Context
Rivers play a critical role in shaping landscapes, ecosystems, and human settlements. Yet, a long-standing question in geomorphology has been why some rivers flow as single-thread channels, while others form multi-threaded or braided systems. Recently, researchers from the University of California, Santa Barbara (UCSB), in a paper published in Science, have claimed to solve this mystery by identifying the physical mechanism behind river splitting.
Research Methodology
- Satellite Data – Used 36 years of Landsat imagery (1985–2021) to study river evolution globally.
- River Selection – Out of 400 surveyed river sections, 84 wide and dynamic rivers were chosen across varied climates, slopes, and flows.
- Particle Image Velocimetry – A computer technique used to detect minute changes in erosion and deposition patterns.
- Image to Maps – Converted satellite images into water vs. land maps for accurate comparisons.
- Cross-sectional Study – Generated millions of vectors capturing direction and speed of erosion/accretion.
- Data Integration – Compiled over 4 lakh measurements of erosion vs. accretion to test balance in river dynamics.
Outcome – The study revealed the physical mechanism explaining why rivers remain single-threaded or split into multiple channels.
Types of Rivers
1. Single-thread Rivers
- Maintain equilibrium between bank erosion and bar accretion.
- Material lost on one bank is compensated by deposition on the opposite side.
- Channel width remains stable.
2. Multi-thread Rivers
- Show higher erosion rates than deposition.
- Channels widen continuously, leading to splitting and instability cycles.
- Erosion, rather than equilibrium, drives the splitting phenomenon.
Relevance of the Study
- Hydrological Insights – Explains flood risks, erosion potential, ecosystem services, and water resource dynamics of rivers.
- Disaster Management – Crucial for tackling intense weather events and climate-induced floods.
- Shift in Research – Earlier studies focused on where rivers occur, now emphasis is on how rivers evolve over time.
- Human Interference – Activities like damming, diking, sediment mining, agricultural expansion have altered natural river systems.
- Correcting Misinterpretations – Challenges the old idea that vegetation and meandering rivers coevolved.
- Role of Vegetation –
- Vegetation induces levee formation, limiting sinuosity (river bending ability).
- Vegetated bends move outward toward valley sides.
- Unvegetated bends migrate straight down valleys.
Insights for India
Rivers Studied –
- Ganga: Stretches near Patna, Farakka, Paksey (Bangladesh).
- Brahmaputra: Sections near Bahadurabad (Bangladesh), Pandu (India), Pasighat (India), Himalayan upstream.
Findings on Brahmaputra –
- Identified as a classical braided river.
- Channels are unstable, with fast lateral erosion exceeding deposition.
- Sub-channels widen and split repeatedly due to cycles of instability.
- Goes against the belief that erosion and deposition are always balanced.
Implications for Flood Risk in India –
- Rating curves (used to measure river flows) must be updated frequently as channels reshape rapidly.
- Artificial embankments worsen flood risks by confining braided rivers into single channels.
Recommended Nature-based Solutions –
- Remove artificial embankments.
- Restore river-floodplain connections.
- Develop vegetated buffer zones.
- Reactivate abandoned channels.
- Build wetlands in braided stretches.
Conclusion
The UCSB study provides a breakthrough in understanding river dynamics, highlighting that erosion, not equilibrium, governs river splitting. For India, especially in the Ganga and Brahmaputra basins, these findings underline the urgency of adopting nature-based flood management and sustainable river restoration. Recognizing the instability of multi-thread rivers is essential for long-term water security, disaster mitigation, and ecological resilience.
Source : The Hindu
