Contour bunds (watershed Management)

Contour bunds, which are sometimes referred to as contour bunding, are a type of microcatchment technique and a relatively straightforward and affordable method of water control. Along the contour lines, the bunds are formed. Additionally, there are tiny earth ties that split the system into microcatchments and run perpendicular to the bunds. Negarim and contour bunds both work to slow down runoff and enhance water infiltration in the soil. Because of this, contour bunds are frequently linked to the cultivation of plants, animals, or trees that are cultivated in between the bunds. Bunds with a contour also prevent soil erosion. For planting trees, contour bunds are acceptable in arid and semi-arid regions with 200–750 mm of annual rainfall. They can be used on slopes up to 5%, but they need flat, level ground free of gullies and rills. To promote appropriate root development and water storage, the soil should ideally be between 1.5 and 2 metres deep.

METHOD OF APPLICATION

Materials needed

line level,

digging tools,

and various-sized stones (for stone-faced bunds).

Suitable native grasses and legumes,

as well as suitable tree seedlings at least 30 cm tall,

if revegetation is combined.
A field with contour bunds appears like a series of parallel earth bunds running along contour lines when viewed from above. Their spacing varies according to the hill's slope and should get smaller as the slope gets steeper, bringing the contour bunds closer together. To increase the stability of the bunds, it is advised to plant vegetation there.

Since the valley floor is typically slightly concave, contour bunds are regularly employed there. To allow water to flow to the sides, the bunds will be constructed in a parabolic shape. The bunds will be created from the soil that was removed from the nearby ditch and moved upslope. The height of a bund is typically between 20 and 40 cm, however it can vary depending on the slope. At least 75 centimetres should be present at their base. On the upslope side of the system, there are also a few tiny earth ridges that run parallel to the bunds and split the system into microcatchments. These cross ties, which are made from the dirt removed during the excavation of the infiltration pits, should not be shorter than 2 m. The design of this intervention also calls for the excavation of infiltration pits, which are typically 80x80x40 cm, at the point where bunds and ties converge.

Trees could also be present in contour bunds. Between the cross-tie and the infiltration pit, planting locations are anticipated. The optimal time to plant is shortly after the first runoff has been collected, when seedlings should be at least 30 cm tall. The planting trench can also be fertilised and made better at holding water if necessary by adding compost or manure. To prevent the entire system from floods during severe rains, the layout may also include a where necessary.

Here is a useful explanation of how to construct contour bunds that follow slope lines.

Early in the first season, repairs to damaged bunds would be necessary, similar to Negarim. Animal invasions or heavy rains are two common reasons for these damages.

OTHER

Contour stone bunds, also known as stone-faced bunds, are a technique that is similar to this intervention and consists of stone lines mixed with bunds that are at least 25 cm high, with a base width of 35 to 40 cm, reinforced with a mixture of large and small stones following the contour. To learn more about stone lines, click here.

Graded bunds, which differ from contour or level bunds in that they aim to dispose of any excess water and hence have a gradient of up to 1% on the side, towards a waterway river, are another technique related to this intervention. When there is a significant runoff (annual rainfall > 700mm) and the straightforward contour bunds are unable to absorb the extra runoff, this technique is used along land slopes. You may get more details regarding graded bunds here

SOCIO-ECONOMIC CONSIDERATIONS

Advantages

• Reduces soil erosion
• Increases availability of food, fodder and fuel
• Cost efficient: whether mechanized or not, the realization of this technique is relatively cheap, especially on a large scale and on even lands because less earth is moved.
• Improves soil and water conservation
• Can be combined with machinery, which enables this technique to be scaled up to large areas.
• Fodder crops can be grown before the trees become productive (However, this would imply a reduction in the amount of water runoff that can reach the trees)

Conditions

• 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.