Landslide Dams In Uttarakhand

LANDSLIDE DAMS IN UTTARAKHAND

• A landslide dam happens when a large landslide blocks a river, forming a natural barrier.
• While these dams can create temporary lakes, they are unstable and can break easily.
• When these dams collapse, they can cause Landslide Lake Outburst Floods (LLOFs), which can harm areas downstream.
• Uttarakhand, with its mountainous landscape, is highly vulnerable to these events.
• A study by researchers at IIT Roorkee highlights the increasing risk, especially in the Garhwal region, where landslide dams are a serious concern.

KEY FINDINGS

• Most Vulnerable Rivers: The research, published under the title “Landslide Dam Studies in Uttarakhand, India: Past, Present, and Future“, identifies the Alaknanda River as the most vulnerable to landslide-induced dams. Other rivers at risk include:
  • Mandakini River
  • Dhauliganga River
  • Bhagirathi River
• Geographical Risk:
  • Uttarakhand’s unique topography — narrow valleys, steep slopes, and deep gorges — significantly increases the risk of landslide dams.
  • In such narrow valleys, landslides are more likely to block rivers, leading to the creation of unstable lakes that can rupture without warning.
• Climate Change and Increased Vulnerability:
  • The study also finds that climate change is exacerbating the problem.
  • Warmer temperatures and unpredictable weather patterns, including heavy rainfall and cloudbursts, have increased the frequency of landslides in the region.
  • Climate-induced changes, such as glacial melting, also contribute to unstable land conditions, making landslide dams more frequent and dangerous.
• Landslide Dam Formation Timeline:
  • Landslide dams have been forming in the region for centuries, with some occurrences dating back to the Last Glacial Maximum (LGM) period (29,000-19,000 years ago).
  • Significant events, however, have been recorded more recently, particularly since the 19th century. This highlights the growing frequency of such occurrences.
• Chamoli’s High Risk:
  • Chamoli district has been identified as the most vulnerable area for landslide dams in Uttarakhand, with other high-risk districts including Rudraprayag and Uttarkashi, all located in the Garhwal region.
  • These areas have witnessed the most frequent and severe incidents of landslide dam formation.
• Historical Example: Gohna Tal:
  • One of the most notable landslide dam incidents in the region was the formation of Gohna Tal in 1893, which was created by a large landslide blocking the flow of a river in Chamoli district.
  • The lake created by this blockage partially breached in 1894 and fully ruptured in 1970, leading to massive downstream flooding.
  • This breach impacted areas as far as Haridwar, around 200 km away.
  • Gohna Tal serves as a chilling reminder of the danger that long-standing landslide dams pose.

TRIGGERS & IMPACT FACTORS

• Seasonal Triggers: The monsoon season — particularly the month of August — is the peak period for landslide dam events. During this time, heavy rainfall triggers landslides, which may block rivers and create natural dams.
• Cloudbursts and Debris Slides
  • In addition to heavy rainfall, cloudbursts are a common trigger for landslides.
  • The study points out that debris slides, which are the most common type of landslide in Uttarakhand’s hills, often block rivers, forming unstable natural dams.
  • These debris slides are made of soil, rocks, and trees, and their unpredictability makes them particularly dangerous.
• Climate Change:

Increased rainfall intensity and the higher frequency of cloudbursts, both linked to climate change, are exacerbating the risk. The more intense weather patterns destabilize slopes, leading to more frequent landslides and, consequently, more landslide dams.

HUMAN ACTIVITIES & THEIR ROLE

• Deforestation:
  • The rapid deforestation in the region, primarily driven by infrastructure development and agriculture, has weakened the soil’s natural resilience.
  • The roots of trees help hold the soil together, preventing landslides.
  • When these forests are cleared, the slopes become much more prone to failure, leading to more frequent landslides and dam formations.
• Road Construction and Hydropower Projects:
  • Infrastructure development such as road construction in steep, mountainous areas disrupts the natural landscape, making it more susceptible to landslides.
  • The construction of hydropower projects also alters river flows and puts pressure on the natural environment, contributing to the risk of landslide dams.

PREPAREDNESS & MITIGATION MEASURES

• Unpredictability of Landslide Dam Stability:
  • A major challenge in managing landslide dams is their unpredictability.
  • The stability of these dams is difficult to assess, and they can fail suddenly, triggering destructive floods.
  • Since these dams can exist for decades before breaching, it’s crucial to continuously monitor their condition.
• Importance of Preparedness:
  • Despite a decrease in major incidents since 2018, the study underscores the importance of disaster preparedness.
• The unpredictable nature of landslide dam breaches means that local authorities must have effective early warning systems in place.
• Communities in high-risk areas like Chamoli, Rudraprayag, and Uttarkashi should be regularly educated on evacuation procedures and the signs of an impending dam breach.
• Monitoring and Risk Assessment: The study emphasizes the need for continuous monitoring of rivers and valleys that are susceptible to landslide dams. Technologies like remote sensing and drone surveillance can help detect landslides before they block rivers, allowing authorities to take precautionary measures in time.

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