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Drone-Based Aerial Mapping of Landslide
Change analysis and volume calculation of Debris
Introduction
Nestled in the heart of the majestic Himalayas, Nepal captivates with its breathtaking beauty. However, amidst this scenic charm lurks a hidden danger — landslides. The extensive topography of Nepal renders it particularly vulnerable to this natural hazard.
Annually, the country grapples with the grim toll of landslides, reporting approximately 111 deaths attributed to these events. This recurring threat is further underscored by a staggering record of more than 4,351 landslides documented over a 49-year period.
Map of Nepal representing all the landslide site of Nepal till 2022
Traditional methods for evaluating landslides can be time-consuming, expensive, and susceptible, and they may not give an accurate image of the magnitude of the damage because the most impacted locations are frequently those with hilly and mountainous terrain.
Focusing on this scenario, In 2017, NFL together with Medair carried out a Drone-based aerial survey of the massive landslide area with a huge elevation change of over 800m between the top and bottom of the landslide. This work also received international recognition in 2016 and won the AUVSI EXCELLENCE Humanitarian Award.
Ramechhap Landslide Site
Over the past six years, we have been eager to do additional research and investigation-related work in this landslide area using drones. Finally, in response to the serious landslide problem, Nepal Flying Labs and WeRobotics collaborated to conduct a joint study/research titled "Change Analysis and Calculation of Run-out Volume of Debris of a Landslide Using Drones to Suggest Sustainable Risk Reduction Measures" on the Ghyapche landslide.
In the context of landslides, Ghyapche landslide is the one of the oldest and largest landslide in Nepal, occurred in 1954 AD (2011 BS). The area prior to the landslide was modest. With the passage of time, the Ghyapche landslide became larger and larger, eventually encompassing vast grazing and farmland.
Drones have the ability to access dangerous locations and rough terrains that are difficult or risky for humans to reach, which is one of the main benefits of employing them for mapping the Ghyapche landslide.
Drone-based data analysis will enable accurate and effective investigation of landslide changes and debris volume calculation. This aids in the evaluation of potential risks and hazards in the impacted area. Additionally, we were able to identify the boundaries and extent of the landslide and provide suitable mitigating strategies.
Location
The Ghyapche landslide is located at Ward No. 3 and 4 of Manthali Municipality, as well as Ward No. 3 of Likhu VDC in Ramechhap District, the central region of Nepal. This area is distinguished by its diverse topography, which includes hills, valleys, and spurs and elevation ranges from approximately 488 to 2080 m.
Location map of Ghyapche landslide: Imagery Hybrid (WGS84)
The recent coverage of the landslide encompassed an area of approximately 4 square kilometers, and it is anticipated to extend further in the future. Notably, there are signs of highly weathered bedrock (specifically, Sericite-containing phyllite) and a wide, deep crack in the upper part extending from 5 to 50 meters beyond the landslide. Additionally, there is undercutting of the slope by the Ranchor River at the location.
There are few meteorological stations nearby the landslides, however, the near real-time data is not available in the Department of Hydrology and Meteorology
- Ramechhap (Station ID 1106)
- Manthali (Station ID 1123)
History
1984-02-20
This is a draft showing the landslide area from the imagery of 1984
1994-02-20
This is a draft showing the landslide area from the imagery of 1994
2004-02-20
This is a draft showing the landslide area from the imagery of 2004
2014-02-20
This is a draft showing the landslide area from the imagery of 2014
2022-02-20
This is a draft showing the landslide area from the imagery of 2022
In the examination of expansive landslides, data collection involved the application of four distinct methodologies: Drone Survey, Geological and Hydrological Survey, Focal Group Discussion (FGD), and Key Informant Interview (KII). The collection of technical data was accomplished through the utilization of drones (specifically Wintra and Phantom) and geological surveys. Simultaneously, theoretical insights were acquired through FGD and KII.
Drone survey
Drone Survey Team
The use of drone surveys is crucial in the exploration of expansive and challenging topographies, particularly those difficult to reach on foot like Ghyapche landslide. In the examination of landslides, two distinct drone models, namely Wintra and Phantom, were utilized to conduct a comprehensive survey, capturing high-resolution orthophoto maps. The Wintra drone, selected for its superior data quality and extended flight time, required a specialized setup, while the compact size of the Phantom drone made it suitable for navigating through demanding terrains. These drones meticulously recorded intricate 3D models of regions affected by landslides, enabling precise calculations of debris volume by comparing models from before and after the landslides occurred. Additionally, aerial surveys were conducted over neighboring areas prone to landslides to evaluate potential extents of future incidents.
Geological and hydrological survey
Collecting soil samples form the site
Hydrological and geological survey were conducted to understand the current status of the landslide, predict its potential future impact, and recommend mitigation measures for stakeholders and local authorities. From a geological perspective, the site is located in the Seti Formation of the Lesser Himalaya, featuring a ~34-degree bedding angle and consisting mainly of weathered sericitic phyllite and schist. Notably, there are signs of wide, deep crack in the upper part extending from 5 to 50 meters beyond the landslide. Creeping phenomenon was also clearly seen in the nearby landslide area.
Local fault, seepage, and drainage such as Lakchya Khola, Ranchor Khola was observed near the landslide area. Furthermore, Soil samples from various locations was collected for laboratory testing, which aids in comprehending soil properties, evaluating stability, and predicting responses to changing environmental conditions, such as rainfall or earthquakes, ultimately enhancing emergency preparedness.
Focal Group Discussion
To involve a group of individuals from the local community or relevant stakeholders and collect qualitative information, experiences, and perceptions regarding landslides, a Focal Group Discussion (FGD) was carried out.
A group discussion took place at Lakuri Danda in Manthali Ward No. 4, involving 36 participants. According to local accounts, the site affected by the landslide was known as "Kangba Danda" before the event. The term "Ghyapche" reflects its landslide nature, with "Ghyappa" in Nepali signifying the "phenomenon of a massive mass covering an area."
The FGD findings revealed that approximately 250 households were impacted, with around 100 households severely affected and requiring relocation. The extensive coverage of the landslide made direct travel to another village impossible, necessitating longer and hazardous routes. The water resources in the area were also adversely affected by the landslide.
Notably, there was a lack of support from government agencies, NGOs, or community organizations addressing landslide risks in the region. While local mitigation methods, such as gabion walls, were previously employed, they proved ineffective against the magnitude of the landslide. Consequently, there have been no recent implementations of mitigation measures in the area.
Key informant interviews (KII)
During the field visit, individual interviews were conducted with key figures possessing specialized knowledge or expertise in landslides, including local authorities, community leaders, and victims. These one-on-one sessions facilitated in-depth exploration of specific topics and provided access to expert opinions.
"This landslide occurred in 2011 BS ( 1954 AD ) before the occurrence of Ghyapche, this place was known as Kangba Dada.”
"Approximately, 250 households were affected by landslide in manthali, likhu VDC and Ramechhap as well as hectors of a agricultural land”
"The landslide resulted in the loss of my son, agricultural assets, and 19 cattle."
"During the winter season, the dust from Ghyapche landslide polluted the village and resulted in respiratory issues among the residents”
"Every monsoon season, we had to temporarily relocate our entire family to a safer location out of concern for landslides, only to return home afterward.”
Causes and triggers of Landslide
Image: Widening the Ranchor Khola due to the landslide
Although the Ghyapche landslide initiated by the intense rainfall but triggered by a combination of factors. Weak geology, characterized by highly weathered, sericitic-containing phyllite, plays a significant role in making the area susceptible to landslides. Intense and prolonged rainfall events in the region contribute to the instability of the terrain. The presence of the Mahabharata Thrust and a local fault near the landslide body adds geological stress, making the area more prone to sliding. Excessive drainage, which can result from both natural and human-induced factors, also heightens the risk of landslides. Additionally, seismic activities (e.g., Gorkha earthquake 2015) in the region can act as a catalyst for the occurrence of landslides, further amplify the vulnerability of the area to such natural disasters.
3D map illustrating rainfall patterns in Ramechhap districts, highlighting the primary factor contributing to landslides in the region.
Key observation/Findings/Impacts
- Loss of life: 6, till 2023
- Damage area: 4 sq km covering agricultural land and grazing land
- Subsidence of landslide, dried up several wells such aale kuwa, Tallo kuwa
- Displaced- 250 households & need to be displaced: 100 Household
- Caused pollution in the area over the winter, causing respiratory problems for the locals as well as disturbing the environment.
Image: Landslide sighted from Sunsapani village, roughly 7 kilometers southwest of the Ghyapche Landslide.
Image: View of a landslide from the crown section.
Image: Slope failure at the crown part of Landslide
Image: Deep crack at ~10m beyond the crown part of landslide.
Image: The bamboo tree was initially in position 'B' prior to the landslide at Khatri Tole. Currently, it is located at position 'A,' situated on the right side of the tail portion of the Ghyapche landslide.
Image: Water bodies near the landslide area
Image: Wide crack due to the effect of landslide.
Image: Subsidence of courtyard by creeping, due to the landslide.
Image: Subsidence of road, near the Landslide area
Comparison map between satellite image and drone image
On the left side, there is a satellite image dated 2022, and on the right side, you'll find a drone image taken in 2023. This arrangement allows for a comparison between the perspectives offered by satellite and drone imagery, showcasing the distinct vantage points and potential differences in details or features captured by each technology.
Comparison between World Imagery 2022 and Drone Image taken of 2023
Comparison map between drone image of 2017 and drone image of 2023
To the left, you'll find the drone-captured image from 2017, and on the right side, there is the drone image taken in 2023. This arrangement allows for a visual comparison between the two snapshots, providing insights into any changes or developments over the specified time period.
Comparison between Drone Orthophoto of 2017 and Drone Orthophoto of 2023
Fly-By
Nepal Flying Labs succeeded in a project with similar scope through a partnership with WeRobotics , organization who supports and connects local experts in drone, data and AI technologies. Together we carried out a survey of a massive landslide in the hills of the Ramechhap district that has claimed damage of vast grazing land and agricultural terrain. The range of elevations involved in mapping of this landslide made it an extremely difficulty challenge, with 488 m to 2080m in elevation change between top and bottom of the landslide. The 3D flight-planning features of senseFly drones, as well as extensive experience in drone-mapping of mountainous terrain, were key to the success of this project. You can see results of this mission in the video fly-by below:
Ramechhap Landslide Fly-through