Tuesday, January 25, 2011

Working With Nature Not Against Nature

SWALES

Water harvesting techniques beside the use of mulch and compost are also to be demonstrated in the Outdoor Class Room.

Swales (absorption beds) as discussed by Bill Mollison can aid in the infiltration of overland water flow for deeper storage for long term use and to increase base flow plus longer term water storage during dry seasons. With tropical down pours common swales also aid in slowing water down to minimize soil erosion and nutrient loss. Swales can also turn into terraces over a period of time through the collection of debris and further back leveling. For tropical sandy soils swale depth and width is best to be wider and shallower to cope with infiltration of the large amounts water falling over a short time.

Swales are designed to follow the contours of your land, to do this you need a surveying instrument as elaborate as a laser level or as simple as an A frame made from recycled timber a few nails and screws a piece of string  and a heavy weight as we did .





Try to make a space of at least one meter apart from each leg then secure with a brace 2/3 of the way down and at the top , it is best to make the A frame rigid. Find level ground by using a builders level then stand the A frame up and with the level mark across both legs. The A Frame will now sit level on all ground once you have cut the legs straight across this mark. Find centre distance between the two legs on the top brace and drive a nail in to secure the string with the weight on it, this will act as plumb bob to find centre on the bottom brace once the weight has stopped swinging mark the point as this will be your level point you look for when surveying your contour.


Logs on contour


 The principle is to find a start point and drive a stake in the ground then to continue from that point finding level ground and staking as you go. It is amazing how the land transforms before your eyes as you drive in every stake and more so when you dig or mound soil along your swale line nature has given you. This best describes “Working with Nature not against it” and Permaculture principle:

8. Use of edge and natural patterns for best effect


Earth mound on contour 

Swales are for growing trees











    




 As Eco Centro was filled with building rubble we were unable to dig the swales so we used soil from the redesign of the access to make earth mounds on contour with jungle logs placed on contour to retain soil, compost and mulches added for soil improvement.       


Pegs mark contour for raised bed

We also used the A Frame to contour swale a raised garden bed to maximize the collection of any surface water running through the garden.  If we harvest all the rain in the classroom which is around 2000m2 we will collect 1205L for every 25mm of rain that falls. Leading to rehydration of the land and drought proofing.  Try it you will like it !!!



Raised bed on contour

The next step is to cover the area with plants which will also aid in water harvesting        




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