Mapping potential soil vulnerability to water erosion in Tafna watershed (North-West of Algeria)

Abstract

Water erosion is the main form of soil degradation in northern Algeria. This inevitable natural phenomenon which particularly affects the north-western part of the country is exacerbated by the human’s appalling practices and the fragility of the soils. The vulnerability of soils to water erosion was studied in the Tafna watershed through a spatial analysis based on the use of remote sensing and geographic information systems. The Tafna watershed, one of the major watersheds of northern Algeria, is the wettest region in the west and the most productive in the Wilaya of Tlemcen. Its total area is 724,500 ha, of which 27% is in Moroccan territory. The cartographic approach followed was developed within the framework of the Priority Action Program of the Mediterranean Action Plan (PAP-MAP) with the General Directorate of Nature Conservation of Madrid (GDCOM) and FAO in 1998. Five classes of vulnerability to water erosion have been distinguished. Very low sensitivity areas cover 7.32% of the pool area, low to medium sensitivity areas cover more than half (51.87%) and high and very high sensitivity areas cover 40.80%. The downstream part of the dock is the most affected by water erosion, especially linear erosion, due to the dominance of rugged terrain and the presence of soft substrates. The upstream part, is more stable thanks to its erosion-resistant lithological composition. The effect of the slope and the degradation of the vegetation cover cause flooding during heavy rains. All forms of water erosion have been observed and the most catastrophic are badlands and landslides, which cause considerable loss of agricultural land and mobilize significant sediments threatening downstream structures (towns, roads, dams, etc.). To slow down this process, the degradation of the plant cover must be slowed down and the use of traditional methods of water and soil conservation should be encouraged.

 Keywords: Vulnerable soils, Water erosion, GIS, Cartography, Tafna watershed, North-West Algeria