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< prev - next > Agriculture Irrigation KnO 100626_Building on a Tradition of Rainwater Harvesting (Printable PDF)
Building on a tradition of rainwater harvesting
Practical Action
An informal chat with a group of elders in the small town of Bula Burti goes something like
this: 'How long have you been using rainwater harvesting techniques?' 'Our fathers used them
... before that, our grandfathers also.' 'Why do you use such techniques?' He gives a look of
mild astonishment. 'Well, how could you grow crops here without harvesting the runoff?' ...
and so on. Rainwater harvesting is obviously well appreciated here!
The caag system of Somalia
Two types of small-scale rainwater-harvesting systems can be distinguished. The gawan
system makes use of a grid of ridges to trap rainfall, and hold some overland flow, whereas
the caag (pronounced 'aag') consists of larger earthern bunds which impound runoff from
small gullies. The bunds arc commonly made by a 'Kawawa' (see photograph), a simple, but
efficient, two-man push-pull shovel.
In the caag system, the main earth bund is made approximately on the contour. This bund is
then extended up the slope at both ends into a 'U' shape, but with one tip shorter than the
other, allowing excess runoff to flow around it. This then automatically controls the depth of
flooding, which is usually not more than 25cm at its deepest. One ingenious alternative
'spillway' sometimes used in Somalia is simply a piece of 30mm-diameter plastic pipe set in
the contour bund, which is unplugged to allow excess water to drain away.
Sudan has probably the richest tradition of rainwater harvesting of any country in SSA.
In many parts of the north, crops just cannot survive unless they are planted where wadis
spread and saturate the earth. Near Kassala, in eastern Sudan, there is a fascinating system -
practically unknown outside the area - of small-scale rainwater harvesting called teras. The
arabic word teras (from which the word 'terrace' originates) refers to the earth bund which
forms three sides of each plot. There are many similarities with the caag system in Somalia.
From the air, the 'teras' appear as a checkerboard design of green rectangles on the barren
plains. Each teras, of about two hectares in size, has a catchment of at least double this area.
Here, perhaps 30 per cent of the rainfall runs off from the plain and thus a plot with a
catchment twice its own size can effectively increase the rainfall available for the crops by
over 50 per cent.
Figure 1: The caag system, showing the live thorn fence surrounding the earth bunds.
Once again, the system uses earth bunds. The main bund, about 40cm in height, is sited
across the slope, approximately on the contour, which ensures an even spread of water behind
it. Side bunds then extend up the slope, and sometimes extra bunds divide the teras into sub-