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1.1.2 Demi-lunes or Semi-circular Hoops.
This is a short slope, micro-catchment technique, although the size of
the semi-circle and its catchment may be varied considerably according to
the rainfall of the region and the preference of the community. Generally,
the catchment to cultivation ratio varies from 10:1 to 3:1, and the size
of the lunes or circles varies from a radius of 2 to 15 m (Figures 2 and
3). Demi-lunes are constructed by hand labour with an emphasis on
rehabilitation of degraded land.
Figure 2. Demi-lunes from Niger (Critchley et al.,
Bund height varies from 15 to 25 cm. The demi-lunes are
laid out along a contour and staggered in successive lines. Some sites are
protected from external runoff by diversion ditches. Soil for the bund is
either drawn from within the hoop thus levelling the land, or by creating
a furrow inside or outside the hoop.
Figure 3. Dimensions as used in Kenya. A cut off drain
may be cut along the contour
(Critchley et al., 1992).
Extent of Use
While widely promoted in Niger (where several thousand hectares are
cultivated using this technology) and demonstrated in several areas of
Kenya, neither country reports the spontaneous adoption by the technique
by the community. It has been adopted by Niger as a recommended measure
for moisture conservation.
Operation and Maintenance
The operation and maintenance requirements are within the means of the
individual farmer to undertake, and involve the regular upkeep of the
Level of Involvement
Entirely developed by community labour once adopted, the initiative to
create demi-lunes is often external to the community. As a result, the
technique has not been spontaneously adopted.
The cost of this technology can be approximated as $150/ha for labour or
about 10 person days/ ha.
Effectiveness of the Technology
The demi-lunes or hoops are used mainly for increasing pasture
production and rehabilitation of degraded lands. This technique is used
only rarely for crop production. The demi-lunes have resulted in
dramatically improved vegetation growth within the hoops, but, in most
cases, production has not been measured.
This technology is currently being used in a wide range of land types
and rainfall regions (in areas with rainfalls ranging from 200 to 800 mm
annually). It would appear to be adaptable to different conditions by
adjusting the catchment to cultivation ratio.
The technology results in increased vegetation cover on degraded lands.
Some dramatic improvements in vegetation within the semi-circular hoops
have been reported. It is cheap and easy to implement this technology with
available manual labour.
It is not a technology that has been taken up by the people - possibly
because of a reluctance to invest much time in improving grazing lands.
Also, the structures are vulnerable to breakages when subjected to high
volumes of runoff, but this is generally a function of the diversion
ditches rather than the technology itself. When breakages due to
overloading by runoff occur, operators should reduce the catchment to
cultivation ratio. This technology is not suitable for use with
mechanisation and in areas where cattle are the primary product, given the
propensity of cattle to trample the lunes.
The demi-lunes or hoops have been most successful where there
was a high population density. It has been least successful when applied
Further Development of the Technology
Little has been done to monitor systematically parameters such as yield,
labour input requirements, or rainfall effects. This information is needed
before further widespread promotion or adaptation of this approach is
Critchley, W., C. Reij, and A. Seznec 1992. Water Harvesting for
Plant Production. Volume II: Case Studies and Conclusions for Sub-Saharan
Africa. World Bank Technical Paper No. 157, 133 p.
Imbira, J. 1989. Runoff Harvesting for Crop Production in Semi-arid
Areas of Baringo. In: D.B. Thomas et al., Editors. Soil
and Water Conservation in Kenya, Proceedings of the Third National
Workshop, Nairobi, 1986. University of Nairobi, SIDA, pp. 407-431.