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,,مقله پهنه بندی زمین لغزش در رودخانه آبخیز خطبه سرا 1

نوشته شده توسط:سجاد یوسفی
سه شنبه 18 آذر 1393-07:15 ب.ظ

Landslide Zoning using LNRF and GIS Methods in the Watershed of Khotbehsara River in Talesh
Taher Sajjadi
Hossein Asghari, PhD2
Abstract
One of the natural hazards which causes a lot of finincial and living damages on the lives of people is the phenomenon of mass movements; the potential factors causing the instability of domains such as rainfall, slope, lithology, and land use are the factors causing huge damages to natural and residential areas, including fast soil waste, destruction of farm and residential lands, forests and roads, etc. Khotbehsara watershed in Talesh is located in the east part of Talesh mountain. Due to erosion rule systems and climate and geology, the movements of domains in this area is not far from expectations; so, in this study, first, the eight factors of slope, the direction of slope, geology, vegetation, rainfall, distance from roads, distance from faults, and distance from stream, as factors in landslides in the region, were detected; after preparing the layers in GIS, landslide inventory map of the study area using aerial photo interpretation and field studies were provided. Then, to analyze data, the proposed method of Landslid Nominal Risk Factor (LNRF) was used as a quantitative and statistical model. In conclusion, combining the layers and the total weight maps, zoning maps were provided in four levels of instability including low, too low, moderate, high. The results showed that percent of the whole study area have high instability, , average instability, low instability, and too low instability. Factors that could cause instability in the watershed of Khotbehsara are high steep and rocks susceptible to erosion, vegetation, and high humidity.
Keywords: Mass Movement, Landslides, Khotbehsara, LNRF, Zoning, Landslide Hazard, GIS
Introduction
By having mountainous physiographic, tectonic and seismic activity, and various geological conditions, and climate, Iran has especial natural conditions for a large range of mass movements. This phenomenon causes a lot of financial and living damages on the lives of people in most regions of the country every year which damages the natural and residential resources such as fast soil waste, destruction of farm land and residential areas, forests, roads, etc.
Geomorphologically, mountains have strong morphodinamic force. (Rajaee, )
1 MA student of Geomorphology in environmental planning, Department of Geography - Islamic Azad University, Astara Branch , astara Iran, email: taher.sajjadi. @gmail.com
2 Corresponding Author of Islamic Azad university, Astara Branch , astara Iran , email: h.asghari@gmail.com
The study area is located in the East part of Talesh Mountains and, in terms of natural factors such as climate, topography, lithology, and morphogenic systems of the region, has relatively high potential regarding mass movements. Hence, paying attention to this phenomenon, identifying, predicting, and controlling it, as a kind of environmental hazards in the sustainable management of sediment, seems imperative. Countries such as the former Czechoslovakia and Italy are among the first countries which are extensively studying in this field and are pioneers in this phenomenon; the valuable actions of researchers in Czechoslovakia in recording information on landslides in has been a model for other countries (Shariat Jafari, ). Studying in the domain of landslides is a recent study, and before , in Roudbar’s earthquake and numerous landslides in this area, the extensive research in this area was felt (Ya’ghoubi, ). Gupta and Joshi ( ) conducted a study using LNRF model in Ramganga watershed in Himalayas to perform Landslide hazard zoning. Brabb et al ( ), at first job on slope stability analysis in Sanmateo County in California, used landslide distribution map for the value of factors such as the slope and geology, and did zoning qualitatively. Kkullar and colleagues, in , using GIS and integrating gradient and rate of landslide, provided landslide hazard zoning of Mizoran in the North of India and expressed that maps correspond with existing landslides. Shadfer et al. ( ), to investigate the landslide event of Chalkroud watershed in Mazandaran province, used density models, informative value, and LNRF as a conceptual tool and influencing variables in landslide. Mohammad Khan, in , did a study to show the influencing factors in landslides and hazard zoning in the Taleghan watershed and indicated that lithology was more effective in landslide.
Sarvar and colleagues ( ), in Nir region to Sarab in Ardebil, to determine the factors influencing the mass movements of LNRF modeling selected factors such as: lithology, distance to fault, slope, elevation and precipitation levels as the most effective natural factors and provided zoning map of the region using layered data with GIS software and data analysis using LNRF modeling. Yelcin provided landslide susceptibility maps for Ardesin area in Turkey based on GIS and using hierarchical and two univariate statistics methods, and concluded that the standard of lithology, weathering, land use, and slope are the most important factors in the occurrence of landslides in the area.
The Area of the Research
Khotbehsara River watershed in Talesh, to east-west direction in the west of Guilan province, is located between Astara and Talesh in the East Mountains of Talesh. The geographical area is hectares and the longitude is between ( ˚ ́ ˝) to ( ˚ ́ ˝) east and the latitude ( ˚ ́ ˝) to ( ˚ ́ ˝) north. figure ( ).
The topography of the basin is located in the mountainous plains. It has luxuriant vegetation and waterways like tree, and has a main stream with a length of meters and a total drainage area of meters. Minimum height is meters, with a maximum height of meters.
Based on the category of Ambrgeh and Domarten, it has very humid climates, and the greatest amount of rainfall is in spring which is mm, mm per year, and the maximum amount of moisture is percent in November; the average total annual frost is days.
Figur( ):Position of the area
Materials and Methods
To perform the study, the following procedures have been done.
- A field visit in order to preliminary identify the area, determine the exact boundaries, digitize the topographic maps, providing information about lithology and distance from the fault using geological maps and aerial photographs.
- Classification of different layers and providing maps of landslide distribution using photo interpretation and application of Gps to recognize points and enter them into the Excel software and providing poligony maps of landslide to complete landslide maps.
- Determining the extent and jurking percentage in different levels and weighting different levels of effective factors in landslide based on LNRF model parameters .
- Effective maps combined with map of the distribution of mass movements and, using the LNRF model, the weight of per unit was calculated and weight maps were prepared for each of these factors.
- In order to analyze the data using the model and equation ( ), the line happening of
landslides in the area was specified.
Equation ( )
B
A
LNRF 
A= Area surface of mass movements occurred per unit
B=The average of mass movements occurred in total units
Using the landslide occurred in any of the homogenious units in terms of the values of the
effecitive factors in landslides and its division on the average level of landslide occurance
in total units, an attempt was done to provide an index of the risk amount of landslide
occurrence. In equation ( ), the weight of each homogeneous unit was calculated and the
weighted map of each of factors was prepared and weighted in three categories (Low =
zero, moderate= , and high= ) (Table ).
Max Min
low 0 0.67 0 1
moderate 1 1.33 0.67 2
high 2 1.33< 1.33 3
Row
Table 1: Determining weighted values based on the size of
LNRF<0.67
0.67<LNRF<1.33
1.33<LNRF
LNRF coefficient
Instability weight Area of Changes LNRF
mass movements in the LNRF method
Studying the factors affecting in landslide
In this study, eight factors of lithology, slope, direction of slope, rainfall, distance from
fault, land use (vegetation), distance from roads, distance from stream were investigated as
factors contributing to landslides.
. Lithology
Lithology is considered one of the main controlling factors of the mass
movements. Recognizing lithological characteristics of the study area, in line with the
purposes of geomorphology is important because the structure of lithology is one of the
components of geomorphology. The mineralogical composition is involved in the
building and how the rocks are set in the process of degradation and erosion. In the study
area, the most landslides occurred in the gray sandy limestone rocks. These rocks spread in
an area of hectares that has of the total allocated area of the
watershed. The extension of the landslide equals hectares ( ). Volcanic rocks
compose percent of the total area of the landslide; regarding the occurance of
landslide, it is located in the second row, and the extension of slides in these formations are
( ). Table ( ).
. Slope
Slope is one of the major causes of the disruption of ranges; an increase in the steep disrupts the balance of formation components of the slopes and increases the amplitude of the tension, thus enhances the occurrence of mass movement (Haeri, ). Steep and the morphology of slopes have huge impact on the occurrence of mass movements range. The movements of slopes occur when the step of slope is greater than the angle of the repose of the domain. In the area of study, the slopes of the levels of - % account for the the most total area of the slope, and the maximum amount of slide ( ) occur in this level; it is seen that there is a linear relationship between the slope and the slide. As the slope increases, the landslide increases too. (Table ).
. The direction of slope
Geographic directions have different function in the occurance of these motions; in table ( ), the four main directions of North, South, West, and East, and four subsidiary directions of North West, North East, South West, and South East have been prepared by GIS software from DEM map. Reviewing Table ( ) of the slope, it can be seen that the most amount landslides in lands with a slope toward south and aouth west are and , respectively, of the whole landslides occurred in this area. Table .
. Rainfall
Rainfall is an important factor in mass movements in the basin. Rainfall intensity and duration has an important role in the occurrence of mass movements. The most number of slope abandonment occurs after the of heavy rainfall or snowmelt in the spring and due to the penetration of water in the gaps. Rainfall intensity factor in the instability of the slopes depends on the weather conditions, local topography, geological structure of slopes, permeability and other properties of rock and soil mass.
Reviewing Tables ( ), it is observed that acres of the study area which is of the total area is in the rainfall level of - milimeters which, in this domain, the most slide equals hectares, which is equivalent to of the total area.
. Distance from fault


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