Landslide characteristics and its impact on tourism for two roadside towns along the Kathmandu Kyirong Highway

Frequent landslide events affect the Kathmandu Kyirong Highway(KKH),one of the most strategic Sino-Nepal highways,with multiple social effects.Amongst them,the impacts on local tourism,although being substantial,have not been studied so far.The aim of this research is to analyze the characteristics of such landslides and their influence on road damages and/or blockages as well as on local tourism industry.We analyzed the co-seismic landslides triggered by the Gorkha Earthquake,2015(7.8 Mw),the post-seismic landslides that occurred during the monsoons following the earthquake,as well as landslides which occurred or reactivated in 2018,with relation to the damage that they caused to the highway.High resolution satellite images from 2015 to 2018,and field data were used for the analysis.The Langtang avalanche that locates off the highway was also mapped due to its high impacts on tourism.Between 2015 and 2018,the number of road damaging landslides in the Betrawati-Rasuwagadhi section of KKH(where Dhunche and Syafrubesi towns are located)was 101 in the main track(MT)and 103 in the new track(NT),with respective average density of 1.46/km and 3.63/km.The dominant observed landslide types were debris slides and rock falls.Landslides were mostly concentrated in the locations with the following characteristics:1)having higher elevated area,2)being located with the‘main central thrust’and other lineaments’belts,3)belonging to the Proterozoic lesser Himalayan rocks,4)having a slope gradient of 25°-45°,5)having northern,western and southern slope aspect,6)being subjected to average annual rainfall of higher than 1,000 mm,and 7)having less than 4 km distance from the past earthquake epicenters.The results further indicated that 7 rain-induced and 4 co-and post-seismic landslides have great impact on tourist flows.An impact analysis was also assessed through a door to door questionnaire survey with local hotel operators from Dhunche and Syafrubesi towns(n=29+31).The results reveal that out of six rigorously affected sectors by landslides leading to road blockage,tourism business is the most impacted livelihood sector in these towns.The reduction of visitors in different hotels ranged from 50%-100%in Dhunche and 70%-100%in Syafrubesi for the first year aftermath of the tremor.This is higher than the respective 5%-50%tourist reduction due to raininduced landslides.Using as a reference the base year 2014,the income loss of hotels in both towns was found to be 50%-100%in 2015,20%-100%in 2016,5%-75%in 2017,and similar to 35%in 2018.These results provide insights on the synergic effect of contributing factors for cut slope as well as down slope instability along mountainous motorways and their impact on income sources for local communities.

Landslide susceptibility assessment at Kathmandu Kyirong Highway Corridor in pre-quake, co-seismic and post-quake situations

Kathmandu Kyirong Highway(KKH)is one of the most strategic Sino-Nepal highways.Lowcost mitigation measures are common in Nepalese highways,however,they are not even applied sufficiently to control slope instability since the major part of this highway falls still under the category of feeder road,and thus less resources are made available for its maintenance.It is subjected to frequent landslide events in an annual basis,especially during monsoon season.The Gorkha earthquake,2015 further mobilized substantial hillslope materials and damaged the road in several locations.The aim of this research is to access the dynamic landslide susceptibility considering pre,co and post seismic mass failures.We mapped 5,349 multi-temporal landslides of 15 years(2004-2018),using high resolution satellite images and field data,and grouped them in aforementioned three time periods.Landslide susceptibility was assessed with the application of’certainty factor’(CF).Seventy percent landslides were used for susceptibility modelling and 30%for validation.The obtained results were evaluated by plotting’receiver operative characteristic’(ROC)curves.The CF performed well with the’area under curve’(AUC)0.820,0.875 and 0.817 for the success rates,and 0.809,0.890 and 0.760 for the prediction rates for respective pre,co and post seismic landslide susceptibility.The accuracy for seismic landslide susceptibility was better than pre and post-quake ones.It might be because of the differences on completeness of the landslide inventory,which might have been possibly done better for the single event based co-seismic landslide mapping in comparison with multitemporal inventories in pre and post-quake situations.The results obtained in this study provide insights on dynamic spatial probability of landslide occurrences in the changing condition of triggering agents.This work can be a good contribution to the methodologies for the evaluation of the dynamic landslide hazard and risk,which will further help to design the efficient mitigation measures along the mountain highways.