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

Document Type: Research Paper

Authors

1 Professor, Faculty of Natural Resources, University of Tehran, Karaj, Iran

2 Ph.D. Student of Wartershed Management, Science and Research Branch, Islamic Azad University, Tehran, Iran

Abstract

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.
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.

Keywords