How the river Kosi’s shifting course exposes the perils of embankments, Pg II

Key Highlights:

• In August 2008, the Kosi River breached its embankment at Kusaha in Nepal, causing floods that killed over 400 people and displaced thousands in Bihar, affecting 33 lakh people.
• The Kosi River, known as the 'river of sorrow,' frequently breaches its embankments, causing loss of life and livelihoods due to its heavy siltation and shifting course.
• Experts suggest that the construction of a barrage in Nepal in the 1950s and subsequent embankments in Bihar have altered the river's natural flow, exacerbating flood risks.
• The National Democratic Alliance (NDA) promised "flood to fortune" in their election manifesto, proposing river-linking projects like the Kosi-Mechi project to promote agriculture and fisheries.

Detailed Insights:

• The Kosi River, originating in Tibet and Nepal, is prone to shifting its course due to heavy sedimentation, having moved 120 km westwards in the last 250 years.
• The G.R. Garg Committee report in 1951 cautioned against embankments, noting they disrupt the river's natural functions of land erosion and deposition, and are only useful when the river carries less silt.
• Embankments on silt-heavy rivers like the Kosi lead to silt accumulation, raising the riverbed and increasing the risk of breaches, as seen in multiple incidents since 1963.
• While embankments may offer short-term protection, they can increase long-term vulnerability by disturbing ecological integrity, groundwater, and biodiversity.
• Alternative solutions include 'learning to live with floods' through early warning systems, rehabilitation outside embankments, and reviving paleochannels to distribute water.
• The Kosi-Mechi project, intended to provide irrigation, may not effectively reduce floodwaters, as the Kosi River can carry significantly more water during peak monsoons.
• Desilting the river using scientific methods and improving palaeochannels are suggested as sustainable solutions to manage floods and prevent waterlogging.

Key Concepts Involved:

• Embankments: Artificial structures designed to control water flow in flood-prone areas.
• Siltation: The process by which fine particles of soil or sediment are deposited in a river or other body of water.
• Paleochannels: Abandoned ancient river or stream channels that can be revived to distribute water and prevent floods.