the banks, and float in the water fingers adjacent to the land fingers. Nutrient rich water is well utilised in this way, and there appears to be no reduction in photosynthetic production in the water because of the extra shading.