Rockfall Early Warning System (REWS) upslope of Manikaran, Himachal Pradesh, NW Himalaya, India

by Raj Kiran Dhiman

Gurudwara, situated at Manikaran along the Parvati River, Kullu District, Himachal Pradesh, India (Source: thenewshimachal.com)

Tragedy Strikes: The Manikaran Sahib Gurudwara Rockfall Disaster

On a seemingly ordinary day in the serene surroundings of the Manikaran Sahib Gurdwara site near Kullu in Himachal Pradesh, tragedy struck in the form of a devastating rockfall. The date was August 18th, 2015, and what began as a relatively small event quickly escalated into a catastrophe of monumental proportions.

The Manikaran Sahib Gurdwara, a place of spiritual significance for many, stood witness to the sheer force of nature as a powerful rockfall engulfed its premises. The impact was immediate and catastrophic, with the gurdwara building being destroyed in the wake of the landslide. However, the destruction didn't end there; the lives of more than 11 people were tragically claimed as they slept in the sarai (guest house) of the gurdwara (Blog by Dave Petley).

Exploring the Geothermal Springs and Rockfall Source in Manikaran: A Journey of Discovery

In January 2019, Dr. Mahesh Thakur, his master's thesis students, and I embarked on an expedition to Manikaran to study its renowned geothermal spring, which boasts temperatures up to 96°C. During our visit, we learned about the tragic rockfall incident that occurred in 2015. Moved by the story, we decided to investigate the source area of the rockfall.

The journey led us to the village of Gargi, located approximately 3 kilometers from Manikaran via the usual local route. However, we struggled to find this route. After seeking directions from some local residents, we were advised to take an older, now-abandoned path. Without hesitation, we began the ascent along this steep and challenging route. The journey was arduous, taking nearly four hours to reach Gargi village due to the difficulty of the old path. Despite the challenges, we persevered, driven by a desire to understand the factors behind the devastating rockfall and to uncover insights that could help prevent future tragedies.

Panoramic view showing Manikaran, Gargi village and rockfall source for 2015 event

Photo taken during field trip to Manikaran geothermal system (steam of geothermal system is clearly visible in the photo)

Gurudwara sahib at Manikaran utilizes the boiling water from geothermal system to cook food

Photo of Manikaran town taken during hike to Gargi village (looking east)

During trek to Gargi village rockfall debris from upslope was encountered (Photo: looking north)

The first view of Gargi village, with a huge boulder present (see house for a scale)

The hospitality of Mr. Teku (the owner of a guest house in Gargi) is unforgettable

Starting new project and first field visit to MAnikaran rockfall site

After the January 2019 trip to Manikaran, Dr. Mahesh Thakur applied for funding from the Government of India to study the rockfall site. Despite the global struggle with the COVID-19 pandemic that began in March 2020, Dr. Mahesh secured funding in December 2020 to investigate the rockfall site and develop an early warning system to predict future rockfall events.

I joined this project as a junior research fellow in February 2021. Our first geological field visit to the rockfall site took place in March 2021. This project aimed to create an early warning system using advanced sensors, so it involved collaboration with engineers from Panjab University's engineering departments. Prof. Naveen Agarwal and Dr. Sukhvir Singh, experts in electronics, machine learning, wireless communication, and IoT, played a crucial role in this interdisciplinary effort.

Our team was dedicated to developing a reliable system that could predict and potentially mitigate the impact of future rockfall events, blending geological expertise with cutting-edge technology to enhance community safety and resilience.

Photo taken in Gargi village showing steep rocky mountain behind (see rockfall deposits in the background). Photo (Right to left) Dr. Mahesh Thakur, Prof. Naveen Agarwal, engineering students (Photo by Me)

Photo of Gargi village taken on the way to the rockfall source area, the source area was a steep 2 km trek from the village

The first glimpse of rockfall source area

Rockfall source area with deposited blocks from the 2015 event (that's me in the photo)

Panoramic view of the rockfall site

Investigating the Manikaran Rockfall: Insights from Local Shepherds

On the first day of our trip (25-03-2021), we focused on investigating the source area of the rockfall. To gain a deeper understanding of the event, we spoke with local shepherds who were living near the site when the rockfall occurred. Their firsthand accounts provided valuable insights.

One particularly interesting detail they shared was about the behavior of the rock blocks during the event. According to the shepherds, most of the rock blocks were deposited on the talus. However, a few blocks traveled farther downslope, triggering static boulders lying on the surface to move. It was these remobilized boulders that posed the greatest danger.

The shepherds explained that one of these remobilized boulders traveled so far downslope that it struck the Gurudwara building, resulting in the tragic loss of many lives. This crucial piece of information highlighted the unpredictable nature of rockfall events and underscored the importance of understanding both primary and secondary movements of rock debris. Considering the effect of remobilization of static blocks is crucial when conducting rockfall propagation modeling. For producing reliable rockfall hazard maps in Manikaran, this consideration is essential. Existing rockfall propagation models did not account for this effect of remobilization. However, after studying the literature, I discovered that Dr. Franck Bourrier from the Institute of Geoscience and Environment (IGE) at Grenoble Alpes University in France had worked on similar problems. I was fortunate enough that he agreed to co-supervise my Ph.D. research, and together, we are developing a novel rockfall propagation model for Manikaran using Siconos software. More details on the modeling can be found in the upcoming section "Advanced Analysis of Rockfall Propagation in Manikaran."

Our conversations with the shepherds enriched our investigation, providing a clearer picture of the Manikaran rockfall dynamics and the devastating impact it had on the community. This local knowledge proved invaluable as we continued our research and worked towards developing an early warning system to prevent such tragedies in the future.

Investigating the Persistent Rockfall Issues in Gargi Village

For years, Gargi village has suffered from frequent rockfall events, which have not only threatened the safety of its residents but also covered their agricultural land with debris, affecting their daily needs. Dr. Mahesh and I decided to investigate the top of Gargi village to understand the causes behind these recurring rockfalls.

On March 26th, 2021, we began our trek at 7 AM from Gargi village, heading upslope. The journey was arduous, taking us five hours to reach the summit. The trail was challenging, strewn with rockfall debris from the top. We observed that the south-facing slope, exposed to more solar radiation, was actively triggering rockfalls into Gargi. In contrast, the north-facing slope, which received less sunlight, was covered with 2 feet of snow.

We chose to climb the north face and eventually reached the top (at 3250 masl). Upon investigating the area, I found that the schistose rock mass at this elevation was highly weathered due to the continuous freezing and thawing cycle. The top layers of the rock were almost converted into soil, indicating significant weathering. This freeze-thaw cycle weakened the rock mass, while rainfall acted as a triggering factor for most of the rockfall events in Gargi.

Our findings highlighted the complex interplay of climatic conditions and geological processes contributing to the persistent rockfall issues in Gargi village. Understanding these factors is crucial for developing effective mitigation strategies to protect the village and its agricultural land from future rockfall events.

Photo taken while trekking to top of Gargi village (see person for scale)

Downslope view while trekking to top of Gargi village (see person for scale)

Potential block for future rockfall activity

Downslope view towards Gargi village showing rockfall path

Top of Gargi village showing weathered rock mass and snow-covered north face (see person for scale that's me) (photo was taken looking East)

Advanced Analysis of Rockfall Propagation in manikaran

Rockfall dynamics are influenced by a variety of factors broadly categorized into substrate properties and fragment properties. Substrate properties encompass surface material, slope angles, topography, and roughness, while fragment properties include the mass and shape of the rock blocks, their kinematic properties during motion such as translational and rotational velocities, incidence angle, and the orientation of the block before impact (Bourrier and Hungr, 2012). To accurately capture these surface properties, high-resolution digital elevation models (DEMs) with a resolution of 2 meters or higher are essential. To achieve this, we conducted a drone survey using a DJI Phantom 4 Pro. By employing photogrammetry techniques, we generated a high-resolution 2-meter DEM of the area.

Given the unique nature of the 2015 rockfall event, I undertook a comprehensive investigation of the entire run-out zone. I meticulously demarcated the blocks deposited during the event and calculated their shapes and dimensions. Leveraging the high-resolution 2-meter DEM, we developed a novel 3D rockfall propagation model. This model takes into account the role of pre-fragmented rock mass from the source area and its impact on static boulders lying on the terrain (Dhiman et al. 2023). This advanced model offers a deeper understanding of rockfall dynamics in Manikaran, providing valuable insights into the factors contributing to such events. By integrating detailed substrate and fragment properties, this model aims to enhance our predictive capabilities and inform the development of effective mitigation strategies to safeguard the community against future rockfalls (Dhiman et al. 2024).

Setting up of RTK-DGPS to capture ground control points

Schistose rock blocks of the event showing alternate quartzite and schist bands

Downslope view from top of rockfall source area showing Manikaran town in the far end, (photo was taken looking south)

Drone shot showing rockfall site and downslope view

Development of rockfall early warning system (REWS)

Our detailed geological investigation of the rockfall site in Manikaran revealed that the source area consists of a schistose rock mass intersected by two joint sets. Geomorphic investigations identified various features in the run-out zone, including talus with static boulders on the surface, talus with embedded boulders in soil, talus with trees, and a hard rock cliff. Some of the deposited blocks from the event measure over 10 meters in dimensions. A total volume of 21,000 cubic meters was involved in the event.

Given the blocky nature of the rock mass, we selected tilt meters and crack meters for monitoring the movement of rock blocks. Additionally, we installed a rain gauge and a piezometer to monitor environmental conditions that might trigger rockfalls.

The installation took place in November 2023, during an extremely cold period. The steep terrain and lack of road access made transporting sensor boxes, accessories, batteries, and construction materials like cement and sand from Manikaran to the rockfall site a significant challenge. Despite these difficulties, we successfully transferred all necessary equipment and materials to the site.

The installation was carried out on the steep 80-meter cliff at the rockfall source area. As shown in the drone footage, we identified two potential zones prone to rockfalls. After thorough field investigations, we installed a total of 10 tilt meters and 4 crack meters at these locations.

On November 24, 2023, after the successful installation, we began receiving data from the rockfall site to the Department of Geology, Panjab University, via an FTP server. We currently receive data six times a day.

Since we lack time series data for this site before the failure in 2015, predicting when the next rockfall will occur is challenging. However, as detailed by Leinauer et al. 2023, a four-step technique has been developed that utilizes regular data and multiple filter windows to read data and predict the onset of acceleration (OOA). Once OOA is predicted, the inverse velocity method can be used to estimate the time of failure of rock blocks. We are utilizing this technique of Leinauer et al. 2023 to predict next rock mass failure in Manikaran.

Gargi village and rockfall site separated by a ridge

Rockfall site (I am standing on the debris of rockfall 2015)

Loading of sensors and accessory items on mule (Photo taken at Manikaran)

Photo taken while transporting equipment on mules from Manikaran to Gargi village

Finally reaching Gargi with sensors and accessories

Relaxing and sunbathing (me) at the Sun View Cafe guest house in Gargi village after transporting all the necessary equipments

Trekking partner from Manikaran to gargi and to the rockfall site @Moti the dog

The establishment of a camp near the rockfall site, with Kamal featured in the photo, who not only assisted in cooking but also contributed to the installation activities

Preparation for colder night

Preparation of sensors and briefing local mountain climbers on installing them on a rocky cliff using harnesses and ropes

Climber Santosh adjusting his position to install tilt meter 3 following the installation of tilt meter 2 (visible with the blue wire attached)

The photograph was taken at the crown of the rockfall source area, can you spot the camp site in the photo?

Climber Bhojraj assisting climber Santosh in transferring sensors, drill machines, and other equipment

In the midst of the photo, climber Santosh can be seen, while Bhojraj, clad in red, is positioned at the top of the block, secured by a yellow rope, actively engaged in their tasks

Santosh in action installing tilt meter 7 (can you spot santosh along yellow rope?)

Santosh in action installing crack meter 1

A group selfie taken after completing the installation of sensors. In the top row is Bhojraj, while in the middle row, you can see Er. Deepak, Kamlesh, and Santosh

Installed gateway powered by solar panel

Piezometer connected with wireless node for data transmission

Rain gauge installed in Gargi village near Sun View cafe

Night view of Manikaran town

Reflections on a Three-Year Journey: Installing the REWS in Manikaran, a New beginning !

The journey from February 2021 until today has been nothing short of a roller coaster. Over these three years, there have been moments of great joy when things went well with our work on the Rockfall Early Warning System (REWS), as well as numerous days of frustration both at the university and in the field when everything seemed to fall apart.

Despite the challenges, I feel a profound sense of satisfaction knowing that I was part of this ambitious project, which seemed nearly impossible given the difficult terrain and the logistical hurdles of transporting equipment on a limited budget.

Many people contributed to the success of this project, and it's impossible to name them all. I am deeply grateful to my supervisor, Dr. Mahesh Thakur, for trusting me to accomplish this task. The co-investigators, Prof. Naveen Agarwal and Dr. Sukhvir Singh were always just a phone call away and provided invaluable guidance during tough times. I am also thankful to engineers Deepak and Manmohan for their resilience in the extreme field conditions and for completing the job on time, just before the snowfall in December 2023.

Special thanks go to the rock climbers, Santosh and Bhojraj, whose skills were crucial during the sensor installation. This project would not have been possible without the unwavering support from Mr. Teku and his partner Mr. Atul, owners of the Sun View Cafe. Of course, I cannot forget the unconditional support from my brothers Kamal and Kamlesh.

The project has achieved significant success with the installation of the sensors, and we are now focused on predicting the next rockfall event in Manikaran. We are also studying the effects of diurnal temperature changes, freezing and thawing, and rainfall, correlating these factors with the movements of the rock blocks.

Early results from the REWS indicate that some blocks are showing permanent deformations on the millimeter scale. This data is crucial for understanding the stability of the rock masses and improving our predictive capabilities.

In conclusion, this three-year journey has been filled with highs and lows, but the collaborative effort and dedication of everyone involved have made it a remarkable and rewarding experience. We are optimistic about the future and committed to making significant contributions to rockfall prediction and safety in Manikaran.

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