Newsletter and Technical Publications
<Sourcebook of Alternative Technologies for Freshwater Augumentation
1.1.9 Earthen Bunds
|Earthen bunds are essentially an external catchment, long slope
technique of water harvesting. Typically a u-shaped structure of earthen
bunds which farmers build on their cultivated lands to harvest runoff from
adjacent upslope catchments, this technique usually collects rainwater
and, sometimes, floodwaters (Figure 14).
The base bund approximately follows the contour line and impounds the
runoff. Two outer arms fulfil the same function and also act as conveyance
structures which direct water to the cultivated lands. Sometimes, shorter
inner arms are added which divide the land into smaller basins and improve
the spread of captured runoff (Figure 15). A shallow channel is left on
the inside of the bund to support the conveyance and circulation of
Figure 14. Typical element of the teras water harvesting
(van Dijk, 1995).
Excess water is normally drained along the tips of the outer arms which are
reinforced with materials such as stones, brushwood or old tyres. Bunds are
usually 0.5 m high and 2 m deep at the base, but these dimensions can vary
greatly depending on both the slope and the amount of runoff expected in the
area. The base can be between 50 to 300 m long, while the arms are usually 20 to
100 m long. The size of the cultivated area serviced by such a structure is 0.2
to 3 ha.
Figure 15. Overview of a teras water harvesting system
(van Dijk, 1995).
Extent of Use
One of the few examples of traditional water harvesting technologies where
the technique is applied over a wide area. The system is called teras in
Somalia, where there are reported to be "thousands" of teras
plots in some regions of the Sudan. The bund system is also widely used in
Ghana, Burkina Faso and Mali.
Operation and Maintenance
This is a labour-saving technique. Generally, between 3 and 18 days/ha of
work is required to ensure that the system runs efficiently. However, breaches
of the bunds will require additional work in order to effect repairs. The local
dynamics of a drainage system may also require that the conservation structures
be continuously adjusted for best performance.
Level of Involvement
Entirely traditional and farmer-managed, earthen bunds may be built by hand
using simple tools, although the use of hired tractors is becoming more common.
There are no data on costs available, but they are not believed to be high
when earthen bunds are constructed manually by a farmer. Mechanical construction
methods increase costs.
Effectiveness of the Technology
The technique allows the production of a crop of millet or sorghum. Based on
data from the Sudan, yields may reach 750 kg/ha in a good year. Quick maturing
millet should be planted immediately after the water from a storm has subsided.
This crop grows and matures in about 80 days.
Use of this technology reduces land degradation.
This technology is appropriate for areas of the Sudan where the foothills
reinforce high intensity and short duration rainfall, with 150 to 400 mm
rainfall, annually. Low infiltration increases the generation of runoff from
teras catchments. Catchments are normally 2 to 3 times the cultivated area in
regions of 150 to 400 mm annual rainfall. Teras irrigation suits the lifestyle
of the Beja in the Sudan, as they are often absent from the land, and this
system lends itself to small-scale private enterprise. In West Africa the
technology is widely found in valley bottoms.
The technology is entirely farmer managed and, therefore, not subject to the
organisational problems of other soil and water conservation techniques. Socio
economic surveys have indicated that application of soil and water conservation
practises contributed about an additional 75% to the total household crop
production income in the 1980s and 1990s.
The lack of a spillway can result in breached bunds.
There are no cultural restrictions. The Muslim population of the Sudan
initiated the use of this technology about 40 years ago.
Further Development of the Technology
The development of spillways may improve the efficiency and reduce
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.
van Dijk, J.A. 1995. Indigenous and Introduced Soil and Water Conservation in
Sudan. Waterlines, 13(4):19-21.