EROSION CONTROL, BURKINA FASO. Yatenga Province,Kalsaka village. Building stone lines to prevent erosion. The lines slow down rain running off the land, giving it time to soak in. The lines, like very low dykes, slow down rain runningoff the land, and dam it back uphill, giving it time to sak in and nourish root crops. The stones have to be aligned exactly along the level contour, by means of a cheap housepipe level. The lines increase crop yields by 50% on average, much more in drier years.