Geomatics Use in the Evaluation of Surface Qualities Degradation in Saline Area (The case of the lower Cheliff plain)

Abstract

The plain of the lower Cheliff is located 220km to the west of Algiers and extends over 60000ha. This plain which is only 40km far from the Mediterranean has an arid climate and has suffered from dangerous degradation problems of its physical environment. This degradation is essentially due to the soil salinization which is manifested in different ground surfaces in relation with the degradation levels. The aim of this work is to use remote-sensing to evaluate the levels of soil degradation by the identification and the mapping of the ground surface. The visual analysis of the Aster image (August 2005) allows us to extract the big agronomic landscape units. And this led us to identify four homogeneous areas representing the different ground surfaces of the plain. The two irrigated perimeters of Ouarizane and Djediouia, the non saline soils of Benziane valley, and the Gaa which contain uncultivated saline soils with halophytic vegetation. The supervised classification of the satellite image allows us to generalize this good discrimination capacity to the whole ground surface and to obtain 9 homogeneous classes corresponding to various degradation levels. Therefore it is evaluated by soil and vegetal cover indicators. The remote-sensing data with salinity measured data of the ground surface classes has been used to map the soil salinity using remote-sensing and apply a comparison with the map obtained by ordinary kriging. The two methods have shown an important extension of the salinity. However, the estimated salinity map by remote-sensing made it possible to better estimate in comparison to the one obtained by ordinary kriging, on the level of extremes values.