Tuesday, May 6, 2008

Permaculture Water Harvesting Swale System


Today saw the start of a very ambitious exercise. Turning a ridge parcel of cropping area into a raised bed/swale system. This is done by surveying the area using several different methods to gain level pathways on contour. It also gives us more planting area as the beds will now be curved following the natural contour of the land. Giving us more “edge” in the process. By doing this we also allow water to sit in the path areas and absorb into the soil slower than normal. Soil stores water more efficiently than any other means. With the soils here being volcanic, I would hope that silt will be transported into the soil and hold water for longer.

I brought from Australia with me a hand level, string-line bubble level, GPS to assist in these processes and to teach people how to use them. Masa sourced a staff (a 5m measuring stick) and we went about marking out beds and pathways.

Now, as contour lines in the landscape are never always parallel, we had to do some figuring out how we would make the system accessible as well as practical. Everywhere that the bed got wider than we expected we put in key-hole paths to gain appropriate access to the wider path to be able to manage working the bed at easy reach. This gave us more “edge” again.

One way to look at edge is to have two lines drawn on paper over the same distance. One line straight, the other curved like a radio wave. Line one might measure say 10cm, but if you measure all the curves of line two over the same distance it will always be longer. Imagine if you stretched line two out straight, it would be longer.

One way to measure level is with an “A” frame. This is a device that can be made from almost any material, keeping in mind its’ maneuverability.

Firstly, we got two pieces of timber the same length (1.4m) and a third piece that we would cut according to the size of the ‘A’ we wanted. We laid the two 1.4m pieces on a flat surface in the shape of a V and measured down the outside edge of both pieces 0.9m and made a mark in pencil. This mark indicates the height that the third piece of timber will cross the other two. Holding all three pieces firmly, screw the third piece to the other two. The two longer pieces should be checked for even and touching together before screwing the third.

The top of the ‘A’ needed some support, so we cut some 1.5cm ply board to suit and screwed it all together. Now we had a measuring device for the job, all we had to do was make sure it reads level. We found a known source of flat level ground and using a piece of string hanging from the center of the top of the ‘A’ with a weight on it (a plum bob), we were able to determine a point of level. We made a mark in pencil on the third piece of timber where the string crossed and then turned the ‘A’ frame on itself and made another mark in pencil. The measurement was the same place as the first. If the measurement was not the same, we would have halved the distance between both and made our mark and that would have been our level mark.

We took this out to the field and started using it. Armed with bamboo stakes, we marked the ground once the weighted string touched our level mark. This process is continued down the slope leaving behind a maze of sticks resembling a slalom ski course. It can get a bit confusing if there are too many stakes out so we dug our paths as we went to save the headache.

Another way to do this is using a hand level which you hold up to your eye and look through to sight the bubble and cross to match up. Someone holds the measuring stick(staff) and you sight a mark on it then get the person to move away from you up and down the slope till the recorded measurement is reached. Then put in a stake and repeat the process.

Also this can be done with a string line and bubble level. The bubble level attaches to the string line and is raised or lowered till the bubble is at a level mark. When the swale is dug out, you use a tape measure to measure the depth from the string line over the distance you want to be level. Very simple and accurate to use.

We expected the job to take a couple of days but it took longer due to weather and other work needing to be done. We used several different ways to dig the paths as well. As there is an excavator on site and manual digging being hard work, we had a go with it to see what result we got. As a lot of Permaculture is experimental, it is always good to try different methods of doing things so you can learn from your mistakes and go with solutions that have proved to work.

As it turned out, it took quite a big bite and made the path too wide. One good result was that it gave us more surface area on the sides of the bed to plant. We learnt from this experiment and stayed with digging manually for a tidy finish. We also used the tractor to help define the paths, but found it was still best to dig ourselves.

We got rain after we finished and all the paths held water for two days and most were fairly level considering the tiring work it was to dig such a big area. We mulched all the beds to suppress the weeds and stabilize the soil till we can get seed to plant. It has been quite hard to source bulk seed here, especially non-hybrid seed. We will probably use soba (used to make soba flour for noodles) as it is fast growing (3 months) and it is sort of like a buck wheat.

1 comment:

Cecilia said...

Very serene looking potato patch. It gives me the ordered feeling of the rice terraces of thailand. Beautiful. And Useful. What a combination.
The whole blog is so practical, I just want to go and imitate what you are doing. The most sincere form of flattery