Yamuna floodplains shrank by a third in a century: Study, Pg5

Key Highlights:

• A study by researchers from the University of Delhi (DU) and the Indian Institute of Science Education and Research (IISER), Bhopal found that Yamuna floodplains in Delhi shrank by one-third over a century.
• The river channel has narrowed by approximately 68%, and its long-term formative discharge has been reduced by nearly 89%.
• Construction of barrages like Tajewala, Wazirabad, and Okhla, along with rapid urbanization, are key drivers of these changes.
• The Hathnikund barrage diverts nearly 90% of the Yamuna's flow upstream, impacting the Delhi stretch.
• The study highlighted that despite lower water volume, the July 2023 floods led to higher water levels in Delhi compared to 1978 due to river constriction.

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Detailed Insights:

• The study analyzed a 50-km stretch of the Yamuna in Delhi using historical maps from 1799, Survey of India records, and satellite imagery up to 2024.
• Formative discharge is crucial for a river's natural ability to shape its channel, remove sediment, and manage high flows.
• Around 45 sq km of the river's floodplains in Delhi have been disconnected by embankments over the last century.
• These disconnected floodplains have been encroached upon for agriculture, settlements, and infrastructure development.
• Sediment deposits within the river have significantly declined from 20 sq km in 1985 to about 4 sq km in 2020.
• The constriction of the river corridor by embankments and urban development prevents floodwaters from spreading laterally, increasing flood vulnerability.
• Recommendations for improving river health include upgrading sewage treatment plants and increasing the use of treated wastewater.
• Improving major drains like the Najafgarh (Sahibi) drain and reducing Delhi's dependence on the Yamuna for freshwater are also suggested.
• The study emphasizes the need for a "long-term hydrogeomorphic perspective" to understand the river's degradation.

Key Concepts Involved:

• Formative Discharge: The long-term average flow that naturally shapes a river channel and maintains its capacity.
• Hydrogeomorphic Evolution: The process by which evolving landforms dictate water flow and shape a river's physical characteristics.
• Floodplains: Flat land areas adjacent to a river, formed by the deposition of sediment, which naturally accommodate floodwaters.
• Environmental Flows: The quantity, timing, and quality of water flows required to sustain freshwater and estuarine ecosystems.