Similar names: level bunds, contour stone bunds, earthen bunds
Contour bunds (also known as contour bunding) are a form of micro-catchment technique and are a very simple and cheap form of water control. The bunds are created along the contour lines. There are also small earth ties, perpendicular to the bunds, that subdivide the system into micro-catchments. Contour bunds are very similar to Negarim in that they aim to slow down runoff and improve water infiltration in the soil. For this reason, contour bunds are often associated with the cultivation of crops, fodder or trees which are grown between the bunds. Contour bunds also help to control soil erosion. Contour bunds for tree planting is suitable in arid and semi-arid areas with rainfall rates between 200 and 750 mm. They can be applied on slopes of up to 5% but they require even terrains, without the presence of gullies or rills. The soil should preferably be 1.5 to 2 m deep in order to ensure proper root development and water storage.
- Maintenance: if the bunds are maintained regularly (annually or after every strong rainfall), the minimum expected life is about 20 years, and they are very effective for improving land fertility.
- Importance of good implementation: contour bunds entail less maintenance costs if they are built well to start with.
- Better results are achieved if the top to bottom treatment is applied: if farmers of the same region that have fields uphill/at the top of the slope use the same technique, then the erosion is more efficiently slowed. Hence, better results to control water runoff are achieved when this technique is applied at large scale, and in cooperation with all the stakeholders along the slope.
- Suitability of the application area: Contour bunds are not suitable in areas with gullies or rills. Uneven or eroded land will cause overtopping of excess water with high risk of breakage of the contour lines.
- Line level,
- digging instruments,
- stones of mixed sizes (for stone-faced bunds).
- If combined with revegetation: suitable native grass and legumes, suitable tree seedlings of at least 30cm height.
Looking at a field with contour bunds from above, it consists of a sequence of parallel earth bunds running along contour lines. Their spacing depends on the slope of the hill and should decrease in size with an increasing slope: the steeper the slope, the closer the contour bunds will be. It is recommended to grow vegetation along the bunds to improve their stability.
Contour bunds are frequently used in the valley bottom, since they are often slightly concave. The bunds will be built with a parabolic shape in order to allow water to spread to the sides. The soil excavated from the adjacent ditch is relocated upslope and will form the bunds. A bund‘s height is usually around 20-40 cm, but this can vary depending on the slope. Their base should be at least 75 cm wide. There are also small earth ridges perpendicular to the bunds, and located on the upslope side, that divide the system into micro-catchments. These cross-ties shouldn’t be less than 2 m long and are formed by the soil obtained from the excavation of the infiltration pits. The layout of this intervention also implies infiltration pits (usually 80x80x40 cm) that are excavated at the intersection between bunds and ties.
Contour bunds might also include the presence of trees. Planting sites are expected to be between the infiltration pit and the cross-tie. It is recommended to plant seedlings that are at least 30 cm high, and the best planting period is right after the first runoff has been collected. If needed, it is also possible to add manure or compost to the planting pit to increase fertility and its water holding capacity. Lastly, where needed, in the layout there might also be a , to protect the entire system from flooding during heavy rainfalls.
A good explanation on how to build contour bunds following slope lines can be found here.
Like Negarim, some maintenance interventions might be required to repair damaged bunds early in the first season. Such damages are frequently caused by animals invading the areas or strong rainfalls.
A Similar technique to this intervention are Contour stone bunds or stone-faced bunds, which consist of stone lines combined with bunds that are a minimum of 25cm high, with a base width of 35 – 40 cm, reinforced with a mixture of large and small stones following the contour. Click here to find out more about stone lines.
Another similar technique to this intervention is Graded bunds, which differ from contour or level bunds in that they aim to dispose of any excess water and therefore have a gradient of up to 1% on the side, towards a waterway river. This technique is applied along land slopes when there is an important runoff (annual rainfall > 700mm) and the simple contour bunds are not sufficient to retain the surplus runoff. Further information about Graded bunds can be found here.
Estimated costs & benefits of intervention
|Establishment cost||about US $30 per ha|
|Labor time||120 person-days for one hectare of contour bunding|
|Maintenance cost||If properly implemented, maintenance costs are 5%-10% of implementation costs.|
|Benefits||Income is boosted by about 20%|
|Products||Paddy, pigeon pea, groundnut, sorghum, cotton, black beans, wheat, gram, vegetables|
Contour bunds can help farmers increase their incomes by 20%, an example of this, in Mali, can be found here.
Contour bunds can also be combined with gully plugging in a watershed area, a good example can be found here.
An example of the positive effect of contour bunds and stone-faced soil bunds on crop yield in Ethiopia can be found here.