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|
|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.