River Kosi and the Problem of Embankments

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1. Background: Kosi River and Floods

  • In August 2008, Bihar faced one of its worst floods in nearly 50 years after the Kosi River breached its embankment at Kusaha in Nepal.

  • More than 400 people died, and around 33 lakh people were affected at the peak of the flood.

  • The Kosi is often called the “River of Sorrow of Bihar” because of its frequent floods and destruction.

Static Fact

  • The Kosi River originates in Tibet, flows through Nepal, and enters Bihar, where it joins the Ganga River.

  • It is called “Sapta Kosi” because it has seven major tributaries.

  • The river carries very high amounts of silt (sediment).

2. Why Does the Kosi Flood So Frequently?

Natural Reasons

  • The Kosi carries huge quantities of sediment from the young and fragile Himalayan mountains.

  • Over centuries, the river has changed its course naturally.

  • According to studies, the Kosi has shifted around 120 kilometres westward in the last 250 years.

Human Intervention

  • A barrage was built in Nepal in the 1950s, followed by embankments in Bihar.

  • These structures restricted the natural flow of the river.

  • As a result, silt started accumulating inside the embankments, raising the riverbed.

3. What Are Embankments? (Static Concept)



  • Embankments are artificial walls made of earth, stone, or concrete.

  • They are built along riverbanks to prevent floodwaters from spreading.

  • They are designed to withstand water pressure and gravity.

Intended Purpose

  • Protect settlements

  • Prevent floods

  • Support agriculture

4. Why Embankments Often Fail in Northern India

Expert Observations

  • The G.R. Garg Committee (1951) warned that embankments:

    • Disrupt the river’s natural role of erosion and deposition

    • Prevent natural drainage of floodwaters

    • Work only when rivers carry low silt

Problem with Silt

  • Northern rivers like the Kosi carry heavy silt.

  • When embanked:

    • Silt gets trapped

    • Riverbed rises

    • River flows above the surrounding land level

  • This makes breaches more dangerous.

Evidence

  • Kosi embankment breaches occurred in:
    1963, 1968, 1971, 1980, 1984, 1987, 1991, 2008, and 2024

5. Influent and Affluent Rivers (Important Static Concept)

Influent Rivers

  • Rivers where rainfall decreases downstream

  • Found mainly in western Himalayan region

  • More stable

  • Embankments may work better

Affluent Rivers

  • Rivers where rainfall increases downstream

  • Found in eastern Himalayan region

  • Carry more water and silt

  • Highly unstable

  • Embankments are risky

➡️ Kosi is an affluent river, making embankments unsuitable.

6. Impact of Embankments on People and Ecology

Social Impact

  • Waterlogging outside embankments

  • Flooding of areas between embankments

  • People unable to escape during floods

  • Lack of proper rehabilitation

Environmental Impact

  • Loss of soil fertility

  • Damage to groundwater recharge

  • Decline in biodiversity

  • Reduced river depth affecting navigation


7. Alternative Approach: Living with Floods

Expert Opinion

  • Many experts argue that floods are natural, especially in floodplains.

  • Countries like the United States have removed embankments in some areas.

  • Floods without embankments are often less destructive.

Suggested Measures

  • Early warning systems

  • Flood-resilient housing

  • Proper rehabilitation

  • Scientific desilting

  • Revival of palaeochannels (old river channels that help distribute excess water)

8. River Linking and Kosi–Mechi Project (Current Issue)

What is Proposed?

  • Linking Kosi River to Mechi River through canals.

  • Aim: irrigation and flood control.

Problems with the Proposal

  • During monsoon, water is already abundant.

  • Kosi carries nearly 6 lakh cusecs of water during floods.

  • Proposed diversion is only 5,247 cusecs, which is negligible.

  • Does not reduce flood intensity.

9. Core Question Raised

Are embankments really flood-control structures, or do they increase long-term flood risk?

  • Evidence suggests embankments:

    • Give short-term relief

    • Increase long-term vulnerability

  • Flood management should shift from flood control to flood resilience.

10. Conclusion

  • The Kosi River’s history shows that engineering solutions alone cannot control natural rivers.

  • Repeated embankment breaches highlight the need for:

    • Ecological understanding

    • Basin-level planning

    • People-centric rehabilitation

  • Each time an embankment is raised, the river eventually reclaims its space.

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