Damage Assessment of Everest Region Nepal - July 15, 2015 Acknowledgment

DAMAGE ASSESSMENT OF EVEREST REGION NEPAL - JULY 15, 2015 ACKNOWLEDGMENT

The assessment of the Everest region’s main trekking routes for structural and geologic earthquake-related damage was funded by the International Finance Corporation (IFC), a member of The World Bank, and conducted on behalf of the Government of Nepal through the Ministry of Culture, Tourism and Civil Aviation. The assessment of the popular tourism treks was proposed by Intrepid Travel, the largest tour operator in Nepal. Intrepidproposed an assessment of the two most popular tourist treks in Nepal to better assess safety for its clients, as well as to assure travellers and the tourism industry. We very much would also like to express our sincere thanks to the Tourism Board and the Tourism Recovery Unit, and the many members of Nepal’s Tourism Industry that contributed to and provided their strong support to this project. TABLE CONTENTS OF CONTENTS

Executive Summary...... 5 Structural Assessment Results ...... 7 Geotechnical Assessment Results...... 7 Conclusions and Recommendations...... 9 ALARP Principle...... 11

Introduction...... 12

Findings and Methodology...... 15

Observed Damage...... 19 Lukla...... 20 Route from Lukla to Phakding...... 28 Phakding...... 29 Route from Phakding to Monjo...... 20 Toktok...... 21 Route to Monjo to TokTok...... 41 Monjo...... 43 Route from Monjo to Namch...... 43 Bridge Assessments ...... 45 Namche Bazaar...... 50 Khumjung and Khunde...... 50 Pangboche...... 52 Dingboche...... 60 Pheriche...... 61 Lobuche...... 66 Gorka Shep...... 67 Bridge at Phunki Tenga......

Summary...... 70

Recommendations...... 72

EXECUTIVE SUMMARY EXECUTIVE SUMMARY The Everest region, one of the most popular tourism destinations of the country, is located in the northeast of Nepal. Following the powerful earthquakes of April and May 2015, the extent and severity of earthquake-related structural damage and geologic hazards were unknown.

With funding from the World Bank’s International Finance Corporation (IFC) and on behalf of the government of Nepal through the Ministry of Culture, Tourism and Civil Aviation, an assessment team was dispatched to the region from June 27 to July 2, 2015 to observe and record seismic damage that occurred along the main trekking routes and in select villages as a result of the earthquakes and aftershocks.

The team was comprised of an expert structural engineer, a geotechnical engineer, a professional mountain guide, a project coordinator and an operations manager. The objective of the rapid reconnaissance of the region is to a) develop a baseline understanding of the extent of earthquake-related damage, b) provide advice on the overall trekking safety of the region’s routes and c) make recommendations on repairs or risk mitigation that will inform tourism recovery and commercial readiness strategies that are currently being developed by the government, its international development partners and Nepal’s tourism industry at large. The aim of these efforts is to promote tourism back to Nepal, which will support the overall economic recovery and return to normalcy in there. The findings of the structural and geotechnical assessment are summarized in this report.

METHODOLOGY A mix of helicopter flyover and trekking was used to access and assess the Everest region. The assessment began at Lukla and proceeded on foot to Namche Bazaar, Khunde and Khumjung. From there, the trail and villages in the Upper Khumbu area were assessed by helicopter.

The methodology applied to conduct the structural damage assessment was a rapid visual assessment per ATC-20 damage assessment methodology and Department of Urban Development and Building Construction (DUDBC) guidelines. A total of 15 villages with approximately 710 buildings were assessed, including accommodation and residential buildings and the nine main bridges along the trekking route.

A visual reconnaissance of the areas of concern was conducted for potential geologic hazards such as rockfall, landslides, debris flows and other related steep terrain hazards to assess earthquake-related geologic damage and risk.

5 Figure 1. ABOVE - The green marks the percentage of undamaged structures and the red marks the percentage of earthquake-damaged buildings in the 15 villages that were assessed following the April and May 2015 earthquakes.

6 ASSESSMENT RESULTS

STRUCTURAL ASSESSMENT RESULTS The green marks the percentage of undamaged structures and the red marks the percentage of earthquake-damaged buildings in the 15 villages that were assessed following the April and May 2015 earthquakes (see Figure 1).

Out of approximately 710 buildings, earthquake damage of structural concern was observed in 120 buildings (17 percent); 83 percent of buildings can be given a green tag per ATC-20/DUDBC guidelines. It was found that most of the buildings that were damaged can feasibly be repaired. Building owners have started reconstructing damaged buildings.

Typical accommodation construction types included uncut stone with mortar and cut rectangular block stone with or without cement mortar. Older construction typically used mud as mortar and it was found that newer construction for the most part used cement. Newer construction that used cement as mortar typically performed well in the earthquake, while construction types with mud as mortar and uncut stone sustained substantial damage and collapse in the earthquakes.

Although it is known that many of the buildings have multi-occupancy categories serving as residences, tourist accommodations and tea houses, a distinction can be drawn between typical residential housing construction used by village locals and typical accommodation structures. The typical residential buildings used by village locals are typically made from only locally available materials such as rock and mud, which performed poorly as noted above. We found that overall the main accommodation structures are typically of better construction and included materials such as cement and cut rock or light-weight wood studs which perform better in earthquakes.

The nine major bridges that were assessed had no structural earthquake damage. GEOTECHNICAL ASSESSMENT RESULTS

Green: No or minor apparent landslide damage. This includes areas with isolated drop outs below the trail, isolated damage to stacked stone walls or occasional rockfall from small moraine walls from above track level. Areas mapped in green are likely to be subject to a number of existing landslide hazards despite not being significantly damaged due to the earthquake.

Yellow: Moderate landslide damage or significant existing geotechnical hazard. This includes areas with significant debris from historic rockfalls, or areas with isolated boulders that fell during the recent earthquakes.

Red: Significant geotechnical damage. This includes areas with debris flows or extensive rockfall during or after the earthquakes.

In addition to the color categorization, the data has been split into two confidence levels:

Reasonable: where the trail was assessed on foot or at low speed by helicopter, or

Poor: where the trail was only assessed by helicopter or when the hillsides above the trail were significantly obscured by cloud.

7 Many of the villages on the Everest Base Camp trail do not appear to have been affected by landslide hazards as a result of the earthquake (e.g. Lukla, Namche, Khumjung, Tengboche, and all villages above Dingboche). For the purpose of this report, “landslide” is considered an all-encompassing term for any of the following:

• Earth/Debris flow or slide, • Rockfall, • Rock Avalanche and • Cliff Collapse A number of the villages have significant existing rockfall hazard (e.g. Phakding and Jorsale), while Toktok, Bengkar and Shomore have been affected by very serious geotechnical hazards.

None of the major suspension bridges appear to be affected by new geotechnical hazards as a result of the earthquake. Much of the trail and most of the rock retaining walls (both above and below) the trail are undamaged. We have observed very little foundation damage to buildings.

The damage in the lower valley (below Namche) is significantly greater than in the upper valley, which is likely because the slopes are generally steeper in the lower valley than the upper. Further, in the lower valley, the damage tends to be concentrated on the true right side of the river. This is likely because the dominant defect orientations within the rock are dipping out of slope on the true right and into slope on the true left. This means that there are more kinematically feasible failure mechanisms on the right side of the river. There may also be a seismic directivity effect since the true right of the river may have been shaken in a different manner from the true left as the USGS modelling shows clear propagation of energy towards the east (i.e. out of slope on the true right of the river).

There was evidence of ongoing slope movement and rockfall during our site assessment from many of the observed slopes. This may be an effect of earthquake-induced loosening of the rock in places, coupled with the early rains of the monsoon season causing an increased rate of slope failure to occur.

The Toktok debris flow and some of the rockfalls between Namche and Khumjung occurred very recently before our assessment. We anticipate that many more failures could occur during the upcoming monsoon season as the loosened rock becomes saturated and more soil material is washed out from within defects. This increased hazard may continue beyond the current monsoon season into future monsoon seasons.

Our observations of pre-earthquake rockfall suggest that many of the hazard areas that we have identified have always been subject to rockfall. We understand that many of the local people were aware of these hazards prior to the earthquakes (both local villagers and trekking/climbing guides using the valley) and that they had implicitly accepted the hazards.

In addition to the rockfall and landslide hazards discussed in this report, a number of other hazards may potentially affect the villages and trails described herein. These include: avalanches in the alpine areas, river scour, very large scale rockfall events (such as those that formed the colluvial fans near Lukla) and landslide or ice dam break in catchments above the immediate area of the trail.

8 CONCLUSIONS/ RECOMMENDATIONS

CONCLUSIONS AND RECOMMENDATIONS The majority of accommodation structures and trails have sustained minimal damaged from the April and May earthquake.

The owners have begun repairing and reconstructing accommodation buildings. They act as general contractors. Although we observed some good structural repair practices such as the use of cement as mortar, the placing of ring-beams and light-weight construction such as wood studs and metal sheet finishing for second floors and upwards, owners and construction workers require engineering support and training on the latest building techniques to build back better.

To provide training and guidelines during these critical months of reconstruction would greatly improve the overall built environment of accommodation structures on the trail.

Additionally, owners also are facing severe shortages in cement, rebar and labor. Supply chains needs to be facilitated to ensure that these materials are readily available and that the quality of the repair works will not be comprised due to these shortages.

In order to manage the risks associated with the geologic hazards identified in this report, we recommend completing a detailed risk-assessment study post-monsoon. This will include assessment of likelihood of failure, occupancy of specific areas of the trails and villages and combining these with hazards to assess the risk.

Once the risk is assessed, we recommend that a tolerable level of risk is defined by the Nepal Government, including consideration of the likelihood of loss of life and a comparison with hazards elsewhere in the country and international standards.

Upon definition of intolerable hazards, which we anticipate will include the main four hazard areas described in the report -- Toktok, Bengkar, Namche to Khumjung rockfall and Shomore rockfall -- the Eliminate, Isolate or Minimize (E/I/M) hierarchy should be used as described in the report.

The best method for risk management is to eliminate the risk, and if this is not possible, isolating the hazard is preferred; only if this is not possible is minimizing the hazard acceptable. In addition to the specific recommendations, all geotechnical risks in the valley should be reduced to a level that is As Low As Reasonably Practical (ALARP).

TOKTOK DEBRIS FLOWS Given the scale of the feature observed (at least 1200 m vertical extent) and the horizontal extent along the band of cliffs (approximately 1000 m), it is unlikely that the hazard can be eliminated. The next best option is to isolate the hazard. This is our preferred option, and may be achieved by relocating the trail and houses of Toktok to the opposite side of the river. Given the difficulty of bridging the Dudh Kosi river, we recommend using the existing bridges at Phakding and the northern end of Bengkar and keeping the trail on the true left of the river throughout this stretch, together with relocating the people living in this area. Consideration should be given to offering assistance and compensation to affected locals to facilitate the relocation of the village as they will lose their land and livelihood.

9 Further assessment of the hazards affecting the trail on the true left should be completed as part of the trail design, but at a concept level, it is likely that this will reduce the hazard to the trail significantly. A detailed assessment should also be completed to identify a safe area in which Bengkar and Toktok locals can rebuild their houses and lodges. A geotechnical entity experienced in designing trails in Nepal can be retained to conduct the assessment. However it is also recommended to put together a team of both national and international geotechnical experts to complete this work, as the mutual knowledge exchange often leads to improved outcomes.

BENGKAR ROCKFALL Similar to the Toktok debris flows described above, we consider that this hazard is too large to eliminate. Doing so would require many thousands of cubic metres of earthworks in a very remote area at an unacceptable environmental cost, even if it were feasible.

The isolation strategy described above to avoid the true right bank of the river would provide effective hazard mitigation for the trail.

In addition to the trail re-routing, it is very important that the government consider relocating the village of Bengkar as we consider that much of the village has an unacceptably high rockfall hazard and that it is not suitably safe for continued occupation. Further, more detailed geotechnical assessment should be completed to define those areas of Bengkar that may be safe for continued occupation.

NAMCHE TO KHUMJUNG ROCKFALL. The recent rockfall on the low trail from Namche to Khumjung may be avoided by using the higher level trail between the two villages. We recommend giving consideration to closing the low trail, and consulting with the owners of the two guest houses near Khumjung that would then be bypassed. While it may be possible to complete scaling works to remove the loose rock from the recent rockfall source, this is a short-term measure, as the geological evidence suggests that rockfall is a frequent occurrence on this stretch of trail.

As a minimum, we recommend placing signage on the low trail informing users of the hazard and strongly suggesting the use of the high trail, particularly when it raining or has rained recently.

SHOMORE ROCKFALL While it does not appear that any new rock fell from the slopes above Shomore, this was based on a rapid fly past in a helicopter and a more thorough assessment should be completed prior to continued use of the trail. However, given the very large boulders among the houses it is clear that the area has been affected by life-threatening rockfall in the past, and it is likely to be affected again, particularly during strong aftershocks or heavy rain.

10 ALARP PRINCIPALALARP

Given the lack of evidence of recent rockfall, it may be appropriate to continue using the trail in this area, but we do not recommend spending time in Shomore. Similar considerations to those outlined for Toktok should be applied to this village (further assessment, risk mapping to identify whether there are any safe locations in the village and if not, a safe place to rebuild, and compensation or assistance for affected landowners).

ALARP PRINCIPLE In other areas of the trail away from the four main hazard areas discussed above where some level of geologic hazard exists, we recommend that risks are managed using the ALARP principle.

There are a number of relatively low-cost measures to reduce the risk to occupants of the area that should be considered:

• Seasonal closure of the trail during the monsoon may be considered, as it is most likely that rockfall and landslides will occur during the wet months. While closures might work for tourists, special consideration should be extended as to how it would impact locals.

• The occupancy of hazard areas should be reduced as much as possible in order to reduce the likelihood of loss of life in the event of a rockfall or landslide occurring. This should be applied to all areas mapped as yellow in this study. Reducing occupancy may be achieved by locating lodges and houses away from the hazard areas. This may not be practical in the lower valley area due to the extensive rockfall hazard present, but lower hazard areas have been identified (for example, the central and true right areas of Phakding or Monjo compared to the southern end of Phakding or Jorsale). This may involve liaison with trekking companies to adjust their itineraries to reduce the risks. If this is undertaken, government assistance may be required to aid those businesses and people affected to relocate their business to safer areas.

• Hazard areas should be signed and communicated to both locals and visitors. This may include signage at the beginning and end of the hazard areas using universal signage, such as that adopted on roads, to encourage people not to stop in these areas.

• A communication program may be initiated and may include meetings or radio broadcasts for locals combined with posters presenting the hazard for visitors. Many of the national park and police checkpoints have posters describing local wildlife and Acute Mountain Sickness, and we recommend preparing a poster on natural hazards in the valley to accompany the existing posters. We have met with the team working on the Imja Tsho lake hazard program (the Community-Based Flood and Glacial Lake Outburst Risk Reduction Project – CFGORRP) and discussed their communication strategy. They have prepared posters to display in affected villages and will be publicizing them shortly. We are unable to combine efforts with them as their posters are published, but could use their communication technique as an example to follow.

11 INTRODUCTION This report summarizes the findings from a five-day rapid structural and geotechnical earthquake- damage reconnaissance of the Everest region’s main trekking routes following the April and May 2015 earthquakes in Nepal.

The objective of the rapid reconnaissance of the region is to a) develop a baseline understanding of the extent of earthquake-related damage, b) provide advice on the overall trekking safety of the region’s routes and c) make recommendations on repairs or risk mitigation that will inform tourism recovery and commercial readiness strategies that are currently being developed by the government, its international development partners and Nepal’s tourism industry at large.

The Everest region in the northeast of Nepal – along with trekking routes in the Annapurna region – are the most popular tourist destinations in the country. Provided that Nepal’s tourism industry accounts for 8 percent of the nation’s gross domestic product and is the country’s largest source of foreign exchange and revenue, the speedy reclamation of the tourism sector will contribute greatly to the nation’s overall economic recovery from the devastating earthquakes that shook the country in the first quarter of 2015.

With funding from the World Bank’s International Finance Corporation (IFC) and on behalf of the government of Nepal through the Ministry of Culture, Tourism and Civil Aviation, an assessment team was dispatched to the Everest region from June 27 to July 2, 2015 to conduct the structural and geotechnical earthquake damage and trekking safety assessment. .

SCOPE OF WORK AND METHODOLOGY: Visual Investigation of structural and geotechnical systems along the Everest trekking route post- earthquake using internationally recognized damage-assessment standards.

The findings of the assessment report are summarized in this report and include the following:

1. A brief description of the structural and geologic systems 2. Record and description of earthquake-related damage 3. Identify how safe the structures and the trails are in their current state 4. Determine whether or not the damage is considered repairable 5. Identification of key structural and geotechnical deficiencies, if any, and a mitigation approach 6. Develop recommendations on repairs, risk mitigation and commercial readiness strategies A mix of helicopter flyover and trekking was used to access and assess the Everest region. The assessment began at Lukla and proceeded on foot to Namche Bazaar, Khunde and Khumjung. From there, the trail and villages in the Upper Khumbu area were assessed by helicopter.

A visual reconnaissance of the areas of concern for potential geologic hazards such as rockfall, landslides, debris flows and other related steep terrain hazards was conducted to assess earthquake- related geologic damage and risk.

12 INTRODUCTION

The structural and geotechnical methodologies are described in greater detail in the relevant sections below.

THE ASSESSMENT TEAM: The technical team was comprised of an expert structural engineer and a geotechnical engineer. The team was supported by an operations team that included a professional mountain guide, a project coordinator and an operations manager.

Dr. H. Kit Miyamoto – Structural and earthquake engineering expert and technical team leader, Miyamoto International, Inc.

Neil Charter – Engineering geologist, ENGEO

Nicholas Cowie –Operations manager and operations team leader, Intrepid Group

Dawa Gyaljen Sherpa – Professional guide, Intrepid Group

Sabine Kast – Project coordinator, Miyamoto International, Inc.

THE 2015 NEPAL EARTHQUAKE The magnitude-7.8 earthquake on April 25, 2015 and its many aftershocks, including the magnitude-7.3 aftershock on May 12, 2015, caused massive damage to the built environment in Nepal. The quake occurred at the fault line between the Indian and Eurasian tectonic plates. This fault is susceptible to earthquakes and also contributes to the rise of the Himalayas. This area is one of the most seismically active regions in the world. As shown in Figure 2 (USGS) many large earthquakes have occurred in this zone in the past hundred years.

Figure 2. Seismicity of Nepal and earthquakes from 1900-now (USGS)

13 The Magnitude (MW) 7.8 event was a shallow event at a depth of 15 km with epicenter east of Lamjung district. Near the epicenter, it had a maximum Mercalli Intensity (MMI) of IX. The main shock was followed by a number of aftershocks, including a magnitude-7.3 major aftershock on May 12, 2015.

It is estimated that it caused over 9,000 fatalities and resulted in more than 20,000 injuries. The cost associated with the earthquake is estimated at roughly $US 5 billion, which is nearly a quarter of Nepal’s GDP. This event is considered the worst natural disaster in Nepal in the past eight decades.

In the aftermath of the earthquake, engineering teams were dispatched to survey the damage for two areas: the Everest and Annapurna regions. Their findings are summarized in this section.

EVEREST AND ANNAPURNA REGIONS

As shown in Figure 3a , the Everest and Annapurna regions are located approximately 200 and 60 km, respectively, from the epicenter of the M7.8 main shock. Furthermore, as shown in Figure 3b, the Everest and Annapurna regions are located approximately 80 and 200 km, respectively, from the epicenter of the M7.3 aftershock. As seen in the figures below, these regions experienced the level of shaking (MMI) , that were considerably less than the MMI value at the epicenters. For example, although the MMI of the main shock was IX close to epicenter, it was only close to MMI of V and VI at the two target locations.

Figure 3a. Main shock Figure 3b. Major aftershock

ABOVE: Location of the Annapurna and Everest region and their proximity to the epicenter of the 2015 events

14 FINDINGS AND METHODOLOGY AND FINDINGS

It is estimated that the eastern part of the Annapurna Circuit experienced the highest peak ground accelerations, (PGAs in 0.1g to 0.2g range, from the M7.8 earthquake. All other regions of the Annapurna Circuit, Annapurna Sanctuary and Everest region experienced PGAs of less than 0.1g according to Figure 2 USGS Shake Map.

STRUCTURAL ASSESSMENT FINDINGS The Everest area building and bridge damage assessment included the area from Lukla to Gorka Sherpa. A total of nine bridges and 15 main villages with approximately 710 accommodations and houses were assessed in the Everest region.

The structural assessment of the buildings and bridges was conducted in accordance with the internationally recognized ATC-20 earthquake damage assessment methodology and the national guidelines for post-earthquake damage assessment specified by the Department of Urban Development and Building Construction (DUDBC) of the Government of Nepal.

ATC-20 METHODOLOGY: ATC-20 is a guideline for the post-earthquake safety evaluation of buildings. It was developed and commissioned by the Applied Technology Council (ATC). ATC-20 is used as a guideline in the United States for post-earthquake damage assessment of buildings. Evaluations are classified and posted using the following methodology:

Rapid evaluation: The goal is the rapid assessment of safety, which can be used quickly to identify obviously unsafe and apparently safe structures, and to identify buildings requiring detailed evaluations.

Detailed evaluation: This is performed by structural engineers (or a geotechnical specialist in the case of geotechnical hazards) who carefully evaluate structures visually. It is used to identify buildings requiring a further engineering evaluation.

Engineering evaluation: This is performed by the structural engineering consultant. A detailed engineering evaluation of the damaged building is done with as-built drawings.

For the purpose of this assessment project, the methodology that was applied was the rapid evaluation, which classifies buildings into categories as described below:

Posting classifications:

• INSPECTED: (GREEN). This means no apparent hazards were found in the building, although repairs may be required. The original lateral load carrying capacity was not significantly damaged. No restrictions on use or occupancy.

• LIMITED ENTRY (YELLOW): Dangerous conditions believed to be present. Entry by owner permitted for emergency purposes and only at one’s own risk. No use on a continuous basis, and public entry is not permitted.

• UNSAFE (RED): Extreme hazard, may collapse. Imminent danger of collapse from aftershocks. Unsafe for occupancy or entry, except by authority.

15 The damages scale is from 0 to 6, based on the structural damage observation.

0 1 2,3,4 5 6

None (0%) Slight (1-10%) Moderate (11-40%) Severe (41-60%) Over 60%

For the purpose of developing a damage index of the structures along the main trekking route in the Everest region, the buildings given a yellow or red tag were marked as red. Structures that were inspected green were green tagged.

DUDBC EVALUATION GUIDELINES The theoretical basis of this guideline comes from different documents from the Federal Emergency management Agency (FEMA) and the Applied Technology Council (ATC). There are four (4) different levels of evaluations. However, the Windshield process is different as it allows for an overall damage assessment from air, such as a helicopter survey.

1. Windshield: Overall scope of damage

2. Rapid: Assessment sufficient for most buildings

3. Detailed : Closer assessment of difficult or complex buildings

4. Engineering: Consultant engaged by owner

The evaluation methods and posting safety status is similar to ATC-20: GREEN and YELLOW/RED.

The level and description of damages is classified as: Insignificant to slight, Moderate, Heavy and Extreme. The detail evaluation of the damages is categorized on a 1 to 5 scale, for both reinforced concrete and masonry building structures.

Grade- 1: Cracks on plaster, falling off of plasters. Building need not be vacated, and only minor architectural repairs or seismic strengthening are required.

Grade-2: Cracks in wall partitions, cracks in beams and columns, which need to be repaired and potentially seismically strengthened.

Grade-3: Cracks in columns and beams and spalling of concrete covers, buckling of steel bars, large cracks in partition and infill walls. Cracks in the walls need to be grouted. Architectural repairs and strengthening are required.

Grade- 4: Large cracks in structural elements with compression failures of concrete and fractures of rebar, bond failures of beams, tilting of columns. The building requires evacuation, demolition or extensive restoration or strengthening.

Grade: 5: Collapse of ground floor or part of the buildings. A cleared site or reconstruction required.

The windshield process specified by DUDBC guidelines were applied to structurally assess buildings in the Upper Khumbu and per our scope of work only the rapid damage assessment method was used to develop a damage index of each village assessed.

16 GUIDELINES AND BUILDING TYPES BUILDING GUIDELINES AND

BUILDING TYPES

Typical hotel construction includes one of the following types of lateral load resisting systems:

• Traditional building (see figure 4a): Bearing walls of uncut stone with mortar and bearing walls of cut rectangular block stone with or without mortar. The older construction used mud as mortar, whereas, newer buildings used cement. Some accommodation structures in Everest utilized horizontal concrete bands spaced intermittently in the stone wall construction; see Figure 4b.

• Wood frame, figure 4c

Typical roof construction used metal corrugated roof panels placed on top of wood framing. In a few, flagstone roof tiles, approximately 25 mm thick, were used on top of wood framing.

Typical floor construction used mud placed over flat wood boards over wood beam framing. In some cases, there was no mud used and wood flooring was placed over wood framing.

Typical foundations, according to local residents, were approximately one m deep below walls and were constructed using the same material as the wall itself, typically stone with mud or cement mortar.

Figure 4a. Traditional construction Figure 4b. Traditional construction with concrete band

Figure 4c. Wood frame construction

17 OBSERVED PERFORMANCE OF SURVEYED BUILDINGS

Figure 5a. Out of plane failure of older traditional building

Figure 5b. Newer traditional with minor cracking

18 OBSERVED DAMAGE OBSERVED

OBSERVED DAMAGE The level of damage in traditional construction (bearing wall with stone and with or without mortar) was highly depended on the construction practice. The buildings with stone and mortar generally performed well. Although cracks (see Figure 5b) were noticed in many of these buildings, these cracks do not pose a safety hazard. Conversely, in older buildings where either no mortar was used or when mud was used as mortar, there was significant damage. For these buildings, the out-of-plane failure of walls (see Figure 5c) was the most common mode of failure, where stone walls fell over or stones fell out, generally at the top of the walls. This observation is also consistent with the results of surveys of unreinforced wall structures in earthquakes worldwide. Since these bearing walls are designed to carry both seismic and gravity loading, their out of plan failure can also compromise the gravity load path and can result in collapse of roofs and floors. For the surveyed buildings, a secondary wood beam supporting the roof was observed in many of the buildings. This member supported the roof after the failure of walls and prevented collapse of the roof. Visual observations also showed that, of the traditional buildings that experienced damage, the mud mortar appeared to be more brittle than the mud in other buildings.

Wood structures were mostly small extensions of the stone hotels and were typically single-story units. There were a few two-story wood structures. Many of the wood structures were open with long bays of windows interrupted by wood posts and lacked a defined lateral load-resisting system. Despite this major shortcoming, no damage (including broken windows) was observed for these buildings; see Figure 5c. The good performance of wood buildings is not unexpected. These buildings have inherently more damping and are lightweight and thus have performed well in the past earthquakes.

Figure 5c. Wood structure without damage

19 Typical repairable earthquake damage observed in Lukla (above and below).

20 LUKLA

LUKLA Lukla has approximately 80 buildings with a mixture of traditional stone construction and lightweight wood studs construction. It is estimated that 50 percent of the buildings in Lukla serve as hotels. From our visual investigation, we estimated that about 20 percent of the structures sustained earthquake damage.

Much of the damage observed was hairline cracks, which are easily repairable and do not compromise the structural integrity of the building. However, there were a few buildings that collapsed. We noted four buildings in this state. These buildings were traditional stone and mud construction. Locals confirmed that the collapsed buildings were residential homes and not typically used to accommodate tourists.

The large majority of the accommodation structures are open for business.

21 Lukla Village The village of Lukla is located on moraine, colluvial and alluvial terraces near the base of thickly vegetated steep hills. The weather was cloudy at the time of our visit so only limited observations of the hillside were possible. The shadow angle between the possible rockfall sources near the ridge crest and the village is approximately 36 degrees. No evidence of earthquake induced rockfall or slope instability was observed on the hillside above the village (see photograph 1 below). Extensive slope failures were observed on the hillside on the opposite side of the Dudh Kosi river, but this hillside is approximately 1 km away from the village, and the village is 600 m above the river, so is unlikely to be affected should these slopes fail.

Lukla is suitably far from the edge of the terrace slope below that it is unlikely to be affected should this slope fail.

Photograph 1: Slopes behind Lukla.

Lukla to Thado Koshigaon Trail From Lukla, the trail sidles at the base of steep slopes, above the terraces on which Lukla, Muse, Chaurikharka and other villages are located. An aerial photograph showing this section of trail

22 and the villages is shown below (photograph 2). As with our assessment of Lukla, the weather was poor, so our observations of the high slopes were limited due to cloud cover.

Lukla

Photograph 2: Aerial view of terraces between Lukla and Chheplung.

Numerous stacked rock walls up to around 2 m high support the downslope side of the trail as it sidles around the hill, and no significant earthquake induced damage was observed in these walls. The upslope side of the trail is cut in to the hillside in places, with unsupported cut slopes up to approximately 5 m high (typically less than 2 m high). The cut slopes expose colluvium, alluvium and isolated rock outcrops. Occasional small (<5 m3) failures were observed in these cut slopes. The failures are typically vegetation and regolith failures, and there are a range of ages of feature, from old re-vegetated failures to recent ones. A small colluvium quarry at Chaurikharka has experienced recent headwall failure, with an estimated volume of debris in the order of 20 m3.

The trail crosses a colluvial terrace through the village of Chheplung, but no evidence of recent rockfall was observed. Immediately after Chheplung, the trail crosses a large slip on an approximately 100 m long swingbridge, which we understand was built in 2005. The Lukla abutment of the bridge is protected by a gabion retaining wall some 3-4 m high, which supports the base of a 10-15 m high slope. The gabion wall does not show any significant signs of damage, and is shown in photograph 4 below. One small failure (<5 m3) was observed on the crest of northern lateral scarp of the failure, but this does not affect the trail. This failure is representative of those that we understand occur relatively frequently as the stream cuts deeper and the side scarps of the slip collapse further. This crest recession may threaten the bridge abutments at some stage in the future.

23 Photograph 3: Gabion wall supporting Lukla end of bridge across slip.

Thado Koshigaon to Phakding Trail From Thado Koshigaon to Phakding, the valley is much narrower and the terraces on which the trail and villages have been located are significantly smaller than further up valley. Beyond Chhuthawa, the terraces disappear entirely. The trail alternately sidles the base of steep slopes, crosses fan deposits, and is confined between the steep slopes and the Dudh Kosi river. The slopes above the trail are very steep (up to 60-70 degrees). Some evidence of historic rockfall was observed in villages and along the trail (see photographs 4 and 5 below, taken in Ghat and Chhuthawa).

24 Photograph 4: Old rockfall deposit in Ghat

25 Photograph 5: historic rockfall and steep slopes. Taken in Chhuthawa, looking south.

Isolated areas of new rockfall and loosened rock were observed on these slopes, but we did not see any evidence of rockfall crossing the trail. Photograph 6 below shows a typical view of the slopes above the trail. The light brown areas are likely to be a result of recent rockfall.

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27 ROUTE FROM LUKLA TO PHAKDING The majority of buildings and accommodations on this stretch of the trekking route did not sustain damage as a result of the earthquakes. However, on occasion earthquake-related damage was observed and, in a rare case, a collapsed house. This was in the softer soil areas in and around Chheplung.

Accommodation structure built with cut rock, cement and ring beams that performed well

Example of a damaged structure. 28 PHAKDING

PHAKDING This town has approximately 80 buildings with a mixture of traditional stone construction and light weight wood studs construction. Much of the building stock is tourist accommodations (26 of 82 buildings). We estimated that about 20 percent of structures have sustained certain earthquake damage. The damage observed is due to a lack of the use of cement as mortar. Many of these accommodation structures are being repaired. The majority of accommodation structures (80 percent) are open for business.

29 Photograph 7. Collapsed cut slope behind Thado Koshigaon

Phakding Village The entrance to the village is located near the base of steep cliffs and slopes as described in the trail section (above). One area of slope between the Yeti Lodge and the main village has been stripped of mature vegetation, but has moss and grass regrowth, which suggests a landslide occurred here in the relatively recent past (but before the earthquakes).

Towards the centre of Phakding, the valley widens and much of the village is on an alluvial fan from the Phakding Khola side valley. This area is subject to a lower rockfall hazard as it is further away from the cliffs, but is potentially prone to debris flows from the side valley (see photograph 8). We did not observe any evidence of the village having been affected by rockfall or debris flows during the recent earthquakes. There is some evidence of small slips caused by river scour on the edge of the terrace slope, but these appear to be at least 100 m from the village.

30 Yeti lodge

Photograph 8: Aerial view of Phakding

At the northern edge of Phakding, the trail sidles around the edge of a steep terrace slope, and has a number of <5 m3 slips from the cut slope on the upslope side of the trail. These have largely been cleared. After the sidle, the trail crosses a small river terrace, some 50 m away from the base of an approximately 100 m high cliff. No evidence of large scale instability of the cliff was observed, but there are a number of debris fans at the base of the cliff that show rockfalls have occurred from this location in the past (see photograph 9 below). Most of these fans are covered with mature vegetation. One fan has approximately 10 m3 of new debris on it, but the debris is located at least 40 m from the trail.

31 Photograph 9: Bridge, cliff and debris fans (outlined) north of Phakding

The trail then crosses the Dudh Kosi river on a long span suspension bridge. No evidence of the bridge having been affected by landslide hazards as a result of the earthquake was observed. Phakding to Bengkar Trail The trail crosses the terrace described above, then sidles around the edge of the upper level terrace for approximately 500 m. This slope consists of dense sandy gravel with sand and boulder layers within it. It is not currently being eroded by the river below, but is oversteepened at between approximately 37 and 45 degrees. This has resulted in many shallow slope failures, both recently (as a result of the earthquakes) and older failures that have become revegetated. These failures are located both below (undermining) and above (inundating) the trail. These two failure modes are shown in photographs 10 and 11. There is also evidence of large boulders which appear to be ancient rockfall debris approximately 200 m before Rimijung.

32 Photograph 10: Shallow slip in alluvium on terrace edge, immediately north of Phakding

Photograph 11: Undermining of trail by slip on terrace edge slope, north of Phakding.

33 We understand that there is an alternative trail located on the upper terrace between Phakding and Rimijung, but have not assessed this trail. Based on the geomorphology of the area, it is likely that the upper trail is less affected by hazards. Aerial reconnaissance suggests that the trail will cross one recent landslip as it descends from the upper terrace to the lower terrace. This slip is directly above the lower buildings at Thulo Gumhela, shown in the photograph below.

There is evidence of further shallow slips (including some that released boulders) between Rimijung and the Nagbuwa Thengga Khola side stream. This is shown in photograph 12, below.

Photograph 12: Shallow slips on trail by Thulo Gumhela.

One building across the river in Gumelha has been severely damaged by the collapse of a 10-12 m high stacked stone wall located immediately behind the building.

Immediately before the village of Toktok the trail has been inundated by a significant debris flow that travelled over a 100 m high waterfall above the trail. The debris has partially dammed the Dudh Kosi river, and we understand that the river was totally blocked for 5-10 minutes immediately after the debris flow. Based on discussions with locals, we understand that this failure occurred on the Friday before our field assessment (June 29th 2015). We were unable to assess the source area of the debris flow as it was within the cloud during our helicopter reconnaissance (Photograph 15), but consider it likely that it occurred as a result of a landslide or rockfall damming the side stream. This dam is likely to have burst, resulting in a debris flow travelling rapidly down the steep stream. This debris then fell over the waterfall above the trail (Photograph 13), and into the Dudh Kosi river (landslide dam shown in Photograph 14).

34 Photograph 13: Waterfall and debris above the trail

35 Photograph 14: Debris partially damming the Dudh Kosi River.

Photograph 15: Aerial view of the upper source area for the debris flow. The cloud base is at approximately 4000 m, the bottom of this image is estimated to be approximately 3500 m, and the Dudh Kosi river below is at approximately 2800 m elevation.

36 Aerial assessment of the hillside in the vicinity of the source area suggests that there are numerous rock failures that did not reach the trail. Some of these have fallen into stream channels but not resulted in landslide damming. There is evidence of a significant debris flow on a hillside that is above the side stream above Rimijung. This debris flow appears to be somewhat smaller than the Toktok feature but still reached the base of the hill. These other features suggest that the hillside is prone to similar scale failures occurring again, and that this hillside therefore poses a very high hazard to the trail (and houses) below.

Beyond Toktok, the trail sidles steep rocky slopes with extensive talus deposits suggesting the rockfall has occurred numerous times. Discussions with locals indicate that rockfall is a known hazard in this area. One area of fractured rock was observed above the trail, and one gully with recent rockfall debris was crossed. This gully had angular rockfall debris up to approximately 1 m diameter. The Bengkar guest house has been struck by two falling rocks, with one rock approximately 1.2 m in diameter in the living room, and one smaller rock penetrating the roof and out through the front wall. We were unable to observe the source area for the rocks due to vegetation on the slope above, but the shadow angle to the source is likely to be approximately 50 degrees. Discussions with the guest house owner suggest that the shaking intensity at this location was moderate (perhaps MM IV-V) as the damage to the building is slight and dishes were not knocked from shelves. This suggests that the hillside poses a very high rockfall hazard as numerous rocks crossed the trail even with moderate shaking intensity. A larger earthquake is likely to cause many more rocks to fall.

Photograph 16 shows the slopes from which the rockfall is sourced. Note that the regional dip of the defects appears to be out of the slope on the true right of the river, and into the slope on the true left. This means that there are many more kinematically feasible failure mechanisms for rockfall on the true right of the river. This is also clear from the vegetation in that the true right is sparsely vegetated, while the true left is more thickly vegetated suggesting a more stable environment.

37 Photograph 17: Rockfall behind Bengkar

There is another suspension bridge crossing the Dudh Kosi river at the northern end of Bengkar. Some scour was observed below the true right abutment, but the abutment is set at least 20 m behind the crest of the slope and therefore is unlikely to be affected by the scour in the near future. This does not appear to have been subject to additional landslide hazards as a result of the earthquakes.

Bengkar to Larja Dobham Trail After crossing the river, the trail traverses small terraces upon which the villages of Chhumowa and Monjo are situated. High cliffs and steep slopes are located above the terraces but no evidence of recent rockfall was observed (see photograph 18). Isolated large boulders were observed in Chhumowa, which indicate that rockfalls have occurred here in the past. One approximately 4 m high stacked stone retaining wall below the trail in Chhumowa had collapsed, but repair work was underway at the time of our assessment..

38 Photograph 18. Looking upstream from Bengkar towards Monjo.

The trail crosses the Manjo Khola side stream in a deep channel between Chhumowa and Monjo. A large, but shallow, terrace edge failure had occurred approximately 100 m downstream of the bridge, and a small (<5 m3) failure had occurred above the trail. This terrace slope is significantly oversteepened as a result of erosion by the side stream and these failures are likely to continue. Monjo is sufficiently far from the top of the terrace slope that it is unlikely to be affected by these failures in the near future.

No evidence of landslide hazards affecting Monjo in the recent past was observed, but it is located within a 30 degree shadow angle from the hillside above, and may be affected by rockfall in future.

From Monjo, the trail descends steeply down a gully between rock faces to the river. No evidence of rockfall was observed from these faces. The trail crosses a long suspension bridge across the river, which shows no evidence of having been affected by landslide hazards. The approaches to the bridge are supported on stacked rock retaining walls, which appear to be in good condition.

The village of Jorsale is located on the opposite end of the bridge, at the toe of a very steep rocky slopes (shown in Photograph 19). While no evidence of recent rockfall or loosening of the rock mass was observed, it is likely that rockfall will occur in the future which may affect parts of the village. Immediately beyond Jorsale the trail traverses a relatively steep soil slope, and has been partially undercut by a small drop out. This does not appear to be caused by the earthquake.

39 ROUTE FROM PHAKDING TO MONJO This route, along Lukla to Namche Bazaar trekking trail, is one of the most heavily damaged areas. In Zam Fute, seven lodges were heavily damaged. In Thulo Gumela and Zam Fute, approximately 50 percent of buildings sustained heavy damage and are red tagged. In Toktok, approximately 90-95 percent of buildings are red tagged due to earthquake damage. The structures in Bengar will need to be given a red tag, due to damage sustained as a result of rockfall.

40 ROUTE TO MONJO • TOKTOK

TOKTOK

The owners of this accommodation structure will be demolishing the building and rebuilding the second story with lighter wood and steel construction.

41 Photograph 18. Looking upstream from Bengkar towards Monjo.

No evidence of landslide hazards affecting Monjo in the recent past was observed, but it is located within a 30 degree shadow angle from the hillside above, and may be affected by rockfall in future.

42 MONJO This town has approximately 20 buildings with a mixture of traditional stone construction and lightweight wood studs construction. Approximately 50 percent of building stock serves as tourist accommodations. We estimated that about 30 percent of structures have damage. Some of damaged structures create a falling hazard to the trail. The majority of accommodations are open for business.

Accommodation structure in Monjo that sustained repairable earthquake damage.

ROUTE FROM MONJO TO NAMCHE In Jorsalle, 50 percent are damaged and 50 percent are undamaged. There is some falling hazard to the trail that will need to be addressed. However, home owners have started repair work. It is recommended that training is provided in better construction practices to support the building back better of repairable structures of the trekking region.

43 From the swing bridge, the trail climbs steeply up a ridge to the village of Namche Bazar. No evidence of rockfall or other geotechnical hazards affecting the ridge trail were observed.

Photograph 20: True left abutment of high bridge below Namche

Namche Bazar Village The village of Namche Bazar is the largest village on the Everest Base Camp trekking route. It appears that Namche, Khumjung and Khunde are located on the failed block of a large (kilometre scale) ancient landslide. The upper reaches of the hillside were obscured by cloud at the time of our assessment, so the feature is annotated on a Google Earth photograph below (Photograph 21). It appears that two intersecting defect sets (one being the dominant defect set observed behind Bengkar, and dipping out of slope) allowed a large wedge failure to occur, and that the debris from this wedge failure moved downslope to form a relatively flat bench (upon which Khumjung and Khunde are now located) with a steep front face above the river (upon which Namche is located). We were unable to assess the scarp of the feature, but anticipate that it did not move during the earthquakes as it is a large feature and has probably reached equilibrium over geological time since it failed. Two recent debris flow fans were observed on the Google Earth photography, and these may pose a hazard to the southern extents of Khumjung and Khunde.

Namche Bazar is located in a basin on the front of the landslide debris some 600 m above the confluence of the Dudh Kosi and Bhote Kosi rivers.

44 MONJO • BRIDGE ASSESSMENTS BRIDGE • MONJO

BRIDGE ASSESSMENTS We assessed 9 steel suspension bridges and steel/concrete bridges along the trail. No earthquake-related damage was observed.

45 BRIDGE AT PHUNKI TENGA No earthquake damages observed.

46 BRIDGE ATBRIDGE TENGA PHUNKI

BRIDGE AT PHUNKI TENGA No earthquake damages observed.

47 Photograph 19: Jorsale. Note the steep rocky hillside behind the village.

From Jorsale, the trail crosses another swingbridge over the Dudh Kosi. No recent geotechnical damage was observed affecting this bridge, but the true left abutment is located below a steep rock face which may be subject to rockfall in the future. Isolated small slips were observed near the base of the slopes adjacent to the trail, though these did not appear to be earthquake damage. Larja Dobham to Namche Bazar Trail The trail from Larja Dobham to Namche Bazar climbs across a steep rock face before crossing a very high swing bridge across a gorge near the confluence of the Dudh Kosi Nadi and Imja Khola rivers. The swing bridge is relatively new and does not appear to be subject to additional landslide hazards as a result of the earthquakes. The true left abutment of the bridge is supported on a retained earth abutment, which does not appear to have been damaged during the earthquakes. A small cut face into soil is located near the true left abutment of the bridge (Photograph 20). We did not cross or assess the lower swingbridge at this location.

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49 NAMCHE BAZAAR This town has approximately 150 buildings with a mixture of traditional stone construction and lightweight wood studs construction. Half of the building stock serves as tourist accommodations. We estimated about 10 percent of structures have certain damage. Most are hairline cracks and damage is minor. Hotels at the top of the mountain sustained more severe earthquake damage. However, the majority of accommodation structures are open for business. Reconstruction and repairs are underway and many of the repairs observed included good building practices. KHUMJUNG AND KHUNDE These sister towns have approximately 180 buildings with a mixture of traditional stone construction and lightweight wood studs construction. Many of the buildings are hotels or tourist accommodations. We estimated about 30 percent of structures have light damage. Most are hairline cracks and damage is minor. Reconstruction and repair is underway and the majority of accommodations will be able to re-open for business in October.

ABOVE: Khumjung BELOW: Minor damage

50 NAMCHE • KHUMJUNG/KHUNDE • PANGBOCHE • KHUMJUNG/KHUNDE • NAMCHE

PANGBOCHE Pangboche has approximately 136 buildings with traditional stone construction. Approximately 5 percent of buildings were damaged by the April and May 2015 earthquakes. Many accommodations can be opened for business.

51 Photograph 28: Pangboche, looking north.

Pangboche Village

Pangboche is located on an alluvial or colluvial fan at the base of a gully below a steep rocky slope (photograph 28). No evidence of earthquake induced geotechnical damage was observed, but the northern portion of the town is likely subject to rockfall hazard due to its proximity to the steep slopes.

From Pangboche, the trail continues sidling steep rocky faces to Shomare. No evidence of earthquake induced damage was observed but the trail is threatened by rockfall due to the fractured nature of the rock. Isolated scree slopes and boulders on the slope show that the trail has been subject to rockfall in the past.

Shomare Village

The village of Shomare is on a steep and active colluvial fan from a stream located behind the village (photograph 29). The slope behind the village is very steep (angle not measured as this assessment was from a helicopter) and has rock outcrops on the slope. Buildings and walls have been built around extensive rockfall debris in the village. No evidence of recent earthquake induced rockfall was observed, but we have serious concerns about the suitability of this village for ongoing occupation. We recommend further, ground based, assessment of this feature following the monsoon.

52 Debris fan

Rockfall source

Select rocks in village arrowed

Photograph 29: Village of Shomare, with active debris fan behind village and rockfall debris within village.

From Shomare, the trail sidles further across the steep rocky slopes through Orsho, before the valley widens out and the trail crosses the river and ascends moraines to Dingboche. The crossing and location of Dingboche is shown in photograph 30, below.

53 Photograph 22: Namche Bazar

Immediately east of the village is another basin, which is located between the police checkpoint and the main village. The slope in this area is somewhat steeper than behind the main village, but does not appear to have experienced instability as a result of the earthquakes.

Namche Bazar to Khumjung Trails The low trail from Namche to Khumjung sidles steep rocky slopes high above the river (photograph 23). A number of scree slopes cross the trail, and numerous areas of recent rockfall were observed. These resulted in at least six impact craters approximately 2-4 m across and 1 m deep on the trail (photograph 24) as well as numerous rocks less than approximately 0.5 m diameter falling onto the trail. The large rocks that caused the impact craters were not visible as they had continued falling down the slope below the trail towards the valley floor. The rockfall appears to have come from a recently fractured rock outcrop on a 50 degree slope some 150 m above the trail. At the time of our assessment, a smell of fresh earth was present near one of the craters, which suggests that the rockfall is an ongoing process rather than only having occurred during the earthquake. The rock outcrops are significantly dilated and there is a very high likelihood of further rockfall occurring. Given the gradient of the slope, it is almost certain that falling rocks will reach and cross the trail.

A large rockslide was also visible below the trail in this area, and we understand that this occurred in the week or two preceding our inspection. While this feature does not pose a hazard to the trail, it suggests that the rockmass on the slope is significantly weaker as a result of the earthquake, and that rockfall is an ongoing process.

54 Defects within the rock that form the release surface shown by arrows

Recent debris flows

Photograph 21: Large landslide at Khunde, Khumjung and Namche

The basin feature within which Namche is located likely to be a relic landslide scar caused by instability of the front face of the landslide debris from the large failure described above (photograph 22). The slope behind the village is extensively terraced and has a slope of 30-35 degrees, and many large boulders (up to approximately 10-15 m in size) are located on the slope. No evidence of movement of the boulders or large scale slope instability was observed in the vicinity of Namche. There are isolated areas where cut slopes have been formed, and these have experienced small scale instability and erosion.

55 Photograph 23. Rockfall sources above the Namche-Khumjung Trail. New sources circled in white; old sources circled in black

Photograph 24. Impact Crater on Namche-Khumjung Trail

56 The high trail from Namche to Khumjung and Khunde climbs the slopes behind Namche. From the top of the slopes, the trail descends gently into Khumjung. This trail is considered significantly safer than the low route.

Khumjung is located within a valley formed by the scarp of the large landslide to the north and the back scarp of the debris from the landslide to the south. Cloud cover precluded assessment of the rockfall hazard from the slopes above the village, but we did not observe any recent rockfall close to the village. Two debris fans were observed at the base of the slopes above the village, but the source areas were obscured by cloud. These features appeared to be relatively active due to the lack of vegetation on them, but did not appear to have increased activity as a result of the earthquake. It is likely that these features respond to rainfall and may move during the monsoon season. The base of the debris flows are shown in photograph 25, below.

Base of debris flow Scarp of large ancient slide

Khunde

Khumjung

Photograph 25: Khumjung (foreground) and Khunde (background), looking west

Khumjung to Dingboche Trails There are two routes from Khumjung to Pangboche. The main route descends to cross the main river and ascends to Tengboche before descending back to the river and crossing to Pangboche. This route will be described first. An alternative route follows a high sidle out of Khumjung before crossing a side river to Phortse, and continuing the sidle along steep slopes to Pangboche. From Pangboche, both these trails merge and follow the true right side of the river through Shomare and Orsho before crossing again to Dingboche.

All of the trails described above were assessed from the helicopter and this assessment is preliminary due to time constraints.

57 Khumjung

Low trail to Tengboche

Photograph 26. Khumjung and nearby trails.

Khumjung – Dingboche Low Trail

The low trail to Dingboche sidles more steep slopes on the way out of Khumjung, with some evidence of rockfall. There is evidence of recent rockfall from rock outcrops on this trail. The trail then crosses the river and ascends a steep slope to Tengboche. No evidence of earthquake induced landsliding affecting this slope was observed. Tengboche is located on a ridge above the river and is in a geotechnically low hazard location as shown in photograph 27 below. No evidence of slope failure was observed from the helicopter, but this should be assessed on the ground to confirm that slope failure will not undermine the buildings.

58 Photograph 27: Tengboche, located on a ridge. The high trail can be seen sidling between Phortse and Pangboche in the background.

From Tengboche, the trail descends and crosses relatively gentle slopes to the river. We were unable to assess the nature of these slopes due to cloud obscuring the tops, but did not observe evidence of recent rockfall. The trail crosses the river and joins the high trail from Phortse in Pangboche. The trail from Pangboche to Dingboche will be described following the high trail from Khumjung to Pangboche.

Khumjung – Dingboche High Trail

The high trail from Khumjung passes below the same cliffs as described in the low trail section, and is subject to rockfall hazard for approximately 500 m. After the junction, the high trail crosses gentle grassy slopes shown in Photograph 26. Rockfall is possible from cliffs further up the slope but no evidence of recent or old rockfall was observed on these slopes. The trail then descends a steep rocky slope to cross the Dudh Kosi Nadi before climbing steeply to Phortse, which is located on a terrace high above the river. The trail into the river is subject to rockfall, but no evidence of earthquake induced damage was observed in Phortse. From Phortse the trail sidles steep rock faces to Pangboche. The dominant defect set within the rock on these faces dips out of the slope, suggesting that rockfall is kinematically feasible, but no evidence of recent rockfall was observed. These faces can be seen in the background in Photograph 27. This was based on rapid assessment from a helicopter rather than a more through foot reconnaissance.

59 DINGBOCHE Dingboche has approximately 40 buildings with traditional stone construction. We provided aerial survey only, due to bad weather. Many of stone fence walls are intact and little damage was observed in buildings.

PHERICHE Pheriche has approximately 24 buildings with traditional stone construction. Approximately 70 percent of buildings were damaged by the April and May 2015 earthquakes. Some accommodations are open for business. This village is one of the most earthquake-damaged villages on the route. Reconstruction is underway, but according to the owner of one of accommodations, it is extremely hard to find labor and materials.

60 DINGBOCHE • PHERICHE 61 From Pheriche, the trail follows the river valley for approximately 3 km before crossing the Khumbu River and climbing onto recent moraines past Thokla as seen in photograph 33, below. From Thokla, the trail follows a small valley between recent and older moraine walls (photograph 34). The moraine walls are unconsolidated angular boulders and pose some rockfall hazard to the trail although no evidence of earthquake induced rockfall was observed.

Photograph 33. Trail above Pheriche. Trail goes up steep valley to the right in background.

62 Photograph 31: Dingboche.

From Dingboche, the trail sidles a gentle moraine slope to Pheriche. Pheriche is located on a low alluvial terrace immediately above river flats (photograph 32). The slopes behind Pheriche are gentle and no evidence of recent slope failure or rockfall was observed.

Photograph 32: Pheriche.

63 Photograph 30: Aerial view of trail crossing river below Dingboche.

Dingboche to Lobuche Trail Dingboche is located on terraces adjacent to the river, as shown in photograph 32. No evidence of recent rockfall or landslides affecting the village were observed. Further, there was no evidence of the village having been affected by rockfall in the past.

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65 LOBUCHE Lobuche has approximately 20 buildings with a mixture of traditional stone construction and lightweight wood studs construction. Approximately 30 percent of buildings were damaged by the April and May 2015 earthquakes. Many accommodations can be opened for business. Reconstruction is underway.

66 LOBOCHE • GORKA SHEP 67 GORKA SHEP GorkaShep has approximately four buildings with a mixture of traditional stone construction and lightweight wood studs construction. It is the highest altitude reached we No damage was observed. Accommodationsat 5180m. are open forbusiness. Photograph 34. Trail climbing recent moraine towards Thokla

Lobuche to Gorak Shep Trail The village of Lobuche is located on old moraine in a shallow valley below gentle slopes (photograph 35). The slope to the north of the village is recent moraine and has numerous angular boulders exposed at the surface. No evidence of recent movement of the boulders was observed. The slope to the west of Lobuche is significantly flatter and well vegetated, which indicates that it is older moraine deposits. There are isolated shallow (less than 0.5 to 1.0 m depth) soil slumps on the slope, but these do not appear to be earthquake triggered or likely to pose a significant hazard to the village.

68 Photograph 35: Lobuche, looking north.

From Lobuche, the trail continues in the moraine valley, away from the slope down to the Khumbu Glacier, and crosses the Changri Glacier before arriving on the moraine at Gorak Shep. The slopes near this stretch of trail are generally composed of recent moraine with angular boulders on the surface. Isolated rockfalls may be expected from the moraine walls, but no evidence of earthquake induced rockfall was observed.

69 Photograph 36: Gorak Shep, looking north. The east face of Pumo Ri is behind Gorak Shep.

Gorak Shep Village Gorak Shep is located on the moraine east of the Khumbu Glacier (photograph 36). It is some 100-200 m east of the crest of the slope down to the Khumbu Glacier, so is unlikely to be affected by instability on this slope. It is sufficiently distant from slopes to the west and north to not be threatened by rockfall or slope instability. The lodge at the south end of the village is relatively close to a 20-30 m high recent moraine wall, but no evidence of earthquake induced rockfall was observed from this slope.

Trail Gorak Shep to Everest Base Camp From Gorak Shep, the route to Everest Base Camp crosses more recent moraine and onto the Khumbu Glacier below the east face of Pumo Ri. The dominant defect set on Pumo Ri appears to dip out of the slope at approximately 60 degrees and forms the east face (as shown in the background of photograph 36). Rockfall and avalanche are possible from this face, but no evidence of major earthquake triggered rockfall was observed. Assessment of this type of alpine hazard was beyond the scope of this report.

Summary The trail and hazard descriptions above have been displayed on Figure 1, which splits the trail into three categories:

 Green: No or minor apparent landslide damage. This includes areas with isolated drop outs below the trail, isolated damage to stacked stone walls, or occasional rockfall from small moraine walls from above track level. Areas mapped in green are likely to be subject to a

70 number of existing landslide hazards despite not being significantly damaged due to the earthquake.  Yellow: Moderate landslide damage, or significant existing geotechnical hazard. This includes areas with significant debris from historic rockfalls, or areas with isolated boulders that fell during the recent earthquakes.  Red: Significant geotechnical damage. This includes areas with debris flows or extensive rockfall during or after the earthquakes.

In addition to the colour categorisation, the data has been split into two confidence levels:

 reasonable, where the trail was assessed on foot or at low speed by helicopter, or  poor, where the trail was only assessed by helicopter, or when the hillsides above the trail were significantly obscured by cloud.

In summary, many of the villages on the Everest Base Camp trail do not appear to have been affected by landslide hazards as a result of the earthquake (e.g. Lukla, Namche, Khumjung, Tengboche, and all villages above Dingboche). A number of the villages have significant existing rockfall hazard (e.g. Phakding and Jorsale), while Toktok, Bengkar and Shomore have been affected by very serious geotechnical hazards. None of the major suspension bridges appear to be affected by new geotechnical hazards as a result of the earthquake. Much of the trail and most of the rock retaining walls (both above and below) the trail are undamaged. Miyamoto will discuss buildings in more detail, but we did observed very little foundation damage to buildings.

There was evidence of ongoing slope movement and rockfall during our site assessment from many of the observed slopes. This may be an effect of earthquake induced loosening of the rock in places, coupled with the early rains of the monsoon season causing an increased rate of slope failure to occur. The Toktok debris flows, and some of the rockfalls between Namche and Khumjung occurred very recently before our assessment. We anticipate that many more failures could occur during the upcoming monsoon season as the loosened rock becomes saturated and more soil material is washed out from within defects. This increased hazard may continue beyond the current monsoon season into future monsoon seasons.

In addition to the rockfall and landslide hazards discussed in this report, a number of other hazards may potentially affect the villages and trails described herein. These include: avalanches in the alpine areas, river scour, very large scale rockfall events (such as those that formed the colluvial fans near Lukla), and landslide or ice dam break in catchments above the immediate area of the trail.

71 Recommendations In order to manage the risks associated with the hazards identified in the report above, we recommend completing a detailed risk assessment study. This will include assessment of likelihood of failure, occupancy of specific areas of trail and villages, and combining these with hazard to assess the risk.

Upon definition of intolerable hazards, which we anticipate will include the main four areas described below, the Eliminate, Isolate or Minimise (E/I/M) hierarchy should be used as described below. The best method for risk management is to eliminate the risk, and if this is not possible, isolating the hazard is preferred; only if this is not possible is minimising the hazard acceptable. Each of the major hazards identified in the field assessment are described below, with E/I/M recommendations. We have provided recommendations for E/I/M options for each of the major hazards described above. In addition to the specific recommendations, all geotechnical risks in the valley should be reduced to a level that is As Low As Reasonably Practical (ALARP). This is discussed after the specific sites. Toktok Debris Flows Given the scale of the feature observed (at least 1200 m vertical extent), and the horizontal extent along the band of cliffs (approximately 1000 m), it is unlikely that the hazard can be eliminated. The next best option is to isolate the hazard. This is our preferred option, and may be achieved by relocating the trail and houses of Toktok to the opposite side of the river. Given the difficulty of bridging the Dudh Kosi river, we recommend using the existing bridges at Phakding and the northern end of Bengkar and keeping the trail on the true left of the river throughout this stretch, together with relocating the people living in this area. Consideration should be given to offering assistance and compensation to affected locals to facilitate the relocation of the village as they will lose their land and livelihood.

Further assessment of the hazards affecting the trail on the true left should be completed as part of the trail design, but at a concept level, it is likely that this will reduce the hazard to the trail significantly. A detailed assessment should also be completed to identify a safe area in which Bengkar and Toktok locals can rebuild their houses and lodges. This work should be done by a local Nepal geotechnical company in order to build the local capacity for such assessments, but ENGEO would be available to advise or peer review the work if required.

Upon completion of the village and trail relocation, a hazard will still exist as it is possible that future debris flows may be larger than the June 2015 event and may result in a landslide dam blocking the Dudh Kosi for a longer period of time and causing a larger dam burst flood. Assessment of this hazard is beyond the scope of this report. Bengkar Rockfall Similar to the Toktok debris flows described above, we consider that this hazard is too large to eliminate. Doing so would require many thousands of cubic metres of earthworks in a very remote area at an unacceptable environmental cost, even if it were feasible.

The isolation strategy described above to avoid the true right bank of the river would provide effective hazard mitigation for the trail.

72 In addition to the trail re-routing, it is very important that the government consider relocating the village of Bengkar as we consider that much of the village has an unacceptably high rockfall hazard and that it is not suitably safe for continued occupation. Further, more detailed, geotechnical assessment should be completed to define those areas of Bengkar that may be safe for continued occupation. Namche to Khumjung Rockfall. The recent rockfall on the low trail from Namche to Khumjung may be avoided by using the higher level trail between the two villages. We recommend giving consideration to closing the low trail, and consulting with the owners of the two guest houses near Khumjung that would then be bypassed. While it may be possible to complete scaling works to remove the loose rock from the recent rockfall source, this is a short term measure as the geological evidence suggests that rockfall is a frequent occurrence on this stretch of trail.

As a minimum, we recommend placing signage on the low trail informing users of the hazard and strongly suggesting the use of the high trail, particularly when it raining or has rained recently. Shomore Rockfall While it does not appear that any new rock fell from the slopes above Shomore, this was based on a rapid fly past in a helicopter and a more thorough assessment should be completed prior to continued use of the trail. However, given the very large boulders among the houses it is clear that the area has been affected by life-threatening rockfall in the past, and it is likely to be affected again, particularly during strong aftershocks or heavy rain.

Given the lack of evidence of recent rockfall, it may be appropriate to continue using the trail in this area, but we do not recommend spending time in Shomore. Similar considerations to those outlined for Toktok should be applied to this village (further assessment, risk mapping to identify whether there are any safe locations in the village, and if not, a safe place to rebuild, and compensation or assistance for affected landowners). ALARP Principle In areas of the trail away from the four areas that have been discussed specifically, we recommend that risks are managed using the ALARP principle.

There are a number of relatively low-cost measures to reduce the risk to occupants of the area that should be considered:

1 Seasonal closure of the trail during the monsoon may be considered as it is most likely that rockfall and landslides will occur during the wet months. Consideration should be given to how this may be extended to encompass local people as well as tourists. 2 The occupancy of hazard areas should be reduced as much as possible in order to reduce the likelihood of loss of life in the event of a rockfall or landslide occurring. This should be applied to all areas mapped as yellow in this study. Reducing occupancy may be achieved by locating lodges and houses away from the hazard areas. This may not be practical in the lower valley area due to the extensive rockfall hazard present, but lower hazard areas have been identified (for example, the central and true right areas of Phakding or Monjo compared to the southern end of Phakding or Jorsale). This may involve liaison with trekking companies to adjust their itineraries to reduce the risks. If this is undertaken, government assistance may be required to aid those businesses and people affected to relocate their business to safer areas.

73 3 Hazard areas should be signed and communicated to both locals and visitors. This may include signage at the beginning and end of the hazard areas using universal signage, such as that adopted on roads, to encourage people not to stop in these areas. 4 A communication program may be initiated, and may include meetings or radio broadcasts for locals combined with posters presenting the hazard for visitors. Many of the national park and police checkpoints have posters describing local wildlife and Acute Mountain Sickness, and we recommend preparing a poster on natural hazards in the valley to accompany the existing posters. We have met with the team working on the Imja Tsho lake hazard program (the Community Based Flood and Glacial Lake Outburst Risk Reduction Project – CFGORRP) and discussed their communication strategy. They have prepared posters to display in affected villages and will be publicising them shortly. We are unable to combine efforts with them as their posters are published, but could use their communication technique as an example to follow.

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