TAILIEUCHUNG - Water harvesting and soil moisture retention - chapter 5,6

Water harvesting techniques contour systems Stone bunds, Living barriers and Trash lines Background Stone bunds along the contour line (Figure 9) are the most simple form of a contour water harvesting system. Because the bunds are permeable, they do not pond runoff water, but slow down its speed | 5 Water harvesting techniques -contour systems Stone bunds Living barriers and Trash lines Background Stone bunds along the contour line Figure 9 are the most simple form of a contour water harvesting system. Because the bunds are permeable they do not pond runoff water but slow down its speed filter it and spread the water over the field thus enhancing water infiltration and reducing soil erosion. Silt trapped on the higher side of the barrier forms natural terraces Figure 10 . A View from above. B Cross-section of a stone bund. a stone bund b crop growing in front of the stone bund c direction of runoff h height difference between stone bunds in metres d distance between two bunds over the ground in metres L horizontal distance of two bunds Figure 9 Stone bunds. Stone bunds can be reinforced with earth and thus be made only semipermeable. Where there a few stones available stone lines can be used to form the framework of the system. Grass or other vegetative material is planted immediately above the stone lines and forms over a period of time a living barrier. Crop residues like millet and sorghum Water harvesting techniques - contour systems 33 stalks piled weeds or branches of trees can also be used to reinforce the stone lines. In this case the barrier is called a trash line. These techniques are used on fairly gentle slopes to 3 . Since these structures are permeable it means that small errors in the contour determination are less important than for constructions which do not let water through. However proper alignment along the contour makes the technique considerably more effective. The advantage of systems based on stones is that there is no need for spillways or diversion ditches to drain excess runoff water in a controlled way. Making bunds or simple stone lines is traditional practice in parts of Sahelian West Africa. It has proved to be an effective technique which is popular and quickly mastered by farmers. Figure 10 Trash lines the land .

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