|Sourcebook of Alternative Technologies for Freshwater Augmentation in Africa (International Environmental Technology Centre - United Nations Environment Programme, 1998, 182 p.)|
|Part B - Technology profiles|
|1. Agricultural technologies|
|1.1 Fresh water augmentation|
Based on the development of bench terraces over a period of time, and known by its Swahili name, fanya-juu terraces are constructed by throwing soil up slope from a ditch to form a bund along a contour (Figure 11). The trench is 60 cm wide by 60 cm deep, and the bund 50 cm high by 150 cm across at the base (Figure 12). Several of these terraces are made up the slope following the contour lines. The distance between bunds depends upon the slope and may be from 5 m apart on steeply sloping lands to 20 m apart on more gently sloping lands.
Similar terracing systems are found in many countries where the stones from rocky slopes are used to build the bunds or terrace walls, often on very steep slopes. Contour ridges may be combined with this system.
Through gradual erosion and redistribution of soils within the enclosed fields, the terraced lands level off, forming the terraces. Soil and rainwater are conserved within the bunds, and the bunds are usually stabilised with planted fodder grasses. In addition, each farm using this technology is surveyed to see if it needs a cutoff drain to be installed in order to protect the terraces from surplus rainfall. The use of stone terrace walls allows surplus water to pass through the bunds by infiltrating between the stones and overtopping the walls.
Extent of Use
The technology is known from the Machakos District of Kenya, which is hilly and subject to widespread erosion. Since the mid 1980s, the District has achieved the installation of an average of 1 000 km of new fanya-juu terraces each year, plus several hundred km of cutoff drains; 70% of the cultivated land in the District is reported to have been terraced.
Between 1974 and 1991, the National Soil Conservation Programme in Kenya prepared and implemented conservation plans on 925 000 farms. The rate of compliance increased to 100 000 farms per year by 1991. A variety of technologies were promoted through this Programme, including fanya-juu terracing. Over 500000 farmers were trained in conservation technologies.
Use of terracing is also reported on steeply sloping lands in Morocco.
Operation and Maintenance
Regular maintenance of the embankment is required
Level of Involvement
In Kenya, the implementation of this technology is normally undertaken by self-help groups who work collectively on each others lands. Some richer members of the community employ others to prepare the terraces since family labour on its own is generally not adequate for constructing these features. Self-help groups in Machakos consider soil conservation to be one of their main activities.
The labour required for construction is estimated at 150 to 350 person days/ha for terraces and cutoff drains. The cost of these structures is approximately $60-460/ha.
Effectiveness of the Technology
In Machakos, crop yields have increased by 50% (or by 400 kg/ha) through the use of fanya-juu terraces.
This technology is suitable for marginal or wetter zones of 700 mm annual rainfall or above. Soils should be deep. The technique is suitable for use on slopes of less than 5% to 50%.
There is effective control of erosion. Where a whole catchment has been conserved there is an improvement in streamflows with consequent benefits for a village water supply.
The technology generally results in a reliable increase in crop yields.
The technology is costly in terms of labour. Unprotected bunds, which have not been planted with grass, are prone to erosion.
This technology has fitted well into culture of the self-help groups present in the areas of application to date, and reinforces their emphasis on full involvement of the community in freshwater augmentation efforts. The technology has already been established in the area and, therefore, there was no cultural resistance to it.
Further Development of the Technology
Application of this technology in other areas needs to be further examined as there were special conditions in the Machakos District of Kenya which enabled it to succeed.
Critchley, W. 1991. Looking After Our Land, Soil and Water Conservation in Dryland Africa, Oxfam, London, 84 p.
Lee, M.D. and J.T Visscher 1990. Water Harvesting in Five African Countries. IRC Occasional Paper No. 14, 108 p.
Pacey, A. and A. Cullis 1991. Rainwater Harvesting. The Collection of Rainfall and Runoff in Rural Areas. Intermediate Technology Publications, London, 216 p.
Eriksson, A. (Editor) 1992. The Revival of Soil Conservation in Kenya. Regional Soil Conservation Unit, SIDA Report No 1, 30 p.