achham landslide

Landslide Disaster and Hazard Zonation in the Landslide Disaster and Hazard Zonation in the parts of Khaptad area, Achham districtparts of Khaptad area, Achham districtby the landslides of 26-27 August 2006by the landslides of 26-27 August 2006

byby

Birendra Piya (Sr. Div Geologist)Birendra Piya (Sr. Div Geologist) G. R. Chitrakar (Sr. Div Geologist)G. R. Chitrakar (Sr. Div Geologist)

S. P. Manandhar (Geologist)S. P. Manandhar (Geologist)

Department of Mines and GeologyDepartment of Mines and GeologyApril 1,April 1, 20072007

ContentsContents IntroductionIntroduction

ObjectivesObjectives

MethodologyMethodology

AnalysisAnalysis

ResultsResults

ConclusionConclusion

RecommendationRecommendation

IntroductionIntroduction Due to the continue 3 days heavy rainfall starting from 25 August to 27 august 2006 in the far western region, landslide disaster took place causing huge damage in the life and property.

The study area lies in the most remote place of Khaptad VDC of Achham District, Far western Nepal, It is about 455 Km away from Nepalgunj up to Sanfebagar by road and from Sanfebagar it is one full day walk towards the Khaptad national park.

The field program was conducted from 10/10/06 to 18/10/06.

The study was carried out upon the request of Disaster Relief Committee Home Ministry, Nepal Government

ObjectivesObjectives

To study the geological conditions of the area and to investigate the cause of disaster.

To investigate whether the region is safe for the continue settlements for the people of the area or need to be relocated them in some other safe areas.

Finally, to prepare a report with some recommendations.

Methods A toposheet map (sheet no. 2989 09D)

of scale 1:25000 was used as a base map.

Field Survey and Interviews with thelocal people were carried out in thefield.

Ilwis 3.3 Academic version developedby ITC, Netherlands was used for the GIS analysis to prepare landslide

Hazard Zonation map.

Present Scenarios; The Balyalta Village and Guta Villages are the most

affected area by the landslide disaster. The people of the villages have been rehabilated in a temporary

rehabilitation center situated at a close distance from their respective villages.

Many landslides along with major cracks in and around the villages have been developed.

Even the rehabilitation center is located at a landslide risk zone.

The individual houses in the village have been completely abandoned.

The people in the rehabilitation center are lacking of warm clothes and safe shelter.

The loss of life and properties of the people due to landslide disaster is given below in the tabular form.

Contd. Present Scenarios;

Details of the lossDetails of the loss

Disater EffectsNo.

Village Name Household Pop Human Injured House Landloss watermillCasualties Cow & Buffa.Goatsdamaged in ropanidestroyed

Guta Village 21 147 1 2 34 3 13Balyalta Village 92 556 6 8 64 94 6 2000

Putru Village 48 327 0 0 15 7 403 3Mathillo Tuka 66 483 0 0 0 208

TalloTuka 57 385 0 0 0Bhedasen-9 32 201 0 0 0

316 2099 7 10 113 94 16 2611 16

Animal Loss

A ladslide view of Balyalta from Patal villageA ladslide view of Balyalta from Patal village

Rehabilitation center in Balyalta and the landslideRehabilitation center in Balyalta and the landslide

SIBIR 2

A landslide crack developed on the side of the sibir, How safe is the sibir??

Landslides in Guta Khola flowing SW to NELandslides in Guta Khola flowing SW to NE

Khaptad National park

SP Manandhar with the villagers observing rocks in Guta SP Manandhar with the villagers observing rocks in Guta

Khola and the landslide behindKhola and the landslide behind

A primary school of Guta village (A landslide is situated just A primary school of Guta village (A landslide is situated just

on the side of it)on the side of it)

Landslide in the upper part of the Argheli KholaLandslide in the upper part of the Argheli Khola

Argheli Khola

Rehabilitation center in Devisthan VDC – 9Rehabilitation center in Devisthan VDC – 9

Children of Guta village in Rehabilitation centerChildren of Guta village in Rehabilitation center

A scarp of the displaced land >3m down part of the Guta A scarp of the displaced land >3m down part of the Guta villagevillage

>3m

1 man killed, 30 cattles (Cows and Buff) died, 10 cowshed swept away by this landslide located near Guta villagelandslide located near Guta village

A landslide near Guta village facing towards northA landslide near Guta village facing towards north

Rice Cultivation along the hill slopes

A local man showing cracks along the cultivated land

Abandoned houses in Guta village (After 2months)

A Rehabilitation at Devisthan VDC

SIBIR 1

View of Guta village from sibir 1

A view of landslides from Sibir 1 situated below theBallyalta village.

Landslides along the sides of Argheli khola

Rotational Landslides in Argheli khola

Rotational slide on the right side of Argheli Khola, It is active and continuous

The lower part of the landslide is activated by the upper landslide

A suspension bridge washed away by the debris flow.Foundation of the bridge is set up in the colluvial materials

A crack developed in the hill slopes

>1m wide

Cultivation land was washed away by the landslides

A place where a number of cowsheds, were buried along with some people and animals. by the debris flow.

Unstable boulder

Upper part of the landslide (Debris flow)

Balyalta village, Cultivated land and the landslides

Houses in Balyalta Village damaged by the debris flowHouses in Balyalta Village damaged by the debris flow

Khaptad National park

Geology of the study area1.Recent Deposit 2. Crystalline Complex

1.Recent Deposits;

Flood Plain Deposit: Consists of loose Colluvial sediments, Boulders, cobbles, gravel, sand

and silt of granite schist and gneiss.

Colluvial Deposit: Consists of Boulder, fine to coarsegrained sand and silty sand materials which are highly

porous.

2.Crystalline Complex: (Precambrian to Paleozoic)a. Khaptad granite gneiss formationConsists of coarse grained porphyroblastic granite, gneiss, augen

gneiss, migmatites and small bodies of granite, pegmatites and Apilites.

b. Kachalo Khola Kyanite garnet mica schistConsists of well foliated coarse grained kyanite bearing garnet mica

schistc. Phulaut chloritic garnet mica schist formationConsists of thinly bedded well foliated medium to coarse grained

chloritic garnet mica schist.

d. Buriganga Quartzo-feldspathic schist formationConsists of coarse grained quartzo-feldpathic schist, gneiss, banded

gneiss, and augen gneiss with quartzite bands and chlorite mica schist at places.

Contd. Geology of the study area

Landslide Hazard Zonation

Methods• Ilwis 3.3 as a software

• Bivariate statistical analysis approach By C. J van westen (ITC, Netherlands)

• Preparation of factor maps:Landslide distribution mapGeology mapLanduse mapSlope mapAspect map

Methods Contd. Crossing of Landslides map with the

corresponding factor maps

Calculation of Landslide densities

Calculation of Weight values

Creation of weight maps

Classification of weight maps

Creation of Landslide Hazard Zonation map

Wi= DensmapDensclass

= ln

map entire of Areamap entire in the landslide of Area

classparameter certain of Areaclassparameter certain in Landslides of Area

Where,Wi = Weight given to certain parameter classDensclass = Landslide density within the parameter classDensmap = Landslide density within the entire map

The Bivariate statistical approach of Landslide Hazard Zonation is based on the following formula

Floodplain Deposit

Colluvial

Khaptad Granite Gneiss

Kachalo Khola Formation

Phulaut Chloritic Garnet Mica Schist Formation

Buriganga

Legend

0 4000 m

Na. Geological Map of the study areaFactor Maps

b. Landuse MapFactor Maps

c. Slope MapFactor Maps

d. Aspect MapFactor Maps

Landslide Distribution Map

High 39%Moderate 21%Low 40 %

ResultsResults• The Landslide Hazard Zonation Map is prepared.• The study area specially the settlement areas lie in the high

landslide hazard zone, hence it is not safe for settlements.• The Landslide disaster was caused due to the following

factors;a. Excessive rainfall: The Nepalgunj station recorded

rainfall of 310 mm in 24 hours 26-27 August 2006. There was continue rainfall for 72 hours in the affected area.

b. Landuse Practice: Rice cultivation with proper canal facilities and over grazing of cattles in the near by forest area are the main occupation of the people in the area .

c. Geological conditions and steep slopes: The area lies in the High Himalayan Crystalline

zone consisting of well foliated coarse grained Kyanite and garnet bearing mica schist, granites and gneiss. The mica schist is highly weathered. Geographically the

area is situated in steep slopes with an altitude range of 1600 m to 1850 mmsl.

d. Toe Cutting: The area consists of narrow and highly gradient

streams and the tributaries, due to which when there is an excessive rainfall, water flows with high velocity leading to toe cuttings along the sides of the streams.

Results Contd.Results Contd.

Results Contd.Results Contd.The landslide hazard zonation map is prepared using Ilwis 3.3 software and it shows that nearly 39 percentage of the study area is covered by high hazard zone, 21 percentage is covered by moderately hazard zone and 40 percent of the area is covered by low hazard zone.

ConclusionConclusion The landslide disaster of 26 and 27th August, 2006

took the lives of 7 people injuring 10 along with the damage in property.

The geological and topographical conditions, Landuse practices, excessive and long duration of rainfall and toe cuttings were the main causes of landslide

disaster.

There are still many huge cracks developed in and around the village area basically in the hill slopes. At some places the ground subsidence has also occurred.

The people of the area are set up in the two rehabilitation camps in the near by areas, one of which is situated near the huge crack area and hence is under the threats of landslide.

The area (Khaptad region) receives high rate of precipitation every year. Very thick snow fall begins to occur there from the month of October.

All the villages ( Balyalta, Guta, Putru, Bhedasen and Tuka villages) are under the threats of further landslides in the future, hence the region is not safe for the

settlement.

Contd. Conclusion

Most of the active and old landslides falls within the high hazard zone indicating good reliability and satisfactory precision of Bivariate-Statistical Model in Landslide Hazard Zonation mapping.

It is found that About 94% of the landslides occurs in High Hazard Zone, About 5 % of the landslides occurs in Moderately hazard zone and the rest

occurs in Low Hazard Zone.

Contd. Conclusion

Recommendations

Rice cultivation and over grazing of the cattle in the area should be discouraged.

Afforestation program should be carried out in the barren slopes.

Proper drainage should be maintained for the seepage, spring water and for the runoff water.

A detail study is essential regarding the stability of the region.

Although many of the landslides can be minimized by applying mitigation measures such as by using bio engineering techniques, Retaining walls, Jute netting, Gabion walls, French drains etc. In this case from the economic point of view and its geographical

situation, it would be wise to relocate the people in some other safe areas instead of trying to resettle them in the same areas just by applying some mitigation measures. It is essential to shift the people in the safe areas before the coming Monsoon Season.

Recommendation Contd.