نوشته شده توسط:سجاد یوسفی
سه شنبه 18 آذر 1393-07:16 ب.ظ
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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تاریخ آخرین ویرایش:سه شنبه 18 آذر 1393 07:17 ب.ظ