In the Himalayan mountainous region of India, flash floods are nothing new. The residents of the Himalayas have witnessed several such incidents before,during and after the monsoon. On Tuesday, 5 August,at around 1.30 p.m., the inhabitants of Dharali, Uttarakhand, witnessed yet another devastating flash flood. Again, we lost many fellow citizens and suffered damage to numerous national assets. At any gauge station, if the water level rises more than one metre above the pre-determined danger mark, it is considered a flood. When the floodwater level exceeds 10 metres above the danger level, it is classified as a devastating flood.
The water level in the Dharali flash flood undoubtedly exceeded this limit. The scale of destruction caused by a flood depends on the water volume, the height of the flood level, and the nature of land use by human settlements along the riverbanks. In mountainous regions, flash floods occur due to various reasons. Sometimes, in a narrow valley, very heavy rainfall over a short period of time can trigger such events. For instance, the village of Harsil near Dharali experienced such an incident in July 2012. At other times, large volumes of water suddenly rush down from higher Himalayan glaciers or glacial lakes into narrow valleys, creating devastating floods.
These events are called Glacial Lake Outburst Floods (GLOFs). Examples include the Kedarnath disaster of 16 June 2013 and the Lhonak Lake Disaster of 4 October 2023 in Sikkim. Another example occurred on 7 February 2021, when a glacier collapse in the Tapovan-Reni area triggered flash floods in the Dhauliganga and Alaknanda rivers. Such floods can also result from the sudden breach of man-made reservoirs or dams. Scientists have found that in some narrow rivers of the mountain regions, massive landslides sometimes block river channels, forming what are called natural temporary dams.
Later, due to heavy rainfall, the large volume of water stored behind boulders and rock masses builds up pressure, causing the dam to break, and leading to flash floods in the lower valleys. In the past, several such incidents have occurred in the Alaknanda River.In 1857, the Nandakini River was blocked for three days, forming a temporary dam that eventually breached, triggering large-scale flooding and widespread damage in the Alaknanda Valley. Similarly, in 1868, a dam formed on the Birahi River near the village of Jhinji, creating an artificial lake known as Gudiyar Tal.
When this lake burst, it claimed 73 lives and destroyed the Lalsanga Bridge near Chamoli. Now, let us look at some specific aspects of the Dharali flash flood. Based on nearly two decades of intensive field surveys, topographic maps from the Survey of India, and satellite imagery from the Indian Remote Sensing Agency, certain points have been highlighted in the present article.
From Uttarkashi to Gangotri, the Bhagirathi Valley is a narrow gorge, enclosed by the Himalayas. The river has very little space to shift its course. Flowing along ancient slopes of the terrain, the Bhagirathi is a consequent river. However, past records indicate that the main course of the Bhagirathi itself has not been the direct cause of major problems. The real danger comes from its right-angled tributaries – subsequent streamswhich, for most of the year, remain almost dry or glacier-fed.
In the lower reaches of the Khera Gad, near its confluence where a narrow man-made embankment standson both sides, Dharali village has spread unscientifically across a small, alluvial-fan-shaped landform at the confluence leaving people to bear the consequences. Now, let us get acquainted with the Khera Gad. Khera Gad, known locally as “Gad” for stream, flows northward from the glaciated terrain of the Greater Himalaya to meet the Bhagirathi near Dharali. Its source lies within the Rudugaira Bamak (6,400 m), surrounded by peaks like Jaonli (6,632 m), Srikanta (6,133 m), and Rudugaira (5,819 m).
The glacier-fed stream drains a steep, avalanche-prone terrain marked by icefalls, cirques, and moraines. The Bhagirathi River in this stretch flows east-west through a deep V-shaped valley, with Dharali occupying a flat alluvial terrace. The surrounding ridges rise abruptly to 3,800 m, and tributary streams descend steeply, forming alluvial fans at the confluence zone. On 5 August 2025, Dharali village witnessed one of the most devastating flash floods in recent Himalayan history. Nestled along the Bhagirathi River, Dharali is more than just a picturesque settlement – it is a vital cultural hub and a key point en route to Gangotri.
On the day of the disaster, the village was alive with the colours and sounds of the HardudhMela, a traditional mountain festival where villagers offer freshly produced cow’s milk to Someshwar Maharaj, their local deity, keeping only a small portion for children. The festival coincided with the celebration of the Panchayat election results, drawing large crowds to the main market area. Around 1:30 PM, a sudden cloudburst over the upper catchment of the Khera Gad transformed joy into tragedy. Within minutes, the small north-flowing tributary – originating from the Rudugaira Glacier at around 4,720m – swelled into a raging torrent, tearing through both banks, flattening apple orchards, sweeping away homestays and hotels, and erasing the main market from the map.
The primary trigger was an intense cloudburst in the upper Khera Gad basin during a period of extremely heavy rainfall over Uttarakhand (3-5 August). IMD data recorded exceptionally high 24-hour rainfall totals across the state. On 5 August, nearby stations in Uttarkashi district recorded daily rainfall between 1.0 cm and 2.7 cm. Although these values appear modest, they mask the possibility of short, intense downpours in the upper Khera Gad catchment. Such localized high-intensity rainfall is typical of Himalayan cloudburst events and can trigger destructive flash floods.
The combination of steep gradients, saturated moraines, and glacial meltwater facilitated the rapid mobilisation of boulders, sediments, and woody debris. This debris-laden flow, travelling at great velocity, magnified the destructive potential downstream. As per news there were at least four confirmed deaths; dozens remain missing and potentially more than 200 people are feared buried under debris. Nine Indian Army personnel from the nearby Harsil camp are among the missing.
Twenty-five hotels and homestays were washed away and over 50houses destroyed or severely damaged. Collapse of bridges, breach of National Highway sections, damage to the Harsil helipad, and loss of army installations were reported. Many roads were blocked or destroyed, severely disrupting regional connectivity. The flash flood dealt a severe blow to Dharali’s tourism-driven economy, destroying key infrastructure and halting visitor inflow. For nearly two decades, Dharali and the Bhagirathi valley have been part of our academic and emotional journey. We have walked its trails, mapped its landforms, and shared tea with its resilient people.
Learning from the Dharali flash flood, villages located at the confluence of major tributaries like the Khera Gad and the Bhagirathi must become more aware and maintain a conscious distance from these tributaries to ensure the safety of human lives. This event is not only a scientific case study but also a deep personal loss. The mountains are sending us a message – through landslides, floods, and glacier retreat. It is time to listen, act, and protect both the people and the fragile Himalayan environment.
(The writers are, respectively, Assistant Professor, Dept. of Geography, Maheshtala College, and Assistant Professor in Geography, Kultali Dr. B. R. Ambedkar College, both affiliated to University of Calcutta.)