|Demi lunes – also known as semi-circular bunds or ‘eyebrows’ – require the creation of small bunds in the shape of a half-moon with their tips on the contour. The ponding area inside the demi lune retains water flowing down the slope from above the bund. Demi lunes capture runoff and are used to improve rangeland and increase grass, tree, and crop production. Demi lunes are more efficient than trapezoidal bunds in terms of the ratio between the bund volume and the ponded area.
The design varies according to topography, climatic conditions, and plant requirements. In dry conditions, the bunds are bigger and equipped with spillways. In wetter conditions, more bunds of smaller radius are constructed per hectare. They are rarely used on slopes steeper than 5%. When used for rangeland improvement, local grasses can be grown, but the introduction of more productive trees and shrubs is recommended. When used to grow crops, drought resistant species such as sorghum, pearl millet and certain pulses must be chosen. To satisfy the plant’s water requirements, farmers tend to reduce the catchment area of the semi-circular bunds to increase the cultivated land.
|Knoop, L., Sambalino, F., & van Steenbergen, F. (2012). Securing Water and Land in the Tana Basin: a resource book for water managers and practitioners. The Netherlands: 3R Water Secretariat.