The study examines geomorphic vulnerabilities and human-induced disaster amplification in relation to the July 2023 floods in the Beas River valley. The study area includes the area between Manali and Mandi, which was severely damaged by heavy monsoon rains and human-caused mismanagement.
The 2023 Beas Flood Causes:
1. Meteorological Trigger:
- Rainfall that was unprecedented (e.g., 812% excess in Kullu in July 2023).
- Interplay between the Indian Summer Monsoon (ISM) and mid-latitude westerlies.
- Because of the heavy rainfall, terraces up to ten meters high were submerged under floodwaters.
2. Changes in Climate Effects:
- In the twenty-first century, the warming trend doubled, rising from 0.16°C to 0.32°C per decade.
- In Himalayan valleys, warmer air increases the atmosphere’s capacity to hold water, leading to frequent cloudbursts and flash floods.
- Water discharge and the paraglacial sediment load are increased by glacier melting.
Study Area & Methodology:
- Encompasses the upper Beas Basin (~5421 km2) between Aut and Manali.
- The Main Central Thrust (MCT) and other thrusts intersect the Tethyan, Higher, and Lesser Himalayas in geology.
Geological and Geomorphic Findings
1. Sediment Assemblages & Landforms
- Fluvial terraces (T1 and T2), alluvial fans, debris flows, and mid-channel gravel bars are the main landforms.
- Terrace T1 is younger and extremely vulnerable, while Terrace T2 is older and more stable.
- Numerous towns, including Manali, Kullu, and Bhuntar, are situated atop shaky alluvial fans.
2. Drainage Morphometry Beas:
- A river of sixth order with more than 1,400 tributaries.
- The drainage density is high in the Manali, Bhunter, and Raison areas and ranges from 0.061 to 3.1 km/km².
- TWI is highest close to regions with the most damage.
- High slope-energy zones are indicated by the SL Index, particularly upstream close to Manali.
Flood Impact Areas & Trends:
- Roads, NH-3, bridges, schools, and homes were destroyed along the 1000–1500 m Haripur–Manali stretch. Debris flow, paraglacial sediments, and lateral scouring.
Reasons for the Severe Damage:
- The majority of the construction was underway
- T1 terrace (unstable, recent alluvium)
- Ephemeral tributary beds and old landslide debris
- Bridges, schools, hotels, and gas stations were washed away.
- Aggressive erosion resulted from mid-channel gravel bars, suspended bridges, and logged tree trunks that blocked flow and redirected force laterally.
Key Findings from Maps and Data:
1. Mismanagement of Land Use
- Urban growth on terraces, floodplains, and alluvial fans.
- Roads, NH-3 segments, and government buildings were built in geomorphically sensitive areas.
2. Disaster Amplifiers:
- Uncontrolled dam releases: 21 hydropower projects unexpectedly released water.
- Debris caused the Malana dam to jam, but a catastrophic breach was prevented.
3. Vulnerability to Geomorphism
- Because of its limited capacity to transport excess debris, the Beas River frequently experiences lateral migration and bank collapse.
- Flood height was increased and sediment surges were caused by tributary–trunk coupling.
Conclusions:
- The July 2023 flood was exacerbated by human mismanagement, including unscientific development, and infrastructure expansion into areas that were prone to hazards.
- The District Disaster Management Plan (2011) was poorly implemented and disaster planning was inadequate.
Demands a Paradigm Change:
- Reevaluate Himalayan tourism, development and urbanization.
- Steer clear of building on unstable alluvium, ephemeral channels, and T1 terraces.
- Before planning any infrastructure, give geological and hydrological assessments top priority.
- Review the NH-3 alignment, particularly in view of the rising frequency of floods brought on by climate change.
Recommendations for Policy:
- Prohibit construction on T1 terraces, debris fans, and floodplains.
- Use geomorphic analysis to enforce floodplain zoning.
- Put early warning systems in place for dam releases.
- Start managing sediment at the catchment level.
- Require planning for risk-sensitive infrastructure.
Source: Reserach Gate