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07 May

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Uttarakhand Flash Floods: Temporary Lake Formed In Harsil Raises GLOF-Like Risk

Introduction

A temporary lake formed in the upper reaches of Harsil in Uttarkashi district of Uttarakhand after the August 2025 Dharali flash floods has emerged as a fresh hazard in the fragile Himalayan region. The lake, formed due to obstruction of water flow along the Bhagirathi River, raised concerns regarding a sudden breach and downstream flooding risk.The incident once again highlights the growing vulnerability of the Himalayan ecosystem to:

  • Flash floods
  • Landslides
  • Glacial hazards
  • Extreme rainfall events
  • Climate-induced hydrological instability

The development also draws attention toward the increasing possibility of Glacial Lake Outburst Flood (GLOF)-like events in the Indian Himalayan Region (IHR).


Formation of the Temporary Lake

The temporary lake developed after debris, trees, and sediments accumulated during the flash flood obstructed the natural flow of the Bhagirathi River near Harsil.Key features:

  • Approximate length: 400–500 metres
  • Location: Upper reaches of Harsil
  • Trigger: Dharali flash flood and debris blockage
  • Threat: Sudden breach leading to downstream flooding

Continuous monsoon rainfall increased the pressure on the temporary obstruction, thereby enhancing disaster risk.


Why Temporary Lakes are Dangerous

Risk of Sudden Breach

Temporary lakes formed by landslides or debris dams are highly unstable because:

  • Their barriers are weak and unconsolidated
  • Water pressure increases rapidly
  • Heavy rainfall accelerates erosion
  • Sudden collapse releases massive water downstream

This creates a phenomenon similar to:

  • Flash floods
  • Debris flows
  • GLOF-type disasters

Connection with GLOF Events

What is GLOF?

A Glacial Lake Outburst Flood (GLOF) occurs when water stored in a glacial lake is suddenly released due to failure of the natural dam.The Indian Himalayan Region contains thousands of vulnerable glacial lakes.

Major Triggers

  • Ice avalanches
  • Landslides
  • Moraine dam failure
  • Excessive meltwater pressure
  • Earthquakes
  • Extreme rainfall

Types of Glacial Lakes in Himalayas

TypeCharacteristics
Supraglacial LakesFormed on glacier surfaces due to meltwater accumulation
Moraine-Dammed LakesFormed near glacier snouts and blocked by loose debris/moraine

Both categories are vulnerable to sudden breaches.


Himalayan Vulnerability

8The Himalayas are among the world’s most fragile mountain ecosystems.

Factors Increasing Disaster Risk

  • Rapid glacier retreat
  • Climate change
  • Intense rainfall events
  • Deforestation
  • Unplanned infrastructure development
  • Slope instability
  • River valley construction

Extreme weather events are becoming more frequent due to warming temperatures.


Disaster Management Measures in Harsil

Authorities initiated multiple emergency measures:

Controlled Drainage Operations

  • SDRF teams worked to create water outlets
  • Obstructing trees and debris were removed
  • Controlled discharge was attempted

Scientific Assessment

A team of geologists and experts was deployed to:

  • Assess lake stability
  • Evaluate downstream risks
  • Recommend safe drainage mechanisms

NDMA Intervention

The National Disaster Management Authority (NDMA) directed:

  • Constant surveillance
  • Joint Army-state coordination
  • Safe water release operations

Infrastructure Impact

The temporary lake submerged:

  • Around 600 metres of the Harsil–Dharali road

The Border Roads Organisation (BRO) stated that restoration work would begin only after water drainage and stability assessment.This demonstrates the vulnerability of Himalayan transport infrastructure to:

  • Flash floods
  • Landslides
  • River erosion
  • Cloudburst events

Lessons from Previous Himalayan Disasters

Kedarnath Disaster (2013)

  • Triggered by cloudbursts, landslides and glacial lake flooding
  • Massive destruction in Uttarakhand

South Lhonak GLOF (2023)

  • Occurred in Sikkim
  • Destroyed the Chungthang hydropower dam
  • Caused major downstream silting and flooding

These disasters indicate the need for:

  • Early warning systems
  • Climate-resilient infrastructure
  • Scientific monitoring of Himalayan lakes

NDMA’s GLOF Mitigation Programme

India has accelerated GLOF mitigation efforts through NDMA.

Major Objectives

  • Hazard assessment of vulnerable lakes
  • Installation of Automated Weather and Water Stations (AWWS)
  • Early Warning Systems (EWS)
  • Water level reduction measures
  • Community engagement

India has identified:

  • Initially 56 high-risk lakes
  • Expanded list to 195 vulnerable glacial lakes

Importance of Remote Sensing and Technology

Modern techniques being used include:

  • Satellite remote sensing
  • SAR interferometry
  • UAV surveys
  • Bathymetry studies
  • Electrical Resistivity Tomography (ERT)

These technologies help in:

  • Detecting slope instability
  • Monitoring lake growth
  • Predicting possible dam failures

Ecological and Developmental Concerns

The repeated occurrence of such events raises concerns regarding:

  • Hydropower expansion in fragile valleys
  • Road widening projects
  • Tourism pressure
  • River valley urbanisation

Balancing development with ecological sustainability has become crucial in the Himalayas.


STATIC PART

Harsil

FeatureDetails
LocationUttarkashi district, Uttarakhand
RiverBhagirathi River
ImportanceHimalayan settlement and strategic region

Bhagirathi River

FeatureDetails
OriginGaumukh Glacier
Major SignificanceOne of the headstreams of the Ganga

NDMA

FeatureDetails
Full FormNational Disaster Management Authority
Established2005
HeadquartersNew Delhi
FunctionDisaster risk reduction and disaster management coordination

SDRF

FeatureDetails
Full FormState Disaster Response Force
FunctionState-level disaster response and rescue operations

BRO

FeatureDetails
Full FormBorder Roads Organisation
FunctionConstruction and maintenance of strategic roads in border regions

Updated – 12 Aug 2025 ; 12:29 PM | TOI

News Source: Times of India

Additional Reference: The Hindu – GLOF Explained

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