In permaculture research, there is a huge concept that surrounds a land formation, called a swale. Permaculture swale design is typically for the rain water harvesting for trees. It is more of a forest tool. There are a few different types of swales, but the main one that I want to discuss is the “on-contour” swale.
If you look at a terrain map, in a very hilly area, the lines would be called contour lines. If you follow the lines you will generally be at the same elevation the entire time.
The swale is a ditch dug about 3-5 feet deep and 3-5 feet wide and runs on a level contour line. The purpose of this ditch is not to drain water, or to move it away from land. It’s whole function is to gather all of the water from a rain, and hold it there while the ground under it and down hill from it absorbe the water.
The swales are most effective when build across a sloping surface. The down-slope side of the swale has a mound built up behind the swale. It will absorb tons of water. The water will actually flow UP into the mound using capillary action from the dirt in the mound.
Swales also reduce soil erosion and will enrich the soil silt and minerals.
Trees are usually planted on the downslope side on or behind the mound. This will dramatically reduce the amount of water required for watering the trees, if not remove the need altogether for outside watering.
It is a new concept to do a reduced version of this for gardening. plants need much less water than trees, so we must scale back the swale design and remove some of the efficiency.
The idea in permaculture it to emulate the things that nature will do, and allow nature to do all of the work for us, so we can spend our time developing new things to help. Swales are one such thing, taking the role of the 8 inch mulch layer in an established forest system. They create a thing called a microclimate, making plantlife more hearty in more extreme weather.
Swales will fill up with water and allow the water to seep into the ground, and eventually when the ground is saturated, will hold water in it like a long narrow pond.
Everyone wants water to go away because it is yucky and they dont want to deal with it, but if your swale dam (the raised hilly part) has lots of mulch on it, there is no issue here. We want water, because during a drought, we will have a resevoir available. It is an underground lake! a 3 foot deep section of ground about 20 feet long and 20 feet wide is around 1200 cubic feet. If the ground will store at 20 percent efficiency, we can see a nice little 240 cubic foot pond below the earths surface.
The ground will store until saturation, then after that the swales themselves become small, slowly emptying ponds themselves. The sun will evaporate them and the ground will leech water slowly as well. We will see lots of biology begin to happen in all of this soil, which is great for plantlife.
I do not plan to build this system in my yard, unfortunately it is too small at the moment, but this concept is extremely important, because I am going to marry the concept with some other gardening techniques to assist is a great semi-permaculture style of garden later.
For more information on swales, you should visit Geoff Lawton’s website.
This would be a great concept to take and run with in a bug out location (BOL) that has much more room because it will allow us to establish a “food forest” in an area that requires very little upkeep.
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