Zonation of Debris Cones and Talus Slopes in Aghlaghan Chay Basin (South Western Slope of Sabalan Mountain)

Debris cones are the form of slope materials, especially in mountainous areas that were streak rapid and dangerous. Because of existence more weathered volcanic rocks, mountainous topography; climatic conditions with high temperature fluctuating and large number of frost days and tectonic forces activity, Aghlaghan basin have greater potential for Debris cones and Talus slopes mass movement is very active. Therefore, Debris cones and Talus slopes are considered as the most important factors in enhancing the sedimentation in rivers. The occurrence of these phenomena every year, leads to severe soil erosion and filling Yamchi dam, in the lower part of basin. The purpose of this study is the assessment and zonation of Debris cones and Talus slopes. In this study, at first, we investigated eleven Debris cones and Talus slopes risk factors in the region. These factors are: slope, aspect, lithology, distance from roads, distance from drainage, distance from fault, rainfall, number of frost days, temperature fluctuating, land use and soil. Then data layers were prepared by GIS. Analysis and modeling was performed by using the Vikor model as one of the multi-criteria decision analysis. Eventually zoning map was prepared on 5 classes very high to very low risky. According to zoning map, 2761.72 and 7854.30 hectares of area located in categories of very risky and high risk, respectively. Most risk areas are located in the weathered volcanic formations, between 35 to 30 percent slopes, slopes with low vegetation and overlooking the valley.
Extended Abstract
1-Introduction
Debris cones are regarded as very important of natural hazard that exert high damages to human and economic property every year. According to this reason, in recent years, evaluation of Debris cones and Talus slopes in term of regional and small scale has been under attention of experts. Aghlaghan chay catchment area with 166 square kilometer area, is bounded by late 38, 10-38,44N and long 47.46-48E. This catchment area is located in north western of Iran and south western slope of Sabalan Mountain. This study area in view of specifically regional situation such as topography (mountainous area), high slop, and existence of soft surface formation and non-resistant material which is located upper resistant layers and condition of climate has high potential of mass movement. Occurrence of mass movement especially Debris cones damages due to human and economic property such as destroy of communicational roads, fill of Yamchi dam resource which is located down ward of catchment area and loss of vital valuable resource soil in catchment area of Aghlaghan. Therefore, zonation of catchment area in view of sensibility to Debris cones is very necessary. The purpose of this study is Assessment and zonation Debris cones and Talus slopes.
2- Materials and Methods
In this research, two methods of library and field study have been utilized to gather data and information. First of all, with study of resources, basic theory of research was investigated. Then according to study resources and field study with visual observation, effective factors in Debris cones were determined. In this research due to zoning of Debris cones and Talus slopes, we utilized Vikor model. 11 factors such as slope, aspect, lithology, distance from roads, distance from drainage, distance from fault, rainfall, number of frost days, temperature fluctuating, land use and soil were embedded to obtain our purpose. In the next stage, maps of effective factors in Debris cones of catchment area by geographical information system (GIS) were produced. Data set layers of access roads, stream network, elevation classes, slope and aspect were derived from digitizing topography map of 1:50000 scale. Layers related to fault and litology were derived from digitizing of 1:100000 Meshkin geological maps. In order to obtain of land use layer, land use map of Nir town was used. In order to obtain, soil map of catchment area, soil of Ardabil Province and the soil map which are produced by Sobhany via survey from Aghlaghan chay catchment area, were inserted. We exert climatology station data and gradient equation, for obtaining precipitation, temperature fluctuating and number of frost day's map. Finally, Vikor model as multiple decisions making according to zoning Debris cones and Talus slopes of Aghlaghan catchment area was applied. Vikor model in seven states has been done and this are described below:
First stage: configuration of decision matrix in respect of criteria number. Second stage: decision matrix normalization, in this stage we exert normalization as framework in fuzzy set (valuable range of 0-1). Third stages: determine of criterion vector weight, in this stage, according to exert weight, we used approach Critic. Forth stages: determine of best and worse variable for every criterion among existing of them. Fifth stages: compute amount of maximum suitable (S) and unsuitable (R). Sixth stages: compute index of Vikor (q).Seventh stages: ordering of criterion in according amount of .R, S, Q.
 
3- Results and Discussion
In present investigate, we classify Debris cones and Talus slopes zonation in to five category include highest and lowest potential risk. The regions which in highest and high potential risk respectively have 2761.72 and 7854.30 hectares area. Most risk areas are located in the weathered volcanic formations, between 35 to 30 percent slopes, slopes with low vegetation and overlooking the valley. In point view of precipitation, these regions have high amount of precipitation about 300-500 mm.This area also has a temperature range 9-12 °, number of frost days are between 120-160 days. Indeed the regions which category in highest and high potential risk are located near to fault, network stream and finally access roads.
4- Conclusion
Debris cones are the form of slope materials, especially in mountainous areas that were streak rapid and dangerous. The Aghlaghan basin because of existence more weathered volcanic rocks, mountainous topography; climatic conditions with high temperature fluctuating and large number of frost days and tectonic forces activity have greater potential for Debris cones and Talus slopes mass movement is very active. Therefore, Debris cones is one of the most important factors in enhancing the sedimentation in rivers. Occurrence of these phenomena on every year, resulting to severe soil erosion and filling Yamchi dam, in the lower part of basin.
In this present research in according to classify of Aghlaghan chay catchment area Debris cones and Talus slopes, we exerted Vikor model which is one of multiple decision making analysis approach. According to finally map of potential Debris cones and Talus Slopes classification, classes of very high risk and high risk respectively owned 17 and 47 percent area of all catchment areas. On the whole, hazardous regions are situated in mountainous unite which are located in the north and southern west section of study area.
Results of our study show that amongst of active factors in Debris cones and Talus slopes region, factors such as slope, lithology and aspect are very important. All to over according to the study results, Aghlaghan chay basin have very high potential for the Debris cones hazard event. Therefore, conservation measures, watershed and basin management studies are warrented.