Identification of Critical Sediment Source Areas at Regional Scale for Environmental Management (Case Study: Dehnamak Basin, Iran)

To identify critical sediment sources in large catchments, using easily available terrain information at a regional scale, a methodology was developed to obtain a qualitative assessment necessary for environmental management. Fargas et al method was employed in the research. The study was carried out in one of the sub-basins of Hableh Rood basin called Dehnamak in the arid and semiarid climate of Iran. The main objective of the model is to use basic terrain data related to the erosive processes that contribute to the production, transportation and accumulation of sediments throughout the main water paths in the watershed. This model is based on a selection of homogeneous zones regarding drainage density and lithology, achieved through interrelating the basic units based on a rating system. The values of drainage density are rated according to an erosion class. The lithology is rated by erosion indexes, adapted from FAO (1977). The combination and reclassification of the results brings about five qualitative classes of sediment risk according to Fargas et al (1997). The advantage of this method is that only two main factors of erosion, namely lithology and drainage density are employed in it, and these factors are available in our geological and topographic maps in Iran. This methodology has been employed for studying the watershed Dehnamak in NE Iran with an area of 248 km2. The mapping scale was 1:50000 and the model implemented through a vector GIS (Arc View). The validation was carried out through interpretation of aerial photos and fieldwork which revealed a viability of 75.15%. The tested methodology has been proven useful as an initial approach for erosion assessment and soil conservation planning at regional level, as well as for a selection of priority areas where further analyses can be made to finally manage the environment.