ABSTRACT
According to the 1982 census, the Tanacherfi commune, which includes the area in question, had a population density ranging from 10 to 20 inhabitants per km2 • In the foothills, where land is relatively abundant, the average is 2.4ha of cultivable land per inhabitant - ie, 25ha per household. In the highlands, by contrast, one irrigated hectare has to feed 15 people, exerting a pressure on land which helps to explain the maintenance and extension of traditional SWC structures. In the foothills, SWC techniques are mainly designed to stem active and obvious erosion, while in the highlands, flat plots of land must be secured and maintained by terracing, permitting irrigation. SWC structures help to store rainwater in the soil, but must enable excess water accumulated behind the terrace to drain away, whilst fostering the growth of trees planted along the structures.
