Research led by geographers at the University of California has identified the physical mechanism determining whether a river flows as a single channel or splits into multiple threads.

Key Findings of the Study

• Single-thread rivers:
  • They are characterised by equilibrium between bank erosion and bar accretion.
  • Material eroded from one bank is balanced by deposition on the opposite bank, maintaining stable width.
• Multi-thread rivers:
  • They exhibit higher erosion relative to deposition.
  • Continuous widening and splitting of channels result in braided systems, where instability dominates and leads to dynamic channel shifts.
• Implication: Erosion imbalance is the main cause of flow-splitting.
• Human Interference: Many rivers historically shifted from multi-channel to single-channel due to human actions such as damming, diking, sediment mining, agricultural development, clearing and snagging.

Research Methodology

• Global Coverage: Analysed 84 rivers worldwide across 36 years (1985–2021) using Landsat satellite images.
• Tool: Applied particle image velocimetry to track erosion and accretion changes.
• Data Volume: Over 4 lakh measurements compared across different climates, slopes, and water flows.
• Indian Rivers: Ganga (Patna, Farakka, Paksey) and Brahmaputra (Bahadurabad, Pandu, Pasighat, upper Himalaya) were also considered.

Insights on Indian Rivers

• Brahmaputra is identified as a classical braided river, with fast lateral erosion and unstable sub-channels.
• Ganga also shows significant instability in braided stretches.
• The conventional assumption of erosion–deposition equilibrium is challenged by findings.
• Implication: Flood forecasting models (rating curves)  for multi-thread rivers like the Ganga and Brahmaputra must be updated more frequently to reflect changing channel shapes.

Role of Vegetation in Shaping River Morphology

• Earlier belief: Vegetated banks were considered essential for meandering rivers.
• Vegetation alters river bend migration.
  • Vegetated rivers → bends move sideways, forming levees, reducing sinuosity.
  • Unvegetated rivers → bends move downstream without lateral migration.
• Findings indicate that sedimentary deposits of vegetated and unvegetated rivers are fundamentally different despite similar forms.

River Management Implications

• Multi-thread rivers return to their natural state faster and at lower restoration cost.
• Artificial confinement of braided rivers (e.g., Ganga, Brahmaputra) into single channels using embankments increases risks.
• Nature-based solutions recommended:
  • Removing artificial embankments.
  • Restoring floodplain connections.
  • Creating vegetated buffer zones.
  • Reactivating abandoned channels.
  • Building wetlands in braided stretches.
• These steps can significantly reduce flooding risks in adjacent areas.

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