Semi Circular Bunds



Similar names: Demi-lunes, banquettes, boomerangs, water bunds, earth bunds, earthworks, micro basins

The technique of creating Demi-lunes belongs to the overall category of water harvesting interventions and consists of half-moon shaped basins dug in earth. The main goal of water harvesting, as the name suggests, is to collect water, and to make moisture available for vegetation for a longer time. This type of microcatchment water harvesting technique is suitable for slopes up to 15%, however bunds made of earth are seldom used in areas with slopes greater than 5% with a precipitation rate higher than 300 mm/y. At lesser slopes, Demi-lunes are also used in areas with higher rain falls.

  • Increase vegetation
  • Improve soil health
  • Erosion prevention
  • Water harvesting
  • Increase crop yields

  • One of the main limitations of the demi-lunes is that their construction cannot be easily mechanized, thus they will require a lot of time and manpower if implemented on a large scale.
  • Bunds need to be protected from livestock and wild animals (such as baboons, porcupines, and rodents)
  • Construction of the bunds will require some skills and training: it is important to well measure the slope and lay the contour accordingly, and to build a correct bund structure.
  • Maintenance: in order to achieve a longer lifespan for the bunds, it is important to maintain them well. This involves immediately repairing any breakages, especially after construction when the bunds are not yet well reinforced by vegetation. If animals are allowed in the area, inspection and maintenance of the demi-lunes must be done more frequently.

Material required

  • Hoe (Jembe) or shovel
  • Pickaxe (for hard soils)
  • String or thin rope
  • Pegs or stones
  • To measure the contour line, here are some examples of tools that could be used: a string line level or spirit level instrument, hose pipe half filled with water, bottle of water half filled with water, A-frame level.

Steps of Implementation

Bunds are created by using earth or stones and have a diameter from 2 to 8 meters (although they can measure up to 12m). The bund tips are usually placed along a contour line, facing upslope. Bunds are usually 30-50 cm high. They are arranged in alternating patterns so that the line below can catch the runoff coming from the line above, and so on. In dry conditions, a bunds’ diameter is bigger, whereas, in wetter conditions, bunds are usually smaller but more copious.

  1. Using a simple surveying instrument, stake out the first contour following the contour line.
  2. With the help of a tape measure, mark the tips of the semi-circular bunds on the contour.
  3. Mark the center point between the two tips. Then, take a piece of string, as long as the radius of the bund (the distance between one tip and the center), and fix it and hold it in place at the center point with the help of a peg or a big stone. Holding the string tight at the other end, trace the semi-circle, following the path of the tight string from one tip to the other. The semi-circle can be traced with the help of a stick drawing in the soil, or by placing pegs or small stones.
  4. Repeat the procedure to draw the other bunds, paying attention to respect the desired alternating pattern, making sure that the center point of each bund coincides with the gap between the bunds in the first row (upslope) and so on.
  5. After you have finished making the design, start the bund construction by excavating a small trench inside each bund, always starting from the inside of the bund. Create layers of 10-15 cm each, compacting and wetting them if possible.
  6. The bund tips can be reinforced with stones, to ensure more resistance against erosion.
  7. The construction of a diversion ditch might be required to protect the first row of bunds from water runoff of the above area. One or more diversion ditches can be built if considered necessary. The size of a diversion ditch should be 1-1.5 m wide and 50 cm deep, with a 0.25% gradient.

    The space between the bunds can vary according to the purpose. Larger and more widely spaced Demi-lunes are more suitable for grazing land rehabilitation or fodder production. Smaller and closely spaced half-moons fit better for growing trees and shrubs.

This intervention contributes to:


Estimation of costs and benefits of intervention

Establishment cost About US $8 per bund, US $150/ha with labor time?
Labor time >20 person days/ha, 2-8 demi-lunes per person per day
Which products Trees, sorghum, maize

Source: Justdiggit, Kenya

A great example of the effect of Demi-lunes over time has been recorded in Kuku, Kenya by Justdiggit, an NGO working on ecosystem restoration, during the rainy and dry season 2017-2018

A good example of demi-lunes used for crops and forest/rangeland in Niger can be found here, in the WOCAT SLM database.

  • Here you can find a very useful video on how to construct demi-lunes.
  • Good instructions on how to lay out a contour or a graded contour and measure the slope of the land can be found here.

Additional information


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Land use

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