چكيده لاتين :
Introduction:
Landslide is move down or integrated movement of bulky sedimentary substance which always quickly occurs across slopes (Mahmoudi, 2008:38). Landslides are very important of natural hazard that exert high damages to human and economic property every year. According to this reason, in recently years, evaluation of landslide in term of regional and small scale has been under attention of experts.
The Aghlaghan chay catchment area with 166 square kilometer area, 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 landslides 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 landslide is very necessary.
Methodology:
In this research for gathering data and information, two methods of library and field study have been utilized. 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 landslides were determined. In this research due to zoning of landslides, we utilized from Vikor model and to obtain our purpose, 10 factors such as slope, aspect, lithology, soil, land use, distance from stream, distance from roads, distance from residential area, distance from faults, precipitation were embedded. In the next stage, maps of effective factors in landslides of catchment area by geographical information system (GIS) were produced. Data set layers of access roads, residential area, 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, landuse map of Nir town used. In order to obtain, soil map of catchment area, soil of Ardabil Province and the soil map which produced by Sobhany via survey from Aghlaghan chay catchment area, were inserted. We exert climatology station data and gradient equation, for obtaining precipitation map. Finally, Vikor model as multiple decisions making according to zoning landslide 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.
Results and discussion:
In present investigate, we classify landslide risk in to five category include highest and lowest potential risk. The regions which in highest and high potential risk respectively have 1402.07 and 4490 hectares area. These regions dominated with hard rock as bedrock which is overlain by soft formation materials. Land use of these regions is cultivation, pasture and residential area. Mentioned regions above, which are located in northern and western slopes have 20-35 percent slope. In point view of precipitation, these regions have high amount of precipitation about 350-550 mm. indeed the regions which category in highest and high potential risk are located near to fault, network stream, residential area and finally access roads.
Regions with average risk have characteristics such as equivalent 502.55 hectares area, 35-45 and 10-20 percent slope, little precipitation approximately 350 mm, land use of residential and gardening, resistance lithology in associate with low surface land cover. Surely regions with high land cover overall have low slope and get receive little precipitation. Therefore possibility of mass movement in these regions slows down. In addition, mentioned regions are located away from faults, roads, stream network and residential area.
The regions allies with lowest and low landslide risk respectively have equivalent 1529.99 and 4974.24 hectares area which overall are located in lower than 10 percent or upper than 45 percent slope with low amount of precipitation about lower than 200 mm, too with lands ally with volcanic rock which are resistance and also associated with low land cover and overall stony land. In addition land use of these lands are crops out, shrub and garden. The regions allies with lowest and low landslide risk are situated away from stream network, fault and road.
Conclusion:
In this present research in according to classify of Aghlaghan chay catchment area landslides, we exerted Vikor model which is one of multiple decision making analysis approach. According to finally map of potential landslides classification, classes of very high risk and high risk respectively owned 27 and 9 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. Lowest dangerous regions and also low dangerous regions on the whole, are located in low slope plain unite and steer slope related to escarpment and resistant volcanic formation and also lack of land cover. Results of our study show that amongst of active factors in landslide region, factors such as slope, precipitation and lithology are very important.
