Rainwater harvesting

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General information

1. Name technique: Teras (Sudan)

2. Pictures

Figure 1: Inspection of base bund as part of Teras water harvesting structure (Source: www.fao.org)

Figure 2. Typical elements of the Teras water harvesting structure (Source: Dijk J.A. van, 1995).

3. Brief description of the situation:
African drylands are vulnerable to food insecurity. Their populations grow rapidly, while most of the best soils for crop production are already being used. The resulting forced expansion into more marginal areas for cultivation results in land degradation, which further increases the hazard of food insecurity (Engelman and Leroy, 1995). In an attempt to halt this downward spiral, several new crop production systems have been introduced in recent decades. Attention is recently being given to building on indigenous knowledge (Warren, 1991). When indigenous techniques are improved, dissemination is usually faster, more widespread and cheaper because it fits better into local environmental and socio-economic niches (Reijntjes, et al., 1994). Socio-economic data and remote sensing in the Border Area in eastern Sudan indicate that the use of indigenous soil and water conservation techniques (ISWC) is expanding. The most elaborate ISWC technique applied in eastern Sudan is the Teras system (bunded landholding, see Figure 1).
This case-study describes the use of the teras ISWC technique in the rural village of Ilat Ayot, near Kassala, eastern Sudan. More information about the Teras technique in other villages in this region is given by van Dijk, 1997.

Technical information

4. Brief description of the technique:
Bunds are small stone or earthen walls, usually constructed along the contour. Bunds act as an obstruction to overland water flow on hill slopes. The bund reduces flow velocity and water percolates behind it, increasing soil moisture and recharging the groundwater.
Teras is the name given to a landholding which is bunded on three sides (Figure 2). The fourth is left open to capture run-off from an adjacent, slightly elevated catchment. The Teras technique consists of a base bund which approximately follows the contour line and impounds the runoff. Two outer arms fulfill 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 runoff. Excess water is normally drained along the tips of the outer arms. The Teras technique is applied to increase agricultural production, and does not directly increase drinking water supply.

5. Attributes overview:

6. Construction:
Teras bunds are built by hand and are made of local alluvial and colluvial material. In the dryer northern parts of the Border Area, land users also erect brushwood to capture sand and dust in order to let bunds rise by wind action. The 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.

7. Capacity:
There are no data on the water storage capacity available. The main crop planted in the structure is millet or sorghum, with okra, rosella and watermelon occasionally being intercropped. The average sorghum production in the 1980s was 400 kg /ha/ year (Van Dijk, 1995). Based on data from 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. .

8. Experiences with Operation and Maintenance:
The labor demands of Teras use are relatively low, with 6±16 man-days per hectare for construction and 3±18 man-days per hectare for annual maintenance (excluding cultivation). Farmers from the Beja tribe increasingly rent tractors for construction and maintenance purposes, to ensure that the system runs efficiently. Breaches of the bunds will require additional work in order to repair the system. The local dynamics of a drainage system may also require that the conservation structures be continuously adjusted for best performance.

9. Experiences with Monitoring and Evaluation:
Field research has been carried out in the programmes of Water Spreading Research Kassala (WARK; National Council for Research, The Ford Foundation) and Livelihood and Environment (L&E; University of Amsterdam).
When the situation is assessed over the 4 years for which data are available, Teras use tends to show advantages in the form of higher returns in the dryer years than any of the other crop production techniques in the Border Area. ISWC by Teras is therefore likely to be continued because it helps to diversify income sources in normal years, and becomes an outright advantage during dry years. Apparently, the Beja are willing to incur costs in terms of labour opportunities and income lost during wet years, in order to buy the greater overall subsistence security which is vital during dry years.

10. Experiences with related subjects (e.a. erosion prevention, quality of drinking water, ..):

• Erosion prevention: Bunds slow down water flowing overland during and after intense rainfall. Bunds also trap sediment washed away by overland flow. Therefore use of this technology prevents erosion and reduces land degradation.
• Cultural acceptability: There are no cultural restrictions. The Muslim population of Sudan initiated the use of this technology about 50 years ago.

Financial information

11. Experiences with management:
Several rural development programmes were initiated in the region. Earth diversion banks and stone-pitched dams were first built in the Border Area under the Anglo-Egyptian Administration (1898±1956). New SWC techniques were introduced in the region on a larger scale from 1983 onwards.
The merits of ISWC were largely ignored in these projects. Land users applying ISWC have only received modest support from 1988 onwards, for example, in the form of subsidized tractor rent for Teras construction and maintenance.

12. Benefits:
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.
Socio economic surveys have indicated that application of soil and water conservation practices contributed about an additional 75% to the total household crop production income in the 1980s and 1990s.

Table 1: Developments in livelihood. Changes in total household income shares in livelihood by sector (%) and total teras income shares in crop production and livelihood (%) for Ilat Ayot in the Border Area, 1983 and 1988

Table 2. Crop production returns. Income per man-hour invested in selected tillage activities (1983 £s) by growing season characteristic and applied technique in four Border Area villages in 1983 and 1988-1990

Source: L&E research (N. 244); Van Dijk (1995: 240, Figure 7.4, adjusted). Note: ISWC includes and brushwood panels; government-introduced SWC includes earth dams and embankments; non-SWC techniques include valley-bottom and flood-recession cultivation.

General conclusions

13. Generic factors of success and traps ('do's and don'ts'): The need for spillways must be assessed. The development of spillways may improve the efficiency and reduce maintenance costs. The lack of a spillway can result in breached bunds.

14. What can be used elsewhere, under which conditions:
This technology is appropriate for areas of 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 in Teras catchments. Catchments are normally 2 to 3 times the cultivated area in this (semi-) arid region. Teras irrigation suits the lifestyle of the Beja tribe in 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.

15. Advantages and disadvantages:

16. Links to detailed information of this project / technique:

Johan van Dijk
University College Dublin. Department of Geography and Environmental Institute
Belfield, Dublin 4, Ireland
Tel +353 1 7068487

Drs Chris Reij
Centre for international cooperation Vrije Universiteit, Amsterdam
Tel +31 20 598 9065 or +31 20 598 9078


17. References

• Dijk J.A. van. 1997. Indigenous Soil and Water conservation by Teras in Eastern Sudan. Land Degradation & Development, Vol. 8, 17 - 26.
• Engelman, R. and Leroy, P. 1995. Conserving Land: Population and Sustainable Food Production. Population and Environment Program. Population Action International, Washington, DC.
• Reij C. 1991. Indigenous soil and water conservation in Africa. Gatekeeper series #27. International Institute for Environment and Development.
• Reijntjes, C., Haverkort, B. and Waters-Bayer, A. 1992. Farming for the Future. An Introduction to Low-External-Input and Sustainable Agriculture. Macmillan and ILEIA, London.
• Warren, D. 1991. Using Indigenous Knowledge in Agricultural Development. Discussion Paper 127, World Bank, Washington, DC.

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