Evaluation and Slope Instability Hazard Zonation in Part of Tajan
Basin, Sari, Iran, by Anbalagan Method
The aim of this study is an experimental investigation
on landslide hazards in Tajan Basin and its increasing due to land use
changing, deforesting, road and other construction. The main strategy
for restricting the damage caused by the activity of landslides is to
avoid these regions. To accomplish this, landslide zonation hazard map
of the area is required. There are different methods for zoning of different
regions in term of susceptibility to landslide. Because of geological
conditions of the study area, Anbalagan method purposed to gain the results.
For landslide hazards zonation map the required maps of slope, aspect,
land use, lithology, structural lithology, ground water, landform and
facet map prepared using GIS software of Arc view and Arc map related
to Anbalagan method. For the accuracy evaluation of the used method landslide
distribution map provided for the study area which has compared with the
landslide zonation map. The results showed that the most of landslides
are occurred in VHH zone (28%) and HH zone (55.5%) and the rest of them
are occurred in MH zone, which have predicted by the mentioned method.
The results of fieldwork performed in summer 2008 with the method of Anbalagan
were used to assess slope failure.
Landslides are occurring frequently in northern part of Alborz in Mazandaran
Province, Iran that results suffering to human and substantial economic and
environmental losses. For that reason the hazard regions should be properly
identified. The mass movements such as landslides cause annual costs in excess
of 38x107 Euro in Iran (Feyznia et al.,
2005). Therefore it has become increasingly important, to plan land use
so that hazards are avoided and so that construction projects can be designed
to limit slope failures. Anbalagan (1992) has produced
landslide hazards map using weighting lithology, relation between construction
and slope, slope, land use, vegetation cover and ground water conditions. This
method has termed Landslide Hazard Evaluation Factor (LHEF). Anbalagan
(1992) was used this LHEF method, to zonation of landslide hazards in Katcom-Ninita
of India. This method is a numerical system which is related to the geology,
roughness, land use, vegetation cover and ground water conditions. Landslides,
as one of the major natural hazards, account each year for enormous property
damage in terms of both direct and indirect costs. Landslides, defined as the
movement of a mass of rock, debris or earth down a slope (Cruden,
1991). Landslides have caused large numbers of casualties and huge economic
losses in mountainous areas of the world. The most disastrous landslides have
claimed as many as 100,000 lives (Li and Wang, 1992). Li
and Wang (1992) conservatively estimated that in China the number of deaths
caused by landslides totaled more than 5000 during the 1951-1989 periods, resulting
in an average of more than 125 deaths annually and annual economic losses of
about US$ 500 million. More sophisticated assessments are involved AHP, bivariate,
multivariate, logistics regression, fuzzy logic, artificial neural network etc.,
analysis (Carrara, 1983; Van Westen,
1997; Dai et al., 2001; Lee
and Min, 2001; Ercanoglu and Gokceoglu, 2004; Lee
et al., 2004; Komac, 2006). Remondo
et al. (2008) and Zolfaghari and Heath (2008)
have investigated on landslide hazard zonation using GIS-based method. Slope
morphology, land use and bedrock lithology are also used in modeling of landslide
susceptibility (Schmidt and Beyer, 2001; Baeza
and Corominas, 2001; Gorsevski et al., 2006).
These parameters can also give an idea of the mass movement runout, a parameter
closely related to potential damage on properties and infrastructure (Chen
and Lee, 2003). Also in Iran, Oroumiei and Aminizadeh
(1998), Oroumiei and Safaei (1998), Keshavarz
and Mehmoodi (2000), Emami and Elhami (2005), Rezaeimoghadam
and Eghbal (2005), Khezri et al. (2006) and
Haghshenas et al. (2007) by Anbalagan method was
applied to landslide hazard zonation which seems be suitable for Iran watershed
such as this study area.
Mass movement and landslide zonation dividing the area into specific and severed
regions which are potentially measured hazards. This process based on natural
characteristics and quantitative modeling (Karam and Mahmoodi,
2002). Empirical methods are generally simple and relatively easy to use
and dat required in such method is usually general and readily available. Where
a local historic landslide database is available, the empirical relationships
can be readily developed. However, empirical methods can only provide a preliminary
estimate of the profile of the travel path (Dai et al.,
The aim of this research is recognizing and classifying the principal
factor which causes landslide to find an appropriate solution for prediction
and control the landslide occurrence in susceptible regions and assessment
the susceptibility measure based on instability factor.
MATERIALS AND METHODS
The study region covering 62.07 km2 is located on the South-Western
part of Sari the capital of Mazandaran Province, Iran. Geographically
is located in Tajan basin in the Northern Alborz range where is limited
between 53° 0` 12" N to 53° 06` 34" N and 36° 20` 48" E to
36° 27` 50" E (Fig. 1). This study conducted in
||Study area related to Mazandaran Province and Iran
||Limitation of each hazard class
The choice of hazard assessment method is basically dependent on the scale
of investigation. For regional scale analysis, where the land-use planning is
of main concern, hazard assessment is in the form of determining landslide-prone
areas. For assessing landslide hazard, different methodologies are proposed.
They are mainly grouped as: qualitative and quantitative methods. Qualitative
approaches based on the site-specific experience of experts with the susceptibility/hazard
determined directly in the field or by combining different index maps. Quantitative
methods are based on numerical expressions of the relationship between controlling
factors and landslides. The product of qualitative methods is usually susceptibility
maps that do not provide information about the probability of sliding (Anbalagan,
1992). Numerous methods are presented by the related studies in the field
of landslide zonation which of them used for specific purpose and area. In our
study area with Mediterranean climatic conditions and effective factors on landslide
occurrence, Anbalagan method was selected to run the related factors in GIS
environment. This is method based on result of combining the basic map that
related to natural characteristic of land. In this method after overlaying of
the basic map, the weights of class were determined. Then the landslide hazard
zonation map was preparing. This method is based on a quantitative data which
is weighting the required factor to preparing the landslide hazard zonation
map or LHEF (Table 1). Based on final factor of hazard evaluation,
hazard classes were determined. Following to the maps overlying it is possible
to identify several types of very low, low, medium, high and very high landslide
hazard classes (Solaimani, 2007).
Work Unit Map
The study area divided into 10 work unit using 1:25000 topography map and
aerial photos. In this division, the work units were determined by topographic
border, sub border, gullies and channels which have similar characteristics
of slope (Solaimani et al., 2007). The work unit
map is basic map that should be overlay on other maps, then entered its weights,
finally, by summing the resulted weights, landslide hazard rate is determined
in each of work unit.
Landslide Inventory Map
For the landslide mapping, at the first stage, geographical coordinates
provided for IRS and ETM data, then, field verification of landside data
using GPS and finally, landslide inventory map and digitization of data
was completed in ArcGIS environment.
Using of different data such as 1:20000 aerial photographs, 1:25000
topography map, 1:100000 geology map, IRS and ETM images together produced
Slope is one of the major factors in model, which is main parameter of the
slope stability analysis (Lee and Min, 2001). Because
the slope angle is directly related to the landslides, it is frequently used
in preparing landslide susceptibility maps (Ercanoglu et
al., 2004; Lee et al., 2004; Lee,
2005; Yalcin, 2005, 2008). The slope map of the study
area is divided to different slope categories based on Table 2.
||The weight of factors
Such as slope, aspect is one of the important factors in preparing landslide
susceptibility maps (Ercanoglu et al., 2004; Lee
et al., 2004; Lee, 2005; Yalcin,
2008). The related parameters of aspect such as exposure to sunlight, drying
winds, rainfall (degree of saturation) and discontinuities may control the occurrence
of landslides (Suzen and Doyuran, 2004; Komac,
2006). Aspect degree are classified according to the aspect class as flat
(-1°), North (315-360°, 0-45°), East (45-135°), South (135-225°)
and West (225-315°).
Based on the used model relative relief is an effective factor, due to its
role in the rate and type of erosion (Ayalew et al.,
2005; Dai et al., 2001) and also on land use
changes (Gritzner et al., 2001). Relative relief
of the study area is mapped using aerial photographs and topographic map.
The main source of data related to the geomorphology of an area is its investigation
by lithology properties (Dai et al., 2001). The
study area contents M2.3 m.s.l, Plqc.s and Q2
formations. These types of lithology are very susceptible against landslide
This factor is prepared from geology map which is used in numerous researches
Land Use and Land Cover
Land use and land cover are play important role in instability of slope
(Jakob, 2000; Anbalagan, 1992).
With using IRS and ETM images, the land use map of the study area was produced
and then their boundaries were determined in conformity with land use state.
As a result of the evaluation, three different land cover are described including
mixed of forest and garden, forests and croplands.
In the study area, this factor is determined using land use map, field
verification and spring survey which is weighted based on Table
This factor is important for zoning the landslide (Lee, 2005) which
is obtained from 1:25000 soil maps for the study area with three different
type of soil. According to the depth and drainage condition, this factor
was weighted. After preparing of these maps using Table
2 each of them were weighted. Finally, using collecting the weights,
the class weight of units was determined (Fig. 2).
RESULTS AND DISCUSSION
Using Table 2, each of factors were weighted, then
by combining the layers of factors and comparing with work unit map, the
weight of each work unit is determined (Table 3). Regarding
to the Table 1, the study area divided into three class
of landslide susceptibility; involve, very high hazard class, high hazard
class and medium hazard class. Finally, the landslide zonation map was
prepared (Fig. 2a-j).
For evaluation the accuracy of landslide zonation, this map is comparing
with landslide inventory map; and the percent of landslide area in each
class is calculated (Fig. 3). Then regarding to the
ratio of landslide area percent to the hazard class area percent, determined
that this model is suitable for the study area where the most of landslide
are occurred in very high and high hazard classes.
Finally, to determine the importance of the used factors, the percent
weight of each factor was calculated in each work unit from total weight
of factors (Table 4). The gained result showed that
lithology and soil are more importance in landslide occurrence. Then,
roughness, land use, slope, ground water condition and structure are effective,
As mentioned lithology is more importance factor; which is the same with
Komac (2006), Van Den Eeckhaut et al. (2006)
and Kamp et al. (2008) and also, Yalcin
The study area is naturally susceptible to landslide occurrence; also Anbalagan
method based on natural characteristics, therefore is suitable for zoning this
area, that showed in Solaimani et al. (2007), Oroumiei
and Safaei (1998), Oroumiei and Aminizadeh (1998)
and Emami and Elhami (2005), also it can be recommended
that this method is best model for landslide zonation of this area. This method
should be performed by assistance of different experts in tectonic, climatology
and hydrology, because this method requires to different factors measurements.
Refer to former researches that performed in similar condition and other regions
of country, this method is appropriate and in compare to other method, gave
better results. Furthermore, the study area is very susceptible; therefore,
the zone of low hazard and very low hazard not existed. Certainly in this method,
road were not contributed, whereas observed in this field. Therefore, road in
this area constructed carefully and not constructed in high hazard zone and
very high hazard zone, so that with lowest long having most of usage. Furthermore,
observed that construction the animal husbandry and site of inhumation garbage,
caused landslide occurrence due to high susceptibility to landslide. Finally
this zonation map is recommended to use for construction design and road in
forest area such as Pahnehkola basin.
||The weights of work unit
||Weight of class to total weight of factor (%)
||Factors, work unit and zonation map
||Comparing area of landslide (%) with area of hazard
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