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 regionalscale, 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 ofthe sub-bas ins of hableh roodbasin called dehnamak in the arid and semiarid climate of iran. the main objective of the model is to use basicterrain data related to the erosive processes that contribute to the production, transportation and accumulation ofsediments throughout the main water paths in the watershed. this model is based on a selection of homogeneouszones regarding drainage density and lithology, achieved through interrelating the basic units based on a ratingsystem. the values of drainage density are rated according to an erosion class. the lithology is rated by erosionindexes , adapted from fao (1977). the combination and reclassification of the results brings about five qualitativeclasse s of sediment risk according to fargas et al (1997) . the advantage of this method is that only two main factorsof erosion , namely lithology and drainage density are employed in it, and these factors are available in our geologicaland topographic maps in iran . this methodology has been employed for studying the watershed dehnamak in neiran with an area of248 krrr' . the mapping scale was 1:50000 and the model implemented through a vector gis (arcview). the validation was carried out through interpretation of aerial photos and fieldwork which revealed a viabilityof 75.15%. the tested methodology has been proven useful as an initial approach for erosion assessment and soilconservation planning at regional level, as well as for a selection of priority areas where further analy ses can be madeto finally manage the environment.