Identification of Erosion Severity Area with Study of FargasModel (Case Study: Sangab Drainage Basin- Iran)

In order to identify critical sediment sources in large catchments, using easilyavailable terrain information at regional scale, a methodology has developed to obtaina qualitative assessment necessary for environmental management. So it has been triedto study and used Fargas and etal, method in this research. This has been done in oneof the sub-basins of Hable Rood basin called Sangab with an area of 7684.71 hac inNE Iran, arid and semiarid climate of Iran. The main objective of this model is to usebasic terrain data related to the erosive processes that contribute to the production,transportation and accumulation of sediments through the main water paths in thewatershed. This model is based on the selection of homogeneous zones regardingdrainage density and lithology, achieved by joining the basic units by a rating system.The values of drainage density are rated according to an erosion class. The lithology israted by erosion indexes, adapted from FAO (1977). The combination andreclassification of the results brings about five qualitative classes of sediment riskaccording to Fargas and etal (1997). The privileges of this method is, it used only twomain factors of the erosion, that are lithology and drainage density, and this factors arein our geologic and topographic maps in Iran. The mapping scale was 1:50000 and themodel were implemented through a vector GIS (Arc GIS9.2). The tested methodologyhas been proved useful as an initial approach for erosion assessment and soilconservation planning at regional level and also to select priority areas where furtheranalyses can be developed and finally for environmental management.