Landslide Hazard Zonation of Babolrood Watershed, Iran

Ali Uromeihy Dept. of Engineering Geology Tarbiat Modares University

Tehran, Iran uromeiea@modares.ac.ir

Maryam Fattahi Soil and Water Research Center

Sari, Mazandaran, Iran

Abstract—Landslides are among the most costly and damaging natural hazards in mountainous regions of Babolrood watershed area. The main causes for the development of the landslides in the area are the influence of earthquakes and rainfall. Landslide Hazard Zonation (LHZ) maps were drawn to evaluate the potential of instability in the region. Although the region faces high potential of landslide occurrence, due to rough geomorphological characteristics and high density of forest cover, the available information is very limited. Therefore, essential spatial database of landslides is established using GIS techniques. Various data layers namely lithology, fault buffer zones, earthquake induced acceleration, drainage layout, slope degree and orientation, rainfall intensity and landuse were considered as main affecting factors. The weighting-rating system based on the relative importance of various causative factors is derived from remotely sensed data and other thematic maps. Field observation and data collection on landslides are employed to evaluate and validate landslide hazard zonation map. According to analyzed data based on five different methods, it is interpreted that a combination of lithology and fault buffer zones is the most influencing factor on the disturbance of landslide in the region. Due to high annual precipitation (over 1800 mm) and sensitivity of clay minerals to absorb water, most of the landslides occurred in the rock units that contain clay minerals. Therefore, marlstone formations of Late Tertiary period demonstrate over 35% of the landslides developed in the region. The LHZ map is employed to evaluate potential damage to infrastructures specifically the life-line system and future development of the region.

Keywords- landslide; hazard zonation; Babolrood watershed; slope instability.

I. INTRODUCTION In recent years, growing population and expansion of

settlements and life-line projects over hazardous areas increased the impact of natural disasters in Mazandaran Province. High potential of landslide events are recorded in the Province where over 12% of the land surface is affected by landslide activities. The study area covers 1370 km2 and includes part of Babolrood watershed which is located along the Caspian Sea, north of Iran (see Figure 1). The average annual precipitation in the area is in the range of 800 to 1200 mm and the area is covered by forest in the south and farmlands in the north.

Figure 1. Location of Babolrood watershed.

Various types of damages are caused by the development of landslide in the area which includes roads, farmlands and other infrastructures. For example, the occurrence of landslide along a local road is shown in Figure 2-a, and Figure 2-b illustrates the development of tensional crack along the farmland and a local school.

The subject of landslide was concerned by many researchers all around the world; for example, Varnes (1978), Guzzetti et al. (1999), Lan et al. (2004), and Neaupane and Piantanakulchai (2006). A number of local research works were also carried out in the area to evaluate the potential of hazards caused by landslide; for example, Uromeihy (2000), Faiz-Nia and Kalarstaghi (2004), and Entezari (2004). The study aims at providing landslide susceptibility maps to show the probability of future landslides for a set of influencing factors.

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2011 2nd International Conference on Environmental Science and Technology IPCBEE vol.6 (2011) © (2011) IACSIT Press, Singapore

Figure 2. Examples of damages caused by the landslides in the study area.

II. GEOLOGICAL SETTING The geological setting of the area consists of a series of

sedimentary rocks mainly limestone, dolomite, marlstone, siltstone and sandstone. These rock units belong to marine geological formations of Jurassic to late Tertiary age. Quaternary deposits of alluvial have a widespread distribution over the land surface especially to the northern part of the area adjacent to the Caspian Sea. The area is part of Alborz Mountain and is known for its active and strong tectonic activity with several destructive earthquakes in the past (Berberian and Yeats, 1999). The highly folded and faulted rocks are associated with active tectonics in the region. These activities are developed due to the Arabian-Eurasia collision, resulting in the inversion of the Caspian Sea margin and the formation of Alborz orogeny (Shahidi et al., 2007). The morphology of the area is directly related to the rock types and geological features of the predominant formation. The geological setting of the area is presented in Figure 3.

III. LANDSLIDE OCCURRENCE Many factors influence the triggering and development of

landslide in the area. In this research, five factors were considered as most affecting. These include rock type, slope angle, distance from faults, drainage pattern, and type of landuse. Each factor with regard to its effect is categorized into five classes. Number of landslide occurrences in each geological unit is presented in TABLE I.

IV. LANDSLIDE ZONATION Although landslides are among the major geohazards in

the Babolrood watershed, the information about them is quite limited. The first essential step in this study is to establish spatial databases for landslides in ArcGIS, including landslides inventory data and the affecting factors. In order to relate landslide occurrences to the affecting factors, three various methods were used. These methods are defined as:

• Area Density Method (ADM), • Information Value Method (IVM), • Index Overlay Method (IOM).

These methods are based on expert evaluations of the main influencing factors which are supported by site recognitions and consideration of the past history of landslide events in the area. The hazard vulnerability of each zonation method is evaluated using the following formula:

Qsn = ∑ (Dr -1)2 S

Where:

Figure 3. Geological setting of the study area.

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Qs: quality value Dr: the ratio of landslide in each category to the total number of the landslides in the area S: the ratio of landslide surface of each category to the total land surface.

The plots of landslide hazard zonation maps referring to

each method are shown in Figures 4, 5 and 6, respectively.

TABLE I. PRESENTATION OF SURFACE AREA AFFECTED BY LANDSLIDE TO THE TOTAL AREA OF EACH GEOLOGICAL UNIT

Geological period

Type of deposits

Total Area (km2)

Affected Area (km2)

Quaternary Alluvial deposits 18943 1129

Pleistocene Weak cemented sandstone & siltstone 31424 1203

Neocene Sandstone and mudstone 14929 2531

Paleocene Sandy limestone and sandstone 4031 183

Cretaceous Marlstone and Marly-limestone 14417 1253

Middle-Jurassic Thin laminated limestone 4490 60

Lower-Jurassic Shale, sandstone and coal 39745 2954

Triassic Dolomite and limestone 6020 184

V. CONCLUSIONS It is concluded that lithology has a great influence on the

development of landslides in the Babolrood watershed area. It was also found that geological formations with higher percentage of clay materials have higher potential for landslide occurrence. Most landslides were activated in areas with slope angles between 8 and 25 degrees. The zonation map based on the area density method (ADM) showed better results in comparison with the information value method (IVM) and the index overlay method (IOM) (TABLE II).

TABLE II. RATE OF HAZARD VULNERABILITY ACCORDING TO EACH METHOD

Zonation Main Vulnerability

Method factors I II III IV V

Are

a D

ensi

ty

Met

hod

Dr 0.16 0.42 0.56 1.43 2.90

S 0.13 0.17 0.27 0.35 0.09

(Dr-1)2S 0.09 0.06 0.05 0.06 0.33

Qs 0.59

Info

rmat

ion

Val

ue M

etho

d Dr 0.04 0.17 0.56 0.61 1.94

S 0.04 0.13 0.13 0.34 0.36

(Dr-1)2S 0.04 0.09 0.02 0.05 0.32

Qs 0.53

Inde

x O

verla

y M

etho

d

Dr 0.29 0.35 0.50 1.46 2.72

S 0.11 0.17 0.25 0.38 0.08

(Dr-1)2S 0.06 0.07 0.06 0.08 0.25

Qs 0.52

REFERENCES [1] M. Berberian and R.S. Yeats, “Patterns of historical earthquake

rapture in the Iranian plateau”, Bulletin of the Seismological Society of America 89, pp. 120-139, 1992.

[2] A. Entezari, “Landslide hazard zonation of Syahbisheh watershed dam’, MSc dissertation, Islamic Azad University, Iran (in Persian). 2004.

[3] S. Faiz-Nia, and A. Kalarstaghi, “Investigation of factors influencing landslide occurrence in Shirinrood watershed”, Natural Resources Journal, Vol, 57, No. 1, (in Persian). 2004.

[4] F. Guzzetti, A. Carrara, M. Cardinali, and P. Reichenbach, “Landslide hazard evaluation: a review of current techniques and their application in a multi-scale study”, Central Italy, Geomorphology, Elsevier, Vol. 31, pp: 181-216, 1999.

[5] H.X. Lan, C.H. Zhoe, L.J. Wang, H.Y. Zhang, and R.H. Li, “Landslide hazard spatial analysis and prediction using GIS in the Xiaojiang watershed, Yunnan, China”, Engineering Geology, Elsevier, Vol. 76, pp:109-128, 2004.

[6] A. Shahidi, E. Barrier, M. Brunet, A. Saidi, and C. Muller, “Tectonic evalution of Alborz since Mesozoic, Iran”, Geological Research Abstracts, Vol. 9, 11074, 2007.

[7] K.M. Neaupane, and M. Piantanakulchai, “Analytic network process model for landslide hazard zonation”, Engineering Geology, Elsevier, Vol. 85, pp: 281-294, 2006.

[8] D.J. Varnes, “Landslide hazard zonation, a review of principles and practice”. IAEG Commission on Landslides. UNESCO, Paris, p. 63, 1978.

[9] A. Uromeihy, “Landslide hazard zonation mapping in Nekarood watershed, Iran” Journal of Geological Survey of Nepal, Vol. 3, pp: 23-35, 2000.

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Figure 6. Landslide hazard zonation according to index overlay method

Figure 5. Landslide hazard zonation according to information value method

Figure 4. Landslide hazard zonation according to area density method

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