Moving sand and its consequences on and near a severely desertified environment and a protective shelterbelt

Sand movement from seriously degraded arid land with active sand dunes, northwest of the Gezira irrigation scheme (Sudan), is a real danger to that scheme. At its periphery, more than 10 cm of top soil was eroded by wind during 1977–1987. The scheme suffers from filling of canals with sand, increases in farm level beyond what is necessary for irrigation water to reach it, and changes in the soil characteristics from clay to more sandy conditions. A Eucalyptus shelterbelt was established to protect the scheme from desert encroachment. The approaching wind speed was significantly (>20% ± 2%) reduced within a distance of 20 m, three times the height of the belt. This reduction of wind speed is responsible for the amounts of deposited sand near and inside the belt, forming a dune within and near its edge that at some places is >2.5 m high and >45 m wide. Simple sand catchers were used for measuring saltating sand close to and within the belt. Because of deposition, the amount of moving airborne sand is reduced with distance to the belt. The decreasing ratio of coarser soil particles to the total amount of saltating sand could also be quantified with distance to the belt and height from the soil surface.