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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
Environmental benefits
Traditional rainwater-harvesting systems are, of course, only found in certain areas of semi-
arid Africa. Such systems are limited, for example, to areas where the soils are clayey and
where therefore, significant run-off occurs. The systems are normally environmentally sound:
by definition, rainwater harvesting is moisture, and therefore soil, conserving. Wind erosion
can cause havoc where fields are cleared in semi-arid areas, but this problem of erosion is
limited to sandy soils, where rainwater harvesting is not practised. The cultivators practising
rainwater harvesting tend usually to preserve useful species of tree when they clear land.
Figure 3: Finding the contour line using a water level, and building a stone bund.
Rainwater harvesting projects need, nevertheless, to beware of the possible dangers to the
environment, especially when earth bunds are used. The concentration of water can often
lead to bund breaches in the first season after construction, before the bunds have become
consolidated. There are plenty of examples of gully erosion caused by projects whose
techniques have not always been appropriate. A common mistake is to assume that the bigger
the bund, the less likely it is to break. It only takes a small crack, or a tunnel caused by a
rodent, to lead to disaster, if it is not spotted in time.
One question often asked is, what is the role of cropping (with or without rainwater
harvesting) in what are essentially pastoral areas? Indeed, the very thought of growing fields
of grain in rangelands horrifies traditional range-management specialists. The bald fact,
however, is that many pastoralists in sub-Saharan Africa are, in fact, agropastoralists, and
their small plots of food crops can contribute significantly to their diet. Why not indeed use
up the spare labour available in the slack period of wet-season herding? And the by-product of
straw, even when the crop fails, often provides more fodder for the livestock than the
rangeland which the field replaces.
Guiding principles
So what are the guiding principles for projects about to embark on rainwater- harvesting
systems? The following points are worthy of consideration: some may seem obvious, but they
are often overlooked in the field.
Find out what the people are doing themselves: to build on a traditional technique is better
than creating something new.
Ignore socio-economic factors at your peril! Talk to the people, establish their felt
needs, encourage participation.
Avoid systems which the people cannot replicate or maintain themselves. Hand tools
and donkey carts beat tractors and bulldozers nine times out of ten.
Consider the cost. Even where subsidies (such as food-for-work) are available, costs