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Nabelek, J., Hetenyi, G., Vergne, J., Sapkota, S., Kafle, B., Jiang,M., Su, H., Chen, J., Huang, B. S., and Hi, C. T., 2009,Underplating in the Himalaya-Tibet collision zone revealedby the Hi-CLIMB experiment: Science, v. 325, no. 5946, p.1371–1374.

Neupane, B., Ju, Y., Allen, C., Ulak, P. D., & Han, K., 2017.Petrography and provenance of Upper Cretaceous–Palaeogenesandstones in the foreland basin system of Central Nepal.International Geology Review 60(2), 135–156.

Ni, J., and Barazangi, M., 1984, Seismotectonics of the HimalayanCollision Zone: Geometry of the underthrusting Indian Platebeneath the Himalaya: Journal of Geophysical Research:Solid Earth, v. 89, no. B2, p. 1147–1163.

Pandey, M. R., and Molnar, P., 1988, The distribution of intensity of the Bihar Nepal earthquake of 15 January 1934 andBounds on the extent of the rupture zone Journal of NepalGeological Society, v. 5, no. 22–44.

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Nabin Bhandari1 and *Subodh Dhakal2

1Central Department of Environmental Science, Tribhuvan University, Kathmandu, Nepal2Department of Geology, Tri-Chandra Campus, Tribhuvan University, Ghantaghar, Kathmandu, Nepal

*Corresponding author: dhakalsubodh@gmail.com

ISSN 2676-1386 (Print); ISSN 2676-1394 (Online)

Assessment of the Landslides triggered by Gorkha Earthquake 2015: A case studyof Shivapuri Nagarjun National Park, Central Nepal

INTRODUCTIONDue to natural conditions or man- made actions, landslides

have produced multiple human and economic losses (Fleming1980, Guzzetti 2007). Earthquakes are one of the main triggeringfactors of landslides and rapidly changes of surface with generatelandslides. Largest earthquakes have capable to trigger thousandsof landslides throughout areas of more than 100,000 km2(Keefer, 1984). Earthquake induced landslides have beendocumented from at least as early as 1789 BC in China (Hansenand Franks, 1991) and 372 BC in Greece (Seed, 1968). Thefirst scientific identification of earthquake induced landslidesand their systematic documentation was undertaken in theCalabria region of Italy after the 1783 earthquake swarm andfirst basic inventory for earthquake induced landslidesaccomplished in 1957 for Daly City after the Californiaearthquake (Keefer, 1994). On the other hand the first largeinventory attempt done by Harp et al. in 1981 for Ms 7.5Guatemala earthquake (1976). According to the results ofdistribution and statistics based studies, the type and localityof landslides caused by earthquakes are affected by the differencesin seismic parameters and distribution of geologicalcharacteristics and topographic factors. Therefore, it isprerequisite to have a comprehensive understanding of seismicparameters, geological and geomorphologic dynamics and therelations between them for better understanding of landslidedistribution induced after the earthquakes. Earthquake-inducedlandslide hazard zoning known to have experienced earthquake- induced slope failures during historical earthquakes, or areas

ABSTRACTThe Gorkha earthquake (25 April 2015, Mw 7.8) Nepal caused a large number of casualties and serious property losses, and alsoinduced numerous landslides. Landslides are recognized as the third type of natural disaster in terms of worldwide importance. Dueto natural conditions or man- made actions, landslides have produced multiple human and economic losses. After the devastatingGorkha earthquake, Shivapuri National Park area has been affected as there has been rise in number of landslides within the area.This paper presents the landslide occurrences in Shivapuri Nagarjun National Park area by using Google Earth images, conductinginteraction with the local people as well as national park staff members and direct field observation. Landslide validation, types oflandslides and the landslide volume were calculated from the field study. Due to the unmanaged construction of the road through loosesoil, potentiality of landslide occurrence was high in the presence of any triggering factors; Gorkha Earthquake 2015 did this job Thisresult shows that the earthquake has increased the number of landslides within the national park area. It is found that the GorkhaEarthquake 2015 triggered altogether 13 small sized landslides in the study area, among them debris flow is the major type.

Key words: Gorkha Earthquake 2015, landslide, Shivapuri Nagarjun National Park

identified as having past landslide movement including bothlandslide deposits and source areas, or areas where the geologicalmaterials are susceptible to earthquake-induced slope failure(Varnes, 1984).

The Geographic Information System (GIS) is “a powerfultool for collecting, storing, retrieving, transforming and displayingspatial data from the real world for a particular set of purposes”(Burrough,1986). Wasowski et al. (2002) investigated the factorsthat control seismic slope susceptibility in the Slopes of ValleySele. It was denoted that most of the slope failures were causedby 1980 Irpina Earthquake. It was also noted that hydrologicalconditions and differences in slope gradient are two importantparameters that cause difference in the distribution of reactivatedlandslides that are caused by seismic effects. Capolongo et al.(2002), used a GIS-based analysis for the slope deformationmodel that was induced from a seismic effect in the SouthernApennines, Italy. Del Gaudio and Wasowski (2004), studiedlandslide hazard in Irpina, southern Italy caused by a seismicactivity in order to map the landslides that were triggered bythe earthquakes using the model of Newmark over aregional scale. Ingles et al. (2006) carried out a research on thedisplacements of earthquake induced landslides using Newmarkmodel, in which the effect of the vertical component of groundshaking was investigated.

Similarly, Nepal is a country consisting of many highmountains and high hills. It is also a prone country to earthquakedue to its tectonic position. Hence it is very important to know

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the pre and post occurrence of landslide in hilly areas of Nepalthat might occur due to the earthquake. This study emphasis onassessing the impact of Gorkha Earthquake 2015 on landslideevents in Shivapuri Nagarjun National Park Area by identifyingthe number, types, materials present and volume of the landmass swept down.

METHODODLOGY

Study AreaShivapuri National Park is the ninth national park of

Nepal and was established in 2002 with an area of 159 km2. Itis located in country’s midhills on the northern fringe of theKathmandu Valley (Fig. 1) and named after Shivapuri peak of2732 m altitude. The national park was upgraded to protect thevalley’s main water sources, as well as 177 species of birds andrare orchids.

Primary Data Collection

Questionnaire Survey

For the primary data collection questionnaire related to

the landslide occurrence, the effect due to the landslide, etc wasdeveloped. The questionnaire was asked to the National Parkstaffs and the local people residing near the landslide area.

Direct Field Observation

For the visualisation of the landslide in the area directfield visit was done during the month of January, 2016. Thetypes of landside were identified observing the way how themass has been slide down and the classification was done usingthe “types of landslides and the Abbreviated version of Varnes’classification of slope movements (Varnes, 1978)”. Also thematerials in the mass were observed and identified. The breadthof the mass which has slide down along with its height measuredand noted. This measurement was taken in order to calculatethe volume of landslide. The coordinates of each site was notedin order to site the landslide area in the google map.

Data Analysis

The measurement of the length and breadth of mass wereentered in excel sheet (Microsoft Office, 2013) in order to findthe volume of mass of each landslide. For the depth, DEM 2011was used through which the previous elevation of the site andthe present elevation was compared and the difference wascalculated for the depth of the mass. The study area map, aspect andslope of the national park were created using ArcGIS version 9.3.

Secondary Data Collection

Secondary information (literature review)

Different reports, papers, thesis and literatures werereviewed along the study period. The reference data andinformation were referred through the literatures of the globaland local landslide and earthquake relations.

RESULTS

From the field study, altogether 13 landslides wereencountered at different elevation points (Table 1, Fig. 2).Landslides were found mostly in the slopes greater than 300.The types of landslide were noted classifying in the basis ofVarnes’ classification of slope movements (Varnes, 1978). Thematerials present in the mass was analysed in the field and noted(Table 1).

Using ArcGIS, the total percentage of the study area(Shivapuri Nagarjun National Park having area of 106.7 sq.km) with the slope area greater than 300 (23.9 sq. km) wascalculated in order to quantify the prone slope area for landslide. The area with slope exceeding 300 was 22.4%. The map wasdeveloped showing the aspect (Fig. 3a), elevation and slopegreater than 300 (Fig. 3b) and aspect and slope greater than 300(Fig. 3c), which helps in identifying the mostly prone areas oflandslide.

Fig. 1: Study area, Shivapuri Nagarjun National Park

Assessment of the Landslides triggered by Gorkha Earthquake 2015: A case study of Shivapuri Nagarjun National Park

275

22.4%. This determines that this area is more prone to thelandslide in respect to the slope angle but due to the vegetationcover over the National Park this has positive point regardingthe resistance of the ground against the landslide that may betriggered by the earthquake.

The overall landslides area are seen within the boundaryarea of the national park, this is due to the road construction inmany areas at the boundary area and the road constructed forthe transportation of the materials to the places like Chisapani,for the dam at Sundarijal and for house construction within theNational Park area. This construction has added positive impactfor easy landslide during the earthquake as well as erosionduring heavy rainfall. But due to the high vegetation cover inother part of the National Park, there is low to no landslide seen.DEM, ArcGIS and Google Earth were used to identify if therewere previous landslides seen before Gorkha earthquake 2015,but they could not be identified. Hence, face-to-face interviewwith the National Park authority, staff and local people weretaken and proved from the interview that the landslide hadoccurred only after the Gorkha Earthquake 2015.

CONCLUSIONSThis study completed the study of landslides triggered

by the Gorkha earthquake 2015 at Shivapuri National Park.Most of the areas were found to contain loose materials i.e.mixture of soil, small rocks and sand. Most of the landslidesseen more or less near the boundary areas of the national park,the main reason is the excavation for road construction at thosearea where the vegetation cover are less and the loose soil areexposed. It is found that the the Gorkha Earthquake 2015triggered altogether 13 small sized landslides. The landslidesare small with highest breadth of 40 m and lowest of 4m causingsome property to animal life and vegetation damage but nohuman casualty occurred. This result shows that the earthquakehas increased the number of landslides within the National Parkarea. Hence, further study in such areas are required in orderto protect the vegetation, human property, animal life, stabilize

DISCUSSIONSThis study provides a rapid assessment of landslide

triggered by the April 2015 Gorkha earthquake and itsaftershocks. Within the study site all the 13 encountered landslideswere triggered by the earthquake. Although the Google imagewas used for the screening of the landslide number, due to thevegetation cover (tree cover area) and also due to the small sizelandslide, clear visualization was not available. The informationwas more available by face-to-face interview with the localpeople residing within and around the park.

The aspect and the slope of the national park were foundusing the ArgGis 9.3. The elevation of the study site wascalculated using DEM where the highest elevation was 2702m and the lowest elevation 1178 m. The National Park hasdifferent slope angle and with the help of ArcMap, it was foundthat the slope with greater than 30° are high in number. Hereslope angle of 30° or greater is considered to induce morelandslides. The calculated total area of Shivapuri National Parkis 106,724,724 sq. meters (107 km2 as calculated). The totalarea of slope greater than 30° is 23,941,318 sq. meters (23km2). So the percentage of slope greater than 30° would be

Table 1: Different landslides triggered by Gorkha Earthquake (2015)

Fig. 2: Different sites showing the landslides occurred afterthe Gorkhal earthquake 2015. Landsides extracted fromGoogle Earth 2016.

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Nabin Bhandari and Subodh Dhakal

the pre and post occurrence of landslide in hilly areas of Nepalthat might occur due to the earthquake. This study emphasis onassessing the impact of Gorkha Earthquake 2015 on landslideevents in Shivapuri Nagarjun National Park Area by identifyingthe number, types, materials present and volume of the landmass swept down.

METHODODLOGY

Study AreaShivapuri National Park is the ninth national park of

Nepal and was established in 2002 with an area of 159 km2. Itis located in country’s midhills on the northern fringe of theKathmandu Valley (Fig. 1) and named after Shivapuri peak of2732 m altitude. The national park was upgraded to protect thevalley’s main water sources, as well as 177 species of birds andrare orchids.

Primary Data Collection

Questionnaire Survey

For the primary data collection questionnaire related to

the landslide occurrence, the effect due to the landslide, etc wasdeveloped. The questionnaire was asked to the National Parkstaffs and the local people residing near the landslide area.

Direct Field Observation

For the visualisation of the landslide in the area directfield visit was done during the month of January, 2016. Thetypes of landside were identified observing the way how themass has been slide down and the classification was done usingthe “types of landslides and the Abbreviated version of Varnes’classification of slope movements (Varnes, 1978)”. Also thematerials in the mass were observed and identified. The breadthof the mass which has slide down along with its height measuredand noted. This measurement was taken in order to calculatethe volume of landslide. The coordinates of each site was notedin order to site the landslide area in the google map.

Data Analysis

The measurement of the length and breadth of mass wereentered in excel sheet (Microsoft Office, 2013) in order to findthe volume of mass of each landslide. For the depth, DEM 2011was used through which the previous elevation of the site andthe present elevation was compared and the difference wascalculated for the depth of the mass. The study area map, aspect andslope of the national park were created using ArcGIS version 9.3.

Secondary Data Collection

Secondary information (literature review)

Different reports, papers, thesis and literatures werereviewed along the study period. The reference data andinformation were referred through the literatures of the globaland local landslide and earthquake relations.

RESULTS

From the field study, altogether 13 landslides wereencountered at different elevation points (Table 1, Fig. 2).Landslides were found mostly in the slopes greater than 300.The types of landslide were noted classifying in the basis ofVarnes’ classification of slope movements (Varnes, 1978). Thematerials present in the mass was analysed in the field and noted(Table 1).

Using ArcGIS, the total percentage of the study area(Shivapuri Nagarjun National Park having area of 106.7 sq.km) with the slope area greater than 300 (23.9 sq. km) wascalculated in order to quantify the prone slope area for landslide. The area with slope exceeding 300 was 22.4%. The map wasdeveloped showing the aspect (Fig. 3a), elevation and slopegreater than 300 (Fig. 3b) and aspect and slope greater than 300(Fig. 3c), which helps in identifying the mostly prone areas oflandslide.

Fig. 1: Study area, Shivapuri Nagarjun National Park

Assessment of the Landslides triggered by Gorkha Earthquake 2015: A case study of Shivapuri Nagarjun National Park

275

22.4%. This determines that this area is more prone to thelandslide in respect to the slope angle but due to the vegetationcover over the National Park this has positive point regardingthe resistance of the ground against the landslide that may betriggered by the earthquake.

The overall landslides area are seen within the boundaryarea of the national park, this is due to the road construction inmany areas at the boundary area and the road constructed forthe transportation of the materials to the places like Chisapani,for the dam at Sundarijal and for house construction within theNational Park area. This construction has added positive impactfor easy landslide during the earthquake as well as erosionduring heavy rainfall. But due to the high vegetation cover inother part of the National Park, there is low to no landslide seen.DEM, ArcGIS and Google Earth were used to identify if therewere previous landslides seen before Gorkha earthquake 2015,but they could not be identified. Hence, face-to-face interviewwith the National Park authority, staff and local people weretaken and proved from the interview that the landslide hadoccurred only after the Gorkha Earthquake 2015.

CONCLUSIONSThis study completed the study of landslides triggered

by the Gorkha earthquake 2015 at Shivapuri National Park.Most of the areas were found to contain loose materials i.e.mixture of soil, small rocks and sand. Most of the landslidesseen more or less near the boundary areas of the national park,the main reason is the excavation for road construction at thosearea where the vegetation cover are less and the loose soil areexposed. It is found that the the Gorkha Earthquake 2015triggered altogether 13 small sized landslides. The landslidesare small with highest breadth of 40 m and lowest of 4m causingsome property to animal life and vegetation damage but nohuman casualty occurred. This result shows that the earthquakehas increased the number of landslides within the National Parkarea. Hence, further study in such areas are required in orderto protect the vegetation, human property, animal life, stabilize

DISCUSSIONSThis study provides a rapid assessment of landslide

triggered by the April 2015 Gorkha earthquake and itsaftershocks. Within the study site all the 13 encountered landslideswere triggered by the earthquake. Although the Google imagewas used for the screening of the landslide number, due to thevegetation cover (tree cover area) and also due to the small sizelandslide, clear visualization was not available. The informationwas more available by face-to-face interview with the localpeople residing within and around the park.

The aspect and the slope of the national park were foundusing the ArgGis 9.3. The elevation of the study site wascalculated using DEM where the highest elevation was 2702m and the lowest elevation 1178 m. The National Park hasdifferent slope angle and with the help of ArcMap, it was foundthat the slope with greater than 30° are high in number. Hereslope angle of 30° or greater is considered to induce morelandslides. The calculated total area of Shivapuri National Parkis 106,724,724 sq. meters (107 km2 as calculated). The totalarea of slope greater than 30° is 23,941,318 sq. meters (23km2). So the percentage of slope greater than 30° would be

Table 1: Different landslides triggered by Gorkha Earthquake (2015)

Fig. 2: Different sites showing the landslides occurred afterthe Gorkhal earthquake 2015. Landsides extracted fromGoogle Earth 2016.

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Nabin Bhandari and Subodh Dhakal

the landslide areas and minimize the damage and to protect thenational park.

REFERENCESBurrough, PA.,1986, Principles of Geographic Information System

and Land Resource Assessment, Claredon Press, Oxford,England,194p.

Capolongo D., Refice A., Mankelow J.,2002, Evaluating earthquake-triggered landslide hazard at the basin scale through GIS inthe Upper Sele river Valley. Surveys in Geophysics, v. 23(6), pp. 595–625.

Del Gaudio V., Pierri P., Wasowski J.,2003, An approach to time-probabilistic evaluation of seismically induced landslidehazard. Bulletin of The Seismological Society of America93: 2, pp. 557–569.

Del Gaudio V., Wasowski J.,2004, Time probabilistic evaluationof seismically induced landslide hazard in Irpinia (SouthernItaly). Soil Dynamics and Earthquake Engineering 24: 12,pp. 915–928.

Fleming, R.W. and Taylor, F.A. (1980) Estimating the costs oflandslide damage in the United States, U.S. Geol. SurveyCircular 832, 21 p.

Guzzetti F., Peruccacci S., Rossi M., Stark CP.,2007, Rainfallthresholds for the initiation of landslides in central andsouthern Europe. Meteorology and Atmospheric Physics98:3-4, pp. 239–267.

Hansen, A. and Franks, C.A.M.: 1991, Characterisation and Mappingof Earthquake Triggered Landslides for Seismic Zonation,Proceedings of the Fourth International Conference on SeismicZonation, Stanford, California, v. 1, pp. 149–195.

Ingles J., Darrozes J., Soula JC.,2006, Effects of the verticalcomponent of ground shaking on earthquake-induced landslidedisplacements using generalized Newmark analysis.Engineering Geology 86: 2-3, pp.134–147.

Keefer, D.K., 1984, Landslides Caused by Earthquakes, GeologicalSociety of America Bulletin, v. 95, 406–421.

Seed, H.B., 1968, Landslides During Earthquakes Due to SoilLiquefaction, American Society of Landslides for SeismicZonation, Proceedings of the Fourth International Conferenceon Seismic Zonation Stanford, California, vol. 1, pp. 149–195.

Varnes, D.J.,1984, Landslide Hazard Zonation: A View of Principlesand Practices,Commission in Landslides of the IAEG, Unesco,Natural Hazards, No.3 , 61p.

Wasowski J., Del Gaudio V., Pierri P., Capolongo D., 2002, Factorscontrolling seismic susceptibility of the Sele valley slopes:The case of the 1980 Irpinia earthquake re-examined. SurveyIn Geophysics 23:5 63–593

Fig. 3: (a) Map of Shivapuri National Park showing theslope aspect, (b) Map showing the different elevation rangeand the slope greater than 30°, and (c) Map showing theslope aspect and the slope angle greater than 30°.

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*Ujjwal Acharya, Madan Bhattari, Deepak Banjade, and Niraj Regmi

Sanima Hydropower Limited, Kathmandu, Nepal*Corresponding author: ujjwal.acharya@sanimahydro.com.np

ISSN 2676-1386 (Print); ISSN 2676-1394 (Online)

Study of stability of slopes of tunnel portals using modified SMR approach:A Case Study of Lower Likhu Hydropoer Project

INTRODUCTIONThe Lower Likhu Hydropower Project (28 Mw) is run-

off-the river type hydropower project located at Ramechhapand Okhaldhunga district. The studied slopes are five headracetunnel portals, namely Seti Outlet, Seti Inlet, Poku Outlet, PokuInlet, Main Outlet, and one surge shaft slope. Modified SMRapproach is used for the slope stability assessment of the area(Anbalagan et al., 1992). The general geology of the areacomprises of mainly two units: phyllite dominated andmetasandstone dominated rock units.

GEOLOGICAL SETTINGThe general geology of the area comprises of two rock

units. Thinly foliated, greenish grey, slightly to moderatelyweathered phyllite with intercalations of metasandstone andquartzite is present on the northern part of the study area (Fig.1). Fine to coarse grained, greenish grey to grey, fresh tomoderately weathered metasandstone with partings of phyllite,and few interbedding of coarse-grained meta-conglomerate ispresent on the southern part of the study area. The regionalgeological map published by DMG (1984) shows that the arealies in Seti Formation of Pokhara Sub-group, which comprisesof grey to greenish grey phyllites, gritty and quartzites withminor conglomeratic layer with some basic intrusions.

METHODSThe field data were collected using standard geological

instruments. Modified SMR approach (Anbalagan et al., 1992)was used for the slope analysis.

The stability of rock mass using SMR approach isobtained using the Bieniawski’s Rock Mass Rating (RMRbasic)and substraction of adjustment factors of the joint-sloperelationship and addition of a factor dependent to the methodof excavation.

ABSTRACTThe Slope Mass Rating (SMR) is widely used for stability assessment of rock slopes. The Modified SMR approach is used for thestability assessment of six rock slopes in tunnel portals and surge shaft area of Lower Likhu Hydropower Project (28.1Mw). The majorrock types of the study area are Phyllite and Metasandstone. The study shows some probability of wedge and planar failures at someslopes, whereas some slopes were found to be stable.

Key words: Likhu Khola Hydropower Project, Likhu Khola, Slope Mass Rating, Planar failure

SMR = RMRbasic – (F1.F2.F3) + F4, in which

RMRbasic is calculated according to Bieniawski (1979,1989) by adding the ratings of five parameters, whichare:

i. Uniaxial Compressive Strength of intact rock material,

ii. Rock Quality Designation (RQD),

iii. Joint or discontinuity spacing,

iv. Joint condition, and

v. Ground water condition.

F1 is dependent on parallelism between joints and slopeface strike. The approximate relationship to obtain thevalue of F1 is:

F1 = (1- sinA)2

Where, A denotes the angle between the strikes of theslope face and that of the joints.

F2 refers to the angle of dip of the joint considered, andvalue ranges from 0.15 to 1.F3 is the relationship between the slope face and jointdip angle.F4 is related to the method of excavation.Romana (1985) used planar and toppling failures for the

analysis using SMR. Anbalagan 1992 considered the plane andwedge failures as different cases and presented a modified SMRapproach for slope stability analysis, which is used for thepresent study. In this approach, the plunge and direction of dipof the line of intersection of unstable wedge were used.

Five different slope faces of the tunnel portals, namelySeti Outlet portal, Seti Inlet portal, Poku Outlet portal, PokuInlet portal and Main Outlet portal, and one in surge shaft area