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close this bookSourcebook of Alternative Technologies for Freshwater Augmentation in Africa (International Environmental Technology Centre - United Nations Environment Programme, 1998, 182 p.)
close this folderPart B - Technology profiles
close this folder1. Agricultural technologies
close this folder1.1 Fresh water augmentation
View the document(introduction...)
View the document1.1.1 Planting pits (zai)
View the document1.1.2 Demi-lunes or semi-circular hoops.
View the document1.1.3 Katumani pitting technical description
View the document1.1.4 Permeable rock dams
View the document1.1.5 Contour stone bunding
View the document1.1.6 Tied contour ridges
View the document1.1.7 Fanya-juu terracing
View the document1.1.8 Flood harvesting using bunds
View the document1.1.9 Earthen bunds
View the document1.1.10 External catchments using contour ridging
View the document1.1.11 Sand abstraction technical description
View the document1.1.12 Lagoon-front hand-dug wells
View the document1.1.13 Sub-surface dams, small dams, and sand dams
View the document1.1.14 Cloud seeding
View the document1.1.15 Tidal irrigation

1.1.2 Demi-lunes or semi-circular hoops.

Technical Description

This is a short slope, micro-catchment technique, although the size of the semicircle 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., 1992).


Figure 3. Dimensions as used in Kenya. A cut off drain may be cut along the contour (Critchley et al., 1992).

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.

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 embankment.

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.

Costs

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.

Suitability

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.

Environmental Benefits

The technology results in increased vegetation cover on degraded lands.

Advantages

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.

Disadvantages

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.

Cultural Acceptability

The demi-lunes or hoops have been most successful where there was a high population density. It has been least successful when applied by pastoralists.

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 undertaken.

Information Sources

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.