Preliminary Study of Sand Erosion in South Khartoum Area, Sudan

摘要

This study aims to evaluate, through aerial photo interpretation, the extent and severity of sand erosion in a 760 km~2 area to the south of Khartoum, between the Blue and the White Nile, Sudan. Two sets of aerial photographs, dating back to the years 1960 and 1990 were assembled to compile two mosaics of the area. Each mosaic was divided into macro units. By stereoscopic examination of the sheets of the area the macro units on each mosaic were divided into micro units. The boundaries between the micro units were transferred to tracing paper to compile two interpretive maps (a map from each mosaic). A light table was then used to draw two erosion maps from these interpretive maps. These two maps were digitized using ILWIS GIS. Then the line maps were changed to area maps, which were crossed to compile a final map showing the extent and degree of wind erosion in the study area. Field checks, along two 38km-long randomly aligned transects, were used to check the correlation, made through aerial photo interpretation between external features as shown on aerial photographs and the actual nature of the soil. In addition the fieldwork intended to test the validity of the tentative boundaries drawn through aerial photo interpretation, and the purity of the mapping units (that is to evaluate the success of the map legend in predicting the nature of the soil in the field). The results of the field checks indicated a very high (90%) purity of the mapping units and that 26.24% of the total area was affected by slight, moderate or severe wind erosion. The laboratory analysis indicated that sand was transported mainly in suspension. During this period either non-eroded areas became eroded (26% of the total area) or the severity of wind erosion increased (0.24% of the total area).