BURKINA FASO, Flooding. . Bund, low rock walls built to prevent soil erosion by flash floods. Stones are placed along the contours on gentle slopes. Sometimes the bunds are reinforced by planting tough grasses along the lines. The stones and grass encourage rain water to infiltrate the soil and reduce the amount of rain water that is lost by run-off. Any soil that has been eroded by run-off is trapped by the bund. Topsoil and organic matter (e.g. leaf litter) is deposited here. Bunds are placed 10 to 25 metres apart.