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نوشته شده توسط : قارانقوش
جمعه 16 آذر 1397-08:36 ب.ظ
نوشته شده توسط:استاد سجاد ی از خطبه سرا
Landslide Zoning using LNRF and GIS Methods in the Watershed of Khotbehsara River in TaleshOne 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.
Hossein Asghari, PhD2
Keywords: Mass Movement, Landslides, Khotbehsara, LNRF, Zoning, Landslide Hazard, GIS
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: email@example.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 ( )
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 ).
low 0 0.67 0 1
moderate 1 1.33 0.67 2
high 2 1.33< 1.33 3
Table 1: Determining weighted values based on the size of
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 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 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 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
Faults, tectonic movements have an intensifying and accelerating role in landslides phenomenon. As the direction of potential faults is on instable points and as the formation of abruption in areas and creation of breakings in layers and break down of stone masses are generally created in the direction of faults, so, the penetration of water into the land causes to decrease the shear strength of the earth (Yaghoubi, : ). Earthquake is stronger near the faults and the impact of faults causes the smashing of rocks which leads to the rock landslides in the steep areas.
Greater penetration of water into the crushed zones that increases the groundwater level and water pressure. (Haeri, : )
In the study area, according to the fault of the basin and their scattering based on the table ( ), it is observed that hectares of the area which is equivalent to of the total area is located at a distance of meters from the fault.
. Land use (vegetation)
Land use is one of the major index in the study of the stability of areas and hazardus domains in these areas and influences the surface characteristics of the land, which cause changing its behavior against geological processes in the area including weathering and erosion. In some cases, unwittingly land use change causes vulnerability of the environment against various types of landslides. The type and severity of vulnerabilities are directly related with changes. (Ahmadi, ).
The effects of vegetation on slope stability depends on local conditions of soil depth, slope, type of vegetation, rocks and weather conditions. Vegetation is sometimes the reason for stability and sometimes instability. The roots of plants, through absorbing water of underground water, helps to dry the slope and increase the stability, and in some
conditions, though penetrating water to the under-layers of soil, causes soil moisture and flood in area soil which leads to the soil mass movement on the slopes.
In the study area, forest land, in addition to having a large area of approximately hectares ( ), it has the greatest extent of landslides in this area of about hectares ( ). Other areas do not have considerable slide. Table ( ).
. Distance from the road
Road construction in mountainous areas usually follow geomorphologic and topographical conditions. The most appropriate anticipated routes for road construction in these areas are more in bottom line and along rivers. At distances along these paths, to construct roads, and to make the distance shorter and wider, they are constructed in the mountains; the prevention factor is removed from the foothill and the equilibrium configuration of the tension reach to each other in the slope of the roads and cause different kinds of slope motion such as landslides, falling rocks, tumbling rock slide. In the area of study, and according to Table ( ), the maximum area of slide is approximately hectares ( ) - meters away from the road. Slip rate is inversely related to the road, in a way that as the distance from the road increases, the slip rate decreases, and finally resches to zero in the distance over meters away from the road.
. Distance from stream
According to Table ( ), it is indicated that the area of hectares of the watershed which is equivalent to of the total area, is located at a distance of - meters of the stream; and the extend of slide in this area is times which is equivalent to percent of the total landslide occurred in the area hectares. A distance of meters and above, the total area of slide is minimal, hectares, equal to of the landslides occurred in the watershed.
AcrePercentAcrePercentMarine deposits41.450.460.000.000.000lowAndesitic lavas2112.7823.230.803.130.160lowFoothills and alluvial depositsVolcanic rocks 2913.3932.037.2328.261.412highSand-lime stone 3760.1941.3417.5568.613.432highSum9095.2310025.58100Average5.12slopelevelsAcrePercentAcrePercent0-243.500.480.020.080.010low2-5149.591.640.220.860.070low5-8171.871.890.311.210.100low8-12286.423.150.431.680.130low12-20729.608.021.566.100.490low20-301176.9812.943.3012.901.031moderate30-604362.3647.969.7538.103.052high<602174.9223.9110.0039.083.132highSum9095.2410025.59100average1136.913.20ion ofSlopeAcrePercentAcrePercentN1458.1216.030.451.760.140lowNE1591.3617.501.164.520.360lowE1573.6717.300.692.690.220lowSE1448.0915.923.6614.301.141moderateS1365.5915.0112.4248.543.882highSW681.627.495.8622.901.832highW417.054.591.295.040.400lowNW559.736.150.060.250.020lowSum9095.2310025.59100Average1136.903.20267.422.940.000.00Table 2: Mass movements size in Lithology and weight measurement of surface LithologySize of levelssize of slide in levelsInstabilityweightLNRFlow0.000Table4: Mass movements size in slope direction levels and weight measurement of surfaceSize of levelSize of slide in levels LNRFweightInstabilityTable 3: Mass movements size based on slope and weight measurement of surface Size of levelSize of slide in levelsLNRFweightInstability
levels ofrainfallAcrePercentAcrePercent900-105062.340.6854130.000.000.000low800-9001836.4720.191554.5617.800.891moderate700-8002950.7932.443233.7514.700.731moderate600-7003137.9434.500916.4764.403.222high500-6001107.712.17890.803.100.160lowSum9095.2410025.59100Average1819.055.12Distance from faultAcrePercentAcrePercent0-13002614.4928.74576.4525.212.522high1300-26002100.7123.096811.867.270.731moderate2600-3900940.6610.342336.1323.952.392high3900-5200626.866.89217710.3540.454.042high5200-6500702.187.7203020.000.000.000low6500-7800637.487.0089410.000.000.000low7800-9100540.365.941130.000.000.000low9100-10400476.515.2391140.000.000.000low10400-11700287.013.1556070.803.130.310low11700-13452168.971.8577850.000.000.000lowSum9095.2399.9998925.59100.00average2.56Table 6: Mass movements size based on distanceSize of levelsize of slide in levelsLNRFweightInstability from fault and weight measurement of surface Table 5: Mass movements size in rainfall levels Size of levelssize of slides in levelLNRFweightInstability and weight measurement of surface
use acre percent area percent
forest 8272.70 90.96 24.49 95.74 3.83 2 high
farm 422.27 4.64 0.55 2.15 0.09 0 low
farming 387.06 4.26 0.54 2.11 0.08 0 low
residential 13.20 0.15 0.00 0.00 0.00 0 low
Sum 9095.23 100 25.58 100 4.00
from road Acre percent acre percent
0-400 4775.20 52.50 24.79 96.87 5.81 2 high
400-800 2510.21 27.60 0.00 0.00 0.00 0 low
800-1200 1148.84 12.63 0.80 3.13 0.19 0 low
1200-1600 431.98 4.75 0.00 0.00 0.00 0 low
1600-2000 167 1.8361 0.00 0.00 0.00 0 low
1600-2000 62 0.6817 0.00 0.00 0.00 0 low
Sum 9095.23 100 25.59 100
stream and weight measurement of surface
stream acre percent area percent
0-250 6444.92 70.86 25.48 99.61 3.98 2 high
250-500 1930.31 21.22 0.10 0.39 0.02 0 low
500-800 577.00 6.34 0.00 0.00 0.00 0 low
800-1300 143.00 1.57 0.00 0.00 0.00 0 low
Sum 9095.23 100 25.58 100
Table 8: Mass movements size based on distance
from road and weight measurement of surface
size of levels size of slides in levels
LNRF weight instability
Table 7: Mass movements size based on land use
size of level size of slide in levels
LNRF weight instability
and weight measurement of surface
Table 9: Mass movements size based on distance from
size of levels size of slide in levels
LNRF weight Instability
By combining layers and the total weight maps, zoning maps have been provided in four
levels of low instability, too low, moderate, and high. Table ( ) shows that percent of
the total area of study has a high instability, % average instability, low instability,
and too low instability. Effective factors that create instability in the watershed of
Khotbehsara are high steep and susceptible stones to erosion, vegetation, and high
humidity. Figure ( ),Figure( )
Table 10 - Percentage and area zoning landslide using LNRF method
size of levels level percentage
Figure ( ): land using map based on the stability of domain movement in the watershed on
Knotbehsara in Talesh
Figure ( ): map of the distributuion of the slide of the area
The results of the research
The most amount of landslides relate to steep - percent with an area of acres equal to % of slides. The result is that steep has a significant relationship with the slide. This means that the as the steep rate increases, the slide increases too. The material of rock plays an important role in the occurance of the slide in the area. The most active slides occur on the formation of gray sandy limestone structures, and the extension of the landslide is approximately . acres, equal to . percent of the total slides. In vegetation section, the most amount of slides is about hectares, equivalent to % of the total landslides occurred in the area, happened in area of forest land use. The highest percentage of landslides in forest area is, on the one hand, from the vast extension of these forest land use of about hectares, equivalent to of the total area, as well as the organization of the section on the formation of gray sandy lime. This result was achieved through fault compliance with landslide distribution maps in which, approximately hectares, equivalent to of the total sliding, occurred in a distance of meters away from the fault. This indicates that there is a direct correlation between the two phenomena.
The amount of slide at the foots of South direction is about and southwest . As a result, south and southwest slopes have more potential and are more prone to landslides. In the area, through the removal of support on the slope, the areas are sensitive to the movements of a domain and, if favorable geological conditions are present,
landslides will be inevitable. of the total landslide occurred at distances up to meters from the road, which the highest percentage of slides is considered in the distance from the road. It indicates that this subject, if the conditions are provided, the landslide on a roadside is more potential and sensitive.
On the sention of stream, it was clear that approximately hectares ( ) of the landslides, occurred in the basin, were in distances up to meters from waterways. The climate, on the basis of the methods of Domarten and Ambrgeh, is very humid and the annual rainfall of milimeters differently affects the morphogenge of the area and are the main causes of mass movements. Most levels of rainfall are - milimeters and the amount of slide is hectares ( %), and the area is very unstable in this level.
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