Newsletter and Technical Publications
<Sourcebook of Alternative Technologies for Freshwater Augumentation
1.1.6 Tied Contour Ridges
Contour ridges are small earthen ridges, 15 to 20 cm high, with an
upslope furrow which accommodates runoff from a catchment strip between
the ridges (Figure 8). The catchment strip is usually uncultivated, but,
where contour ridging is used to control erosion rather than for water
harvesting, the whole area may be cultivated.
Ridges may be from 1.5 to 10.0 m apart, but, as this is a micro-catchment
system and the catchment is a function of the distance between ridges, the
precise distance should be calculated for the expected rainfall of the
region (Figure 9).
Figure 8. Contour ridges as used in Kenya
(Critchley et al., 1992).
Small earthen ties are made within the furrows at 4 to 5 m intervals to
prevent lateral flow (Figure 10). The objective of the system is to
collect local runoff and store it within the soil profile in the vicinity
of the plant roots. Micro-catchment contour ridging is usually not
designed to accommodate overflow, so the system should be protected with a
The tied contour ridging system is used for tree planting (with a wider
distance between ridges) and crop production. Crops are planted on the
ridges as well as in the furrows.
Figure 9. Field layout for contour ridging which varies
to the catchment to harvest area ratio (Critchley et al., 1992).
Extent of Use
It has been adopted in Kenya, Niger, Zimbabwe, amongst others. It does not
seem to be taken up spontaneously, however, and is mainly promoted through
projects and government policy. Nevertheless, tied ridges are widely used in
commercial farming situations in southern Africa as a means of controlling soil
Operation and Maintenance
Minimal maintenance is required if the ridges are properly constructed
initially. Maintenance involves reconstruction of any lines and ridges that
might have collapsed.
Level of Involvement
While possible to prepare with hand implements, most projects have used
mechanised equipment to construct the contour ridges. Farming practices
thereafter are left in the hands of the community. The siting of contours can be
done by the community after training.
With human labour, an estimated 32 person days/ha is required. Using
machinery, the time requirement is reduced, but the costs are increased to an
estimated $100/ha. This technology is considered low cost, although the rate of
its adoption has not been high.
Figure 10. Tied furrows as used in Zimbabwe (Critchley et
Effectiveness of the Technology
Data from Kenya suggest that there are considerable yield advantages in using
the contour system. The data also show that, when used in combination with
appropriate crops, it has a demonstrated ability to reduce the risk of crop
failure due to drought by concentrating the runoff. This technology has been
used with millet, cowpeas and sorghum.
The application and effectiveness of the technology is believed to be
greatest in those areas where soils have been degraded to the extent that the
people cannot reverse the trend using their own resources. An external input of
mechanical equipment can have a large impact in these situations.
The technology is being used in a variety of climatic and soil conditions and
can be adapted to rainfall by adjusting the distance between contours and also
the area of cropping. Water harvesting potential is reduced or lost if the
catchment area is planted. At Baringo, Kenya, where there is a mean annual
rainfall of 655 mm, the project area has a catchment to cultivated area ratio of
2:1. Further, a range of slopes may be treated, though the dimensions need to be
increased as slope increases. In the relatively higher rainfall area of
Zimbabwe, there is only a 1.5 m spacing between the ridges, and the ridges
themselves act as the catchment. Planting is carried out alongside the furrow to
take advantage of the concentrated water but to avoid waterlogging.
The system is suitable for areas where cultivation is limited by water
shortages and in areas where there is severe environmental degradation.
Benefits of land rehabilitation and reduced soil erosion are normal results
when this technology is used.
This low cost technology has the potential to increase food security in below
normal rainfall years. The system can be implemented using either a mechanised
or manual labour approach. As with other water harvesting methods, it is more
likely to be successful in areas which experience severe dry spells and/or
highly variable rainfalls. The technology reduces soil erosion and increases
soil moisture content.
The unusual cropping system of planting on ridges and next to furrows, but
leaving the catchment unplanted, is thought to be a disincentive for adopting
this technology. Further, the labour-intensive approach is not thought to be
attractive in the areas where the technology has been tried. In Baringo, Kenya,
farmers were reportedly reluctant to repair bunds after they were washed away.
The relatively low planting density discourages farmers, especially in a good
year, and the technique does not work well on steep slopes.
No data have been reported on this aspect of the technology.
Further Development of the Technology
Globally, this is a well-documented and widely-practised technology which can
be adapted to a variety of conditions. However, in Africa, it requires effective
extension and promotion before it is widely adopted.
Institute of Agricultural Engineering, Post Office Box BW 330,
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.