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

Abstract

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